Aravind Krishnan's Posts (19)

Sort by

Thumb Sucking - Oral Habits Series 1

Few of my friends have been asking about the different oral habits assosciated with children. As there is a wide array of oral habits we will discuss few in details .

• Today we are gonna discuss about Thumb sucking .

• Thumb sucking and finger sucking can more generally be termed as digital sucking .A broader category of sucking habits includes any form of non nutritive sucking that include pacifiers ,hairs etc.

• Thumb Sucking can be a Normal or Abnormal , Psychological or Habitual .

• Normal Thumb sucking habit is considered normal during the first and second year of life .As the child matures it will disapper as well .The habit at this age doesn’t produce any mal occlusion (mal occlusion means imperfect positioning of teeth when the jaws are closed )

• Abnormal : persists beyond the preschool period .It can cause deleterious effects to the dentofacial structures .

• Psychological : Have deep rooted emotional factor involved .Associated with insecurities ,neglect or loneliness experienced by the child .

• Habitual : Doesn’t have a psychological backing .This is a cause for concern due to its potential to cause mal occlusion .

There is a term that needs to be addressed along with this topic .
• The process of sucking is a reflex occurring in the oral stage of development and is seen even at 29 weeks of i.u and may disappear during normal growth between the ages of 1 and 3 ½ years.
There has been several theories trying to explain the psychology behind thumbsucking viz Classical Freudian theory ,The learning theory by Davidson ,Oral Drive theory by Sears and wise ,Johnson and Larson etc .
So we will jump directly to the commonly observed Clinical problems .
1. Maxillary Anterior proclination and Mandibular Anterior retroclination : 
• Maxillary means Upper jaw , Anterior means the front teeth and proclination is teeth being inclined forward .
• Mandibular means lower jaw ,Anterios means the fron teeth and retroclination means tooth being pushed backwards toward tongue
2. The Anterior open bite : 
• There will be a space between upper and lower front teeth and no contact will be there 
3. Constriction of Maxillary arch : 
Due to the placement of thumb between the teeth ,the tongue must be lowered ,the cheek pressure against the teeth is increased which causes the upper jaw arch to become V shaped .
4. Posterior cross bite :
Posterior tooth means Back side tooth . Crossbite is lateral mis alignment of dental arches .

How do we prevent ?
1. Motive based Approach – find the cause ! 
2. Child’s engagement in various activities 
3. Parent’s Involvement in prevention – advised to spend ample time with the child so that child doesn’t feel insecure .Soothing music and bed time stories are also effective .
4. Duration of Breast feeding – Should be adequate to enable the child to exhaust his sucking urge .
5. Mothers Presence and attention during bottle feeding .
6. Use of a psychological nipple 
7. Use of a dummy or pacifier

1. Psychological therapy: 
• Screen the patient for the underlying psychological disturbances that sustain a thumb sucking habit.
• Once the psychological dependence is suspected, child is referred to professionals for counselling 
• Thumb sucking children between the ages of 4 and 8 years of age need only reassurance ,positive enforcement and friendy reminders.
2. Reminder Therapy 
i. Extra oral approaches : It employs Hot tasting ,bitter flavoured preparations or distasteful agents applied to finger or thumbs eg : Cayene pepper ,quinine ,asafoetida – effective only when habit is not firmly entrenched . Thermoplastic thumb post is another method .6 weeks of treat ment time is must 
ii. Intraoral approaches – Various orthodontic appliances – Removable appliances like Palatal crib ,rakes ,arch ,lingual spurs ,Hawleys retainer with and without spurs . Fixed ones such as Upper lingual tongue screens .
3. Mechano therapy : Fixed Intra oral and thumb sucking appliance 
4. Blue grass appliance and Quad helix .

Recent advances include Thumbsucking Silicone thumb sucking stop Guard protector ,electronic habit reminder (extra oral )

Ref :
1. Shobha Tandon ,Text book of pedodontics 

Read more…

Antibiotics and pregnancy conception

Few Days Back one of my patient came to clinic with a complaint of severe pain in the left posterior region of lower arch .On examination it was found to be due to an infected impacted 3rd molar.
As usual ,antibiotics was prescribed .But patient seemed to be reluctant .She came to me and asked a question "Doc,I am planning to have a baby and we are trying for that.Does antibiotics affect conception ?"

Ans : Antibiotics have no fertility-inducing properties. 
An antibiotic, however, can interfere with the effectiveness of the daily birth control pill that a woman may be taking to prevent pregnancy. This is because the antibiotic may interfere with the way the birth control pill is absorbed. The degree to which this happens varies depending on the kind of antibiotic, the daily dose, and how long it's taken. Recent studies show that the risk of conceiving on antibiotics is actually rather small.
A woman who takes antibiotics continuously, however, should always use a barrier method of birth control

Read more…

Paedodontics : Teeth Eruption Chart & FAQs

Do you have a child in your home ? Then the following chart may give you an idea about the teeth and their eruption status .

Few terminologies i would like to introduce

1.Natal Teeth and Neonatal Teeth - According
to the definition presented by Massler and Savara
(1950),taking only the time of eruption as reference, natal
teeth are those observable in the oral cavity at birth and neonatal
teeth are those that erupt during the first 30 days of life.

2. Deciduous teeth - now more commonly known as primary teeth. They are also known as baby teeth, temporary teeth and Milk teeth

3.Permanent teeth - Permanent teeth or adult teeth are the second set of teeth formed in diphyodont mammals.

Ok Now we will come to the topic and will try to answer few FAQs asked by patients in daily routine .

1. How many milk teeth does human have ?

Ans : 20.

The primary dentition is made up of Central incisors,Lateral incisors, Canines, First molars, and Secondary molars.

2. What is the importance of milk teeth ? does it have any significance ?

Ans : Primary teeth are essential in the development of the oral cavity.
a.Important for Speech production and development
b.Eating and nutrition 
d.Straighter smiles 
e.Excellent oral health

3. How many Permanent teeth does human have ?

Ans : 32
They are six maxillary and six mandibular molars, four maxillary and four mandibular premolars, two maxillary and two mandibular canines, four maxillary and four mandibular incisors.

4.What is mixed dentition period and its importance ?

Ans : Mixed dentition stage starts when the first permanent molar appears in the mouth, usually at five or six years, and lasts until the last primary tooth is lost, usually at ten, eleven, or twelve years.


Ans :UGLY DUCKLING STAGE (Broadbent phenomenon) is a transient/self-correcting malocclusion seen in the maxillary incisor region between 8-9 yrs of age. Erupting permanent canines displace the roots of lateral incisors mesially, resulting in transmission of force on to the roots of central incisors which also get displaced mesially.

Read more…

Mental Attitude of the patient

Introduction :

 Mental attitude of the patient is important in diagnosis and treatment planning

1.Cornell Medical index id a health questionnaire used to obtain a large amount of relevant medical and psychiatric information

2.Psychological testing [ Psychometrics] is a field characterised by use of behaviour samples to assess the cognitive and emotional functioning of an individual.

3.Graphology is described as a scientific study and analysis of hand writing ,art of interpreting character and personality from pecularities in Hand writing -GARDNER 1977

4.First serious treatise on Hand writing analysis -1622- By Camillo Baldo -"How to Judge the nature and character of a person from his letter "

Classification :

1.Blum In 1960 - [Sharry 1974]

1.reasonable /unreasonable


The psychological changes assosciated with ageing were well described by BURDACH [1819]

2.M.M House classification 

a.The Philosophical patient 

b.The Exacting 


D.The Hysterical

3.Heart well classification 

a.the realists

b.the resenters

c.the resigned

4.Dr.Suzanne Richard Classification [1957]

a. the Mature group

b.The rocking chair group

c.the armoured 

d.the angry men

e.the self haters

4.Winklers Traits of an ideal patient 

5.Simon Gamer's Classification 

-Modification of House classification 

a.Level of involvement

b.Level of trust

+ -disengaged

+++- reasonably engaged [ideal patient ]

engagementt ++ -- Submitter

engagement ++, trust ++ -Reluctant

eng -+ ,trust + - Indifferent + - Resistant 

++++- over involovement

6.Pankey system by Dr.L.D Pankey

Class I -High level Dental I.Q

Class II - Good dental I.Q

Class III- Poor Dental I.Q

Class IV-  Very Low Dental I.Q

7.O'Shea Classification 




8.Koper classification

a.Problem patients

b. Difficult denture wearers

Jamieson stated that fitting the personality of the aged patient is often more difficult than fitting the prostheses to the patient mouth .

Krochack, recognizing the critical need to understand the behaviour of the edentulous patient stated that many patients with favourable anatomy cannot tolerate a well fabricated prosthesis and yet other patient with unfavourable anatomy willing endure prosthesis that may be ill fitting. He asserted that the inconsistencies of patient adaptation in this situation may be related to the patient psychological state .

Kent stated that the ability of a doctor to determine when a patient has unrealistic expectation and the ability to manage that interaction effectively may avert a conflict

A specific classification system has been presented to identify response by individuals who are edentulous. Three types of maladaptive responses are considered as probable consequences of fear, anxiety and depression associated with complete edentulism. In class1, the patient adapts physically but is maladaptive psychologically. In maladaptive class 2, the so called difficult patients is maladaptive physically and psychologically and there by keeps the doctor involved technically and emotionally for a protracted period of time . The maladaptive class 3 patient collapses with complete edentulisim. Physical and emotion maladaptibility is accompanied by much suffering and social withdrawal

Read more…

ANSI/ADA Specification numbers


Specifications and Technical Reports


    * Specifications and Technical Reports


    * ANSI/ADA Specification No. 1—Alloy for Dental Amalgam: 2003

    * ANSI/ADA Specification No. 6—Dental Mercury: 1987 (Reaffirmed 2005)

    * ANSI/ADA Specification No. 12—Denture Base Polymers: 2002 (Reaffirmed 2008)

    * ANSI/ADA Specification No. 15—Artificial Teeth for Dental Prostheses: 2008

    * ANSI/ADA Specification No. 17—Denture Base Temporary Relining Resins:1983 (Reaffirmed 2006)

    * ADA Specification No. 18—Alginate Impression Materials: 1992

    * ANSI/ADA Specification No. 19—Dental Elastomeric Impression Materials: 2004

    * ANSI/ADA Specification No. 23 (with Addendum)—Dental Excavating Burs: 1982 (Reaffirmed 2010)

    * ANSI/ADA Specification No. 25—Dental Gypsum Products: 2000 (Reaffirmed 2005)

    * ADA Specification No. 26—Dental X-Ray Equipment: 1991

    * ADA Specification No. 27—Resin-Based Filling Materials: 1993

    * ANSI/ADA Specification No. 28—Root Canal Files and Reamers, Type K: 2008

    * ANSI/ADA Specification No. 30—Dental Zinc Oxide - Eugenol and Zinc Oxide - Non-Eugenol Cements: 2000 (Reaffirmed 2005)

    * ANSI/ADA Specification No. 32—Orthodontic Wires: 2006

    * ANSI/ADA Specification No. 33—Dental Product Standards Development Vocabulary: 2003

    * ADA Specification No. 34—Dental Aspirating Syringes: 1978

    * ANSI/ADA Specification No. 37—Dental Abrasive Powders: 1986 (Reaffirmed 2005)

    * ANSI/ADA Specification No. 38—Metal-Ceramic Dental Restorative Systems: 2000 (Reaffirmed 2010)

    * ANSI/ADA Specification No. 39—Pit and Fissure Sealants: 2006

    * ANSI/ADA Specification No. 41—Recommended Standard Practices for Biological Evaluation of Dental Materials: 2005

    * ANSI/ADA Specification No. 43—Electrically Powered Dental Amalgamators: 1986 (Reaffirmed 2010)

    * ADA Specification No. 44—Dental Electrosurgical Equipment: 1979

    * ANSI/ADA Specification No. 46—Dental Patient Chair: 2004

    * ANSI/ADA Specification No. 47—Dental Units: 2006

    * ANSI/ADA Specification No. 48—Visible Light Curing Units: 2004 (Reaffirmed 2009)

    * ANSI/ADA Specification No. 48-2—LED Curing Lights: 2010

    * ANSI/ADA Specification No. 53—Polymer-Based Crown and Bridge Materials: 2008

    * ANSI/ADA Specification No. 54—Double-Pointed, Parenteral, Single Use Needles for Dentistry: 1986 (Reaffirmed 2009)

    * ANSI/ADA Specification No. 57—Endodontic Sealing Material: 2000 (Reaffirmed 2006)

    * ANSI/ADA Specification No. 58—Root Canal Files, Type H (Hedstrom): 2010

    * ANSI/ADA Specification No. 62—Dental Abrasive Pastes: 2005

    * ANSI/ADA Specification No. 63—Root Canal Barbed Broaches and Rasps: 2006

    * ANSI/ADA Specification No. 69—Dental Ceramic: 2010

    * ANSI/ADA Specification No. 70—Dental X-Ray Protective Aprons and Accessory Devices: 1999 (Reaffirmed 2005)

    * ANSI/ADA Specification No. 71—Root Canal Filling Condensers (Pluggers and Spreaders): 2008

    * ANSI/ADA Specification No. 73—Dental Absorbent Points: 2008

    * ANSI/ADA Specification No. 74—Dental Operator's Stool: 2010

    * ANSI/ADA Specification No. 75—Resilient Lining Materials for Removable Dentures - Part 1: Short Term Materials: 1997 (Reaffirmed 2003)

    * ANSI/ADA Specification No. 76—Non-Sterile Natural Rubber Latex Gloves For Dentistry: 2005 (Reaffirmed 2010)

    * ANSI/ADA Specification No. 78—Dental Obturating Cones: 2006

    * ANSI/ADA Specification No. 80—Dental Materials - Determination of Color Stability: 2001 (Reaffirmed 2008)

    * ANSI/ADA Specification No. 82—Dental Reversible/Irreversible Hydrocolloid Impression Material Systems: 1998 (Reaffirmed 2009)

    * ANSI/ADA Specification No. 85-Part 1—Disposable Prophy Angles: 2004

    * ANSI/ADA Specification No. 87—Dental Impression Trays: 1995 (Reaffirmed 2003)

    * ANSI/ADA Specification No. 88—Dental Brazing Alloys: 2000 (Reaffirmed 2006)

    * ANSI/ADA Specification No. 89—Dental Operating Lights: 2008

    * ANSI/ADA Specification No. 94—Dental Compressed Air Quality: 1996 (Reaffirmed 2003)

    * ANSI/ADA Specification No. 95—Root Canal Enlargers: 2003 (Reaffirmed 2009)

    * ANSI/ADA Specification No. 96—Dental Water-based Cements: 2000 (Reaffirmed 2005)

    * ANSI/ADA Specification No. 97—Corrosion Test Methods: 2002 (Reaffirmed 2008)

    * ANSI/ADA Specification No. 99—Athletic Mouth Protectors and Materials: 2001 (Reaffirmed 2007)

    * ANSI/ADA Specification No. 100—Orthodontic Brackets and Tubes: 2004 (Reaffirmed 2009)

    * ANSI/ADA Specification No. 101—Root Canal Instruments: General Requirements: 2001 (Reaffirmed 2010)

    * ANSI/ADA Specification No. 102—Non-Sterile Nitrile Gloves: 1999 (Reaffirmed 2010)

    * ANSI/ADA Specification No. 103—Non-Sterile Poly Vinyl Chloride Gloves For Dentistry: 2001 (Reaffirmed 2010)

    * ANSI/ADA Specification No. 105—Orthodontic Elastomeric Materials: 2010

    * ANSI/ADA Specification No. 108—Amalgam Separators: 2009

    * ANSI/ADA Specification No. 109—Procedures for Storing Dental Amalgam Waste and Requirements for Amalgam Waste Storage/Shipment Containers: 2006

    * ADA Technical Report No. 110—Standard Procedures for the Assessment of Laser-induced Effects on Oral Hard and Soft Tissue: 2008

    * ANSI/ADA Specification No. 113—Periodontal Curettes, Dental Scalers and Excavators: 2008

    * ANSI/ADA Specification No. 116—Oral Rinses: 2010

    * ANSI/ADA Specification No. 119—Manual Toothbrushes: 2008

    * ANSI/ADA Specification No. 120—Powered Toothbrushes: 2009

    * ANSI/ADA Specification No. 122—Dental Casting and Baseplate Waxes: 2007

    * ANSI/ADA Specification No. 125—Manual Interdental Brushes: 2009

    * ANSI/ADA Specification No. 126—Casting Investments and Refractory Die Materials: 2009

Read more…


Synonyms : Spare denture, back-up denture.


There are mainly three techniques.

(1)Modified denture flask method-(Brewer and Morrow 1975)-

  • Remove a rectangular section from the upper pat of the flask for the wax sprue.
  • Add utility or orthodontic tray wax in thin areas in the external surface of the denture.
  • 75mm long with a diameter of 15mm wax is rolled to make the sprue which is attached the lingual surface of the mandibular heel region.
  • Apply adhesive on the interior surface of the flask to aid in the retention of alginate.
  • Mix alginate and place in the lower part of the flask and the remaining alginate is painted on the interior of the denture.
  • Place the denture in to the alginate in the flask with the sprue projecting out through the triangular opening and supporting the denture.
  • After alginate has set, the other half of the flask is filled with another mix of alginate and the flask is closed.
  • After alginate has set separate the flasks and remove the denture.
  • Dry the tooth indentations using tissue paper and mix tooth coloured acrylic and add in to the indentations till the cervical region.
  • Now assemble the flask together and mix pour type acrylic resin and pour it through one sprue hole till the other sprue hole fills.
  • Gently rock the flask to avoid air entrapment. Sprue should be upward facing and the flask is immersed in warm water at 20psi for 30minutes

(2)Pour resin flask method (Boos and Carpenter 1974)-

  • Attach the denture in the base of the flask using modeling clay.
  • Place the counter and pour a mixture of alginate.
  • Allow it to set.
  • Open the flask and remove the clay.
  • Mix alginate and pour it.
  • Once the second pour of alginate is set open the flask and remove the denture.
  • Mix tooth coloured self cure resin and pour it in the teeth indentation and later pink colour pour type resin the denture base area.

(3)The cup flask method(Wanger 1970) or zipper technique by singer (1975)-

  • In this method a 12 ounce ceramic cup is used to duplicate the denture using hydrocolloids. Singer modified it by adding a dental floss to section the alginate.
  • A  16 inch floss is dipped in melted orthodontic tray wax and this is placed 2-3mm below the border of maxillary denture and across the posterior region.
  • In case of mandibular denture the 2 floss are used one on buccal side and another on lingual side and extend it to the sprue wax which is attached to the heel of the cast.
  • Suspend the denture using two wooden rods.
  • A modeling clay wedge is placed on the inner surface of the cup and the alginate is mixed with three times the water recommended by the manufacturer.
  • Fill the cup with alginate and sink the denture in to it.
  • Wooden rod and the clay wedge is removed and a stream of air is blown through the space of the clay wedge to remove the mold from the cup.
  • Now the floss is pulled across the posterior border and flanges to section the mold in to two halves.
  • Tooth coloured self cure resin is placed in the tooth indentations and the halves are assembled back in the cup.
  • Through the sprue holes the pour type resin is mixed and poured.
Read more…

Definition :


“The creation of functional materials, devices and systems through control of matter on

the nanometer scale (1-100 nm), and exploitation of novel phenomena and properties (physical, chemical and biological) at that length scale”.

-Indian Journal of Multidisciplinary Dentistry, Vol. 1, Issue 5, July-August 2011


Ò  The term “Nanotechnology” was coined by Prof. Kerie E.Drexler

Ò   «Nano»-the Greek word - “dwarf”.

Ò   Nanotechnology- science of manipulating matter measured in the manometer, roughly the size of 2 or 3 atoms

Ò  The basic idea of nanotechnology- to employ individual atoms and molecules to construct functional structures.

Ò  The late Nobel Prize winning physicist Richard P. Feynman in his historic lecture in 1959,

this is a development which I think cannot be avoided





Nanoelectronics :

Ò  Use Of nanotechnology on electronic components,especially transistors,computer processors etc.

Nanomaterials :

Ò  Essentially Polymers Reinforced by nanoparticles

Ò  Results in  novel materials –used as light weight replacements for metal

Ò  Can affect the mechanical properties like Stiffness or elasticity

The various nanoparticles are

Ò  1. Nanopores

Ò  2. Nanotubes

Ò  3. Quantum dots

Ò  4. Nanoshells

Ò  5. Dendrimers

Ò  6. Liposomes

Ò  7. Nanorods

Ò  8. Fullerenes

Ò  9. Nanospheres

Ò  10. Nanowires

Ò  11. Nanobelts

Ò  12. Nanorings

Ò  13. Nanocapsules

Classification of Nanomaterials :

1.Carbon based

2.Metal based



Ò  Nano assemblers –smaller than cell nucleus

Ò  Potential

Ò  Customisation of diagnosis and treatment

Nanodiagnostics –

 is the use of nanodevices for the early disease identification or predisposition at cellular and molecular level

in-vitro diagnostics,

Ò  increase the efficiency and reliability of the diagnostics

Ò   uses human fluids or tissues samples by using selective nanodevices, to make multiple analyses at subcellular scale


In vivo diagnostics,

Ò  devices able to work inside the human identify the early presence of a disease,

2. to identify and quantify toxic molecules, tumor cells


Ò  maintenance of comprehensive oral health by employing nanomaterials, including tissue engineering, and ultimately,dental nanorobots.

Ò  1.local anaesthesia,

Ò  2. dentitionrenaturalization, and permanent hypersensitivity cure,

Ò  3.Complete orthodontic realignments during a single office visit,

Ò  4. covalently bonded diamondised enamel,

Ò  5. continuous oral health maintenance using mechanical dentifrobots

Nanomaterials in dentistry

1.Nano composites


3.Impression materials


5.Local nanoanesthesia

6.Dentinal hypersensitivity

7.Tooth durability and appearance

8.Orthodontic treatment

Uses of Nanomaterials in dentistry:

Ò  Nano impression materials

Ò  Nano bonding agents

Ò  Nano drug releasing systems

Ò  Nano composites

Ò  Nano Ceramics

Ò  Nano Sterilizing agents

Ò  Dental implants

Nanocomposites :

Ò  nonagglomerated discrete nanoparticles that are homogeneously distributed in resins or coatings to produce nanocomposites

Ò  The nanofiller used is

Ò   aluminosilicate powder having a mean particle size of 80 ran

Ò  a 1:4 M ratio of alumina to silica and

Ò   a refractive index of 1.508.


• Superior hardness

• Superior flexural strength, modulus of elasticity andtranslucency

• 50% reduction in filling shrinkage

• Excellent handling properties


Ò  Nanosolutions produce unique and

dispersible nanoparticles, which can be used in bonding agents.

Ò  Ensures homogenecity and ensures that the adhesive is perfectly mixed everytime


Ò  targeted release systems that encompass nanocapsules including novel vaccines, antibiotics and drug delivery with reduced side effects

Ò  targeted delivery of genes and drugs to human liver -developed by Osaka University in Japan 2003

Ò  Engineered Hepatitis B virus envelope L particles were allowed to form hollow nanoparticles displaying a peptide that is indispensable for liver-specific entry by the virus in humans.

Ò  Future specialized nanoparticles could be engineered to target oral tissues, including cells derived from the periodontium

Local nanoanaesthesia

Ò  colloidal suspension containing millions of active analgesic micron-size dental robots will be instilled on the patient’s gingiva.

Ò   After contacting the surface of crown or mucosa,the ambulating nanorobots reach the pulp via the gingival sulcus, lamina propria and dentinal tubules

Ò  Once installed in the pulp, the analgesic dental robots may be commanded by the dentist to shut down all sensitivity in any particular tooth that requires treatment.

Ò  After oral procedures are completed, the dentist orders the nanorobots to restore all sensation, to relinquish control of nerve traffic and to egress from the tooth by similar pathways used for ingress

Dental hypersensitivity

Ò  Natural hypersensitive teeth have eight times higher surface density of dentinal tubules and diameter with twice as large than nonsensitive teeth.

Ò  Reconstructive dental nanorobots, using native biological materials, could selectively and precisely occlude specific tubules within minutes, offering patients a quick and permanent cure

Tooth durability and appearance

Ò  Durability and appearance of tooth may be improved by replacing upper enamel layers with covalently bonded artificial materials such as sapphire or diamond, which have 20-100 times the hardness and failure strength of natural enamel or contemporary ceramic veneers and good biocompatibility.

Ò  Nanorobotic dentifrice (dentifrobots) delivered by mouthwash or toothpaste could patrol all supragingival and subgingival surfaces at least once a day metabolizing trapped organic mater into harmless and odorless vapors and performing continuous calculus debridement.

Orthodontic treatment :

Ò  Orthodontic nanorobots could directly manipulate the periodontal tissues, allowing rapid and painless tooth straightening, rotating and vertical repositioning within minutes to hours

Nanotechnology in Dental Implants:

Ò  Coating of nanoparticles over the dental implants.

Ò  The surface of the implant plays a critical role in determining biocompatibility and biointegration because it is in direct contact with the tissues.

Ò  Implant surface composition

Ò   surface energy

Ò  surface roughness

Ò  surface topography

-the four material related factors which can influence events at bone-implant interfaces.

Ò  Surface textures are of three types- macro, micro and nano

Ò  Nanostructured (NS) materials contain a large volume fraction (>50%) of defects such as grain boundaries, inter phase boundaries, and dislocations, and this strongly influences their chemical and physical properties.

Ò  Biomimetic dental implants may be the next development in the field.

Ò  Coating implants with nanotextured titanium, hydroxy apatite, and pharmacological agents such as bisphosponates –

1. may induce cell differentiation and proliferation and

2. may promote greater vascularity in highly cortical bone,

-improves conditions for early and long-term

Ò  (in response to functional loading) bone remodeling

Ò  Successful osseointegration is influenced by both the chemical composition and the surface geometry or topography of the implant

Ò  Surface nanotopography affects cell interactions at surfaces and alters cell behavior when compared to conventional sized topography

Ò  Nanoscale topography is a powerful way of altering protein interactions with the surface.

Methods of Synthesis of Implant Nanomaterials:

1.Top down                            2.Bottom up

Top down: Produced from larger structures by use of ultrafine grinders,lasers and vaporisation followed by cooling

Bottom up: Arranging molecules to form complex structures with new and useful properties

Imaging of nanomaterials:

Ò  X-ray diffraction[XRD]

Ò  Atomic force microscopy[AFM]

Ò  Scanning electron microscope[SEM]

Ò  Transmission electron microscopy[TEM]

Ò  Magnetization measurements

Ò  Nuclear magnetic reasonance[NMR]

Ò  Spectroscopy

Ò  2-D electrophoresis and Mass spectrometry of proteins

Ò  Confocal Microscopy

Nanobiotechnology :

Ò  Nanorobotics

Nanorobots are theoretical microscopic devices measured on the scale of nanometers (1 nm equals one millionth of 1 mm).

Hazards of nano :

Ò  The potential deleterious effect analyzed so that expanded development and use

Ò  of nanotechnology can proceed.

Ò  rapid withdrawal of a nanotechnology-based

Ò  product, Magic Nano, a spray-on ceramic sealant to repel dirt.

Ò  Over 110 consumers in Europe reported respiratory symptoms after using the spray.The product was withdrawn in March 2006.







Read more…


I have been asked a zillion times !! "Doctor ,What about Mouth wash ?? can i use it regularly ?"

According to WIki pedia :
*"Mouthwash, mouth rinse, oral rinse or mouth bath, is a liquid which is held in the mouth passively or swilled around the mouth by contraction of the perioral muscles and/or movement of the head, and may be gargled, where the head is tilted back and the liquid bubbled at the back of the mouth." -An Antiseptic in nature !

*Important information regarding Mouth wash should be about its Ingredients !!
Most of the Indian Brands Marker Chlorhexidine Gluconate !! 0.12 % C G is required for healing of oral tissues !

*Major ingredient of a mouth wash include "Alcohol "!

*Continued use of products containing chlorhexidine for long periods can cause stains on teeth, tongue, and gingiva,[gum] 

*Prolonged use can also reduce bitter and salty taste sensations – this latter symptom can be reversed by ceasing use of chlorhexidine.

* The brownish discoloration of teeth and tongue is due to the disintegration of bacterial membranes, leading to the denaturation of bacterial proteins.


*A "magic mouthwash" (or "magic swizzle"),[citation needed] refers to a non-standardized mixture of ingredients prescribed for a specific purpose, e.g. oral surgery, or to treat the pain associated with mucositis caused by radiation therapy or chemotherapy. 

*It is also prescribed for aphthous ulcers, other oral ulcers, and other mouth pain
*Because magic mouthwash has no standard formulation, its use involves concerns about patient safety..

Conclusion :START USING A MOUTH WASH ONLY IF THE DOCTOR SUGGESTS YOU TO ! Mostly a good oral hygiene practice doesnt require administration of Mouth wash .
Patients do complain of halitosis or odour mouth ! Bt mouth wash is not the first line of treatment ! Hence pls do consult a doctor prior to !

Read more…

ORBIT chewing gum

Many of my friends have asked this " Bro ,if i chew orbit chewing gum , shud i brush every day ?" !!

err ...

"You have to brush every other day !! 2 times daily !- morning and night !!

Chewing gum, especially after meals, has clinically proven oral care benefits. There is overwhelming published scientific evidence from laboratory studies and clinical trials showing that chewing sugarfree gum has many beneficial qualities. 
A key ingredient of Wrigley’s sugarfree gum is the presence of several types of polyols, mainly sorbitol and xylitol. Research shows that xylitol prevents harmful bacteria from growing. It also reduces plaque as it can help prevent harmful plaque from building up on teeth.
Chewing sugarfree gum can help moisten and refresh the mouth and 
sweeten the breath. Studies have shown that chewing gum is one of the most preferred treatments for xerostomia or dry mouth.
A key factor in the development of decay lies in the correct balance 
of acid demineralisation and remineralisation of the teeth which 
is in turn dependent on the pH of dental plaque. Caries occur when 
there is an imbalance between the demineralisation of the enamel 
surface following acid generation in the plaque and remineralisation 
produced by the return of mineral ions into enamel from the plaque and saliva.

So happy chewing and please brush your teeth daily !♥

Read more…

Biomimetic Dentistry

Biomimetic dentistry


  • Biomimetic dentistry is based on the philosophy that the intact tooth in its ideal hues and shades and, more importantly, its intracoronal anatomy, mechanics and location in the arch, is the guide to reconstruction and the determinant of success.
  • This approach is conservative and biologically sound and in sharp contrast to the porcelain fused- to-metal technique in which the metal casting with its high elastic modulus makes the underlying dentin hypo functional.
  • The goal of biomimetics in restorative dentistry is to return all of the prepared dental tissues to full function by the creation of a-tissue bond that allows functional stresses to pass through the tooth, drawing the entire crown into the final functional biologic and esthetic result.
  • Bio: meaning life and mimesis meaning imitation are from Greek.
  •  Biomimetics is the field of scientific endeavor which attempts to design system and synthesize materials through biomimicry.
  • It’s the concept of taking ideas from nature and implementing them in another technology such as engineering design computing etc.
  • The subject matter of biomimetics is known by several names bionics, biognosis etc .
  • Biomimectics is an emerging inter disciplinary field that combines information from the study of  biological structures and their function with physics mathematics chemistry and engineering in the development of principles that are important for the generation of novel synthetic materials and organs.


  • The name biomimeitcs was coined by Ottoschmit in the 1950s. The term bionics coined by JackE.Steele in 1960 at continence in Dayton.
  • The foundation of this broad new field has ancient roots. Replacing body parts goes back at least 2,500 years when bridges made them artificial teeth carved them the bones or oxen.
  • Evidence of crude dental implants dates back to roman population of the first or second century AD and to pre-Columbian cultures of central and south America.
  •  The first use of dental amalgam to repair decayed teeth was recorded in the Chinese literature in the year 659.
  • The middle of 20th century same sophisticated inventions in the heart pacemaker the artificial heart valve and hip and knee joint replacement historically organ and tissue loss have been treated by surgical reconstruction and more recently the use of mechanical devices such as kidney dialyzers and the transplantations of organs from one individual to another.


Regeneration of the dentin pulp complex :-

  • The recombinant human BMP2 and BMP4 can induce new dentin .
  • Recombinant BMP delivered in a scaffold of demineralized dentin matrix induces classic tubular dentin in amputated pulp where as BMP delivered using reconstituted type I collagen matrix induces instead osteodentin .
  • Reparative dentin is also induced on freshly cut healthy pulp tissue in nonhuman primate using recombinant human BMP7 with an insoluble type I collagen matrix.
  • The size and shape of the inductive material controls the size and shaped of the reparative dentin.
  • The reparative dentin appears initially with cellularand soft tissue inclusions a portion of which (comprising only about 20% of the reparative dentin ) subsequently changes into a more tubular form of matrix with associated odontablast like cells attached to the mass of a tubular matrix.
  • Therefore the extra cellular matrix scaffolding is a critical component and a prerequisite to odontoblast differentiation and tubular dentin formation.

Periodontal regeneration :-

  • The periodontium which consist of cementum PDL and alveolar bone functions to anchor the teeth to the jaws.
  • The morphogenetic potential of BMPs makes them ideal candidates for use in periodontal regeneration o p t i m i z i n g  t h e r e s p o n s e o f s t e m cells to BMP induction requires the use of a delivery system that is conducive to the migration and attachment of the responding stem cells on to the scaffolding using a baboon model recombinant BMP7 and baboon type I collagen has been used as a biomimetic scaffold to regenerate surgically created function defects in molars.
  •  The formation of alveolar bone and the creation of cementum and sharpey’s fibers inserted at the optimal orientation into the root surface.
  • Platelet rich plasma (PRP) used in different surgical procedures.
  • It consists of thrombocyte concentrates and high amounts of growth factors (GFs) especially platelet desired growth factor (PDGF), insulin like growth factor (IGF -I) and transforming growth factor (TGF- beta ) which are important in wound healing and regeneration combination of PRP and tricalcium phosphate can be used in the treatment of periapical inflammatory lesion.
  • Platelet gel biotechnology a method which has all the components of “tissue engineering” techniques with healing process of guided tissue regeneration procedures (GTR) by multiplying the number of molecules that activate the healing response and by grafting in the host site various cell types among which stem cell host is applied to regenerative surgery of intrabony defects in patients with refractory g e n e r a l i z e d a g g r e s s i v e p e r i d o n t i t i s .


  • There are two major perspectives to which the term “biomimetic” is applied: a purist perspective that focuses on recreating biological tissues and a descriptive perspective that focuses on using materials that result in a mimicked biological effect.
  • Although different, both share a common goal of mimicking biology in restoration. This has been an increasingly common goal for dentists and patients alike in achieving esthetic and functional dentistry.
  •  The goal of biomimetics in restorative dentistry is to return all of the prepared dental tissues to full function by the creation of a hard tissue bond that allows functional stresses to pass through the tooth drawing the entire crown into the final functional biologic and esthetic result .
  •  Bonded porcelain restorations are recommended to treat the most perilous situation ( non vital or fractured teeth) thus avoiding the use of intraradiucular parts or full coverage crowns e.g.- inlay onlay laminates cemented with the adhesive resins .
  • Biomimetic dentistry techniques provide the patient with minimally invasive options that conserve sound tooth structure as a clinical imperative.
  •  Biomimetics is essentially described as a mimicking of natural life, which can be accomplished using contemporary composite resins and adhesive dental procedures.
  • Conservation and biological mimicry make up the foundation of a biomimetic philosophy and together produce the effect that today’s patients expect.
  • From an esthetic/restorative perspective, biomimetics or biomimicry is the application of methods and systems to artificially replace biologic elements in order to recreate optimal oral health.
  •  Practicing interdisciplinary esthetic restorative dentistry enables dentists to achieve biomimetic results with cosmetic dentistry.
  •  These techniques and materials are crucial to modern dentistry in that they combine a focus on dental health and appearance.
  • A biomimetic material should match the part of the tooth that it’s replacing in several important ways, including the modulus of elasticity and function of the respective areas (e.g., pulp, dentin, enamel, dentoenamel junction)
  • The low elastic modules of most composites can never fully compensate for the loss of strong proximal enamel ridges especially in extremely large class II restorations .
  • In these situations including those with cusp coverage indirect ceramic inlays onlays seem to be best alternative .
  •  In case of total occlusal coverage in vital teeth with a short clinical crown ceramic indirect overlays are indicated. .
  • With the development of improved adhesives and immediate dentin sealing the use and indications for base lines have decreased.
  • This group of materials traditionally performs many different function including the partial lining as a biologic protection for deep preparation areas the total lining for the dentin insulation against chemical or thermal injuries and the dentin replacement as a base prior to further restoration procedures.
  • The indication for placing a linear under on adhesive restoration is mainly for pulp protection in the form of a partial lining using Ca (OH2) cements.
  • Modern adhesives are capable replacing the total living function of former varnishes and cements.
  •  Base materials are mainly indicated to reduce the volume of the inlay/ onlay (e.g.- excessive depth ) and to create an adequate preparation geometry by providing an even cavity floor and filling up internal undercuts .
  • Endodontically treated teeth are more susceptible to fracture not because of pulp removal but due to the increased strain resulting them tooth substance loss.
  • For posterior teeth total cuspal coverage with porcelain is recommended as it will significantly stiffen the crown and increase cusp stabilization for vital teeth
  • .A composite resin base in indicated to reduce the volume of the inlay/onlay and to create an adequate preparation geometry (by providing an even cavity floor and filling up internal undercuts)


  • Many people suffer a loss of salivary gland function as a result of radiation treatment for head and neck cancer, and also many people affected for sjogren’s syndrome an autoimmune disease whose symptoms include dry mouth and dry eyes without adequate saliva patient may experience difficulty in speaking, chewing and swallowing.
  • The application of state – of – the- art methodologies include the use of adult and embryonic stem cells for the regeneration of the salivary glands, parenchyma and restorations of its secretary functions.
  • Efforts have focused on creating a rather simple device a “blind- endtube” suitable to graft in the buccal mucosa of patients whose salivary parenchyma has been destroyed.
  • The lumen of these tubes would be lined with compatible epithelial cells and be physiologically capable of unidirectional water movement. A realistic opportunity to develop a first generation artificial salivary gland suitable for clinical testing is believed to exists.


  • According to Douglas A. Terry, DDS, in dentistry there is no one biomaterial that has the same physical, mechanical and optical  properties as tooth structure (i.e., dentin, enamel, cementum) and possesses the physiological characteristics of intact teeth in function.
  •  By utilizing biomimetic therapeutic approaches, dentists can improve and become closer to natural biological structures and their function
  • Synthetic Polymer: The polymer can be biodegradable or non degradable .biodegradable polymers include polylactic acid and polyglycolic acid and co polymers.
  •  These polymers are used as suture materials but are also being examined for usage such as bone ,skin and liver substitutes.
  • These polymers are broken down in the body hydrolytically to produce lactic acid and glycolic acid.
  • Newer biomaterials are polyanhydrites, Polyphosphazenes. Polymethyl Methacrylate(PMMA),Polytetrafluoroethylene(PTFE)andPMMA, polyhydroxyethylmethacrylate (PHEMA) may be described as alloplastic , synthetic, Nonbiodegradable polymers.
  • PMMA used for dentures and as a cement for many orthopedic prosthesis. PTFE used for augmentation and guided bone regeneration.


  • It is used in dental applications and are being examined for bone tissue engineering application.
  • Two common ceramics used in dentistry and hip prosthesis are alumina and hydroxyapatite.
  • Alumina has excellent corrosion resistance, high strength, high wear resistance.
  • Hydroxyapatite is a calcium phosphate based ceramic and it is a major component of inorganic compartment of bone.
  • Advantages of a BioMimetic crown

• Less healthy tooth structure is removed.

• Less potential chances of damaging the nerve inside the tooth.

• T he visual look of the restoration is identical to the natural tooth structure.

• Chances of decay getting under the restoration are small compared to a conventional crown.

  • Disadvantages of a BioMimetic crown

• There is the possibility that the porcelain crown could fracture.

• T here is the possibility that the porcelain crown could de-bond (fall off) the tooth. This would require a new crown to be made.



  • Biomimetic dental implants may be the next development in the field.
  • A variety of biomimetic coatings may prove helpful for application in individual patients.
  •  For example, coating implants with factors known to induce endothelial cell differentiation and proliferation may promote greater vascularity in highly cortical bone, thereby improving conditions for early and long-term (in response to functional loading) bone remodelling.
  • Ceramics such as the calcium phosphate hydroxyappatite and various types of aluminum oxides are proved to be bio compatible and they are coated to implant which increases osteointegration.
  • Coating implants with pharmacological agents such as bisphosphonates6 may be a way of locally improving bone density in highly cancellous bone.
  • Coating implants with BMPs may also accelerate initial healing times during integration of the dental implant, thereby reducing overall treatment times and improving implant success rates.
  • Experimental investigations with a BMP known as recombinant human BMP-2 (rhBMP-2) in animal models have shown that it promotes initial integration of dental implants and “rescues” implants affected by experimentally induced peri-implant bone loss.
  •  Modifying the surface characteristics of the implant can promote migration of mesenchymal cells to the implant surface, enhance attachment and proliferation of these cells, and, in some instances, stimulate osteoblastic differentiation.


  • Biologist study biomimetics not only for an understanding of the biological processes but also to trace the evolution of various classes of organism biochemist have interest in the field due to the complexities associated with the interaction of biopolymers with ions of metal leading to the mineralization in living organisms.
  • On the whole the field of biomimetics addresses more than one issue those engaged in this field of research activity try to mimic natural method of manufacture of chemicals in order to create new ones, learn new principles from phenomenon observed in nature, reproduce mechanism found in nature and copy the principles of synthesizing materials under ambient conditions and with easily available raw materials.
  •  Design of biodegradable scaffolds to serve as platforms for cells to organize tissues for repair and regeneration of teeth and periodontal tissues.
  • Develop biodegradable synthetic polymers for gene therapy identify isolate culture and characterize multipotent stem cells for adult tissues type for repair of TMJ associated structures.


  • There is a need for a firmer scientific and technical basis in order to develop the next generation of medical implants that are safe reliable smart and long lasting integrated and multidisciplinary research should advance our understanding of biological system and provide the basis for the design and development of normal synthetic medical materials that are compatible with the environment of the host and significantly increase the functional life time of implants.
  • Future advances in this field will require materials and computer scientist, physicists, bioengineers, clinicians, biologist and industries working together towards a shared vision rather than pursuing their separate objectives











Read more…

Stem Cell Therapy in Dentistry



Tissue Stem cells :

  • Potten and Loeffler, 1990 definition
  • Stem cells of a particular tissue are undifferentiated cells (relative to a functional tissue) capable of


2. production of a large number of differentiated functional progeny;

3.self-maintenance of their population;

4. regeneration of the tissue after injury;

5.flexibility in the use of these options

  • Amended Definition of Tissue Stem Cells

Stem cells of a particular tissue are:

1. a potentially heterogeneous population of functionally undifferentiated cells, capable of:

2. homing to an appropriate growth environment;


4. production of a large number of differentiated progeny;

5.self-renewing or self-maintaining their population;

6.regenerating the functional tissue after injury with

7. flexibility and reversibility in the use of these options

  • Potency -differentiation potential (the potential to differentiate into different cell types) of the stem cell.

1.Totipotent /omnipotent stem cells

  • differentiate into embryonic and extraembryonic cell types. –
  • a complete, viable organism.
  • produced from the fusion of an egg and sperm cell.
  •  Cells produced by the first few divisions of the fertilized egg are also totipotent.

2.Pluripotent stem cells

  • descendants of totipotent cells
  • can differentiate into nearly all cells,  i.e. cells derived from any of the three germ layers.

3. Multipotent stem cells

  •  -can differentiate into a number of cells,
  • - but only those of a closely related family of cells.

4.Oligopotent stem cells

  • can differentiate into only a few cells, such as lymphoid or myeloid stem cells.

5.Unipotent cells

  • can produce only one cell type, their own,but have the property of self-renewal,
  • - distinguishes them from non-stem cells (e.g., muscle stem cells)


  • Russian histologist Alexander Maksimov in 1908
  • Stem cells grew out of findings by Canadian scientists in the 1960s
  • Dental exfoliation-genetically regulated event
  • Lost- donot regenerate
  • Stem cells-divide to produce one stem cell and one cell capable of differentation .
  • Stem Cells in Dentistry
  • 2000- Discovery of adult Stem-cells in dental pulp cells, the living tissue at the centre of tooth.
  • 2003- Stem-cells found in baby teeth.
  • 2004- Stem-cells found in periodontal ligament, which holds the teeth in place in gums.
  • 2007- Researchers learn how to reprogram some adult cells from mice to assume a State like Embryonic Stem-cells called induced pluripotent Stem-cells.
  • 2008- Cells in dental pulp identified as adult Stemcells.
  • 2003 Dr. Songtao Shi - baby tooth Stem-cells by using the deciduous teeth of his six year old daughter-  isolate, grow and preserve these Stem cells with regenerative ability, and he named them as SHED (Stemcells from Human ExfoliateD Deciduous teeth)
  • two broad types of Stem-cells
  • Embryonic stem- cells
  •  Adult Stem-cells.
  • Embryonic Stem cells
  • Pluripotent-differentiate into all types of somatic cells and theoretically divide an unlimited number of times
  • Embryoblast cells –part of blastocyst –interest for stem cell research
  • Ability to self regenerate
  • Adult-Stem cells
  • cells are also called as somatic Stem-cells because they refer to body cells
  • can only proliferate a limited number of times.
  • Distinguished according to their developmental potential. There are uni- and bipotent progenitor cells-only be differentiated into mature cells of their parent tissue
  • Multipotent adult stem cells-are not identical to the parent tissue
  • Sources Of Stem-Cells
  • Bone marrow -from the long bones. The best sources are pelvic bones, femur and sheen bone.
  •  Umbilical cord blood -collected just after the birth of the baby.
  •  Embryonic cells -from the blastocyst phase of the embryo.
  • Placental Stem-cells
  •  Menstrual Stem-cells -extra-ordinary improvement over the umbilical cord blood cells-  have a rapid growth rate.
  •  Dental Stem-cells -from the pulp of deciduous or wisdom teeth. - has been found to produce bones, cartilage, and muscle cells if cultured.
  •  Present in natal teeth, mesiodense or supernumerary teeth.
  • Applications- Parkinson’s diseases,paraplegia, leukemia, and brain tumors
  • therapeutic use in dentistry - to regenerate individual tissue types- such as bone,periodontal tissue
  • Someday even entire teeth
  • 2 means of regenerating teeth
  • 1.conventional tissue engineering-the application of cells in a carrier material in vitro under the influence of a stimulus leads to tissue regeneration.
  • 2. using dental epithelium and mesenchymal cells in vivo after direct implantation
  • - Based on knowledge of general embryogenesis and physiological tooth development during childhood
  • Craniofacial applications.
  •  Dental pulp applications.
  • Creation of artificial embryonic teeth primordia fromcultured cells.
  • Cementoblast like cells applications.
  • Periodontal regeneration.
  • Over 200 regulatory genes-odontogenesis
  • Growth factors from four families
  • 1. fibroblast growth factor (FGF),
  • 2.Hedgehog,
  • 3.wingless (WNT)
  • 4. transforming growth factor- (TGF-), to which the bone
  • morphogenic proteins (BMPs) belong
  • The basis for the regeneration of teeth or individual dental tissues –
  • is the acquisition of suitable stem cells and
  •  a suitable environment in which these cells can
  •  differentiate into the target tissues
  • Carrier materials
  • collagen sponges
  • HA/TCP (hydroxyapatite tricalcium phosphate
  • calcium phosphate
  • fibrin polymer ceramic
  • alginate
  • or polymers
  •  PCL gelatin scaffolds
  • the use of growth factors such as fibroblast growth factors
  • and some of the transforming growth factor  family, e. g. bone morphogenic proteins

Dental epithelial stem cells

  • The embryonic oral epithelium induces odontogenesis
  • Ameloblasts- arise from epithelial stem cells
  • the only cells of ectodermal origin which play a role in odontogenesis.
  • Lost after tooth eruption- leaving no adult human ectodermal stem cells available for cell therapy.
  • Dental epithelial stem cells –obtained from third molars of newborn or juvenile, still developing animals
  • A source of epithelial stem cells,
  • -the apical bud cells (ABCs), in the apical epithelium is responsible for continuous enamel production
  • Dental mesenchymal stem cells
  • With the exception of ameloblast progenitor cells,all stem cells involved in odontogenesis originate in mesenchyme
  • Mesenchymal stem cells - differentiate into nerve, muscle, vascular, fat, cartilage or bone cells


Target  Tissue /tissue  cells


Odontoblasts, dentin and pulp tisue,osteoblast





Odontoblsts ,Osteoblasts,neurons,Adipocytes,endotheliocytes


Odontoblasts,Periodontal  tissue ,Osteoblasts,Cementoblasts,



PDL progenitor cells






  • Dental pulp stem cells
  • isolated from the dental pulp
  • Depending on specific signals from their environment, DPSCs can either regenerate new stem cells or undergo  a differentiation process.
  • Dental pulp acquired from third molars or pulpectomized teeth left in situ.
  • Even after temporary storage in liquid nitrogen- the DPSCs do not lose their multipotent ability to differentiate
  • In vitro, DPSCs - differentiate to odontoblasts, osteoblasts, endothelocytes, smooth muscle cells, adipocytes, chondrocytes, and neurons.
  • DPSCs differentiate in vitro to osteoblast progenitor cells and mature into osteoblasts which produce LAB (living autologous fibrous bone tissue
  • DPSCs in vivo can form calcified bone tissue with Haversian canals and osteocytes and dentin/pulp-like tissue complexes
  • odontogenic, myogenic, adipogenic, and osteogenic differentiation.
  •  DPSCs influence angiogenesis
  • Regeneration potential of adult stem cells in human dental pulp - tertiary dentin
  • therapeutically employed for direct and indirect pulp capping after caries excavation near the pulp
  • Stem cells from human exfoliated deciduous teeth (SHEDs
  • relatively easily accessible source of adult stem cells
  • coronal pulp of exfoliated deciduous teeth
  • Role
  • in the eruption of permanent teeth
  • influence the osteogenesis
  • In vitro-odontogenically, osteogenically, adipogenically, chondrogenically, or neurally
  • In vivo- neurons, adipocytes, odontoblasts, and osteoinductive and endothelioid cells
  • Periodontal ligament stem cells (PDLSCs)
  • Periodontal ligament - contains stem cells which have the potential to form periodontal structures such as cementum and ligament
  • from the roots of extracted teeth
  • In vitro-differentiate into osteoblasts, cementoblasts,
  • and adipocytes.
  • In vivo, after transplantation into mice, structures resembling bone, cementum, cartilage, and PDL have been found.
  • Dental follicle stem cells (DFSCs)
  • The dental follicle plays a major role in the genesis of cementum, periodontal ligament, and alveolar bone.
  • isolated from the follicles of impacted third molars
  • in vitro exhibit characteristics of cementoblasts and osteoblasts-can differentiate neurally.
  • In vivo, tissue similar to dental cementum and differentiation into PDL progenitor cells
  • Stem cells from the dental apical papilla (SCAPs)
  • SCAPs - stem cells from the apical part of the papilla,
  • a precursor tissue of the dental pulp.
  •  Impacted third molars
  • In vitro, SCAPs -differentiate osteogenically, odontogenically, and adipogenically.
  • In vivo, SCAPs -differentiate into odontonblasts and osteoblasts.
  • Non-dental stem cells
  • Human bone marrow-bone marrow derived mesenchymal stem cells (BMSCs) can replicate themselves and, in experiments, be differentiated into osteoblasts, myoblasts, adipocytes, and neuron-like cells
  • In humans, BMSCs -used therapeutically in bone augmentation by sinus lifts
  • -minimally invasively harvested from the iliac crest and inserted into the maxillary sinus on a carrier.
  • MBMSCs -(mandibular bone marrow stem cells)
  • -possess a high osteogenic potency
  • Mesenchymal cells can be isolated from odontomas and differentiated into dental hard tissue, such as dentin
  • Other sources :
  • From umbilical cord blood
  • cartilage
  • the cornea
  • mammary glands
  • adipose tissue
  • Renal stem cells
  • Medical research- multipotent neural stem cells
  •  from areas such as the hippocampus and subventricular zone
  • Dermal multipotent cells -differentiated to odontoblasts in embryonic tooth-bud medium
  • Dental Stem cell markers
  • Identify,characterize, and isolate stem cells.
  • STRO-1, a trypsin-resistant cell-surface antigen- most common-early surface markers of mesenchymal stem cells
  • STRO-4, binds to heat shock protein–90 beta of multipotent MSCs
  • The osteoblast marker osteocalcin -a stem cell marker of DPSCs
  • The neural marker nestin on dental stem cells
  • Conclusion
  • For dentistry, stem cell biology and tissue engineering are of great interest.
  • A great deal of research must be done before it is possible to cultivat eentire teeth as natural, autologous tooth replacements










Read more…

Cleft lip classification systems


  1. 1.    Veau classification

Classification system proposed in 1938.

Group I (A)

  • Defects of the soft palate alone

Group II (B)

  • Defects involving the hard and soft palates (not extending anterior to the incisive foramen)

Group III (C)

  • Defects involving the palate through to the alveolus

Group IV (D)

  • Complete bilateral clefts.

2,Kernahan and Stark classification [2]

Embryology-based classification system proposed in 1958 that designates the incisive foramen as the dividing line between the primary and secondary palates.

The incisive foramen is a funnel-shaped opening through which neurovascular bundles pass. It is located in the hard palate behind the middle upper teeth (incisors). This structure is an important embryological landmark, which is used to define the boundary between the primary and secondary palate.

  • Primary palate includes those structures anterior to the incisive foramen (lip, pre-maxilla, anterior septum).
  • Secondary palate includes those structures posterior to the incisive foramen (lateral palatine shelves, soft palate, and uvula).

3.Kernahan classification [3]

Classification system based on the resemblance of an intra-oral view of a cleft lip and palate to the letter 'Y', proposed in 1971.

The area affected by the cleft is marked on the 'Y' and labelled from 1 to 9, each of which represents a different anatomical structure. Combinations of the numeric values represent the appearance of the cleft lip, alveolus, or palate. View image

  • Areas 1 and 4 represent the right and left side of the nasal floor, respectively.
  • Areas 2 and 5 represent the right and left side of the lip, respectively.
  • Areas 3 and 6 represent the right and left side of the paired alveolar segment, respectively.
  • Area 7 represents the primary palate.
  • Areas 8 and 9 represent the secondary palate.

4.Harkins' classification [4]

Classification system proposed in 1962.

  1. Cleft of primary palate
  • Cleft lip
  • Alveolar cleft
  1. Cleft of secondary palate
  • Soft palate
  • Hard palate
  1. Mandibular process clefts
  2. Naso-ocular clefts: involving the nose towards the medial canthal region
  3. Oro-ocular clefts: extending from the oral commissure towards the palpebral fissure
  4. Oro-aural clefts: extending from the oral commissure towards the auricle.

5.Spina classification [5]

Classification system proposed in 1974.

  1. Pre-incisive foramen clefts (lip ± alveolus)
  • Unilateral
  • Bilateral
  • Median
  1. Trans-incisive foramen cleft (lip, alveolus, palate)
  • Unilateral
  • Bilateral
  1. Post-incisive foramen clefts (secondary cleft palate)
  2. Atypical (rare) facial clefts.

6.Tessier's classification [6]

Tessier described a classification scheme that is universally utilised, in a landmark article of 1976. View imageView image

Oro-facial clefts can manifest as:

  • Unilateral or bilateral
  • Complete, incomplete, or microform (e.g., sub-mucous cleft palate)
  • Clefting of the lip with or without the palate, or of the palate in isolation
  • Atypical cranio-facial clefts.



  • The following classification was proposed by
  • Davis and Ritchie in 1922.
  •  This system broadly categorized the clefts into three groups according to position of cleft in relation to alveolar process.
  • Group I – Pre alveolar clefts:
  • • Unilateral cleft lip
  • • Bilateral cleft lip
  • • Median cleft lip
  • Group II - Post alveolar clefts:
  • • Cleft hard palate alone
  • • Cleft soft palate alone
  • • Cleft soft palate and hard palate
  • • Sub mucous cleft
  • Group III-Alveolar clefts:
  • • Unilateral alveolar cleft
  • • Bilateral alveolar cleft
  • • Median alveolar cleft


Santiago A8 proposed a classification in 1969 in which he used four digits to indicate presence of cleft and its location. Each digit is followed by letter to indicate condition of cleft (complete, incomplete or

sub mucous). Four digits represent the following four structures

affected by cleft.

• The first digit refers to the lip.

• The second digit refers to the alveolus.

• The third digit refers to the hard palate.

• The fourth digit refers to the soft palate.

The numbers used as digits represents the condition of cleft.

• 0= No cleft

• 1= Midline cleft

• 2= Cleft on right side

• 3= Cleft on left side

• 4= Bilateral cleft

The letters indicate more specifically the type of cleft.

• A = An incomplete midline cleft

• B = An incomplete cleft of right side

• C = An incomplete cleft of left side

• D = Bilateral incomplete cleft

  • • E = Sub mucous cleft

Kreins O (cited by Hodgkinson et al)9 proposed

LAHSHAL system for classification of cleft lip and

palate patients which was modified on the recommendation

of Royal College of Surgeons Britain in 2005

by omitting one “H” from the acronym “LAHSHAL”. LAHSAL system is a diagrammatic classification

of cleft lip and palate. According to this classification,

mouth is divided into six parts.

• Right lip

• Right alveolus

• Hard palate

• Soft palate (LAHSAL)

• Left alveolus

• Left lip

• The first character is for patient’s right lip and

last character for patient’s left lip.

• LAHSAL code indicates complete cleft with

capital letter and an incomplete cleft with small


 No cleft is represented with a dot.

  1. 10.                       ELNASSRY CLASSIFICATION:

Elnassry10 proposed following classification in

2007. He divided cleft lip and palate patients in to

seven classes.

Class I: Unilateral cleft lip

Class II: Unilateral cleft lip and alveolus

Class III: Bilateral cleft lip and alveolus

Class IV: Unilateral complete cleft lip and palate

Class V: Bilateral complete cleft lip and palate

Class VI: Cleft hard palate

Class VII: Bifid uvula




  1. 1.    Veau classification

Classification system proposed in 1938.

Group I (A)

  • Defects of the soft palate alone

Group II (B)

  • Defects involving the hard and soft palates (not extending anterior to the incisive foramen)

Group III (C)

  • Defects involving the palate through to the alveolus

Group IV (D)

  • Complete bilateral clefts.

2,Kernahan and Stark classification [2]

Embryology-based classification system proposed in 1958 that designates the incisive foramen as the dividing line between the primary and secondary palates.

The incisive foramen is a funnel-shaped opening through which neurovascular bundles pass. It is located in the hard palate behind the middle upper teeth (incisors). This structure is an important embryological landmark, which is used to define the boundary between the primary and secondary palate.

  • Primary palate includes those structures anterior to the incisive foramen (lip, pre-maxilla, anterior septum).
  • Secondary palate includes those structures posterior to the incisive foramen (lateral palatine shelves, soft palate, and uvula).

3.Kernahan classification [3]

Classification system based on the resemblance of an intra-oral view of a cleft lip and palate to the letter 'Y', proposed in 1971.

The area affected by the cleft is marked on the 'Y' and labelled from 1 to 9, each of which represents a different anatomical structure. Combinations of the numeric values represent the appearance of the cleft lip, alveolus, or palate. View image

  • Areas 1 and 4 represent the right and left side of the nasal floor, respectively.
  • Areas 2 and 5 represent the right and left side of the lip, respectively.
  • Areas 3 and 6 represent the right and left side of the paired alveolar segment, respectively.
  • Area 7 represents the primary palate.
  • Areas 8 and 9 represent the secondary palate.

4.Harkins' classification [4]

Classification system proposed in 1962.

  1. Cleft of primary palate
  • Cleft lip
  • Alveolar cleft
  1. Cleft of secondary palate
  • Soft palate
  • Hard palate
  1. Mandibular process clefts
  2. Naso-ocular clefts: involving the nose towards the medial canthal region
  3. Oro-ocular clefts: extending from the oral commissure towards the palpebral fissure
  4. Oro-aural clefts: extending from the oral commissure towards the auricle.

5.Spina classification [5]

Classification system proposed in 1974.

  1. Pre-incisive foramen clefts (lip ± alveolus)
  • Unilateral
  • Bilateral
  • Median
  1. Trans-incisive foramen cleft (lip, alveolus, palate)
  • Unilateral
  • Bilateral
  1. Post-incisive foramen clefts (secondary cleft palate)
  2. Atypical (rare) facial clefts.

6.Tessier's classification [6]

Tessier described a classification scheme that is universally utilised, in a landmark article of 1976. View imageView image

Oro-facial clefts can manifest as:

  • Unilateral or bilateral
  • Complete, incomplete, or microform (e.g., sub-mucous cleft palate)
  • Clefting of the lip with or without the palate, or of the palate in isolation
  • Atypical cranio-facial clefts.



  • The following classification was proposed by
  • Davis and Ritchie in 1922.
  •  This system broadly categorized the clefts into three groups according to position of cleft in relation to alveolar process.
  • Group I – Pre alveolar clefts:
  • • Unilateral cleft lip
  • • Bilateral cleft lip
  • • Median cleft lip
  • Group II - Post alveolar clefts:
  • • Cleft hard palate alone
  • • Cleft soft palate alone
  • • Cleft soft palate and hard palate
  • • Sub mucous cleft
  • Group III-Alveolar clefts:
  • • Unilateral alveolar cleft
  • • Bilateral alveolar cleft
  • • Median alveolar cleft


Santiago A8 proposed a classification in 1969 in which he used four digits to indicate presence of cleft and its location. Each digit is followed by letter to indicate condition of cleft (complete, incomplete or

sub mucous). Four digits represent the following four structures

affected by cleft.

• The first digit refers to the lip.

• The second digit refers to the alveolus.

• The third digit refers to the hard palate.

• The fourth digit refers to the soft palate.

The numbers used as digits represents the condition of cleft.

• 0= No cleft

• 1= Midline cleft

• 2= Cleft on right side

• 3= Cleft on left side

• 4= Bilateral cleft

The letters indicate more specifically the type of cleft.

• A = An incomplete midline cleft

• B = An incomplete cleft of right side

• C = An incomplete cleft of left side

• D = Bilateral incomplete cleft

  • • E = Sub mucous cleft

Kreins O (cited by Hodgkinson et al)9 proposed

LAHSHAL system for classification of cleft lip and

palate patients which was modified on the recommendation

of Royal College of Surgeons Britain in 2005

by omitting one “H” from the acronym “LAHSHAL”. LAHSAL system is a diagrammatic classification

of cleft lip and palate. According to this classification,

mouth is divided into six parts.

• Right lip

• Right alveolus

• Hard palate

• Soft palate (LAHSAL)

• Left alveolus

• Left lip

• The first character is for patient’s right lip and

last character for patient’s left lip.

• LAHSAL code indicates complete cleft with

capital letter and an incomplete cleft with small


 No cleft is represented with a dot.

  1. 10.                       ELNASSRY CLASSIFICATION:

Elnassry10 proposed following classification in

2007. He divided cleft lip and palate patients in to

seven classes.

Class I: Unilateral cleft lip

Class II: Unilateral cleft lip and alveolus

Class III: Bilateral cleft lip and alveolus

Class IV: Unilateral complete cleft lip and palate

Class V: Bilateral complete cleft lip and palate

Class VI: Cleft hard palate

Class VII: Bifid uvula



Read more…




1.Patron Saint of dentistry  : St.Appolonia of Alexandria,249 AD

2.First Known dentist : Egyptian , Hesi-Re [3000 B.C]

3.First speciality : Orthodontics [1901]

4.Order of specialities : Ortho [1901]-Oral surgery [1918]-Periodontics [1918]-Prosthodontics[1918]-Pedodontics[1927]-Public health [1937]-Oral pathology[1946]-Endodontics[1963]

5.Earliest Practice of Prosthetic arts –Phoenicians Circa

6.First Dental engine was invented in 1870

7.Pulpitis was recognized by “Archigenus “ in 100 A.D

8.Chirurgia Magna –French Surgeon “GUY de Cahuliac “ in 1386- was the first to coin the term Dentator And Dentists

9.Vesalious In 1500 of Belgium –Accurately Described the teeth of Pulp and pulp chambers

10.Fallopius – Dental Follicle ,Trigeminal nerve,auditory nerve ,Glossopharyngeal ,Hard and Soft palate

11.Credit for the accurate description of Maxillary Sinus : Dr.Nathaniel Highmore of England

12. Ambrose  Pare- a babrber surgeon at 16 years of age –a member of College of Surgeons at age 37- Palatal Obturators and transplant techniques

13.Purman of Breslau – Known for Wax impressions

14.Philip Pfaff in 18th century introduced POP for pouring up models

15.Pierre Fauchard- Father of Scientific dentistry ,Father of Orthodontics

16.Dentistry’s First Pharmacopea –Robert Bunon 1743

17.John Green wood 1789 dentures for George Washington

18.Charles Good year – 1840- Vulcanite rubbers

19.EJ Dunning -1844- Made plaster of paris impressions ,first shown in America

20.First Women dentist in England – widow of Dr.Povey in 1719

21.First Women dentist In US – Emeline Rupert Jones of Connecticut

22.First Women Graduate – Dr.Lucy Hobbs in 1865-She  graduated From OHIO dental college

23.Introduction Of porcelain into dentistry –Duchantenu

24.John Baker – MD surgeon Dentist –earliest qualified Dentist to practice in Boston and in America -1763 A.D

25.1769 A.D – Title Of Doctor Began to be used

26.1788 A.D – Improvement and development of Porcelain dentures by de Chemant

27.First dental book to be published in America – Richard Cotland Skinner

28.First dental chair – James  Snell 1832

29.American Journal of Dental Science – 1839 A.D – First dental periodical

30.First dental school –Baltimore dental college of Surgery –Founded By Harris and Harden

31.Rubber Dam suggested By Sanford .C.Barnum

32.First Foot /threadleengine – Morrison in 1872

33.Hydraulic Chair – Wilkerson -1877 AD

34.System of Dental nomenclature –G.V Black

35.Roentgen- discovered Xray

36.Edward kells – Demonstrates the use of Roentgen rays in dentistry

37.Weston A Price recommends the use of X-ray in RCT

38.Dr.Willaim H Taggart –cast gold inlays

39.Castan –invented epoxy resins

40.Microwave Amplification By stimulated emission of radiation –MASER – Bell Labs’ Arthur L Schawlow and Charles H Townes

41.Theodore Maimans’s Ruby Laser- First working laser in history-May 16 1960

42.Dr.Ali Javan – First Gas laser with Helium Neon 1960

43.Carbon Dioxide Laser – Kumar Patel in 1964

44.L’Esperance –First to report clinical use of an Argon laser in ophthalmology-1968

45.First artificial fluoridation plant at Grand Rapids ,USA

46.First water turbine hand piece by Dr.Nelson in 1954

47.First air turbine –Dr.Borden in 1957

48.Father of Indian Dentistry-R.Ahmed

49.First Indian dental School –Dr.R Ahmed Dental College ,Kolkata

50.Mother of Orthodontics-Anna Hopkins


Read more…




-         Fixed prosthodontic treatment can offer exceptional satisfaction for both patient and the dentist.

-         Fixed prosthodontics can transform an unhealthy, unattractive dentition with poor function into a comfortable, healthy occlusion capable of giving years of further service while greatly enhancing esthetics.

-         To achieve success, requires meticulous attention to every detail from initial patient interview through the active treatment phases to a planned schedule of follow-up care.

-         Problems encountered during treatment can often be traced to errors and omissions during history taking and initial examination.

-         Diagnosis: It is the examination of the physical state, evaluation of mental or psychological makeup and understanding the needs of each patient to ensure a predictable result.

-         Treatment planning: It means developing a course of action that encompasses the ramifications and sequelae of treatment to serve the patient’s needs.

Chief Complaint:

            It should be recorded in patients own words. The accuracy and significance of patient’s primary reason /reasons should be analyzed first. This will reveal problems and conditions of which the patient is often unaware.


            A patient’s history should include all necessary information concerning the reasons for seeking treatment, along with any personal details and past medical and dental experiences that are pertinent. A screening questionnaire is useful for history taking.

Medical History:

            An accurate and current general medical history should include any medication the patient is taking as well as all relevant medical conditions.

a)     Any disorders that necessitate the use of antibiotic premedication, any use of steroids or anticoagulants and any previous allergic responses to medication or dental materials should be recorded.

b)     Any conditions affecting the treatment plan e.g.: various radiation therapy, haemorrahgic disorders etc. should be recorded.

c)     Possible risk factors to the dentist and auxiliary personnel, e.g. carriers of Hepatitis B, Aids or Syphilis are recorded so that adequate measures can be followed when treating known carriers.

Dental History:

            Periodontal, restorative and endodontic history are first noted.

Orthodontic history should be an integral part of the assessment of a prosthodontic dentition. Occlusal adjustment may be needed to promote long term positional stability of the teeth and reduce or eliminate parafunctional activity. Restorative treatment can often be simplified by minor tooth movement. When a patient is contemplating orthodontic treatment, much time can often be saved if minor tooth movement for restorative reasons is incorporated from the start.

TMJ dysfunction history

            A history of pain or clicking in the temporomandibular joints or neuromuscular symptoms, such as tenderness to palpation, may be due to TMJ dysfunction which should be treated before fixed prosthodontic treatment begins.


            Cervical lymph nodes, TMJ and muscles of mastication are palpated.

Temporomandibular joints:

            The TMJ is palpated bilaterally just anterior to the auricular tragic while having the patient open and close his lower jaw.

Tenderness, clicking or pain on movement is noted. Maximum jaw opening less than 40mm indicates jaw restriction, because the average opening is greater than 50mm. Any deviation from the midline is also recorded. Maximum lateral movement can be measured (normal is about 12mm).

Muscles of mastication

            A brief palpation of masseter, temporalis, medial pterygoid, lateral pteregoid, trapezius and sternocleido mastoid muscles may reveal tenderness. The patient may demonstrate limited opening due to spasm of the masseter or temporalis, muscle.


Next, the patient is observed for tooth exposure during normal and exaggerated smiling. This may be critical in treatment planning and particularly for margin placement of metal-ceramic crowns.


-         First the patient’s general oral hygiene is observed.

-          The presence or absence of inflammation should be noted along with gingival architecture and stippling. The existence of pockets should be entered in the record and their location and depth chartered.

-          The presence and amount of tooth mobility should be recorded with special attention paid to any relationship with occlusal prematurities and to potential abutment teeth.

-          Check for a band of attached gingiva around all the teeth, particularly around teeth to be restored with crowns. Mandibular 3rd molars frequently do not have attached gingiva around the distal segment (30% to 60% of cases).

-          The presence and location of caries is noted. The amount and location of caries, coupled with an evaluation of plaque retention, can offer some prognosis for new restorations that will be placed. It will also help the preparation designs to be used.

-          Finally an evaluation should be made of the occlusion. The amount of slide between the retruded position and the position of maximum intercuspation should be noted. Non-working interferences if present, should be evaluated. The presence or absence of simultaneous contact on both sides of the mouth should be observed.


            Articulated diagnostic casts are essential in planning fixed prosthodontic treatment. They provide critical information not directly available during the clinical examination, static and dynamic relationships of the teeth can be examined without interference from protective neuromuscular reflexes. They also reveal those aspects of occlusion not detectable within the confines of the mouth.

            To accomplish their intended goal, they must be accurate reproductions of the maxillary and mandibular arches made from distortion free alginate impressions. (The casts should contain no bubbles as a result of faulty pouring, nor positive nodules on the occlusal surfaces ensuing from air entrapment during the making of the impression).

            The diagnostic casts should be mounted on a semiadjustable articulator with a face bow. By the use of lateral interocclusal records or check bites, a reasonably accurate simulation of jaw movements will be possible. It is important that the mandibular cast be set in a relationship determined by the patient’s optimum condylar position (centric relation position).

Advantages of diagnostic casts:

1)     For diagnosing problems and arriving at a treatment plan.

2)      Allow an unobstructed view of the edentulous spaces and an accurate assessment of the span length, as well as occlusogingival dimension.

3)      Curvature of the arch in the edentulous region can be determined so that it will be possible to predict whether the pontic/pontics will act as a lever arm on the abutment teeth.

4)     Length of the abutment teeth can be accurately gauged to determine which preparation designs will provide adequate retention and resistance.

5)     The true inclination of the abutment teeth will also became evident, so that the problems in a common path of insertion can be anticipated.

6)     Mesiodistal drifting, rotation and faciolingual displacement of prospective abutment teeth can be clearly seen.

7)     A thorough evaluation of wear facets – their number, size and location is possible.

8)     Discrepancies in the occlusal plane become very apparent on the articulated casts.

9)     Occlusal discrepancies can be evaluated and the presence of centric prematurities or excursive interferences can be determined.

10)   Teeth that have supraerupted into the opposing edentulous spaces are easily spotted and the amount of correction needed can be determined.

11)   Diagnostic wax-up can be carried out in situations calling for the use of pontics which are wider or narrower than the teeth that would normally occupy the edentulous space.

Full-mouth Radiographs

            Radiographs provide the information to help correlate all the facts that have been collected in listening to the patient, examining the mouth and evaluating the diagnostic casts.

-         Radiographs should be examined carefully for signs of caries, both on unrestored proximal surfaces and recurring around previous restorations.

-         The presence of periapical lesions, as well as the existence and quality of previous endodontic treatments, should be noted.

-         General alveolar bone levels, with particular emphasis on prospective abutment teeth should be observed.

-         The crown-root ratio of abutment teeth can be calculated. The length, configuration and direction of these roots should also be examined.

-         Any widening of periodontal ligament should be correlated with occlusal prematurities or occlusal trauma.

-         Any evaluation of the thickness of cortical plate of bone around the teeth and of the bone trabeculae can be made.

-         The presence of retained root tips or other pathosis in the edentulous areas should be recorded.

Vitality Testing

            Prior to any restorative treatment, pulpal health must be assessed, usually by measuring the response to percussion and thermal and electrical stimulation. A diagnosis of non-vitality can be confirmed by preparing a test cavity before the administration of local anesthetic.


            A distinction must be made between mounting for diagnosis and mounting for treatment. The attachment of casts to an articulator for diagnosis will be done with the condyles in a centric relation position. Also when the casts are articulated for restoration of a significant portion of occlusion, it may also be done with condyles in centric relation position. Mounting casts for restoration of only a small part of occlusion will be done with teeth in a portion of maximum intercuspation.

            Articulators vary widely in the accuracy with which they reproduce the movements of the mandible.

1)     At the lower end of scale is a non-adjustable articulator. It is usually a small instrument that is capable of only a hinge opening. The distance between the teeth and the axis of rotation on the small instrument is considerably shorter than in the skull with a resultant loss of accuracy. Drastic differences between the radius of closure on the articulator and in the patient’s mouth can affect the placement of morphologic featuers such as cusps, ridges and grooves on the occlusal surface of the teeth being restored.

2)     A semi-adjustable articulator is an instrument whose larger size allows a close approximation of anatomic distance between the axis of rotation and the teeth. If the casts are mounted with a facebow using no more than an approximate transverse horizontal axis, the radius of movement produced on the articulator will reproduce the arc of closure with relative accuracy and any resulting error will be slight. The semiadjustable articulator reproduces the direction and endpoint, but not the intermediate track of some condylar movements. Inter condylar distances are not totally adjustable on semiadjustable articulators. They can be adjusted to small, medium and large configurations. This type of articulator can be used for the fabrication of most single units and fixed partial dentures.

3)     A fully adjustable articulator is designed to reproduce the entire character of border movements, including immediate and progressive lateral translation, and the curvature and direction on condylar inclination. Intercondylar distance is completely adjustable. Since this instrument is very expensive and demands high degree of skill and time, it is used primarily for extensive treatment, requiring the reconstruction of an entire occlusion.

            (To set the condylar inclinations on a semiadjustable instrument, interocclusal records or check bites are used, when the interocclusal record is removed from an arcon articulator, and the teeth are closed together, the condylar inclination will remain the same. However, when the teeth are closed on a non-arcon articulator, the condylar inclination changes, becoming less steep).

            Arcon articulators are more widely used because of their accuracy and the ease with which they disassemble to facilitate the occlusal waxing required for cast restorations. This feature makes this type of articulator (arcon) more difficult for arranging denture teeth. The centric position is less easily maintained when occlusion on all of the posterior teeth is being manipulated. Therefore the non-arcon instrument has been more popular for the fabrication of complete dentures.

Locating the transverse hinge axis

            To achieve the highest possible degree of accuracy from an articulator, the casts mounted on it should be closing around an axis of rotation that is as close as possible to the transverse horizontal axis of the patient’s mandible.

A)    The most accurate way to determine the hinge axis is by the “trial and error” method developed by McCollum and Stuart in 1921 (using a kinematic face bow).

B)    Arbitrary face bows can also used. But they must have an acceptable accuracy. Caliper style ear face bows possess a relatively high degree of accuracy with 75% of the axes located by it falling within 6mm of the true hinge axis. These face bows are designed to be self centering, so that little time is wasted in centering the bite fork and adjusting individual side arms.


            The most common question arising in treatment planning for single tooth restorations is than in what circumstances should cemented restorations made from cast metal or ceramic be used instead of amalgam or composite resin restorations. The selection of the material and design of the restoration is based on several factors:

  1. Destruction of tooth structure: If the amount of destruction previously suffered by the tooth is such that the remaining tooth structure must gain strength and protection from the restoration, cast metal or ceramic is indicated over amalgam or composite resin.
  2. Plaque control: The use of cemented restoration demands the institution and maintenance of good plaque-control program to increase the changes for success of the restoration. Many teeth are seemingly prime candidates for cast metal or ceramic restorations, based solely on amount of tooth destruction that has previously occurred. However, when these teeth are evaluated from the oral environment, they may in fact be poor risks for cemented restorations.
  3. Retention: Full veneer crowns are unquestionably the most retentive. However, maximum retention is not nearly as important for single-tooth restorations as it is for fixed partial denture retainers. It does become a special concern for short teeth and removable partial denture abutments.


            When sufficient coronal tooth structure exists to retain and protect a restoration under the anticipated stresses of mastication, an intracoronal restoration can be employed. Here the restoration itself is dependent on the strength of the remaining tooth structure for structural integrity.

a)     Glass ionomer:

i)                   In small lesions where extension can be kept minimal.

ii)                Useful for restoring Class 5 lesions caused by erosion or abrasion.

iii)              Also employed for incipient lesions on the proximal surfaces of posterior teeth by the use of “tunnel” preparation which leaves the marginal ridge intact.

iv)              Very useful for the restoration of root caries in geriatric and periodontal patients.

v)                 Serves as an interim treatment restoration to assist in the control of a mouth with rampant caries.

b)     Composite resin

i)                   In minor to moderate-lesions in esthetically critical areas.

ii)                Due to polymerization shrinkage and insufficient abrasion resistance, its use on posteriors should be restricted to small occlusal and mesio-occlusal restorations on first molars.

c)     Simple amalgam

i)                   Simple amalgam, without pins or other auxiliary retention is widely used for one-to-three-surface restoration of minor-to-moderate sized lesions in esthetically non-critical areas.

ii)                They are best used when more than half of coronal dentin is intact.

d)     Complex amalgam

i)                   Augmented by pins or other auxiliary means of retention, it can be used to restore teeth with moderate to severe lesions, in which less than half of the coronal dentin remains.

ii)                It can be used as a final restoration when a crown is contraindicated because of limited finances.

Ideally, however, a crown should be constructed over the pin retained amalgam, using it as a core or foundation restoration.

e)     Metal inlay

i)                   Minor to moderate lesions on teeth where the esthetic requirements are low can be restored with this restoration.

ii)                Pre-molars should have one intact marginal ridge to preserve structural integrity.

iii)              Additional bulk of the tooth structure found in a molar, permits the use of this type in a MOD configuration.

f)      MOD Inlay:

i)                   Can be used for restoring moderately large lesions on premolars and molars with intact facial and lingual surfaces.

ii)                It can accommodate a wide isthmus and up to one missing cusp on a molar.

iii)              Cannot be used as a retainer for fixed partial denture.


            If insufficient tooth structure exists to retain the restoration within the crown of the tooth, an extracoronal restoration, or crown is needed.

a)     Partial veneer crown:

i)                   Leaves one or more axial surfaces unveneered.

ii)                It will provide moderate retention and can be used as a retainer for short span fixed partial dentures.

b)     Full metal crown:

i)                   To restore teeth with multiple defective axial surfaces or when less than half of coronal dentin remains.

ii)                Provides maximum use restricted to situations, where there are no esthetic requirements.

c)     Metal-ceramic crown

i)                   Provides maximum retention.

ii)                Combines full coverage with good cosmetic result.

d)     All-ceramic crown

i)                   Their use must be restricted to situations likely to produce low to moderate stress usually used for incisors.

e)     Ceramic veneer

i)                   Produces good cosmetic result on otherwise intact anterior teeth that are marred by severe staining or developmental defects restricted to facial surface of the tooth.


            Several factors must be weighed when choosing the type of prosthesis to be used in any given situation. Important ones are:

a)     Biomechanical factors.

b)     Periodontal factors.

c)     Esthetics.

d)     Financial factors.

e)     Patient’s wishes.

Abutment Evaluation

-         Abutment teeth are called upon to withstand the forces normally directed to the missing teeth, in addition to those usually applied to the abutments.

-         Whenever possible an abutment should be a vital tooth. However, a tooth that has been endodontically treated which is asymptomatic with radiographic evidence of a good seal and complete obturation of the canal, can be used as an abutment. If the endodontically treated tooth does not have sound tooth structure, it must treated through the use of a dowel core, or a pin-retained amalgam or composite resin core.

-         Teeth that have been pulp capped in the process of preparing the tooth should not be used as FPD abutments unless they are endodontically treated.

-         The supporting tissues surrounding the abutment teeth must be healthy and free from inflammation before any prosthesis can be contemplated.

-         Normally, abutment teeth should not exhibit mobility, since they will be carrying an extra load.

The roots and their supporting tissues should be evaluated for 3 factors:

  1. Crown-root ratio.
  2. Root configuration.
  3. Periodontal ligament area.

1)     Crown root ratio

            It is a measure of the length of the tooth occlusal to the alveolar crest of bone compared with the length of the root embedded in the bone. As the level of the alveolar bone moves apically, the lever arm of that portion out of bone increases and the chance for harmful lateral force is increased.

-         The optimum crown-root-ratio for a tooth to be utilized as a fixed partial denture is 2:3 and a 1:1 ratio is the minimum acceptable under normal circumstances.

-         However, there are situations in which a crown-root-ratio greater than 1:1 (i.e. length of crown greater than length of the tooth) may be considered adequate. If the occlusion opposing a proposed fixed partial denture is comprised of artificial teeth, occlusal force will be diminished, with less stress on abutment teeth.

Studies by Klaffenbach in 1936 have shown that occlusal forces exerted against prosthetic appliances has been shown to be considerably less than that against natural teeth.

FPD against RPD à 26.0lb

FPD against FPD à 54.4 lb

FPD against natural teeth à 150.0lb

2)     Root configuration

-         Roots that are broader labiolingually are preferable to roots that are round in cross section.

-         Multirooted posterior teeth with widely separated roots will offer better periodontal support than roots that converge, fuse or generally present a conical configuration. The tooth with conical roots can be used as an abutment for a short span fixed partial denture if all other factors are optimal.

-         A single rooted tooth with evidence of irregular configurations or with some curvature in the apical third is preferable to the tooth that has a nearly perfect taper.

3)     Periodontal ligament area:

-         Larger teeth have greater surface area and are better able to bear added stress.

-         Kalkwarf in 1986 showed that millimeter per millimeter, the loss of periodontal support from root resorption is only 1/3 to ½ as critical as the loss of alveolar crestal bone.

-         Johnston et al in 1971 in their statement designated as “Ante’s law” said that the root surface area of the abutment teeth had to equal or surpass that of the teeth being replaced with pontics.

-         Fixed partial dentures with short pontic spans have a better prognosis than those with long spans. Failures with long span bridges have been attributed to leverage and torque than overload. Biomechanical factors and material failure play an important role in the failure for long span restorations.

-         There is evidence that teeth with poor periodontal support can serve successfully as fixed denture abutments in carefully selected cases. Nyman S, Lindhe in 1976 said that teeth with severe bone loss and marked mobility can be used as fixed partial denture and splint abutments. Elimination of mobility is not the goal in such cases, but to prevent further increase in mobility of that tooth. They said that this is possible in highly motivated patients who are proficient in plaque removal.

Biomechanical Considerations

            All fixed partial dentures, long or short spanned bend and flex.

-         Bending or deflection varies directly with the cube of the length and inversely with the cube of occlusogingival thickness of the pontic.

-         Compared with a fixed partial denture having a single tooth pontic span, a two tooth pontic span will bend 8 times as much. A three tooth pontic will bend 27 times as much as a single pontic.

-         A pontic with a given occlusogingival dimension will bend 8 times if the pontic thickness is halved. To minimize flexing caused by long/short spans, pontic designs with a greater occlusogingival dimension should be selected. The prosthesis may also be fabricated of an alloy with a higher yield strength, such as nickel-chromium.

-         The dislodging forces of a fixed partial denture retainer tend to act in a mesiodistal direction, as opposed to the more common buccolingual direction of forces on a single restoration. Preparations should be modified accordingly to produce greater resistance and structural durability. Multiple grooves, including some on buccal and lingual surfaces are commonly employed for this purpose.

-         Double abutments are sometimes used as a means of overcoming problems created by unfavourable crown-root ratios and long span. There are several criteria that must be met, if a secondary abutment is to strengthen the fixed partial denture.

a)     A secondary abutment must have atleast as much root surface area and as favourable a crown-root ratio as the primary abutment.

E.g.: A canine can be used as a secondary abutment to a first premolar primary abutment, but it would be unwise to use a lateral incisor as a secondary abutment to a canine primary abutment.

-         Arch curvature has its effects on the stresses occurring in a fixed partial denture. When the pontics lie outside the intraabutment axis line, the pontics act as a lever arm which can produce a torquing movement. This is a common problem in replacing all 4 maxillary incisors with a fixed partial denture. The best way to offset this torque is by gaining additional retention in the opposite direction of the lever arm. The secondary retention must be at a distance equal to the length of the lever arm from the interabutment axis.

-         E.g.: The first pre-molars some times are used as secondary abutments for maxillary four-pontic canine-to-canine FPD.


A)   Pier abutments: An edentulous space can occur on both sides of a tooth, creating a lone, freestanding pier abutment. Physiologic tooth movement, arch position of the abutments and a disparity in the retentive capacity of the retainers can make a rigid 5-unit fixed partial denture as a less than ideal plan of treatment.

-         It has been theorized that forces are transmitted to the terminal retainers as a result of the middle abutment acting as a fulcrum, causing failure of the weaker retainer.  However a photoelastic stress analysis study conducted by Standlee and Caputo in 1988 has shown that the prosthesis bends rather than rocking.

-         The retention on the smaller anterior tooth is usually less than that of the posterior tooth because of its smaller dimensions. The loosened casting will leak around the margin and caries is likely to become extensive before discovery.

-         The use of a non-rigid connector has been recommended to reduce this hazard. The movement in a non-rigid connector is enough to prevent the transfer of stresses from the segment being loaded to the rest of the FPD.

-         The most commonly used non-rigid design is a T shaped key that is attached to the pontic and a dove tail key way placed within a retainer.

-          The key way of the connector should be placed within the normal distal contours of the pier abutment and the key should be placed on the mesial side of the distal pontic.

B) Tilted Molar Abutments

            A common problem that occurs is the mandibular second molar abutment that has tilted mesially into the space formerly occupied by the first molar. There is further complication if 3rd molar is present. It will usually have drifted and tilted with the 2nd molar.

-         If the encroachment is slight, the problem can be remedied by restoring or recontouring the mesial surface of the third molar with an overtapered preparation on the second molar.

-         If the tilting is severe, other corrective measure will have to be followed. The treatment of choice is uprighting of the molar by orthodontic treatment. The third molar if present is often removed to facilitate the distal movement of the 2nd molar. After removal of the appliance, the teeth are prepared and a temporary FPD is fabricated to prevent post treatment relapse.

-         A proximal half crown can be used as a retainer on the distal abutment. This preparation design is a 3 ¼ crown that has been rotated 90°. It can be used only if the distal surface is untouched by caries.

-         A telescoping crown and coping can also be used as a retainer for the tilted molar. A full crown preparation with heavy reduction is made to follow the long axis of the tilted molar. An inner coping is made to fit the tooth preparation. The proximal half crown that will serve as the retainer for the FPD is fitted over the coping.

-         A non-rigid connector is another solution to the problem. A full crown preparation is done on the tilted molar, with its path of insertion parallel with the long axis. A box form is placed on the distal surface of the premolar to accommodate a keyway in the distal of the premolar crown.

C)    Canine Replacement Fpds

            This is a problem because often the canine lies outside the interabutment axis. The abutments are the lateral incisor, usually the weakest in the entire arch and the first premolar, the weakest posterior tooth. A FPD replacing  maxillary canine is subjected to more stress than that replacing a mandibular canine, since forces are transmitted outward on the maxillary arch. So the support from secondary abutments will have to be considered. An edentulous space created by the loss of a canine and any 2 contiguous teeth is better restored with a removable partial denture.

D)    Cantilever FPDs

            A cantilever FPD is one that has an abutment or abutments at one end only, with the other end of the pontic remaining unattached. This is a potentially destructive design with the lever arm created by the pontic.

-         Abutment teeth for cantilever FPDs should be evaluated for lengthy roots with a favourable configuration, good crown root ratios and long clinical crowns.

-         Generally, cantilever FPDs should replace only one tooth and have atleast 2 abutments.

-         A cantilever can be used for replacing a maxillary lateral incisor with canine as the abutment. There should be no occlusal contact on the pontic in either centric or lateral excursions.

-         A cantilever pontic can also be used to replace a missing 1st premolar with second premolar and 1st molar as abutment. The occlusal contact should be limited to the distal fossa on the 1st premolar pontic.

-         Cantilever FPDs can also be used to replace molars when there is no distal abutment present. Most commonly the 1st molar is replaced with the 2 premolars as abutments. The pontic should have maximum occlusogingival height, there should be light occlusal contact on the pontic with no contact in any excursions. Buccolingual width should be kept minimum and the pontic should resemble more of a premolar.


            The scope of fixed prosthodontic treatment can range from the restoration of a single tooth to the rehabilitation of the entire occlusion. Single teeth can be restored to full function and improvement in cosmetic effect can be achieved. Missing teeth can be replaced with fixed prosthesis that will improve patient comfort and masticatory ability, maintain the health and integrity of the dental arches, in many instances elevate the patient’s self image.

            It is also possible by the use of fixed restorations, to render supportive and long range corrective measures for the treatment of problems related to the temporomandibular joint and its neuromuscular system. On the other hand, with improper treatment of the occlusion it is possible to create disharmony and damage to the stomatognathic system.


1)     Kalkwarf K.L., Krejci R.F., Pao Y.C. : Effect of root resorption on periodontal support. J.P.D. 1986; 56: 317-319.

2)     Malone W.F.P., Koth D.L., Cavazos E. : Tylman’s theory of practice of fixed prosthodontics. 8th Ed., Ishiyaku publications, 1977.

3)     Markley M.R. : Broken-stress principle and design in fixed prosthesis. J.P.D., 1951; 1: 416-423.

4)     Reynolds J.M. : Abutment selection for fixed prosthodontics. J.P.D., 1968; 19: 483-488.

5)     Rosenstiel R.F., Land M.F., Fujimoto J. : Contemporary fixed prosthodontics. 1st Ed., Mosby Publications, 1988.

6)     Shillingburg H.T., Hobo S., Whisett L.D., Jacobi R., Brackett S.E. : Fundamentals of fixed prosthodontics, 3rd Ed., Quintessence Publication, 1997.

7)     Sutherland J.K., Holland G.A. : A photoelastic analysis of the stress distribution in bone supporting fixed partial denture of rigid and non-rigid designs. J.P.D., 1980; 44: 616-23.

Read more…

Dental materials a complexity that involves the mathematics of Engineering, the science of materials, and arts of dentistry (without one the others are useless) each of these is depended on the other only together can they be effective so let us explore the mathematical complexities of dental materials

Mechanical properties D.M

Out of the four common material property categories namely physical, chemical mechanical and biological. We shall discuss mechanical properties

Definition: mechanical properties are subset of physical properties that are based on the laws of mechanics that is the physical science that deals with energy and forces and their effects on the bodies. They are the measured response, both

Elastic reversible on force removal
And plastic irreversible or non elastic
Of material under an applied force are distribution of forces.

Mechanical properties are expressed most often in units of stress and stain.
They can represent measurement of
1) Elastic or reversible deformation (i.e. proportional unit resilience and modulus of elasticity)
2) Plastic are irreversible deformation (Percent elongation and hardness)
3) A combination of elastic and plastic deformation such as toughness and yield strength

To discuss these properties one must first understand the concepts of tress and strain

Depending on the forces three simple types of tresses are classified
a) Compressive stress
b) Tensile stress
c) Shear stress
d) Flexural (bending) stress

Compressive stress: if a body is placed under a load the tends to compress are
shorten it, the internal resistance to such a load is called a” compressive stress” a compressive stress is associated with the strain here forces are directed to each other in a straight line

Tensile stress: a tensile stress is caused by a load that tends to stretch or elongate a body. A tensile stree is always accompanied by a shear strain, Here forces act paralled to each

d) Flexural Bending stress
is produced by bending forces and may generate all three types of stress in a structure. It can occur in fixed partial dentures or cantilever structures

As shown in above figure. Tensile stress develops on the tissue side of the FPD. And compressive stress develops on the occlusal side.

For a cantilevered FPD the maximum tensile stress develops with the occlusal surface if you can visualize the unit bending downward toward the tissue the upper surface becomes more convex or stretched and the opposite surface becomes compressed

Mechanical properties based on elastic deformation

There are several important mechanical properties measuring reversible deformation and includes
1) Elastic modulus ( young’s modulus or modulus of elasticity or hook’s law )
2) Dynamic young’s modulus
3) Flexibility
4) Resilience
5) Poisson’s ratio

! ) elastic modulus ( young’s modulus or modulus of elasticity
Definition : if any stress value equal to or less than the proportional limit
Is divided by its corresponding strain value, a constant of proportionality will result. This constant of proportionality is known as the modulus of elasticity or young’s modulus it is represented by the letter E
E = Stress
----------- giga Newton’s / sq m or giga pascules
Strain ( 1 giga Newton / m2 6N / m2 = 10. 3 MN / M2
Elastic modulus describes the relative stiffness or rigidity of a material

This phenomenon can play a role in burnishing of margins of crown

Elastic modulus of various materials

Materials Elastic modulus (G N/m2)
1)Enamel 84.1
2) Destin 18.3
3) Feld spathic porcelain 69.0
4) Composite resin 16.6
5)Acrylic denture resin 2.65
6) Cobalt – chromium partial 218.0
denture alloy
7) Gold (type-4) alloy 99.3

Enamel has higher elastic modulus (3-4 times) then dentin and is stiffer or more brittle, while dentin is more flexible and tougher, ceramic have higher modulus then polymers and composites.

2) Dynamic Young’s modulus
Elastic modulus can be measured by a dynamic method, since the velocity at which sound travels through a solid can be readily measured by ultrasonic longitudinal and transverse wave transclucers and appropriate receivers. The velocity of the sound wave and the density of the material can be used to calculate the ‘elastic modulus’ and
‘Poisson ratio’ values. This method of determining ‘dynamic elastic moduli’ is less
complicated than conventional tensile or compressive tests.
If instead of uniatial tensile or compressive stress a shear stress was induced
The resulting shear strain could be used to define a shear modulus for the material. The
Shear modulus (G) \, can be calculated from the elastic modulus (I) and poisons ratio
(V), using equation

G= ----------- = ------------ = 0.38 E
2 (1+V) 2 (1+0.3)

A value of 0.3 for Poisson’s ratio is typical. Thus, the shear modulus is usually about 38% of the elastic modulus.

4) Flexibility :
The maximum flexibility is defined as the strain occurring when the material is stressed to its proportional unit. A larger strain or deformation with slight stresses is called flexibility and is an important consideration in orthodontic appliances.

5) Resilience:
Resilience can be defined as the amount of energy absorbed with in a unit volume of a structure, when it is stressed to its proportional limit. It is popularly associated with springiness .for example when an acrobat falls on a trapeze net the energy fall is absorbed by he resilience of the net and when this energy is released the acrobat is again into the air.
The above is a stress-strain that illustrates the concepts of resilience and toughness. The area bounded by the elastic region is a measure of resilience and the total area under the stress-strain curve is a measure of toughness.
The restorative material should exhibit a moderately high elastic modulus and relatively low resilience thus limiting the elastic strain.

6) Poisson’s Ratio:
When a tensile stress or compressive stress is applied to a cylinder or rod, there is simultaneous axial and lateral strain, within the elastic range, the ratio of the lateral to the axial strain is called POISSONS RATIO
Lateral strain
POISSONS= ----------------------
Axial strain
For ideal isotropic material it is 0.5
For most engineering materials it is 0.3

(Irreversible deformation)
Now, we come to properties that are determined from stresses at the end of elastic region of stress-strain, plot viz
1) Proportional limit
2) Elastic limit
3) Yield strength (proof stress)
4) Permanent (plastic) deformation.

*) Strength:
Strength is the stress necessary to cause either fracture or plastic deformation.
The strength of a material can be described by one or more of the following properties,
1)Proportional limit
2) elastic limit
3) Yield strength
4) Permanent deformation

1) Proportional limit:
Defn: The greatest stress that may be produced in a material such that the stress is directly proportional to strain.
For E.g.: A wire is loaded in tension in a small increments until the wire ruptures without removal of the load each time, and plotted stress on vertical co-ordinate and the corresponding strain is plotted on the horizontal co-ordinate a curve as shown below

The point ‘P’ is the proportional limit and up to point ‘B’the is proportional to strain and beyond ‘P’ the strain is no longer elastic and stress is no longer proportional to strain.

2) Elastic limit:
The elastic limit is defined as the maximum stress that a material will withstand without permanent deformation,(for all practical purposes, therefore). The elastic limit and the proportional limit represent the same stress within the structure and the terms are often interchangeable in referring to the stress involved. However they differ in that one describes the elastic behavior of the material where as the other deals with stress to strain in the structure.

3) Yield Strength it is the stress at which the material begins to function in a plastic manner, this yield strength is defined as the stress at which a material exhibits a limiting deviation from proportionality of stress to strain. It is used when proportional limit cannot be accurately determined.
It is described in terms of percent offset.
Elastic limit, proportional limit and yield strength though defined differently have close values but yield strength is always greater than the other two (proportional limit, elastic limit).
4) Permanent (plastic) deformation
If a material is deformed by a stress beyond its proportional limit before fracture and the force removed. The strain does not become 0 due to plastic or permanent deformation, thus it refers to the stress which a material get permanently deformated i.e it remains bent, stretched or deformed

It is the stress at which the material begins to function in a plastic manner. Thus yield strength is defined as the stress at which a material exhibits a limiting deviation from proportionality of stress to strain. It is used when proportional limit cannot be accurately determined.
It is described in terms of percent offset.
Elastic limit, proportional limit and yield strength though defined differently have close values but yield strength is always greater then the other two.
(i.e. proportional ;limit , elastic limit)

3) Permanent (plastic) Deformation:
If a material is deformed by a stress beyond its proportional limit before fracture and the force removed the strain doesn’t become zero due to plastic or permanent deformation. Thus it refers to the stress beyond which a material get permanently deformated i.e. it remains bent stretched or deformated .

Now, Let’s have a look at different types of strength
It is the material stress required to fracture a structure.

1) Diametral Tensile Strength:
Tensile strength is generally determined by

Now let’s have a look at different types of strength,

It is the maximal stress required to fracture a structure

1) Diametral Tensile Strength:
Tensile strength is generally determined by subjecting a rod, wire or dumbbell shaped specimen to tensile load, since such test is quit difficult to perform for brittle materials because of alignment and gripping problems, another test has become popular for brittle materials because of alignment and gripping problems, another test has become popular for determining this property for brittle dental material is refered to as” Diametral compression test”

Compressive load is placed against the side of a short cylindrical (specimens). The vertical compressive forces produces a tensile stress and fracture occurs along this vertical plane, Have tensile stress is directly proportional to compressive load

_2P_ P= Load
Tensile Stress = Dt D= Diameter
T= Thickness

This test simple to conduct and provides excellent reproducibility of result.

Flexure Strength ( Transverse strength or Modulus of rupture)

This property is essential a strength test of a beam supported at each end, under static load. It is a collective measurement of all types of stress.

When the load is applied, the specimen bends, the principal stress is applied, the specimen bends, the principal stress on the upper surface are compressive, where as those on the lower surface are tensile.

The mathematical formula for computing the flexure strength is

= 3Pl = flexural strength
2 bd2 = Distance between support
= Width of the specimen
=Depth or thickness specimen
= Maximum load at the point of fracture

it is preferred for brittle materials

Fatigue strength:

Stress values well below the ultimate tensile strength can produce premature fracture of a dental prosthesis or material because microscopic flows grow slowly over many cycles of stress. This phenomenon is called fatigue failure

Fatigue strength is the endurance limit i.e. maximum stress cycles that can be maintained without failure

It can be determined by subjecting a material to a cyclic stress of a maximum known value and determining the number of cycles that are required to produce failure.

Static fatigue is a phenomena attributed to the interaction of a constant tensile stress with structural flow over time. It is a phenomenon exhibited by certain ceramic materials in wet environment; certain ceramics also demonstrate dynamic fatigue failure.

1) Impact strength:

Impact strength may be defined as the energy required to fracture a material under an impact force

A charpy type impact tester and Izod impact tester are used to test.

A material with a low elastic modulus and a high tensile strength is more resistant to impact forces.

A low elastic modulus and a low tensile strength suggest low impact resistance

Other mechanical properties: Toughness is defined as the amount of elastic and plastic deformation energy required tp fracture a material and is a measure of resistance to fracture, Toughness is stress stain cure upto fracture and depends on strength and ductility

Fracture toughness:

Fracture toughness is a mechanical property that describes the resistance of brittle materials to the catastrophic propagation of flows under times the square root of crack length i.e Mpa. M½ or tnN.M 3/2

Brittleness is the relative inability of a material to sustain plastic deformation before fracture of a material occurs. It is considered as the opposite of toughness for example Amalgams, ceramics and composites are brittle at oral temperature; They fracture without plastic strain. Hence, brittle materials fracture at or near their proportional limit however, a brittle material is not necessarily weak, for example Glass is drum in to a fibers or Glass infiltrated alumina core ceramics.

3) Ductility and Malleability:
Ductility represents the ability of a material to sustain a large permanent deformation under a tensile load before it fractures. For example a metal that may be readily drawn into a wire is said to be ductile

Malleability: The ability of a material to sustain considerable permanent deformation without rupture

Under Compression:
As in the most ductile and malleable metal which silver is second, platinum B 3rd rank in ductility and copper ranks 3rd in malleability

Ductility is measured by 3 common methods

a) Percent elongation after fracture:

The simplest and most commonly used method is to compare the increase in length of a wire or rod after fracture in tension to its length before fracture. Two marks are placed on the wire as the gauge length (for dental, materials, the standard gauge length is usually 51mm) the wire or rod is then pulled a part under a tensile load, the fractured ends are fitted together, and the gauge length is again measured, the ratio of the increase in length after fracture to the original gauge length is called the present elongation and represents ductility

b) The reduction in area of tensile test specimens:
The necking or cone-shaped constriction that occurs at the fractured end of a ductile wire after rupture under tensile load, the percentage of decrease in cross-sectional area of the fractured end in comparison to the original area of the wire or rod is referred to as the reduction in area

c) The cold bend test:
The material is clamped in a vise and bent around a mandrel of specified radius, the number of bends to fracture is counted, with the grater the number, the greeter the number, the greater is the ductility of the material.

The term hardness is difficult to define, in mineralogy the relative hardness of a substance is based on its ability to” resist scratching” In metallurgy and most other disciplines, the concept of hardness is” resistance to indentation”

Numerous properties like strength proportional limit and ductility interact to produce hardness

Hardness tests, are included in ADA specifications for dental materials, there are various scales and tests mostly based on the ability of the material surface to resist penetration by a point under a specified load, these test include Burcol, Brinells Rock well, share, Vickers and Knoop

1) Brinell bard ness test:
- One of the oldest test used to
determining the hardness of metals
- A hardness steel ball is pressed under a specified load into the polished surface of a material the load is divided by the area of the projected surface of the indentation and the quotient is referred to ad Brinell hardness number or BHN

- Brinell hardness test has been extensively used for determining the hardness of metals and metallic materials used in dentistry.

- BHN is related to the proportional limit and the ultimate tensile strength of dental gold alloys

Rockwell hardness test:

It is some what similar to the
Brinell test in that a steel ball or conical diamond point is used. Instead of measuring the diameter of the impression the depth of penetration is measured directly by a dial gauge on the instrument. Different indenting points for different materials are used and designated as RHN

These two BHN and RHN are unsuitable for brittle materials

Vickers Hardness test:
- Is the same principle of hardness
- Testing that is used in the Brinell test
- Instead of a steel ball, a square based
- Pyramid is used. Although the pression
- Is square instead of round the load is divided by the projected area of indentation and
designated as VHN
- The Vickers test is employed in the ADA specification for dental casting gold alloys,
also it is suitable for brittle materials, Hence used for measure tooth hardness

4) Knoop Hardness test:
This employs a diamond tipped tool cut in geometric configuration. The impression is rhombic in outline and the length of the largest diagonal is measured the projected area is divided into the load to give the KHN

The hardness value is virtually independent of the ductivity of the tested material thus hardness of tooth enamel can be compared with that of gold, porcelain, load can be varied from 1g to 1kg so that both hand and soft materials can be tested

The knoop and Vickers tests are classified as micro hardness test while Brinell and Rock well are macro hardness test. Knoop and Vickers can measure hardness in thin object too

Other less sophisticated tests are SHORE and BARCOL to measure hardness of materials like rubber and plastics, types of dental materials; these utilize portable indenters and are used in industry for quality control the principle of these tests is alos based on resistance to indentation

Stress concentration factors of material

Stress concentration factors refer to the microscopic flows or micro and macro structural defects on the surface or within the internal structure, these factors are more accentuated in brittle material and are responsible for unexpected fractures at stress much below ultimate strength. The stress higher when the flow is perpendicular to direction of tensile stress and flows on the surface accumulated higher stresses

Areas of high stress concentration are caused by following factors

1) Surface flows i.e. voids are inclusions
2) Interior flows i.e. voids or inclusions
3) A sharp internal angle at the pulpal axial angle of a tooth preparation for an amalgam or composite restoration
4) A large difference in elastic modulus or thermal expansion coefficient across a bonded interface
5) Hertzian load i.e. applied at a point on a brittle material

There are several waysto minimize these stress concentrations, thus reduce the risk of clinical fracture
1) The surface can be polished to reduce the depth of the flow
2) Internal line angles of tooth preparation should be wel rounded to minimize the risk of cosp fracture
3) The materials must be closely matched in their coefficient of expansion or contraction
4) The cusp tip of an opposing crown or tooth should be well rounded distribute stress over a larger area for brittle materials
Mechanical properties of tooth structure and mastication forces

The mechanical properties of enamel and dentin varies one type of tooth to another, within individual teeth than between teeth and position of tooth.
That is cuspal enamel is stronger than enamel on other surfaces of tooth stronger under longitudinal compression than lateral compression

On the other hand, Dentin is considerably stronger in tension (50MPa) than enamel (10MPa), compressive strength of enamel and dentin are comparable the proportional limit and modulus of elasticity of enamel are higher than dentin

Mastication forces :
Mastication or bitting forces varies mankedly varies from one area of the mouth to another and from one individual to another.
For the molar

Bibe force range from: 400 to 890N (90 to 200 pounds)
Premolar area : 222 to 445N (50 to 100 pounds)
Cuspid region : 133 to 334N (30 to 75 pounds)
Incisor region : 89 to 111N (20 to 55 pounds)

Generally higher metals than and greater in beyond adults than in children

As we have seen there are various properties governing the performance of the material. Different properties make to particular material more suitable for a given situation for example Higher strength in posterior restoration Better electivity is required in cast restorations.

Thus, a through knowledge and in-depth understanding of these mechanical properties will help us to select and deliver the most suitable material for every situation.
Read more…

Casting Procedures

Casting is the process by which a wax pattern of a restoration is converted to a replicate in dental alloy. The casting process is used to make dental restorations such as inlays, onlays, crowns, bridges, and removable partial dentures. Because castings must meet stringent dimensional requirements, the casting process is extremely demanding. In dentistry, virtually all casting is done using some form or adaptation of the lost-wax technique. The lost-wax technique has been used for centuries, but its use in dentistry was not common until 1907, when W.H. Taggart introduced his technique with the casting machine.
Casting can be defined as the act of forming an object in a mold .The object thus formed is also called as a casting .
Objectives of casting
1) To heat the alloy as quickly as possible to a completely molten condition.
2) To prevent oxidation by heating the metal with awell adjusted torch .
3) To produce a casting with sharp details by having adequate pressure to the well melted metal to force into the mold.
- There are 4 methods for making wax patterns for a cast restoration .
a) Sprue Former . (sprue pin ).
-provides channel for the molten metal .
-made of wax , plastic or metal .
-reservoir is attached to the sprue .
-ideally length of sprue is 3/8 th” to ½”
Lost Wax Process
The lost wax casting process is widely used as it offers asymmetrical casting withnvery fine details to be manufactured relatively inexpensively. The process involves producing a metal casting using a refractory mould made from a wax replica pattern.
The steps involved in the process or the lost wax casting are:
1 .Create a wax pattern of the missing tooth / rim
2 .Sprue the wax pattern
3 .Invest the wax pattern
4. Eliminate the wax pattern by burning it (inside the furnace or in hot water). This will create a mould.
5 . Force molten metal into the mould - casting.
6 .Clean the cast.
7 .Remove sprue from the cast
8 . Finish and polish the casting on the die .
The lost-wax technique is so named because a wax pattern of a restoration is invested in a ceramic material, then the pattern is burned out ("lost") to create a space into which molten metal is placed or cast. The entire lost-wax casting process . A wax pattern is first formed on a die of the tooth to berestored or, occasionally, directly on the tooth. All aspects of the final restoration are incorporatedinto the wax pattern, including the occlusion, proximal contacts, and marginal fit. Once the wax pattern is completed, a sprue is attached, which serves as a channel for the molten metal to pass from the crucible into the restoration. Next, the pattern and sprue are invested in a ceramic material, and the invested pattern is heated until all remnants of the wax are burned away. After burnout, molten metal is cast into the void created by the wax pattern and sprue. Once the investment is broken away, the rough casting ispickled to removed oxides. Finally, the sprue is removed and the casting is polished and deliveredto the patient. If all steps have been done well, the final restoration will require minimal modification during cementation into the patient's mouth.
Dimensional Changes in the Lost-Wax Technique
If materials used during the casting process didn't shrink or expand, the size of the final cast restoration would be the same as the original wax pattern. However, dimensional changes occur in most of the steps and, in practice, the final restoration may not be exactly the same size as the pattern. The management of these dimensional changes is complex, but can be summarized by the equation:
wax shrinkage + metal shrinkage = wax expansion + setting expansion + hygroscopic expansion + thermal expansion .This equation balances the shrinkage (left sideof equation) against the expansion (right side ofequation) that occurs during the casting process. If the final restoration is to fit the die, the shrinkage and expansion during the casting process bmust be equal. Shrinkage forces in the casting process come from two sources: wax and metal. Although the die restricts the wax from shrinking to a large degree while the pattern is on the die, residual stresses may be incorporated into the pattern and released during investing, when the pattern isremoved from the die. Furthermore, if the investingis done at a temperature lower than that atwhich the wax pattern was formed, the wax willshrink significantly because of the high coefficientof thermal expansion of waxes. Metal shrinkage occurs when the moltenmetal solidifies, but this shrinkage is compensated by introducing more metal as the casting solidifies. However, once the entire casting has reached the solidus temperature of the alloy, shrinkage will occur as the casting cools to room temperature. As for wax, the metallic shrinkage that occurs below the solidus is caused by the coefficient of thermal expansion for the alloy. Cooling shrinkage may reach 2.5% for an alloy that cools from a high solidus temperature (1300" to 1400' C), depending on the coefficient of thermal expansion of the alloy. A typical shrinkage range for most alloys is 1.25% to 2.5%. Furthermore, because the casting is solid at this point, the only possible compensation mechanismis to start with a void space that is 1.25% to2. 5% too large. Thus, shrinkage of wax and metalmust be compensated with expansion in the investment if the casting is to have the appropriate dimensions.

Accuracy of the Lost-Wax Technique
A casting should be as accurate as possible, although a tolerance of rt0.05% for an inlay casting is acceptable. If the linear dimension of an average dental inlay casting is assumed to be 4 mm, +0.05% of this value is equal to only +2ym, which suggests that if two castings made for the same tooth have a variation of 4 ym, the difference may not be noticeable. To visualize this dimension, recall that the thickness of an average human hair is about 40 ym. Therefore the tolerance limits of a dental casting are approximately one-tenth the thickness of a human hair. To obtain castings with such small tolerancelimits, rigid requirements must be placed not only on the investment material but also on theimpression materials, waxes, and die materials. Naturally, technical procedures and the proper handling of these materials are equally important. The values for the setting, hygroscopic, and thermal expansions of investment materials may vary from one product to another, and slightly different techniques may be used with different investments. In each case, the values obtained for any one property should be reproducible from one batch to another and from one casting to another.
The Sprue :
Its a channel through which molten alloy can reach the mold in an invested ring after the wax has been eliminated. Role of a Sprue: Create a channel to allow the molten wax to escape from the mold. Enable the molten alloy to flow into the mold which was previously occupied by the wax pattern.

1 . Forms a mount for the wax pattern .
2 . Creates a channel for elimination of wax .
3 .Forms a channel for entry of molten metal
4 . Provides a reservoir of molten metal to compensate for the alloy shrinkage .
It should be approximately the same size of the thickest portion of the wax pattern .
Too small sprue diameter suck back porosity results .
Sprue should be attached to the thickest portion of the wax pattern .
It should be Flared for high density alloys & Restricted for low density alloys .
Based on the
1 .Individual judgement .
2 .Shape & form of the wax pattern .
Patterns may be sprued directly or indirectly ..
Indirect method is commonly used
Reservoir prevents localised shrinkage porosity .
Reservoir And Its Location
Reservoir portion of a Spruing system is a round ball or a bar located 1mm away from the wax pattern. Reservoir should be positioned in the heat centre of the ring . This permits the reservoir to remain molten for longer and enables it to furnish alloy to the pattern until they complete solidification process . Round ball reservoir & a bar reservoir also called connector
Significance of Reservoirs:
Reservoir is the largest mass of any part of the Sprue system & it is present in the heat centre of the ring, it is the last part to solidify. These properties allow continuous feeding of the molten alloy to compensate for Solidification shrinkage & avoid Shrinkage porosity
Spruing Technique:
Direct Spruing:
The flow of the molten metal is straight(direct) from the casting crucible to pattern area in the ring. Even with the ball reservoir, the Spruing method is still direct. A basic weakness of direct Spruing is the potential for suck-back porosity at the junction of restoration and the Sprue.
Indirect Spruing:
Molten alloy does not flow directly from the casting crucible into the pattern area, instead the alloy takes a circuitous (indirect) route. The connector (or runner) bar is often used to which the wax pattern Sprue formers area attached. Indirect Spruing offers advantages such as greater reliability & predictability in casting plus enhanced control of solidification shrinkage .The Connector bar is often referred to as a “reservoir .

Armamentarium :
1. Sprue .
2 . Sticky wax .
3 . Rubber crucible former .
4 . Casting ring .
5 . Pattern cleaner .
6 . Scalpel blade & Forceps .
7 . Bunsen burner .
I . Procedure for single casting :
A 2.5 mm sprue former is recommended
for molar crowns 2.0 mm for premolars & partial coverage crowns .
II . Procedure for multiple casting :
Each unit is joined to a runner bar .
A single sprue feeds the runner bar
Sprue Should be directed away from the delicate parts of the pattern
It should not be at right angles to a flat surface .(leads to turbulance  porosity .)
Ideal angulation is 45 degrees .
Depends on the length of casting ring .. Length of the Sprue former should be such that it keeps the wax pattern about 6 to 8 mm away from the casting ring. Sprue former should be no longer than 2 cm. The pattern should be placed as close to the centre of the ring as possible.
Short Sprue Length:
The gases cannot be adequately vented to permit the molten alloy to fill the ring completelyleading to Back Pressure Porosity.
Long Sprue Length:
Fracture of investment, as mold will not withstand the impact force of the entering molten alloy.
Top of wax should be adjusted for :
6 mm for gypsum bonded investments .
3 -4 mm for phosphate bonded investments .
I . - Wax . II . Solid
- Plastic . Hollow
- Metal .
Small auxilliary sprues or vents improve casting of thin patterns .
Acts as a HEAT SINK .
Pattern should be removed in line with its path of removal
To minimise the irregularities on the investment & the casting a wetting agent can be used .

1 . Reduce contact angle between liquid & wax surface .
2 .Remove any oily film left on wax pattern .
Distortion is dependant on temperature &time interval before investing .
To avoid any distortion ,
Invest the pattern as soon as possible .
Proper handling of the pattern .
Wax pattern should be evaluated for smoothness , finish & contour .
Pattern is inspected under magnification & residual flash is removed .
It serves as a base for the casting ring during investing .Usually convex in shape.
May be metal , plastic or rubber .
Shape depends on casting machine used .
Modern machines use tall crucible to enable the pattern to be positioned near the end of the casting machine .
Casting ring
Most common way to provide investment expansion is by using a liner in the casting ring .Traditionally asbestose was used .
Non asbestose ring liner used are :
1) Aluminosilicate ceramic liner .
2) Cellulose paper liner .
The aim of using a resilient liner is to
-. allow different types of investmentbexpansion (act as a cushion)
_. facilitate venting during casting procedure.
_. facilitate the removal of the investment block after casting.&. prevent the distortion by permitting the outward expansion of the mold.
The casting ring holds the investment in place during setting and restricts the expansion of the mold. Normally a resilient liner is placed inside the ring leaving about 2-3 mm from both ends to allow for supporting contact of the investment with the casting ring.
Purpose of Casting Ring Liner
Ringer liner is he most commonly used technique to provide investment expansion. To ensure uniform expansion , liner is cut to fit the inside diameter of the casting ring with no overlap. Thickness of the liner should not be less than approximately 1mm. Place the liner somewhat short of the ends of the ring, 3mm, tends to produce a more uniform expansion, therefore less chance for distortion of the wax pattern & mold .
Traditional material for lining casting rings until it was learned that it posed a potential health risk to dental laboratory technicians . Asbestos fiber bundles were found to produce hazardous-size respirable particles capable of causing lung disease.
Non-asbestos Ring Liners: Ceramic (aluminum silicate) Cellulose (paper) Ceramic-cellulose combination Safety of the ceramic ring liners remains uncertain, because aluminum silicate also appears capable of producing hazardous-size respirable particles
Used for phosphate bonded investments .
This method uses paper or plastic casting ring .
It is designed to allow urestricted expansion .
Useful for high melting alloys .
Investing Technique
Investing is the process by which the sprued wax pattern is embedded in a material called an investment. The investment must be able to withstand the heat and forces of casting, yet must conform to the pattern in a way such that the size and surface detail are exactly reproduced. In dentistry, gypsum- and phosphate-bonded investment materials are the two types of materials used for this purpose . After spruing, the pattern a casting ring is added to contain the investment while the investment material is poured carefully around the pattern. For the setting and hygroscopic expansion of an investment to take place more uniformly, some allowance must be made for the lateral expansion of the investment. Solid rings do notpermit the investment to expand laterally duringthe setting and hygroscopic expansions of themold.
To overcome this lateral restriction, a ceramic paper liner is placed inside the ring.The ceramic paper liner is cut to fit the inside ofthe metal ring and is held in place with the finger.The ring containing the liner is then dipped intowater until the liner is completely wet and wateris dripping from it. The ring is shaken gently toremove the excess water. After the liner has beensoaked, it should not be touched or adaptedfurther with a finger because this reduces itscushioning effect, which is needed for the lateral expansion of the investment. A liner that is about3 mm short at each end of the ring is preferred.When the liner is equally short at each end of thering, the investment is locked into the ring, and uniform expansion of the cavity form occurs.
During investing, the water-based gypsummaterial must flow around the pattern and captureevery surface detail. However, the wax sur-faces generally are not easily wetted by water.The surface of a wax pattern that is not completelywetted with investment results in surface irregularities in the casting that destroy its accuracy.These irregularities can be minimized byapplying a surface-active wetting agent on thewax. The function of the wetting agent is toreduce the contact angle of a liquid with the waxsurface. Wetting agents also remove any oily filmthat is left on the wax pattern from the separatingmedium. Thecontact angles are 98' for the plain wax surfaceand 61" for the treated wax surface. The lowercontact angle indicates that the treated wax surfacehas an affinity for water, which results in theinvestment being able to spread more easily overthe wax. Because the surface-active agents arequite soluble, rinsing the wax pattern with waterafter the application defeats the purpose of theiruse.
The distortion of the wax pattern after itsremoval from the die is a function of the temperatureand time interval before investing. Thenearer the room temperature approaches the softening point of the wax, the more readilyinternal stresses are released. Also, the longer apattern is allowed to stand before investing, thegreater the deformation that may occur, even atroom temperature. A pattern should therefore beinvested as soon as possible after it is removedfrom the die, and it should not be subjected to awarm environment during this interval. In anycase, a pattern should not stand for more than20 to 30 minutes before being invested. Once itis properly invested and the investment has set,there is no danger of further pattern distortion,even if it remains for some hours before the finalstages of wax elimination (burnout) and casting
Investment Techniques
During investingof the pattern, the correct water powder ratioof the investment mix, a required number ofspatulation turns, and a proper investing techniqueare essential to obtain acceptable castingresults. There are two methods of investing thewax pattern: hand investing and vacuum investing.In both cases, the proper amount of investmentpowder and water should be used, followingthe manufacturer's instructions exactly. Thewater is added first, followed by the slow additionof the powder to encourage the removal ofair from the powder. The powder and liquid aremixed briefly with a plaster spatula until all thepowder is wetted.
In hand investing, the cover of the bowl containingthe investment mix is placed over thebowl . The cover contains a mechanicalmixer, and the mixing is done by hand,usually for 100 turns of the spatulator. The settingrate of an investment depends on the number ofspatulation turns, which also affects the hygroscopicexpansion. The investment, after beingspatulated, is placed on the vibrator to eliminatesome of the air bubbles from the mix and tocollect all of the mix from the sides of the rubber bowl into the center. Thefilled ring is then set aside for the investment toset completely, which usually requires 45 to60 minutes. When a phosphate-bonded investmentis used, the ring is slightly overfilled, the topof the ring is not leveled off, and the investmentis allowed to set. After the investment has set, the excess investment is ground off using a modeltrimmer. This procedure is necessary because anonporous, glassy surface results, which must beground off to improve the permeability of the
investment and allow for gases to readily escape from the mold during casting.
In vacuum investing, special equipment is used to facilitate the investing operation. With this equipment, the powder and water (or special liquid) are mixed under vacuum and the mixed investment is permitted to flow into the ring and around the wax pattern with the vacuum present. Although vacuum investing does not remove all the air from the investment and the ring, the amount of air is usually reduced enough to obtain a smooth adaptation of the investment to the pattern. Vacuum investing often yields castings with improved surfaces when compared with castings produced from hand-invested patterns. The degree of difference between the two procedures depends largely on the care used in hand investing. Whether hand- or vacuum-investing procedures are used in filling the casting ring, the investment should be allowed to harden in air before burnout of the wax.
Single step investing technique:
The investing procedure is carried out in one step either by brush technique or by vacuum technique.
a). Brush technique:
The accurate water-powder ratio is mixedunder vacuum. A brush is then used to paintthe wax pattern with mix then the casting ringis applied over the crucible fromer and thering is filled under vibration until it iscompletely filled.

b). vacuum technique:
• The mix in first hand spatulated, and then withthe crucible former and pattern is place, then ring is attached to the mixing bowl.
• The vacuum hose is then attached to theassembly. The bowel is inverted and the ring isfilled under vacuum and vibration
Two-step investing technigue:
The investing procedure is carried out in twosteps:
• First, the wax pattern is painted with a thick mix andis left till complete setting, the set investment block(first cost) is immersed in water for about tenminutes . the casting ring is then applied over the crucible former and filled with the properly mixedinvestment (second coat) till the ring is completely filled and the mix is left to set.The two-step investing technique is recommendedwhenever greater amount of expansion is required. Thistechnique also minimizes the distortion of the waxpattern and provides castings with smoother surfaces.
• The investment is allowed to set for the recommendedtime (usually one-hour) then the crucible former isremoved. If a metal sprue former is used, it is removedby heating over a flame to loosen it from the waxpattern. Any loose particles of investment should beblown off with compressed air should be placed in ahumidor if stored overnight.
Wax elimination (burnout):
Wax elimination or burnout consists of heating the investment in a thermostatically controlled furnace until all traces of the wax are vaporized in order to obtain an empty mold ready to receive the molten alloy during procedure.

• The ring is placed in the furnace with the sprue hole facing down to allow for the escape of the molten wax out freely by the effect of gravity .
• The temperature reached by the investment determines thethermal expansion. The burnout temperature is slowly increased in order to eliminate the wax and water without cracking the investment.
•For gypsum bonded investment, the mold is heated to650 -6870 c )to cast precious and semiprecious
precious alloys.
• Whereas for phosphate-bonded investment, the mold is heated up to 8340 c to cast nonprecious alloys at high fusing temperature.
The ring should be maintained long enough at the maximum temperature (“heat soak”) to minimize a sudden drop in temperature upon removal from the oven. Such a drop could result in an incomplete casting because of excessively rapid solidification of thealloy as it enters the mold.
• When transferring the casting ring to casting, a quick visual check of the sprue in shaded light is helpful to see whether it is properly heated. It should be a cherry-red color .
Melting & Casting Technique Melting & Casting requires Heat source to melt the alloy Casting force, to drive the alloy into the mould

Casting Torch Selection Two type of torch tips: Multi-orifice Single-orifice Multi-orifice tip is widely used for metal ceramic alloys. Main advantage is distribution of heat over wide area for uniform heating of the alloy. Single-orifice tip concentrate more heat in one area.Three fuel sources are used for Casting Torch; Acetylene ,Natural Gas ,Propane
Four types are available ;
1) Clay .
2) Carbon .
3) Quartz .
4) Zirconia –Alumina .
Casting Machines
It is a device which uses heat source to melt the alloy casting force .
Heat sources can be :
1) Reducing flame of a torch .
( conventional alloys & metal ceramic alloys )
2) Electricity .(Base metal alloys )
Advantages of electric heating :
-heating is evenly controlled .
-minimal undesirable changes in the alloy composition .
- Appropriate for large labs .
Disadv :
Expensive .
Casting machines use :
1) Air pressure .
2) Centrifugal force .
3) Evacuation technique .
Alloys can be melted by :
1) Alloy is melted in a separate crucible by a torch flame & is cast into the mold by centrifugal force .(centrifugal C M )
2) Alloy is melted by resistance heating or by induction furnace & then cast centrifugally by motor or spring action (springwound CM electrical resistance )
3) Alloy is melted by induction heating cast into mold centrifugally by motor or spring action .(Induction CM )
4) Alloy is vacum melted by an argon atmosphere
Torch melting / Centrifugal casting machine
Electrical resistance /Heated casting machine
Melting of the alloy should be done in a graphite or ceramic crucible .
Adv :
-Oxidation of metal ceramic restorations on
overheating is prevented .
-Help in solidification from tip of the casting to the button surface .
Induction casting machine
Commonly used for melting base metal alloys.
Adv :
- Highly efficient .
- Compact machine withlow power consumption
-No pre heating needed ,
- safe & reliable.
Direct current arc melting machine
A direct current arc is produced between two electrodes :
The alloy & the water cooled tungsten electrode .Temp used is 4000 degrees .
Disadv :
High risk of overheating the alloy .
Vacuum or pressure assisted casting machine
Molten alloy is drawn into the evacuated mold by gravity or vacuum & subjected to aditional pressure
For Titanium & its alloys vacuum heated argon pressure casting machines are used .
Accelerated casting method
This method reduces the time of both bench set of the investment & burnout .
Uses phosphate bonded investments which uses 15 mnts for bench set & 15mnts for burnout by placing in a pre – heated furnace to 815 degrees .
Effect of burnout on gypsum bonded investments
Rate of heating has influence on smoothness & on overall dimensions of the investment
Rapid heating causes cracking & flaking which can cause fins or spines .
Avoid heating gypsum bonded investment above 700 degrees .Complete the wax elimination below that temp .
Effect of burnout on phosphate bonded investments
Usual burnout temp is 750 -1030 degrees.
Although they are strong they are brittle too .
Since the entire process takes a long time two stage burnout & plastic ring can be used .CLEANING AND PICKLING ALLOYS
The surface oxidation or other contamination of dental alloys is a troublesome occurrence. The oxidation of base metals in most alloys can be kept to a minimum or avoided by using a properly adjusted method of heating the alloy and a suitable amount of flux when melting the alloy . Despite these precautions, as the hot metal enters the mold, certain alloys tend to become contaminated on the surface by combining with the hot mold gases, reacting with investment ingredients, or physically including mold particles in the metal surface. The surface of most cast, soldered, or otherwise heated metal dental appliances is cleaned by warming the structure in suitable solutions, mechanical polishing, or other treatment of the alloy to restore the normal surface condition.
Surface tarnish or oxidation can be removed by the process of pickling. Castings of noble or high-noble metal may be cleaned in this manner by warming them in a 50% sulfuric acid and water solution . . After casting, the alloy (with sprue attached) is placed into the warmed pickling solution for a few seconds. The pickling solution will reduce oxides that have formed during casting. However, pickling will not eliminate a dark color caused by carbon deposition The effect of the solution can be seen by
comparing the submerged surfaces to those that have still not contacted the solution. the ordinary inorganic acid solutions and do not release poisonous gases on boiling (as sulfuric acid does). In either case, the casting to be cleaned is placed in a suitable porcelain beaker with the pickling solution and warmed gently, but short of the boiling point. After a few moments of heating, the alloy surface normally becomes bright as the oxides are reduced. When the heating is completed, the acid may be poured from the beaker into the original storage container and the casting is thoroughly rinsed with water. Periodically, the pickling solution should be replaced with fresh solution to avoid excessive contamination.
Precautions to be taken while pickling
With the diversity of compositions of casting alloys available today, it is prudent to follow the manufacturer's instructions for pickling precisely, as all pickling solutions may not be compatible with all alloys. Furthermore, the practice of dropping a red-hot casting into the pickling solution should beavoided. This practice may alter the phase structure of the alloy or warp thin castings, and splashing acid may be dangerous to the operator. Finally, steel or stainless steel tweezers should not be used to remove
castings from the pickling solutions. The pickling solution may dissolve the tweezers and plate the component metals onto the casting. Rubber-coated or Teflon tweezers are recommended for this purpose.
To prevent oxidation of gold alloys during melting always use a reducing flux .
Boric acid & borax are used .
Casting of glass or ceramic
A castable ceramic is prepared in a similar manner as metal cast preparation .
Glass is heated to 1360 degrees & then cast.
Phosphate bonded investments are used for this purpose .
Classification (combe ):
1) Distortion.
2) Surface roughness .
3) Porosity .
4)Incomplete casting .
5) Oxidation .
6) Sulfur contamination .
It is usually due to the distortion of wax pattern.
To avoid this :
Manipulation of the wax at its softening temp
Invest the pattern at the earliest .
If storage is necessary store it in a refrigerator .
Surface roughness
May be due to :
Air bubbles on the wax pattern .
Cracks due to rapid heating of the investment .
High W/P ratio .
Prolonged heating of the mold cavity .
Overheating of the gold alloy .
Too high or too low casting pressure .
Composition of the investment .
Foreign body inclusion.

May be internal or external .
External porosity causes discolouration .
Internal porosity weakens the restoration .
Classification of porosity .
I .Those caused by solidification shrinkage :
a) Localised shrinkage porosity .
b) Suck back porosity .
c) Microporosity .
They are usually irregular in shape .
II ) Those caused by gas :
a) Pin hole porosity .
b) Gas inclusions .
c) Subsurface porosity .
Usually they are spherical in shape .
III ) Those caused by air trapped in the mold :
Back pressure porosity .
Localised shrinkage porosity
Large irregular voids found near sprue casting junction.
Occurs when cooling sequence is incorrect .
If the sprue solidifies before the rest of the casting , no more molten metal is supplied from the sprue which can cause voids or pits
(shrink pot porosity )
This can be avoided by -
- using asprue of correct thickness .
- Attach the sprue to the thickest portion of the pattern .
-Flaring of the sprue at the point of atttachment .
-Placing a reservoir close to the pattern .
Suck back porosity
It is an external void seen in the inside of a crown opposite the sprue .
Hot spot is created which freezes last .
It is avoided by :
Reducing the temp difference between the mold & molten alloy .
Microporosity :
Fine irregular voids within the casting .
Occurs when casting freezes rapidly .
Also when mold or casting temp is too low .
Pin hole porosity :
Upon solidification the dissolved gases are expelled from the metal causing tiny voids .
Pt & Pd absorb Hydrogen .
Cu & Ag absorb oxygen .
Gas inclusion porosities
Larger than pin hole porosities .
May be due to dissolved gases or due to gases Carried in or trapped by molten metal .
Apoorly adjusted blow torech can also occlude gases .
Back pressure porosity
This is caused by inadequate venting of the mold .The sprue pattern length should be adjusted so that there is not more than ¼” thickness of the investmentbetween the bottom of the casting .
This can be prevented by :
- using adequate casting force .
-use investment of adequate porosity .
-place the pattern not more than 6-8 mm away from tne end of the casting .
Casting with gas blow holes
This is due to any wax residue in the mold .
To eliminate this the burnout should be done with the sprue hol facing downwards for the wax pattern to run down.
Incomplete casting
This is due to :
- insufficient alloy .
-Alloy not able to enter thin parts of the mold .
-When the mold is not heated to the casting temp .
-Premature solidification of the alloy .
-sprues blocked with foreign bodies .
-Back pressure of gases .
-low casting pressure .
-Alloy not sufficiently molten .

Too bright & shiny casting with short & rounded margins :
occurs when wax is eliminated completely ,it combines with oxygen or air to form carbon monoxide .
Small casting :
occurs when proper expansion is not obtained & due to the shrinkage of the impression .
Contamination of the casting
1) Due to overheating there is oxidation of metal .
2) Use of oxidising zone of the flame .
3) Failure to use a flux .
4) Due to formation sulfur compounds .
Black casting
It is due to :
1) Overheating of the investment .
2) Incomplete elimination of the wax .
Investing and casting , a series of highly technique sensitive steps , converts the wax pattern into metal casting . Accurate and smooth restorations can be obtained if the operator pays special attention to each step in the technique .
When initial attempts in the casting procedure produce errors or defects , appropriate corrective measures must be taken so that they do not recur .

• Fundamentals of fixed prosthodontics: Shillingburg
• Dental laboratory procedures: Rudd and Morrow.
• Philip’s science of dental ceramics;Anusavice.
• Dental materials: Craig.
• Tylman’s theory of fixed prosthodontics
• * Notes on Dental Materials , E .C . Combe .
• Applied Dental Materials , Mc Cabe .
• Contemporary fixed Prosthodontics; Rosensteil.
1 . The effect of sprue attachment design on castability and porosity .J Prosthet Dent , 61 :418 -24 , 1989 .Flared & straight sprue attachment optimised castability and minimised porosity
2 . Setting & thermal reactions of Phosphate bonded investments . J of Dentistry rest :1478 -1485 , 1980 .
3) Delayed hygroscopic expansion of phosphate bonded investments . Dental Mater 3 : 165 -7 ,1987 .
Delayed hygroscopic expansion occurs when the investment is immersed in water after setting .
4) Sprue design in RPD casting : J of dentistry ,Nos 1-2 .vol 24 ,99-103 ,1996 .
Correct sprue designs is a major factor in reduction of casting defects .
5)Creating buttonless casting by using preformed wax sprues ; JOP Sept 1996 ; 327 -329 .
This method conserves metal by allowing a minimum of metal for each casting .Smaller button size allows more new metal to be added with subsequent castings .
6) Effect of burnout temp in strength of phosphate bonded investments ,J of Dentistry ,vol 25 ; No :2 , 153 -160 ,1997 .

Read more…