Blogs

In a report on a preclinical investigation titled "Flagellin Enhances Saliva Ig A Response and Protection of Anti-caries DNA Vaccine," lead author Wei Shi, Wuhan Institute of Virology, Chinese Academy of Sciences, and his team of researchers demonstrate that anti-caries DNA vaccines, including pGJA-P/VAX, are promising for preventing dental caries. However, challenges remain because of the low immunogenicity of DNA vaccines.

This study is published in the Journal of Dental Research, the official publication of the International and American Associations for Dental Research (IADR/AADR).

In this study, Shi and team used recombinant flagellin protein derived from Salmonella as mucosal adjuvant for anti-caries DNA vaccine (pGJA-P/VAX) and analyzed the effects of Salmonella protein on the serum surface protein immunoglobulin G and saliva surface protein immunoglobulin A antibody responses, the colonization of Streptococcus mutans (S. mutans) on rodent teeth, and the formation of caries lesions. The results showed that Salmonella promoted the production of surface protein immunoglobulin G in serum and secretory immunoglobulin A in saliva of animals by intranasal immunization with pGJA-P/VAX plus Salmonella.

Furthermore, Shi found that enhanced surface protein immunoglobulin A responses in saliva were associated with inhibition of S. mutans colonization of tooth surfaces and endowed better protection with significant less carious lesions. In conclusion, the study demonstrates that recombinant Salmonella could enhance specific immunoglobulin A responses in saliva and protective ability of pGJA-P/VAX, providing an effective mucosal adjuvant candidate for intranasal immunization of an anti-caries DNA vaccine.

Daniel Smith, The Forsyth Institute, wrote a corresponding perspective article in response to the Shi et al report titled "Prospects in Caries Vaccine Development." In it, he states that DNA vaccine approaches for dental caries have had a history of success in animal models. Dental caries vaccines, directed to key components of S. mutans colonization and enhanced by safe and effective adjuvants and optimal delivery vehicles, are likely to be forthcoming.

"These papers highlight the exciting potential of using vaccines to protect against dental caries," said JDR Editor-in-Chief William Giannobile. "This research is promising and provides optimism to help promote public health of caries-susceptible individuals."

Source:  Science Daily

Journal Reference:

1. W. Shi, Y. H. Li, F. Liu, J. Y. Yang, D. H. Zhou, Y. Q. Chen, Y. Zhang, Y. Yang, B. X. He, C. Han, M. W. Fan, H. M. Yan. Flagellin Enhances Saliva IgA Response and Protection of Anti-caries DNA Vaccine. Journal of Dental Research, Published online Oct. 25, 2011 DOI: 10.1177/0022034511424283

I work since 1985 as a dentist.

I found some ideas which  make our work easier..

Some other dentsist who like ti share those ideas ?

For many dental implant patients, restoring facial volume can be as critical as the dental restoration for optimizing cosmetic outcomes.  In a workshop at the American Academy of Implant Dentistry Annual Scientific Meeting in Las Vegas, Pankaj Singh, DDS urged attendees to pay close attention to facial structures and consider using Botox and dermal filler agents for patients who need facial volume restorations.

"Besides creating beautiful smiles, we like to create harmony between the dento-facial complex by addressing the deep lines and wrinkles in the face that can prevent our patients from looking their best," said Singh.  "Soft tissues that ring the mouth are as important as perfectly restored teeth for an attractive and confident smile," said Singh.  

Botox is a natural and purified protein that relaxes facial muscles by blocking nerve impulses.  Once the muscles are at rest, the skin becomes smoother, creating a more natural and relaxed appearance.  The effects last about three to four months and patients feel little, if any, discomfort after the procedure.  

For older dental implant patients with facial aging, the corners the mouth begin to turn down and wrinkles appear around the lips.  "Botox can be used by dentists to relax affected muscles to raise mouth corners and smooth wrinkles to assure successful and satisfying outcomes," said Singh.

Dermal filler agents, such as Restylane, treat fat and collagen volume loss due to the aging process that causes static lines to develop.  "As we age, our body's production of Hyaluronic Acid (HA), the body's natural filler decreases, which causes facial lines to appear," Singh explained.  He added that it takes about two weeks for dermal filler agents to show results and some patients experience side effects, such as localized pain, infection, bleeding, swelling, redness, bruising and tenderness in and near the injection site.  Results are not permanent and injections will need to be repeated periodically to maintain the cosmetic improvement.

An estimated 8 percent of dentists in North America now provide Botox and dermal filer cosmetic treatments for patients and the number is growing, as state dental boards lobby to allow dentists to use the agents for cosmetic dentistry.    

"Facial volume restoration is the future for the achieving optimal aesthetic outcomes in the delivery of cosmetic and restorative dental care," said Singh.  "Dentists have as much training and knowledge in the oral and maxillofacial area as dermatologists and other providers, so they, with proper training, can be as proficient in administering these agents," said Singh.  

About AAID

AAID is the leading professional society dedicated to maintaining the highest standards of implant dentistry through research and education.  The annual meeting is the field's leading venue for cutting-edge, evidence-based implant research presentations and demonstrations of state-of-the art implantation techniques.  

AAID can help consumers find a local credentialed implant dentist at www.aaid.com.  AAID is based in Chicago and has more than 3,500 members.  It is the first organization dedicated to maintaining the highest standards of implant dentistry by supporting research and education to advance comprehensive implant knowledge.

SOURCE American Academy of Implant Dentistry

Bad teeth can pose more of a health problem to a person than just an aesthetics problem.   More and more studies indicate that the health of the teeth and gums can affect the health of the whole body, and inflamed gums (periodontitis) can especially negatively affect the health of the whole body.   The chronic inflammation weakens the immune system, and is an increased risk of diabetes, heart attacks , rheumatism and lung diseases.

Periodontitis is mostly painless

Inflamed gums – popularly known as gum disease  – usually affects people over the age of 40.  Caused by poor oral hygiene or improper brushing technique itself is a bacterial plaque that eventually attacks the gums. The onset of infection often remains undetected because it causes no pain. The trouble usually begins with bleeding gums, swelling of the gums and bad breath. In extreme cases, it will form gum pockets and bone loss is reduced.

Inflammation spreads throughout the body

But the inflammation is not restricted to the oral cavity.  From the gingival pockets, bacteria and pro-inflammatory mediators travel into the bloodstream.   Inflammation occurs in the blood vessels or even in previously damaged heart valves. The result: the risk for atherosclerosis, heart attack and stroke increases. Studies show, for example, that the likelihood of cardiovascular disease in people with periodontal disease is increased by 70 percent.

Bacteria attack the heart and lungs

The connection between bad teeth and the lungs was showed recently by researchers from the U.S.. They found that people with bronchitis or COPD often have bad teeth.  Lung disease is caused when bacteria from the upper throat are inhaled and reach the lower respiratory tract. Various factors such as smoking or a weakened immune system increase the risk of developing lung disease. However, further research is needed to clarify the precise relationship, the researchers said.

Diabetics often have inflamed gums
Particularly well studied is the relationship between diabetes and gum disease. Those with poorly controlled blood sugar levels can result in bad wounds. The excess sugar in the blood promotes inflammation and inhibits healing. Diabetics can suffer up to 3.5-fold increased risk of developing periodontal disease. Conversely, the inflamed gums increase the insulin resistance.

Preventing periodontal disease

To prevent gum disease proper oral hygiene is essential.  Teeth brushing should occur at least twice a day.   The spaces between the teeth should also be cleaned daily with floss or special interdental brushes.   At least twice a year a prophylaxis should be performed by a dentist.   Here, the deposits and tartar are removed, and the teeth are treated with fluoride and given a thorough guide to dental care.

Periodontal Associates

Source:  News Around The World

It's almost Halloween.  As each October creeps up on Cindy Flanagan, DDS, MAGD, spokesperson for the Academy of General Dentistry(AGD), her mind always wanders to the amount of sweets both children and adults will be consuming during the last few months of the year.

"Too many sweets can cause a spooky mouth," says Dr. Flanagan. "People have the tendency to graze on the sugary treats lying around the house during the holidays, and this increases the likelihood of cavities."

Dr. Flanagan knows that candy consumption is almost unavoidable at this time of the year, so she's offering some advice as to which sweets are less damaging to your teeth than others.

The Good:

1. Sugar-free lollipops and hard candies: These treats stimulate saliva, which prevents dry mouth. A dry mouth allows plaque to build up on teeth faster, leading to an increased risk of cavities.

1. Sugar-free gum: Chewing gum can actually prevent cavities, not only because it helps to dislodge food particles from the teeth, but also because it increases saliva. Saliva works to neutralize the acids of the mouth and prevent tooth decay.

1. Dark chocolate: Chocolates are loaded with sugar, but studies have shown that the antioxidants in dark chocolate can be good for the heart and may even lower blood pressure. Just be sure to eat it in moderation.

The Bad:

1. Sugary snacks: Candy corn, cookies, and cake all contain a high amount of sugar, which can cause tooth decay.

1. Chewy/sticky sweets: Gummy candies, taffy, and even dried fruit can be difficult for children and adults to resist, but they are a serious source of tooth decay, particularly when they get stuck in the crevices between teeth and make it nearly impossible for saliva to wash away.

1. Sour candies: High acid levels in these treats can break down tooth enamel quickly. The good news: Saliva slowly helps to restore the natural balance of the acid in the mouth. Dr. Flanagan recommends that patients wait 30 minutes to brush their teeth after consuming acidic foods or drinks, otherwise they will be brushing acid onto more tooth surfaces, increasing the erosive action.

Dental students in a Seattle study had very high rates of colonization with MRSA, the drug-resistant strain of staph, raising new questions about the prevalence of the bacteria outside of hospitals in community health care settings.

People who are colonized with MRSA carry the bacteria in their nose or on their skin, but they may or may not have signs or symptoms of infection. They can spread MRSA to others, however.

Nasal swabs from one in five University of Washington (UAW) Dental School students tested showed evidence of methicillin-resistant Staphylococcus aureus (MRSA), and four of seven dental clinics at the school also tested positive for the bacteria in samples taken from dental chairs and floors.

The rate of MRSA colonization was significantly higher than that reported in the general population and in other non-hospital medical settings, but an official with the CDC says the public should not be overly alarmed by the findings.

Arjun Srinivasan, MD, says the high MRSA rate suggests a specific transmission at the UAW facility and is probably not indicative of rates in dental offices in general.

Srinivasan is assistant director for the CDC's Healthcare-Associated Infection Prevention Program.

"This study is one of the first to look at MRSA in the dental setting, but it was a small study with just 61 dental students in one facility," Srinivasan tells WebMD. "We don't believe this study necessarily represents a systematic problem in dental clinics across the country."

Community MRSA Rates Rising

MRSA is usually highly resistant to the antibiotics most often used to treat staph infections, and it is a significant cause of illness and death among hospitalized patients with compromised immune systems.

Infections that happen outside the hospital setting -- known as community-acquired MRSA -- tend to occur in otherwise healthy people and they typically show up as skin infections.

Recent surveys suggest that hospital-acquired MRSA has declined within the past few years, while rates of community-acquired MRSA appear to be increasing, according to the CDC.

Outbreaks of community-acquired MRSA have been reported in locker rooms, gymnasiums, prisons, military barracks, and other facilities where skin-to-skin contact is common and people share close quarters.

It is not clear how many people carry MRSA, but studies suggest that health care workers have slightly higher rates of colonization than the general population, University of Washington professor of environmental and occupational health Marilyn C. Roberts, PhD, tells WebMD.

MRSA Common in Buffalo Dental Study

In a study reported earlier this year, Roberts and colleagues found a high rate of MRSA colonization among a group of Seattle-area firefighters.

In their latest investigation conducted at the UAW dental school, the researchers took nasal swabs from 61 dental students and swabbed 95 surfaces considered potential reservoirs for MRSA.

Thirteen (21%) of the students and eight (8.4%) surfaces from four of the seven clinics harbored MRSA.

The study was published online today and will appear in the October issue of the American Journal of Infection Control.

An unrelated study of dental school students and instructors in Buffalo, N.Y., showed an even higher rate of colonization, with 31% of the 84 people showing evidence of MRSA.

That study was presented at a 2009 meeting of dental researchers held in Miami.

Roberts says the Buffalo findings show that the high MRSA colonization rate reported in her study is not limited to her institution.

Roberts and the CDC's Srinivasan do agree that more study is needed to develop a better understanding of the rate of MRSA colonization in non-hospital health care settings.

The extent to which this colonization impacts MRSA infection rates is also not clear, he adds.

"We know a great deal about the infection control challenges related to MRSA in acute care hospital settings, but we know a lot less about this issue in non-acute care settings such as dental and dialysis centers and ambulatory surgical centers," Srinivasan says.

Srinivasan says it does not appear that these settings represent a major source of community-acquired MRSA transmission.

Source:  WebMD

The 2010 House of Delegates resolved to encourage certified dental technicians to attend ADA continuing education seminars, including as presenters.

That resolve will be carried out at ADA Annual Session in Las Vegas this month when Dentists and Dental Laboratory Technicians Team Up for Success is presented. The course, created for both dentists and dental laboratory technicians, is scheduled for 8-10:30 a.m. Oct. 13 in room L3 Palm C. Its goal is to outline techniques dentists and dental lab technicians can use for successful long-term collaborative treatment planning.

“This course is designed to deepen and further define the long-standing symbiotic relationship between dental laboratory technicians and dentists, which has proven through the years to deliver the highest quality dental solutions available to patients in the world,” said Dr. Charles (Bill) D’Aiuto, member of the Council on Dental Practice and chair of its Subcommittee on the Future of Dental Laboratory Technology. “As the dental office paradigm shifts so will the working relationships, needs and requirements that dentists share with our dental laboratory technicians colleagues.”

The course will be presented by Nelson Rego, certified dental technician, who will help participants learn how to communicate about lab prescriptions more effectively, create better impressions and more successful restorations and understand how digital photography can be used for treatment planning.

"In the past, we have become aware of the need to strengthen the long-standing working relationship we as dentists have with our dental technician colleagues,” Dr. D’Aiuto said. “With the advent of vast new technologies in delivering dental prostheses with facilities available around the world to fabricate them, it is now starkly evident that no amount of outsourcing of basic dental prostheses can or ever will replace the need for the collaboration of the dentist with the domestic dental technician in delivering the total dental product that has become the envy of the world. "

Source:  American Dental Association

The British Dental Health Foundation released a rather shocking report that may cause many women to step up their oral hygiene routine. The report, released on February 11, 2011, states that women with gum disease and or missing teeth may be up to 11 times more likely to develop breast cancer.

Sweden's Karolinska Institute studied over three thousand patients, ending with 41 women developing cancer. The women with gum disease and tooth loss were found to be 11 times more likely to develop cancer. This study is said to be the first to examine the relationship between gum disease, tooth loss and cancer. More studies will be necessary in order to fully explain the link, if any, between gum disease, tooth loss, and cancer.

Gum disease is continually popping up in the news as a link or result of serious health concerns. Diabetes, preterm birth, and heart disease are only a few conditions related to this preventable disease.

Source:  About.com

When considering a potential new dentist, there are many important factors to take into account. Blindly picking  a name out of your insurance provider's list of in-network dentists without getting the right information about the practice is not the ideal option! In this article, we'll cover the top 10 key questions to ask your possible future dentist.

Basic Questions

These basic questions can help you figure out if you can work with a dentist in the first place.

1. Are you taking new patients?

Some dentists will only work with a certain number of patients at a time. Once they reach that number, they stop taking new patients and just focus on the ones they already have.

2. Do you treat children, and if so, what types of accommodations do you make for them?

Not all dentists work with kids. Even if you're looking for a dentist for yourself and not your kids right now, it might be better to find a practice that works with children. This way,  you'll already have a good relationship with an office by the time your kids need a check-up or dental work.

If you have kids, it's important to find someone who makes adjustments for young children. This should include smaller tools for smaller mouths, plus comforting items like happy decorations or even TV sets.

3. Do you make accommodations for people with dental anxiety?

If the thought of going to the dentist scares you stiff, you're not alone. According to a study published in the Journal of the American Dental Association, approximately 35 million Americans experience significant apprehension about dental procedures. Plus, an extra “10 to 12 million are considered to be 'dental phobic' and avoid needed dental care altogether.”

However, dentists are getting better at working with anxious people. Many dentists now offer calming music, nitrous oxide, anti-anxiety medications, and other accommodations to help patients chill out. Again, if you don't have dental anxiety, but someone else in your family does, you may want to start building a relationship with a helpful practice now.

Expertise Questions

These questions are meant to determine if your dentist has what it takes to take care of you.

4. How long have you been practicing?

All else being equal, it's clearly better to pick a dentist who has been practicing longer. Experience is the best teacher.

5. How often do you take continuing education classes?

Both dentists and dental hygienists are supposed to take continuing education courses throughout their careers. If your potential new dentist can't tell you the last time they've taken a continuing education course, that's a big red flag.

6. Do you have any area of expertise, other than general dentistry?

If you know you're going to need a certain procedure soon, like a root canal, it makes sense to start building a relationship with a dentist that specializes in endodontics.  Endodontics deal with how a tooth's pulp and tissues work.

7. Do you have patient testimonials as well as before and after pictures from past patients that I can look at?

Yes, even with online reviews widely available, dentists should still keep patient testimonials, as well as before and after pictures on hand. If a dentist can't provide these, that might be a red flag.

Financing Questions

Daniela Baker from CreditDonkey says, “Of course, finding the best dentist in the world won't do you much good if there's no way you can afford their services, so ask about payment options ahead of time.”

 8. Which types of dental insurance do you accept?

It's important to ask which types of dental insurance your potential dentist accepts, or just ask if they accept your insurance. Also, ask if they will file your insurance claims for you, or if you have to do it yourself.

9. Do you take credit card payments, and if so, which credit cards do you accept?

Many dentists today accept credit card payments, since they are popular with patients. Even if you don't think you'll need this option, it's good to know you'll have it as a plan B in case your co-pays are higher than expected.

10. Do you accept discount dental plans?

Dental offices that accept discount dental plans will perform services at a discounted price for discount dental plan members. If you already have dental insurance, you can still use a discount dental plan to keep costs down after you reach your insurance plan maximum.* Unlike insurance plans, discount dental plans usually do not have annual limits.

These are just 10 of many important questions you should ask a potential new dentist. You should also ask questions that apply to your own needs. The Forestream Dental Group in Buffalo, New York advises making an appointment with a potential new dentist to interview them before having work done.

Remember, the oral health of you and your family depends, in part, on your new dentist, so go the extra mile to get to know them!

*Please consult with your provider prior to beginning treatment.

Only 62% of adults visited a dentist in 2009. It doesn’t take a psychology degree to know that patients aren’t avoiding your office because they love tooth decay. Many times, the fear of dentists is based on traumatic dental experiences. A successful dentist is not only good at cleaning teeth, filling cavities, and restoring smiles, but also at putting patients at ease so that they will keep returning. Here are a few tips to help reduce your patients’ dental fears and anxieties so that you can best treat them and send them home smiling:

• Communicate clearly: Talking through the steps of the treatment with patients can significantly reduce their fear. When a patient comes to your office, sit down with them and talk through what you will be doing, even if it is only a cleaning. 

• Soothe with music: According to a study by the American Dental Association, music is a great tool for distracting patients and reducing their dental anxiety. Have soothing music playing in the examination room, or better yet, encourage your patients to bring an iPod or MP3 player with their favorite song to listen to throughout their appointment. 

• Try a relaxation technique: One of the most effective ways to reduce fear in particularly anxious patients is to have them do a short relaxation exercise prior to their treatment. Consider getting a relaxation DVD or written instructions for a relaxation exercise and encourage anxious patients to listen to it through headphones or read it quietly while in the waiting room before their appointment.

• Distract, Distract, Distract: Some dental offices are beginning to set up television screens above the dental chairs, and allowing patients to choose from a DVD collection or set of television stations prior to their procedure. This is particularly helpful for longer procedures, and can offer a distraction from their fear and anxiety.

As a dentist, you know that dental work does not have to be scary. By communicating clearly with your patients, creating a relaxing and welcoming environment, and offering them distractions such as music and television, you can help your patients to reduce their anxiety and keep fear at bay. Even for patients that do not have obviously high levels of dental anxiety, these tips can help make them feel more relaxed and create a welcoming atmosphere that gives patients positive associations with the dentist.

Allison Gamble has been a curious student of psychology since high school. She brings her understanding of the mind to work in the weird world of internet marketing with psychologydegree.net.

So much more than than a pair of upturned lips, the smile is the most scientifically studied human facial expression. In her new book, Lip Service, Yale psychology professor Marianne LaFrance, PhD, draws on the latest research—in fields from biology to anthropology to computer science—in an effort to shed some light on the happy face. Here, six facts that may make you, well, you know.

People with big grins live longer. In a study published last year, researchers pored over an old issue of the Baseball Register, analyzing photos of 230 players. They found that on average, the guys with bright, bigmouthed beams lived 4.9 years longer than the players with partial smiles, and 7 years longer than the players who showed no grin at all. We can’t credit wide smiles for long life spans, of course, but smiles reveal positive feelings, and positive feelings are linked to well-being.

Smiles exert subliminal powers. When study subjects are shown an image of a smiling face for just four milliseconds—a flash so quick, the viewers don’t consciously register the image—they experience a mini emotional high. Compared with control groups, the smile-viewers perceive the world in a better light: To them, boring material is more interesting, neutral images look more positive, even bland drinks seem tastier.

There are three degrees of happiness… An article in the British Medical Journal reported that it is indeed possible to spread the love: Within social networks, when one person is happy, the feeling migrates to two people beyond her. So if you smile, a friend of a friend is more likely to smile, too.

…and two types of smiles. Genuine smiles and fake smiles are governed by two separate neural pathways. We know this is true because people with damage to a certain part of the brain can still break into a spontaneous grin even though they’re unable to smile at will. Scientists speculate that our ancestors evolved the neural circuitry to force smiles because it was evolutionarily advantageous to mask their fear and fury.

To spot a faker, check the eyes. When someone smiles out of genuine delight, a facial muscle called the orbicularis oculi involuntarily contracts, crinkling the skin around the eyes. Most of us are incapable of deliberately moving this muscle, which means that when a person fakes a smile, her orbicularis oculi likely won’t budge.

Smiles have accents. When reading facial expressions, different cultures home in on different parts of the face. In the United States, we focus on mouths; the Japanese, by contrast, search for feeling in the eyes.

These emoticons say it all:

HappySadU.S.:):(JAPAN(^_^)(;_;)

Source:  Oprah.com

Leading dental and pharmacy organizations are teaming up to promote oral health and raise public awareness of dry mouth, a side effect commonly caused by taking prescription and over-the-counter medications. More than 500 medications can contribute to oral dryness, including antihistamines (for allergy or asthma), antihypertensive medications (for blood pressure), decongestants, pain medications, diuretics and antidepressants. In its most severe form, dry mouth can lead to extensive tooth decay, mouth sores and oral infections, particularly among the elderly.

Nearly half of all Americans regularly take at least one prescription medication daily, including many that produce dry mouth, and more than 90 percent of adults over age 65 do the same. Because older adults frequently use one or more of these medications, they are considered at significantly higher risk of experiencing dry mouth. 

The American Dental Association (ADA), Academy of General Dentistry (AGD), American Academy of Periodontology (AAP) and the American Pharmacists Association (APhA) are collaborating to expand awareness of the impact of medications on dry mouth, a condition known to health professionals as xerostomia.

With regular saliva production, your teeth are constantly bathed in a mineral-rich solution that helps keep your teeth strong and resistant to decay. While saliva is essential for maintaining oral health and quality of life, at least 25 million Americans have inadequate salivary flow or composition, and lack the cleansing and protective functions provided by this important fluid. 

“Each day, a healthy adult normally produces around one-and-a-half liters of saliva, making it easier to talk, swallow, taste, digest food and perform other important functions that often go unnoticed,” notes Dr. Fares Elias, immediate past president, Academy of General Dentistry. “Those not producing adequate saliva may experience some common symptoms of dry mouth.” 

Signs and symptoms
At some point, most people will experience the short-term sensation of oral dryness because of nervousness, stress or just being upset. This is normal and does not have any long-term consequences. But chronic cases of dry mouth persist for longer periods of time. Common symptoms include trouble eating, speaking and chewing, burning sensations or a frequent need to sip water while eating. 

“Dry mouth becomes a problem when symptoms occur all or most of the time and can cause serious problems for your oral health,” explains Dr. Matthew Messina, ADA consumer advisor. “Drying irritates the soft tissues in the mouth, which can make them inflamed and more susceptible to infection.”

According to Dr. Messina, who practices general dentistry in the Cleveland area, without the cleansing and shielding effects of adequate saliva flow, tooth decay and periodontal (gum) disease become much more common. “Constant dryness and the lack of protection provided by saliva may contribute to bad breath. Dry mouth can make full dentures become less comfortable to wear because there is no thin film of saliva to help them adhere properly to oral tissues,” he adds. “Insufficient saliva can also result in painful denture sores, dry and cracked lips and increased risks of oral infection.”

Common causes
Once considered an inevitable part of aging, dry mouth is now commonly associated with certain medications and autoimmune conditions such as Sjogren’s syndrome. Both of these can reduce salivary production or alter its composition, but experts agree that the primary cause of dry mouth is the use of medications.

Radiation treatment for head and neck cancer is also an important cause of severe dry mouth. The treatment can produce significant damage to the salivary glands, resulting in diminished saliva production and extreme dry mouth in many cases. 

“Saliva plays an important role in maintaining oral health,” says Dr. Donald Clem, president of the American Academy of Periodontology. “With decreased saliva flow, we can see an increase in plaque accumulation and the incidence and severity of periodontal diseases.”

How to relieve dry mouth
Individuals with dry mouth should have regular dental checkups for evaluation and treatment. “Be sure to carry an up-to-date medication list at all times, and tell your dentist what medications you are taking and other information about your health at each appointment," advises Mr. Thomas Menighan, executive vice president and Chief Executive Officer, American Pharmacists Association. "In some cases, a different medication can be provided or your dosage modified to alleviate dry mouth symptoms. Talk to your pharmacist if you have any questions regarding your medication.” 

Increasing fluid intake, chewing sugarless gum, taking frequent sips of water or sucking on ice chips can also help relieve dry mouth symptoms. Avoiding tobacco and intake of caffeine, alcohol and carbonated beverages may also help those with the condition. Your dentist may recommend using saliva substitutes or oral moisturizers to keep your mouth wet. Your local pharmacist is also a helpful source for information on products to help you manage dry mouth.

Source: American Academy of Periodontology

 Scientists have discovered the tool that bacteria normally found in our mouths use to invade heart tissue, causing a dangerous and sometimes lethal infection of the heart known as endocarditis. The work raises the possibility of creating a screening tool -- perhaps a swab of the cheek, or a spit test -- to gauge a dental patient's vulnerability to the condition.

The identification of the protein that allows Streptococcus mutans to gain a foothold in heart tissue is reported in the June issue of Infection and Immunity by microbiologists at the University of Rochester Medical Center.  S. mutans is a bacterium best known for causing cavities. The bacteria reside in dental plaque -- an architecturally sophisticated goo composed of an elaborate molecular matrix created by S. mutans that allows the bacteria to inhabit and thrive in our oral cavity. There, they churn out acid that erodes our teeth.

S. mutans invading a human coronary artery endothelial cell.

(Credit: Image courtesy of University of Rochester Medical Center)

Normally, S. mutans confines its mischief to the mouth, but sometimes, particularly after a dental procedure or even after a vigorous bout of flossing, the bacteria enter the bloodstream. There, the immune system usually destroys them, but occasionally -- within just a few seconds -- they travel to the heart and colonize its tissue, especially heart valves. The bacteria can cause endocarditis -- inflammation of heart valves -- which can be deadly. Infection by S. mutans is a leading cause of the condition.

"When I first learned that S. mutans sometimes can live in the heart, I asked myself: Why in the world are these bacteria, which normally live in the mouth, in the heart? I was intrigued. And I began investigating how they get there and survive there," said Jacqueline Abranches, Ph.D., a microbiologist and the corresponding author of the study.

Abranches and her team at the University's Center for Oral Biology discovered that a collagen-binding protein known as CNM gives S. mutans its ability to invade heart tissue. In laboratory experiments, scientists found that strains with CNM are able to invade heart cells, and strains without CNM are not.

When the team knocked out the gene for CNM in strains where it's normally present, the bacteria were unable to invade heart tissue. Without CNM, the bacteria simply couldn't gain a foothold; their ability to adhere was about one-tenth of what it was with CNM.

The team also studied the response of wax worms to the various strains of S. mutans. They found that strains without CNM were rarely lethal to the worms, while strains with the protein were lethal 90 percent of the time. Then, when Abranches' team knocked out CNM in those strains, they were no longer lethal -- those worms thrived.

The work may someday enable doctors to prevent S. mutans from invading heart tissue. Even sooner, though, since some strains of S. mutans have CNM and others do not, the research may enable doctors to gauge a patient's vulnerability to a heart infection caused by the bacteria.

Abranches has identified five specific strains of S. mutans that carry the CNM protein, out of more than three dozen strains examined. CNM is not found in the most common type of S. mutans found in people, type C, but is present in rarer types of S. mutans, including types E and F.

"It may be that CNM can serve as a biomarker of the most virulent strains of S. mutans," said Abranches, a research assistant professor in the Department of Microbiology and Immunology. "When patients with cardiac problems go to the dentist, perhaps those patients will be screened to see if they carry the protein. If they do, the dentist might treat them more aggressively with preventive antibiotics, for example."

Until more research is done and a screening or preventive tool is in place, Abranches says the usual advice for good oral health still stands for everyone.

"No matter what types of bacteria a person has in his or her mouth, they should do the same things to maintain good oral health. They should brush and floss their teeth regularly -- the smaller the number of S. mutans in your mouth, the healthier you'll be. Use a fluoride rinse before you go to bed at night. And eat a healthy diet, keeping sugar to a minimum," added Abranches.

Abranches presented the work at a recent conference on the "oral microbiome" hosted by the University's Center for Oral Biology. The center is part of the Medical Center's Eastman Institute for Oral Health, a world leader in research and post-doctoral education in general and pediatric dentistry, orthodontics, periodontics, prosthodontics, and oral surgery.

Additional authors of the study include laboratory technician James Miller; former technician Alaina Martinez; Patricia Simpson-Haidaris, Ph.D., associate professor of Medicine; Robert Burne, Ph.D., of the University of Florida; and Abranches' husband, Jose Lemos, Ph.D., of the Center for Oral Biology, who is also assistant professor in the Department of Microbiology and Immunology. The work was funded by the American Heart Association.

Source:  University of Rochester Medical Center

Have you thought about chipped teeth, drooling, gum damage, nerve damage, taste loss, tooth loss or infection? The problems that can arise from an oral piercing might surprise you.

Fractured teeth are a common problem for people with tongue piercings. People chip teeth on tongue piercings while eating, sleeping, talking and chewing on the jewelry. The fracture can be confined to the enamel of your tooth and require a filling, or it may go deep into the tooth; in which case, a root canal or tooth extraction may be necessary.

"Every time you swallow, the barbell hits the teeth, causing constant irritation that can result in mouth ulcers," says Academy of General Dentistry spokesperson Manuel A. Cordero DDS, FAGD.

Infections are also common. Dentists are learning that oral infections can be linked to other infections. "The tongue is covered with bacteria," Dr. Cordero said. "The moment the tongue is punctured, bacteria are introduced into the blood. When that happens, bacteria can travel to the heart and cause a variety of serious problems."

If you decide to pierce your tongue, take care of it. Once the tongue has been pierced, it takes four to six weeks to heal. Barring complications, the jewelry can be removed for short periods of time without the hole closing. Always remove the jewelry every time you eat or sleep.

Gum recession is another big problem associated with tongue piercing.  Many people with pierced tongues get into the habit of rubbing the gums on the inside of the bottom teeth with the ball at the end of the pierce.  This causes the gum, and ultimately the bone, to become stripped away from the teeth resulting in gum recession.  This will oftentimes necessitate repair of the damage by a periodontist.

To avoid serious infections such as HIV or hepatitis, make sure the piercer sterilizes everything in an autoclave, which uses extreme heat to sanitize surgical instruments. Ask the piercer questions about after-care, cleanliness, equipment and other concerns.

Clean your piercing with an antiseptic mouthwash after every meal and brush the jewelry the same as your teeth to remove plaque.

CARY FEUERMAN, DMD

PERIODONTAL ASSOCIATES

Source:  AGD

A new study in the Journal of Dental Research finds bone fluoride levels are not associated with osteosarcoma, a rare bone cancer more prevalent in males.

A team of researchers from Harvard University, the Medical College of Georgia and the National Cancer Institute analyzed hundreds of bone samples from nine hospitals over an eight year period from patients with osteosarcoma and a control group to measure fluoride levels in the bone.

Considered the most extensive study to date that examines a potential association between fluoride levels in bone and osteosarcoma, the results indicated no correlation. Three branches of the National Institutes of Health were involved in the study. The National Cancer Institute (NCI) approved the design of the study, and funding for the research was provided by the NCI, the National Institute of Environmental Health Sciences, and the National Institute of Dental and Craniofacial Research. 

The ADA has issued a press statement and ADA News contains more details about the study.

Patients may ask about the findings of this new study. Here are some points that may be helpful:

• This new study adds to an already strong base of scientific evidence that fluoride is safe and effective at preventing cavities.
• An inconclusive animal study conducted twenty years ago first raised the question of an association between fluoride and osteosarcoma. Since that time, other studies have examined the issue.
• This new study is considered by researchers to be the best science to date because a more accurate and reliable scientific method was used to measure exposure from all sources of fluoride.
• Tooth decay rates have declined dramatically over the past several decades, thanks in part to the use of fluoride.
• The AmericanDentalAssociation advises that people should brush twice a day with fluoride toothpaste, floss daily, eat a balanced diet and maintain regular dental appointments to help prevent tooth decay.

CARY FEUERMAN, DMD

PERIODONTAL ASSOCIATES

Source:  American Dental Association

In a study, Identification of Unrecognized Diabetes and Pre-diabetes in a Dental Setting, published in the July 2011 issue of the Journal of Dental Research, researchers at Columbia University College of Dental Medicine found that dental visits represented a chance to intervene in the diabetes epidemic by identifying individuals with diabetes or pre-diabetes who are unaware of their condition. The study sought to develop and evaluate an identification protocol for high blood sugar levels in dental patients and was supported by a research grant from Colgate-Palmolive. The authors report no potential financial or other conflicts.

"Periodontal disease is an early complication of diabetes, and about 70 percent of U.S. adults see a dentist at least once a year," says Dr. Ira Lamster, dean of the College of Dental Medicine, and senior author on the paper. "Prior research focused on identification strategies relevant to medical settings. Oral healthcare settings have not been evaluated before, nor have the contributions of oral findings ever been tested prospectively."

For this study, researchers recruited approximately 600 individuals visiting a dental clinic in Northern Manhattan who were 40-years-old or older (if non-Hispanic white) and 30-years-old or older (if Hispanic or non-white), and had never been told they have diabetes or pre-diabetes. 

Approximately 530 patients with at least one additional self-reported diabetes risk factor (family history of diabetes, high cholesterol, hypertension, or overweight/obesity) received a periodontal examination and a fingerstick, point-of-care hemoglobin A1c test. In order for the investigators to assess and compare the performance of several potential identification protocols, patients returned for a fasting plasma glucose test, which indicates whether an individual has diabetes or pre-diabetes.

Researchers found that, in this at-risk dental population, a simple algorithm composed of only two dental parameters (number of missing teeth and percentage of deep periodontal pockets) was effective in identifying patients with unrecognized pre-diabetes or diabetes. The addition of the point-of-care A1c test was of significant value, further improving the performance of this algorithm.

"Early recognition of diabetes has been the focus of efforts from medical and public health colleagues for years, as early treatment of affected individuals can limit the development of many serious complications," says Dr. Evanthia Lalla, an associate professor at the College of Dental Medicine, and the lead author on the paper. "Relatively simple lifestyle changes in pre-diabetic individuals can prevent progression to frank diabetes, so identifying this group of individuals is also important," she adds. "Our findings provide a simple approach that can be easily used in all dental-care settings."

Other authors who contributed are: Dr. Carol Kunzel, associate clinical professor at the College of Dental Medicine and at Columbia's Mailman School of Public Health; Dr. Sandra Burkett, at the College of Dental Medicine; and Dr. Bin Cheng, an assistant professor in the Department of Biostatistics at the Mailman School of Public Health.

According to the Centers for Disease Control and Prevention, one in four people affected with type 2 diabetes in the United States remains undiagnosed. And those with pre-diabetes are at an increased risk for type 2 diabetes and also for heart disease, stroke and other vascular conditions typical of individuals with diabetes.

Your comments are appreciated.

Cary Feuerman, DMD

Periodontal Associates

Source:  Science Daily

INTRODUCTION
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.
STEPS IN MAKING A CAST RESTORATION
1 . TOOTH PREPARATION .
2 . IMPRESSION .
3 . DIE PREPARATION .
4 .WAX PATTERN FABRICATION .
- There are 4 methods for making wax patterns for a cast restoration .
5. SPRUING .
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 :
Definition:
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.

FUNCTIONS OF SPRUE
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 .
SELECTION OF SPRUE
1 . DIAMETER :
It should be approximately the same size of the thickest portion of the wax pattern .
Too small sprue diameter suck back porosity results .
2 . SPRUE FORMER ATTACHMENT :
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 .
3 . SPRUE FORMER POSITION
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
4 . SPRUE FORMER DIRECTION
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 .
5 . SPRUE FORMER LENGTH
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.
Significance
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 .
TYPES OF SPRUES
I . - Wax . II . Solid
- Plastic . Hollow
- Metal .
VENTING
Small auxilliary sprues or vents improve casting of thin patterns .
Acts as a HEAT SINK .
WAX PATTERN REMOVAL
Pattern should be removed in line with its path of removal
WETTABILITY
To minimise the irregularities on the investment & the casting a wetting agent can be used .

FUNCTIONS OF A WETTING AGENT
1 . Reduce contact angle between liquid & wax surface .
2 .Remove any oily film left on wax pattern .
DISTORTION OF THE 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 .
PREREQUISITES
Wax pattern should be evaluated for smoothness , finish & contour .
Pattern is inspected under magnification & residual flash is removed .
CRUCIBLE FORMER
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
CASTING RING LINERS
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
RINGLESS INVESTMENT TECHNIQUE
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 .
CASTING
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
CASTING CRUCIBLES
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.
FLUXING
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 .
CASTING DEFECTS
Classification (combe ):
1) Distortion.
2) Surface roughness .
3) Porosity .
4)Incomplete casting .
5) Oxidation .
6) Sulfur contamination .
Distortion
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.

POROSITY
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 .
CONCLUSION
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 .

REFERENCES
• 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.
JOURNAL REFERENCES
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 .

I have listed a few simple steps to help prevent gingivitis and periodontal disease as a reminder to all of our patients.

STEP 1.  When normally healthy, pink, and firm gums become red, swollen, and spongy, you have a problem -- a problem called gingivitis. If the condition becomes severe enough, it can lead to periodontal disease -- a deterioration of the teeth and bone that anchor the teeth. So the first step in combating gingivitis is to make sure you’re brushing twice a day, flossing once a day, and visiting a dentist at least twice a year for a checkup and cleaning.

STEP 2.  When you brush your teeth, make sure you’re working it for at least two minutes. Most dentists suggest spending 30 seconds on each quadrant of your mouth.

STEP 3.  When it comes to germs, your tongue can be like Velcro, so brushing it along with your gums and teeth will not only help keep your breath fresher, but will reduce the chance that bacteria, viruses, or fungi find harbor in your mouth.

STEP 4.  Next, make the most out of your flossing time. Floss between every tooth, all the way down to the edge of the gum line at least once a day.

STEP 5.  Finally, use an ADA-approved antimicrobial mouth rinse to finish off your routine. If these steps don’t keep gingivitis away, you’ll need to see a dentist right away. He or she may need to perform a more extensive cleaning or provide you with a prescription dental rinse, or both.

Cary Feuerman, DMD

Periodontal Associates

Source:  American Dental Association