I. Why named PFM?
Porcelain fused to metal crowns (PFM) has been successfully used for many decades, providing clinicians with reliable, esthetically pleasing, and long-lasting restorations.
PFM crowns with a substructure made from dental alloys and covered with an outer layer of cosmetic porcelain. Commonly used alloys are Nickel-Chromium, Chromium-Cobalt, Titanium, or Gold.
Before Zirconia and Emax appeared, PFM and metal crowns were the types of crowns that were favored and widely used by dentists. If metal crowns have aesthetic limitations, PFMs can overcome that disadvantage because the metal substructure is covered with porcelain outside. After decades of use, PFMs are still trusted by many dentists because of their durability, aesthetic pleasing, and high biocompatibility.
Nowadays, due to the big advantages of Zirconia and Emax, PFMs are gradually losing their appeal to dentists, an increasing number of dentists prefer choosing Zirconia and Emax crowns over PFMs. However, PFM with its proven advantages over many decades still has a certain position in the dental industry.
II. Types of PFM crowns
Generally, there are two different categories of dental alloys used when fabricating PFMs
1. PFM with a base metal substructure
Ni-Cr or Co-Cr are basic alloys commonly used for the frame of this type of PFMs. The outside is covered with a layer of white porcelain. The advantages are these PFMs can apply for various dental restorations: single crown, small bridges, large bridges and have a low-cost, suitable for many customers.
2. PFM with Noble metal substructure
Titanium and gold are two typical alloys commonly used in this case. Although titanium is a basic metal alloy, its quality is superior to other basic alloys. Thus, in addition to its application in dental restorations, it is also applied to implants.
PFMs made of gold alloy provide the best quality because of the following characteristics:
- Gold alloy is not subject to corrosive effects from saliva, so the grayish color line will not appear after a period of use.
- PFM teeth made of Gold Alloy have outstanding resistance and strength even with low thickness.
- Gold alloys are lighter than base alloys (except titanium)
- Gold alloy does not produce any harmful reaction to users
PFM with gold and titanium
III. Questions about PFM crowns?
1. Are PFM crowns good in use?
Because PFMs have a metal structure inside (Ni - Cr or Co - Cr) and are covered with a layer of porcelain, this type of restoration can withstand good forces. PFMs ensure your chewing function like natural teeth. With good care and maintenance, PFMs can last 10 years.
2. The price of PFM crowns?
According to Dental Care of Lombard, porcelain fused to metal crowns typically costs $500 to $1,500 or more per tooth in the USA.
3. Characteristics of PFM crowns?
PFM crowns are very durable and are suitable for most areas of the mouth
The safe of PFM restorations has been proven through long-term research
Clinical research has shown that single PFM crowns and PFM bridges also have a relatively long lifespan
The aesthetic of PFM crowns is quite good, especially during the first few years
PFM teeth can combine with many different dental attachments in precision
4. Problems when using PFM crowns
The disadvantage of PFM teeth is related to the long-term aesthetic factor because of the metal frame structure. Although the opaque is masked to cover the defects of the metal ribs, the inner metal substructure can remain slightly visible. The opaque prevents light from passing through like natural teeth.
The PFM crowns usually respond well to the esthetic factor during the first 1,2 years. However, after a long period of use, gum recession was recognized as a potential problem in PFMs teeth. As gum tissue recedes, a grayish-colored line becomes more visible when the metal margins of PFM crowns are exposed. In addition, another problem related to dental restorations is that PFM crowns can wear down opposing teeth.
Black gum from PFM
5. Are PFM crowns made from metal and titanium the same?
PFM crowns usually have inner ribs made from Cr-Ni or Cr-Co metal. However, the number of people who get allergic to Nickel is higher than Cobalt. Thus, PFM crowns with Cr-Co are more chosen in dentistry.
PFM crowns with titanium structure have internal ribs made of 4-6% Titanium alloy are widely used in dentistry because it is benign in the oral environment and compatible with gums
6. Compare PFM crowns with Emax, Zirconia crowns?
Both are porcelain teeth, so porcelain crowns and PFM crowns have common advantages such as:
• Use for treatment sparse teeth, messy teeth, decay, and medium protruding teeth
• Improve teeth color
With the characteristic of the metal structure, PFM crowns bring the feeling of chewing and biting more like natural teeth than all-porcelain teeth. However, in terms of color, PFM crowns are not good as porcelain teeth as the metal rib will be black when the light shines. Therefore, PFM crowns can only improve teeth color to 2-3 levels. Meanwhile, porcelain teeth can improve up to 4-8 levels. This is a big difference that those who like bright teeth should note.
All-porcelain teeth have the most noticeable disadvantage in that the cost is often in the middle-high level. However, in terms of long time and effectiveness, all-porcelain teeth usually last a long time, from 10-20 years to permanent in good care condition. Therefore, this cost is reasonable.
Metal porcelain teeth have a lower cost. That means that the lifespan and aesthetics are also worse than all-porcelain teeth. A major disadvantage of metal porcelain teeth is that after about 3-5 years, the gums around the stumps will be blackened due to the oxidation of the metal part in the acidic mouth environment. This black gum is not harmful to health, but it causes loss of aesthetics for the teeth. Usually, dentists will advise you to put PFM crowns on your posterior areas which do not require high vision.
7. Should I choose PFM crowns?
PFM crowns usually have the lowest cost of all types of porcelain teeth. Besides the advantages, metal porcelain teeth also have disadvantages such as:
• After a period of use, the alloy layer is oxidized by the reaction of acid in saliva with metal, causing the toothed rim to gradually turn black.
• The durability and strength of metal porcelain teeth compared to all-porcelain teeth are also weaker, so they are easily chipped if chewing hard food
• The color of metal porcelain teeth is quite like that of natural teeth, but the color is not as natural as that of all-porcelain teeth.
• Because of metal ribs, there is a risk of irritation to the body. If you are allergic to metal, don't do it.
• In addition, PFM crowns are thicker, so the natural teeth need to be ground smaller to fit the crown.
The choice of PFM teeth will depend on the position to be replaced and the customer's financial situation. PFM teeth will be the best choice for patients who have problems with the posterior area, do not require high aesthetics, and want low prices.
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Author: Xdent team