Several years ago some dentists, mostly in western states, started advocating the removal of silver fillings and their replacement with resin (tooth colored) fillings. It is tempting for a dental practice to claim that the practice is metal free or mercury free because it plays on the fears of many patients. The fact is that the mercury in dental amalgam binds with silver during the mixing process and is chemically and biologically inert. The use of silver amalgam filling is supported by the American Dental Association and the F.D.A. has concluded that silver amalgam fillings are safe. All dental schools in the country teach the use of silver amalgam fillings.
At West Augusta Dental Associates we can do silver fillings or we can do white composite resin fillings. In areas of the mouth where esthetics are important, we use tooth colored filling materials. If a patient does not want silver fillings, we respect their wishes and we can do tooth colored fillings. Many insurance companies, however, will allow a lower benefit for the tooth colored fillings for back teeth. Below are some of the advantages and disadvantages of tooth colored vs. silver fillings.
Advantages Of Resin (Tooth Colored) Fillings For Back Teeth
- Resin fillings are tooth colored.
Disadvantages Of Resin (Tooth Colored) Fillings For Back Teeth
- Teeth are often very sensitive after resin fillings have been done. Resin fillings are basically a plastic (resin) with a filler of quartz power. Resin fillings are also called composite fillings. The resin is the problem with resin filling material. When resin sets up, it shrinks. Shrinkage can be controlled to some degree, but the shrinkage is a problem. Resin filling material is now glued or bonded to the tooth structure. This is good in a way and bad in a way. Bonding is good because it gives a better seal between the tooth and the filling, but it is bad because when the resin sets up during the curing process the shrinkage of the resin actually pulls on the walls of the cavity and sets up pressure lines within the tooth.
- Resins wear much faster than metal. To understand this, think about the asphalt that a road is paved with. Asphalt is a petroleum product (like tar) plus gravel or rocks. After an asphalt road has been exposed to the elements for years, the asphalt on the surface erodes and the gravel and rocks are left exposed and are gradually dislodged from the asphalt. The exact same thing happens with resin fillings. All resin fillings have some quartz particles in them to add strength and to control shrinkage. The resin wears away, the quartz particles are dislodged, and the fit of the filling to the tooth starts to open causing the filling to become very worn on the chewing surface. This is one reason that many dental practices, including ours, do not recommend large resin fillings for back teeth. Most chewing is done on the back teeth and the resin fillings simply wear away too quickly.
- The worst characteristic of resin filling material relates to how it is used in the mouth. It is extremely difficult to maintain a dry field in the mouth. In laymans terms, this means it is hard to keep saliva out of the area in which we are working. Some dentists attempt to keep a dry field with the use of a device called a rubber dam. A rubber dam is used by practically all dentists that do root canals because strong chemicals are used to irrigate canals and also there is a safety issue because small needle-shaped files are used that the patient could accidentally swallow if a rubber dam were not used. A rubber dam cannot always keep a tooth being filled dry because the decay may be just below the gumline and it is extremely difficult to keep saliva and blood out of the area when the cavity extends below the gumline.
If resin filling material is contaminated with any saliva or blood while it is being placed, the filling is compromised. If the bond between the resin is not sealed, the filling immediately begins leaking since it shrinks when it sets up. This causes more decay to form around the filling quicker, and the tooth will be very sensitive.
As if that is not bad enough, it is very difficult to get a large resin filling on a back tooth to contact the adjacent teeth in such a way that floss is not frayed and that food is not packed during chewing. In the case of silver amalgams, the filling is packed into a mold-like device called a matrix band to form the sides of the tooth. For the first few minutes after it is mixed, silver amalgam has the perfect consistency to pack it into the matrix band so that the amalgam actually shapes the band to the right contour, so the amalgam can be carved. In the case of resin filling material, it cannot really be packed into place or carved to shape before the material sets up. Other techniques that are less reliable must be used to shape the side walls of the resin filling.
At West Augusta Dental Associates we can do large resin fillings on back teeth, but we know that the handling characteristics of the material make it different for any dentist, using any technique, to be able to consistently do restorations on back teeth with the same quality as with silver amalgam fillings.
Disadvantages of Silver Amalgam Fillings For Back Teeth
- They are not tooth colored.
Advantages of Silver Amalgam Fillings For Back Teeth
- Silver amalgam fillings tend to fit the tooth better. When silver amalgam sets up, it does not shrink; it expands slightly. This is the perfect characteristic of a filling material. Think of a filling as plugging a hole in a wooden boat hull. If you were going to plug a hole in a wooden boat hole you would want the plug to expand slightly after it was placed. A filling material that expands just slightly after it is placed is an advantage, and this is exactly what silver amalgam does.
- Small amounts of saliva do not harm a silver amalgam filling when it is placed. Actually, it is best to maintain a dry field for amalgam placement, but if a small amount of saliva or blood enters the field, the packing process of the amalgam actually pushes the saliva out and the restoration is not significantly compromised. Any moisture contamination at all for a resin filling will cause a very poor result.
- Silver amalgam filling will last longer than resin fillings. The reason for this is that silver fillings do not wear down a significant amount during chewing. The wear rate of resin fillings is much higher than the wear rate of silver amalgam.
Summary Of Fillings
There are a few other disadvantages to silver fillings claimed by some dentists. One disadvantage is they are not bonded into place. At West Augusta Dental Associates we do commonly place bonded bases or liners under silver amalgam fillings. If you look in the mouth of a typical patient who is in his or her 40s or 50s or older, you will find many silver restorations, even large silver restorations that are 30, 40, 50 years old or older. This is going to be very rare with large resin restorations for the reasons stated. Remember, resin fillings are relatively new in dentistry.
Some dentists that advocate the removal of silver fillings recommend that the silver fillings be replaced with porcelain inlays (inlay is a term for a filling that is made on a model then cemented into the prepared cavity). Porcelain inlays do not shrink and contour can be controlled, but they cost about the same as a crown. A crown protects a tooth from fracture much better than a porcelain inlay. Therefore, we generally recommend crowns for back teeth that need protection from fracture. The crowns we recommend are generally porcelain over a metal substructure (porcelain fused-to-metal). For front teeth we recommend all porcelain crowns or porcelain fused-to-metal crowns.
Many of the practices around the country that recommend porcelain inlays have invested a lot of capital in a system that utilizes computer technology to fabricate the inlays. The problem is not the computer technology; the problem is the diagnosis. If you are going to the expense of doing a laboratory fabricated restoration, then a crown is a better service than an inlay. In the case of a porcelain inlay, the tooth can still crack. If a crown is on a tooth, the tooth cannot crack.
The dentists at West Augusta Dental Associates have investigated the computer driven technology to scan teeth for porcelain inlays and porcelain crowns. Many dentists using the system makes comments like the crowns fit almost as good as crowns made from an impression. We feel that we do not want almost as good for our patients simply because it gives the appearance of high-tech. If it develops that computer scanning is better than impressions to make crowns, we will incorporate this technology into our practice.
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