Since the mid-70’s, we have been able to bond tooth colored dental material or fillings to enamel. Even when I entered dental school in 1975, we could replace a chip on a front tooth by bonding. It works like this: W e first do is place a mild acid on the tooth. This etching process creates million of rough surfaces that we can then place a clean bonding agent, or resin which latches into the roughened enamel surface, creating a micro-mechanical adhesion. We then place the tooth colored filling material over that resin, which bonds to the resin chemically.
Well if this process has been around so long, what improvements have you seen in the material you now use over the earlier materials?
The improvements in this procedure has been truly fantastic over the past thirty years. When I first started using plastic fillings, or composites as they are better known, the handling of the material was difficult as it hardened very quickly after mixing, the three shades were inadequate. Also, we could only bond to the enamel, so if a patient fractures the corner off a front tooth, we were really only bonding around the edges, not any exposed dentine in the middle.
This was a problem with using the material for fillings on “back” teeth. If there was any areas where the bond was not well done, decay would be down and around these fillings in months. However, in the 80’s we started to be able to bond to the dentine of the tooth also, which really begat the explosion of all types of cosmetic tooth-colored dental options, from bonded all-porcelain crowns, the conservative porcelain or pressed-resin onlays, to what I like to call “minimally invasive dentistry”.
When I started providing dentistry in 1975, we really needed to amputate an awful lot of tooth structure to make the final crown or filling work. If we were placing a silver-mercury filling, we needed to remove the decay, and then create undercuts in the remaining tooth. We then placed the filling material in when it was soft, and after it hardened, the undercuts held the filling in place. When we needed to place a crown because there was not enough tooth structure to hold a filling in place, we would created the sides of the prepared tooth to create a retentive form. The crown was held on with cement, but you really needed somewhat parallel sides, most time requiring more tooth to be removed.
Now with our ability to bond to both enamel and dentine, with bond strengths improving every year, it is almost irrelevant as to what the shape of the filing or crown restoration is. We only need to eliminate the decay, and strengthen any portion of the tooth that has fractures. The other major advance happened in the early 80’s when we moved from a self polymerizing material (i.e. two material were mixed on a pad and it set in 2 minute) to a light polymerizing product. We can now place and sculpt the material and it does not set until it is exposed to a light which is blue in color.
This is one of the advantages of going to an office that does a lot of bonded cosmetic cases. The same care and techniques that are employed to bond 20 veneers is used to place a very conservative filling.
Also, we can diagnose cases earlier, when less decay is present. We employ a laser which can diagnosis very early decay in the groves of a molar. Traditionally we took a pointy instrument called an explorer and push it into the groves. When there is enough softened tooth, the explorer gets “stuck” or has a ping as it is removed form the softened decayed tooth. With this instrument, which measured the vapor given off by the decay, we can detect the need for a filling 12-18 months earlier, hence a smaller problem to fix.
We then can remove the decay only, we do not need to create undercuts, and can place a tooth colored filling material that actually strengthens the remaining tooth.
How long should these bonded fillings last?
Well, that would be hard to answer, as the material we are using today were not even born 6 years ago. I do know the bond strength improves every year. I also know I have veneer cases I did 20 years ago which are just fine today, and the material available then were not even close. So between strengthening the tooth, conservative removal of only diseased tooth structure and the cosmetic final product, it is just such a pleasure to be able to provide this type of service for my patients.