Why do dentists bevel teeth when preparing them for a crown?

Bevels ave been used by dentists for many years in the belief that they help achieve a more intimate fit for the crown. When I was in dental school we were taught that a bevel on a tooth that was being crowned helped insure that the margin have a smaller gap when seated. There is a definite logic to this when compared to chamfer and shoulder finish lines, but It is hard to explain in a short blog post.

Now a days, with the advent of a number of metal free types of crowns(Emax,Lava,Procera,and Zirconium) chamfer finish lines are becoming more popular since these the manufacturers of these crowns do not advocate a bevel at the finish line.

In my practice for first molar and bicuspid teeth I continue to bevel and use Pfm crowns. I find that these work well and possibly better than some of these new crowns, especially for teeth with weakened coronal tooth structure. One possible reason for their success is that the bevel shifts some of the flexural forces to a relatively uncut an intact portion of the tooth tha is below the gingiva. Most chamfer or shoulder preps seem to depend more on the integrity of the coronal tooth structure and need to have considerable intact coronal tooth to be predictably successful.

Many teeth that require full coverage restorations have weakened coronal tooth structure and many have internal cracks that should be isolated from the forces involved with chewing. In my opinion the beveled preps (pfms) or feather edge preps(full metal crowns) do the best job of isolating the weakened portion of posterior teeth from flexing forces that can be generated during a patients chewing.

Although the newer types of metal free crowns are beautiful, the verdict is out on how well and predictably they will stand up in patients mouths over the long haul.