Over the years there has been contradictory information about placing a bevel on the margin of a posterior composite. I learned to place a bevel on the margins of all of my composite preparations. The rational was that it increased enamel bonding. The literature supports that a small bevel does increase the surface area of enamel. This increased surface area in some studies results in a 25% increase in bond strengths of the final restoration. As dentin adhesives have improved over the years the importance of increasing bondable enamel surfaces has lessened and some claim is no longer necessary.
Another question is about the ability of composite to function against a bevel. Unlike most of our restorative materials composite does very well in thin layers and does not require a “minimum” thickness of material to achieve it’s physical properties. the presence of a bevel significantly increases marginal adaptation when placing composite restorations. This adaptation increase has multiple benefits from decreased leakage, decreased post operative staining at the margins, and increased esthetic blending. The presence of a bevel also has been shown to mitigate the effect of polymerization shrinkage, which again will increase the seal and longevity of the marginal interface and decrease post operative sensitivity.
In the US most dental schools are teaching the placement of a bevel on all composite preparations. Interestingly, on most of the board exams across the country the placement of a bevel is optional. The belief is this more accurately reflects what is happening in the majority of dental offices which is no bevel. The only technique change is the limited time it takes to place the bevel and the benefits are many. I for one hate when I can see the interface between the tooth and the margin, so this alone is sufficient motivation to bevel.