Final answer:
The main purpose of a cavosurface bevel on an inlay preparation is to enhance the fit and seal of the inlay to the tooth by improving marginal adaptation, which can also help in minimizing marginal percolation.
Step-by-step explanation:
The principal reason for a cavosurface bevel on an inlay preparation is to improve marginal adaptation. A bevel helps in creating a more gradual transition between the material of the inlay and the tooth structure, which enhances the fit and seal at the margin. It also serves to eliminate any undermined enamel that could weaken the restoration. Furthermore, proper adaptation reduces the likelihood of marginal percolation, which is the seepage of fluids and microorganisms between the tooth and the restoration that can lead to secondary decay. Although resistance and retention forms are also important considerations in the preparation design, they are not primarily addressed by the bevel.