At what angle should proximal cavosurface walls be finished in Class II preparation for amalgam?

In a Class II preparation for amalgam, the proximal cavosurface walls should be finished at a right angle. This is important because a right angle promotes adequate retention of the amalgam material. The design of the preparation must ensure that the walls provide sufficient support and stability for the filling material, preventing the amalgam from being displaced or easily fractured during function.

A right-angle finish also contributes to a well-sealed margin, which is crucial in minimizing microleakage and potential recurrent caries. Additionally, this configuration allows for proper condensation of the amalgam during the filling process, essential for achieving the desired density and strength of the restoration.

In contrast, an acute angle could lead to inadequate retention and a higher risk of failure, while an obtuse angle might compromise the integrity of the filling. Similarly, a 45-degree angle is not suitable for amalgam restorations, as it does not provide the optimal bond and support required for the material used. Overall, a right angle is the standard and recommended practice in dental preparations for amalgam to ensure durability and longevity of the restoration.