The angle at the junction of the walls of the cavity preparation and the external surface of the tooth.

It is of two types

[Ref Sturdevant 4th ed. Pg 300]

Butt joint

Lap / Slip joint

90o cavosurface angle

Advocated in amalgam restorations because amalgam is a brittle material and has low edge strength

Butt joint produces maximal strength for both tooth and amalgam.

It is also advocated in silicate and porcelain restorations

> 90 degree cavosurface angle.

Advocated in cast and composite restorations

30 – 40o marginal metal and 140 – 150o cavosurface angle.

Beveling enables superior adaptation and burnishability of marginal metal