60.The cavo surface angle for inlay cavity preparation :

a. 90 degree b. 150 degree
c.<90 d. 180

Ans. B

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

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