What features provide retention in an amalgam Class II preparation?

• A. Smooth, parallel walls with no grooves
• B. Proximal grooves
• C. Proximal grooves, dovetails or slight convergence of walls, and a well-defined gingival seat
• D. Use of pins exclusively

Answer: (C)

Retention in an amalgam Class II preparation comes from creating mechanical locks in the proximal box. Proximal grooves furnish undercuts in the cavity walls that grab the filling. A dovetail or slight convergence of the walls adds a wedging effect, increasing resistance to dislodgement as the tooth flexes during chewing. A well-defined gingival seat ensures the restoration seats fully on solid dentin and provides a stable base at the gingival margin. Together, these features give amalgam something to grip onto rather than rely on bonding, making the restoration resistant to functional forces. Using pins exclusively is not appropriate for retention in this context because pins alone weaken tooth structure and are not the recommended approach for Class II amalgam preparations.