What prevents proximal displacement of a restoration?

• A. Matrix extension
• B. Dovetail
• C. Bevel
• D. Pin

Answer: (B)

Proximal displacement is resisted by a mechanical lock in the proximal box, which is created by a dovetail. The dovetail shapes the proximal wall into an undercut so the restorative material engage with the tooth structure and cannot easily move toward the adjacent tooth under chewing forces. This retention is especially important for amalgam restorations that rely on mechanical retention rather than bonding. Other features like extending the matrix or giving the surface a bevel don’t provide this kind of lock against lateral or proximal movement, and pins, while they can add retention in some cases, don’t create the same proximal undercut and carry other risks.