Proximal retention in the box of a Class II amalgam preparation is provided by:

Correct answer: C. Retention grooves together with occlusal convergence of the facial and lingual walls

• A. The axiopulpal bevel serves resistance form, not retention.
• B. A gingival bevel is a feature of CAST restorations and is not placed for amalgam, which needs a 90° cavosurface margin.
• C. CORRECT. Two features work together to resist PROXIMAL displacement. RETENTION GROOVES are cut into the axiofacial and axiolingual line angles of the box, creating positive mechanical locks. The facial and lingual walls CONVERGE occlusally, so the restoration cannot lift out. Together they prevent the proximal portion from being displaced proximally or occlusally.
• D. A flat pulpal floor resists occlusal displacement of the occlusal portion but does nothing for the proximal box.

Note: Grooves must be cut in DENTINE, just inside the enamel-dentine junction, and must not undermine the marginal enamel.