What is the purpose of bevelling the axiopulpal line angle in a Class II amalgam preparation?

Correct answer: D. To reduce stress concentration and increase resistance form

• A. The bevel is an INTERNAL feature and has no contact with the cavosurface margin, so it cannot affect marginal seal.
• B. Liner space is created by the depth of the preparation, not by this bevel.
• C. Retention comes from converging walls and retentive grooves; the axiopulpal bevel does not contribute to it.
• D. CORRECT. A sharp internal line angle acts as a STRESS RISER — occlusal load concentrates there and initiates a fracture that propagates across the isthmus, which is the classic site of Class II amalgam failure. Rounding or bevelling the AXIOPULPAL line angle (the junction of the axial wall of the box and the pulpal floor) distributes the stress over a broader area and adds bulk of material at the most vulnerable point.

Note: Distinguish RESISTANCE form (preventing fracture of tooth or restoration under load) from RETENTION form (preventing displacement). The axiopulpal bevel serves resistance.