If extension of preparation is more than half the distance from the primary groove to the cusp tip, what should you consider?

• A. Cap the cusp
• B. Extend margins further
• C. Remove more tooth structure
• D. Do nothing

Answer: (A)

When you’re extending a preparation for prevention, the cusp needs to stay strong enough to withstand biting forces. If the extension into a cusp goes beyond half the distance from the primary groove to the cusp tip, the remaining cusp is often left too thin and vulnerable to fracture under function. In this situation you should cap the cusp. Capping the cusp reinforces it by building up the cusp with restorative material, restoring height and distributing stresses more evenly across the cusp so it can resist occlusal loads.

Extending the margins further or removing more tooth structure would further weaken the cusp and increase fracture risk, while doing nothing would leave the cusp inadequately supported. Cap the cusp is the best option to preserve tooth structure and durability.