All ceramic crown preparations typically require which type of margin?

All-ceramic crown preparations often utilize a -90-degree heavy chamfer margin due to its effectiveness in ensuring proper retention and providing a strong bond for the ceramic material. The heavy chamfer allows for a sufficient amount of tooth structure to be retained while also providing a smooth transition from the crown to the tooth, which is essential for aesthetics and preventing stress concentrations.

The design of the heavy chamfer margin aids in minimizing the potential for chipping that can occur with more acute angles, which is particularly important because ceramics can be more brittle than other materials. Additionally, this type of margin helps to accommodate the thickness of the ceramic material, ensuring that it is strong enough to withstand the forces during function while also maintaining a natural appearance.

In comparison, other margin types, such as the -90-degree shoulder or -120-degree bevelled shoulder, may not offer the same balance of retention, strength, and aesthetics that the heavy chamfer can provide in all-ceramic restorations. Using an inappropriate margin design can lead to complications like inadequate adhesion or increased risk of crown failure. Therefore, selecting a -90-degree heavy chamfer is widely preferred in the context of all-ceramic crowns.