In the case of a patient with a porcelain jacket crown, what edge preparation would minimize the risk of crown failure?

Minimizing the risk of crown failure in a porcelain jacket crown involves selecting the most appropriate edge preparation. A shoulder or butt joint preparation is beneficial because it provides a well-defined, flat surface for the crown to seat onto. This type of margin offers superior resistance to fracture and better adapts to the porcelain material.

Porcelain is inherently brittle, and any sharp or unsupported edges can lead to stress concentrations, making these areas more susceptible to chipping or fracture. By using a shoulder or butt joint, the preparation creates a thick, strong margin that enhances the mechanical retention of the crown and helps distribute occlusal forces more evenly across the restoration.

Round edge preparations might provide some advantages regarding aesthetics and less stress concentration compared to sharp edges, but they generally do not offer the stability and resistance to fracture that a shoulder or butt joint can provide.

Bevels can also be used to improve aesthetics at the margins but do not provide the same structural support as a shoulder or butt joint. Thus, choosing a shoulder or butt joint preparation is critical in reducing the likelihood of failure in a porcelain jacket crown.