When creating a wax pattern for crowns, where should the sprue be attached?

Attaching the sprue to the area of greatest bulk in a wax pattern for crowns is the optimal choice because it facilitates the flow of metal during the casting process. The thickest areas of the crown provide a stable support structure, ensuring that the molten metal can fill the mold without creating weak or incomplete areas in the final product.

This approach helps to minimize the risk of defects such as porosity or cold shuts, which can occur if the metal does not fill the mold properly due to inadequate sprue placement.

On the other hand, if the sprue is placed at the margin of the preparation or the thinnest part of the crown, it could lead to issues during casting, as thinner sections can solidify quicker and trap gas or create voids. Similarly, placing the sprue at the incisal edge may not provide the optimal flow and could compromise the integrity of the crown. Thus, attaching the sprue to the area of greatest bulk ensures the best outcome in terms of both structure and function of the cast crown.