The chamfer must be smooth and continuous, and when evaluated, a distinct resistance to what should be felt?

A smooth and continuous chamfer is crucial in the preparation for crowns and other restorations. When evaluating the chamfer, the resistance felt denotes how well the preparation can withstand opposing forces during mastication and other functional movements. Feeling a distinct resistance to vertical displacement indicates that the crown or restoration will be properly retained in place, as the forces applied during biting and chewing typically act in a vertical direction. This is essential for ensuring that the restoration will remain stable and function effectively without dislodging.

The other options do not appropriately highlight the primary forces acting on a dental restoration. While lateral and horizontal forces are indeed relevant in a broader context of dental mechanics, vertical forces are typically the most significant in terms of retention and stability of crowns and prosthetics. Resin displacement relates more to the material and bonding aspect rather than the structural resistance of the preparation itself. Thus, the focus on vertical displacement aligns with the fundamental principles of how dental restorations are designed to function under typical conditions.