What is the preparation margin design used at the incisal edge of porcelain veneer preparations?

For porcelain veneers, three incisal preparation designs are used: (1) Window preparation (incisal edge not included), (2) Incisal overlap (veneers overlaps incisal edge), and (3) Butt joint/shoulder preparation at the incisal edge. The shoulder (butt joint) preparation is the most common incisal design for porcelain veneers. It provides a clean, defined margin for the ceramist, allows adequate thickness of porcelain at the incisal edge for strength, and facilitates precise seating of the veneer. A chamfer is used for full-coverage crowns. A feather edge is generally not used at the incisal margin of veneers as it provides inadequate support for the porcelain.