When preparing a metal ceramic crown, which margin design is generally not used on anterior teeth?

The feather edge margin design is typically not utilized for anterior teeth in metal ceramic crown preparations due to its lack of adequate thickness for both the ceramic layering and the metal substructure. This design creates a very thin edge that may result in the porcelain being too fragile and prone to chipping, particularly in the esthetically important anterior region, where strength and durability are crucial.

In contrast, shoulder and beveled shoulder margins provide a more substantial interface that supports the metal ceramic structure and enhances aesthetics by allowing for more porcelain thickness at the margins. Chamfer margins are also used, especially for posterior teeth, as they allow for better adaptation and provide a smoother finish with adequate support. Thus, the feather edge, while occasionally considered for certain applications, does not provide the necessary characteristics for a functional and durable restoration in anterior teeth.