Principles Of Tooth Preparation Practice Test

Feather-edge margins are not indicated for crown preps because a crown needs a definite, reproducible finish line to seat accurately and to create a reliable marginal seal. A knife-edge margin blends gradually into the tooth and provides almost no platform or shoulder for the crown to sit against. This makes precise seating difficult, can result in inconsistent cement thickness, and increases the risk of marginal leakage, margin breakdown, or esthetic and functional problems after cementation. For crowns, margins are typically designed with a defined finish line (such as a shoulder or a deep chamfer) to ensure adequate tooth reduction, predictable seating, and durable marginal adaptation. That’s why feather-edge margins aren’t recommended in any crown-prep scenario, regardless of material or esthetic goals.