In a class I preparation, the pulpal floor depth at the fossa is typically which value?

• A. 1.5 mm
• B. 1.0 mm
• C. 2.0 mm
• D. 2.5 mm

Answer: (A)

In a Class I amalgam preparation, you want a pulpal floor that is deep enough to provide a solid, well-defined base for the restoration but not so deep that you risk pulpal exposure or leaving the dentin too thin. About 1.5 mm at the fossa is the standard target because it balances these needs: it gives enough dentin between the pulp and the restoration to protect the pulp, while still leaving enough tooth structure to resist occlusal forces and to support proper condensation of the amalgam. If the floor is too shallow, walls may be undermined and resistance form becomes weaker; if it’s much deeper, the chance of pulpal irritation or exposure increases and the remaining dentin may be insufficient for a durable restoration. That makes 1.5 mm the best-supported, most commonly taught depth.