In a class I preparation, how deep should the pulpal floor be at the fossa?

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

Answer: (C)

In a Class I preparation, the pulpal floor must be deep enough to provide enough bulk of restorative material and a safe buffer between the pulp and the restoration. About 1.5 mm at the fossa is the recommended depth. This depth gives sufficient space for proper condensation of the amalgam and ensures the restoration has enough thickness to resist occlusal forces and avoid fracture or leakage. If the floor is too shallow, such as around 1.0 mm, there isn’t enough material to stabilize the restoration and withstand biting forces, increasing the risk of fracture or marginal leakage. If it’s too deep, like 2.5 mm, you encroach on the pulp and unnecessarily remove tooth structure, which can lead to pulp sensitivity or exposure and weaken the tooth. Thus, 1.5 mm strikes the right balance between protection of the pulp and durability of the restoration.