In a class I preparation, the pulpal floor depth at the ridges is within which range?

• A. 1.0-1.5 mm
• B. 2.0-2.5 mm
• C. 1.75-2 mm
• D. 3.0-3.5 mm

Answer: (C)

In a Class I amalgam prep, target a pulpal floor depth of about 1.75–2 mm at the ridges. This depth provides enough space for a strong, well-condensed amalgam restoration while keeping enough dentin to protect the pulp. If the preparation is too shallow (around 1.0–1.5 mm), there isn’t enough material thickness to resist occlusal forces and to maintain wall and marginal integrity. If it’s too deep (3.0–3.5 mm), the risk of pulpal exposure or needing pulp therapy increases. The 1.75–2 mm range is the balanced, practical depth for these preparations.