How much of the marginal ridge gets reduced for a rest seat?

How much of the marginal ridge gets reduced for a rest seat?

• A. 0.5 mm
• B. 1.0 mm
• C. 1.5 mm
• D. 2.0 mm

Answer: (C)

Preparing a rest seat on the marginal ridge of a posterior abutment tooth needs enough depth to accept the rest and seat it fully without interference. The recommended depth is about 1.5 mm. This provides sufficient space for the rest’s thickness while conserving tooth structure and avoiding weakening the tooth or exposing dentin or pulp. Shallower depths, like 0.5 or 1.0 mm, may not give enough thickness for the rest and could compromise seating or strength, while a depth of 2.0 mm would remove too much tooth, increasing the risk of damage. So, 1.5 mm is the standard reduction for a marginal ridge rest seat.

Preparing a rest seat on the marginal ridge of a posterior abutment tooth needs enough depth to accept the rest and seat it fully without interference. The recommended depth is about 1.5 mm. This provides sufficient space for the rest’s thickness while conserving tooth structure and avoiding weakening the tooth or exposing dentin or pulp. Shallower depths, like 0.5 or 1.0 mm, may not give enough thickness for the rest and could compromise seating or strength, while a depth of 2.0 mm would remove too much tooth, increasing the risk of damage. So, 1.5 mm is the standard reduction for a marginal ridge rest seat.