Undercut Gauge Usage — NDEB AFK MCQ
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Correct answer: A — Undercut gauge (0.25 mm, 0.50 mm, 0.75 mm) on the dental surveyor
Undercut gauges (precision wires or carbon rods of known dimensions: 0.25 mm, 0.50 mm, 0.75 mm) are used with the dental surveyor to measure the depth of undercut below the survey line on abutment teeth. The depth of undercut determines which type of clasp is appropriate: cast circumferential clasps require 0.25 mm undercut (Type IV gold) to 0.50 mm (Co-Cr); wrought wire clasps use 0.50-0.75 mm undercut. Excessive undercut causes difficulty in RPD insertion/removal and clasp distortion.
Reference: Carr – McCracken's Removable Partial Prosthodontics, 13th ed., 2015