Prosthodontics & Occlusion · single question
What does the survey line (height of contour) on a tooth identify for RPD design?
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Correct answer: B. Where the tooth provides undercut for retentive clasp tips vs. no undercut for non-retentive elements
The height of contour (survey line) divides the tooth into: SUPRABULGE (above the line — no undercut, safe for rigid elements like minor connectors) and INFRABULGE (below the line — undercut zone, where retentive clasp tips are placed). It guides where clasps engage the tooth for retention vs. where to avoid engagement.
- A. ❌ Rest seat location is determined by design principles (occlusal, cingulum, incisal) — not directly by the survey line.
- B. ✅ Survey line identifies where undercut exists (below) vs. no undercut (above) — guiding clasp placement for retention.
- C. ❌ Bone support is assessed via probing and radiographs — not by the dental surveyor.
- D. ❌ VDO is determined by multiple clinical measurements — not by the surveyor.
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