Prosthodontics & Occlusion · single question
What is the primary advantage of the RPA clasp assembly (rest, proximal plate, I-bar) in RPD design?
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Correct answer: A. It minimizes torquing forces on the abutment tooth
The RPA clasp (Rest on mesial, Proximal plate on distal, Aker's I-bar retentive arm) is specifically designed for distal extension cases. Its advantage is that it minimizes torquing forces on the abutment tooth through: (1) the I-bar engages a shallow 0.01" undercut in the gingival third (least stress), (2) the proximal plate and I-bar disengage from the tooth under functional loading, reducing rotational forces on the abutment. This is the RPI (mesial rest, proximal plate, I-bar) philosophy.
- A. ✅ CORRECT – The RPA clasp minimizes torquing on abutment teeth in distal extension RPDs by allowing controlled disengagement under load.
- B. ❌ The RPA/RPI clasp uses shallow undercuts — not designed for deep undercuts.
- C. ❌ Indirect retainers are still required in distal extension RPDs regardless of which direct retainer clasp is used.
- D. ❌ The RPA is specifically designed for distal extension (Kennedy Class I and II) — not all Kennedy classes.
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