Prosthodontics & Occlusion · single question
In a mandibular distal extension RPD, why is the occlusal rest placed on the MESIAL surface of the abutment tooth rather than the distal?
Show answer and explanation
Correct answer: C. Mesial rest directs occlusal forces toward the edentulous ridge, reducing torque on the abutment
In a distal extension (Kennedy Class I or II) RPD, a mesial rest on the abutment tooth is preferred because: when the prosthesis base is loaded, force is directed mesially (toward remaining teeth) rather than distally (toward the edentulous ridge). This reduces the tipping/torquing moment on the abutment tooth. The distal rest would create a class I lever system that tips the abutment distally — harmful to the periodontal support.
- A. ❌ Clasp undercut engagement is not the rationale for mesial vs. distal rest placement.
- B. ❌ A mesial rest does not inherently provide better retention than a distal rest.
- C. ✅ CORRECT – In a distal extension RPD, a mesial rest reduces the tipping force on the abutment by directing load toward the remaining dentition.
- D. ❌ Food impaction prevention is not the primary reason for mesial rest placement in distal extension RPDs.
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