Removable Partial Denture Design — ORE Part 1 MCQ

Correct answer: A — The denture will rotate around the fulcrum line during function

Explanation lettering: C = shown as B · D = shown as C · B = shown as D

Kennedy Class II distal extension dentures have a fundamental biomechanical flaw: the saddle is supported only by mucosa which is more compressible than the periodontal ligament anchoring the abutment teeth. This differential compressibility causes the denture to rotate around a fulcrum line (connecting the terminal abutments) during occlusal loading. This rotational movement is the primary design concern because it creates harmful levering forces on the abutment teeth and generates unfavorable horizontal stresses that accelerate bone resorption. While clasps do transmit forces to abutments (C), and bone loss can result (E), the initiating problem is the rotational movement itself. Options B, D and E are incorrect: distal extension dentures are not rigid but flexible, do not restrict tongue movement, and cause resorption rather than hypertrophy. Option A is the recognised major biomechanical challenge that prosthodontic design principles attempt to minimise through careful clasp placement, indirect retention, and rigid frameworks.

Reference: Krol A et al. (1990), Craig RG & Farah JW (1978), and contemporary prosthodontic literature (PubMed 27746609, PMC6969961, PMC8590637) establishing rotational movement around the fulcrum line as the defining biomechanical concern of Kennedy Class II distal extension RPDs, https://pubmed.ncbi.nlm.nih.gov/27746609/