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Free-End Saddle Biomechanics — ORE Part 1 MCQ

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HardProsthodonticsFree-End Saddle BiomechanicsORE Part 1

A patient wears a complete maxillary denture and a mandibular Kennedy Class I cobalt-chromium removable partial denture. They report recurrent soreness of the mucosa beneath both distal-extension saddles after eating. The denture framework fits the teeth, and there is no occlusal interference. Which biomechanical mechanism most likely explains the soreness?

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Correct answer: B — Tissueward saddle displacement under functional loading

**A is correct.** A Kennedy Class I denture combines rigid tooth support anteriorly with resilient mucosal support beneath the distal-extension bases. During mastication, the mucosa compresses and each free-end saddle moves tissuewards, with rotation around the rest-defined fulcrum. Repeated pressure on the residual ridge mucosa causes post-function soreness. Loose clasps may reduce retention but do not primarily explain pressure trauma beneath both saddles during chewing. A bulky lingual connector would traumatise lingual soft tissues rather than the saddle-bearing mucosa. Light occlusion would reduce, not create, loading-related tissue compression. An underextended base can reduce support and worsen instability, but the decisive inherent mechanism in a bilateral free-end saddle denture is differential tooth-versus-mucosal support causing tissueward displacement.

Reference: Ben-Ur Z, Aviv I, Maharshak B. Factors affecting displacement of free-end saddle removable partial dentures. Quintessence International. 1991;22(1):23-27. https://pubmed.ncbi.nlm.nih.gov/1784716/