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RPI Clasp Design — ORE Part 1 MCQ

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HardProsthodonticsRPI Clasp DesignORE Part 1

A mandibular Kennedy Class I cobalt-chromium removable partial denture is being designed. Each terminal abutment has a favourable mesio-buccal retentive undercut. The buccal sulcus is sufficiently deep, there is no relevant soft-tissue undercut, and a mesial occlusal rest is planned. Which clasp assembly is most appropriate for each terminal abutment to reduce torque during functional loading of the free-end saddles?

Educational content. Not a substitute for clinical judgement or local policy.

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Correct answer: E — Mesial rest, proximal plate and I-bar

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

A is correct: the RPI assembly comprises a mesial rest, distal proximal plate and gingivally approaching I-bar. In a distal-extension RPD, this arrangement is designed to permit relative release of the retentive element as the free-end saddle rotates under load, thereby limiting distal torque on the terminal abutment. The stem deliberately confirms a suitable mesio-buccal undercut and adequate sulcus depth, so an I-bar is feasible. A distal-rest Akers clasp tends to transmit more torque to the abutment in a free-end saddle. Ring clasps are principally selected for difficult tooth contours, especially tilted molars, rather than distal-extension stress release. Embrasure clasps require an adjacent tooth and are not the conventional terminal-abutment design here. Back-action clasps do not provide the intended stress-releasing assembly.

Reference: Hakkoum MA. New Clasp Assembly for Distal Extension Removable Partial Dentures: The Reverse RPA Clasp. Journal of Prosthodontics. 2016. https://pubmed.ncbi.nlm.nih.gov/26102601/