Pseudo-Class III malocclusion from anterior displacement — ORE Part 1 MCQ

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HardOrthodonticsPseudo-Class III malocclusion from anterior displacementORE Part 1

An 8-year-old has an anterior crossbite in the mixed dentition. In retruded contact position the incisors meet edge-to-edge, but the mandible slides forwards into intercuspation, producing a mild Class III appearance. There is no family history of mandibular prognathism. What is the most likely diagnosis?

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Correct answer: C — Pseudo-Class III malocclusion due to anterior displacement

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

This case exemplifies pseudo-Class III malocclusion (Option B). The key diagnostic feature is the edge-to-edge incisor relationship in retruded contact position, followed by a functional anterior mandibular displacement that creates the crossbite appearance only during intercuspation. This is pathognomonic for pseudo-Class III: the underlying skeletal and dental relationships are normal or Class I, but a neuromuscular reflex causes the mandible to posture forward to achieve posterior occlusion. True skeletal Class III (A) would show a Class III pattern even in RCP and typically presents with a family history and true mandibular prognathism—both absent here. Class II division 2 (C) presents with increased overbite and overjet, not crossbite. Posterior open bite from thumb sucking (D) is unrelated to the anterior crossbite presentation, and bimaxillary protrusion (E) causes increased overjet, not anterior crossbite. Early treatment of pseudo-Class III in mixed dentition is recommended to eliminate the functional displacement and prevent secondary skeletal adaptation.

Reference: Diagnosis and Treatment of Pseudo-Class III Malocclusion. PMC National Center for Biotechnology Information (NCBI), 2014. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4265381/