Normal Mouth Opening — ORE Part 1 MCQ
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Correct answer: A — 35–55 mm
Explanation lettering: D = shown as B · B = shown as C · E = shown as D · C = shown as E
The normal range for adult maximum interincisal opening is 35–55 mm (option A). This range is supported by clinical consensus and evidence: the TheraBite standard defines the usual range as 40–55 mm; the mean inter-incisal distance across populations is 47 mm (range 33.7–60.4 mm); and the minimum limit of normal function is 34 mm, below which trismus is diagnosed. Population studies consistently show means of 41–51 mm. Options B (15–25 mm) and C (20–30 mm) represent severe restriction; options D (60–80 mm) and E (55–70 mm) exceed normal physiological opening. This is a foundational clinical measurement for assessing temporomandibular joint function and mandibular mobility.
Reference: TheraBite Range-of-Motion Scale clinical standard (ClinicalTrials.gov NCT03875118) and supporting peer-reviewed population studies (Jayasinghe et al. 1998 on Nepalese population; Gallagher et al. 2004 on Irish population), establishing consistent international norms applicable to UK dental practice. https://pubmed.ncbi.nlm.nih.gov/9043002/