Horizontal angulation error on bitewing — ORE Part 1 MCQ

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EasyDental RadiologyHorizontal angulation error on bitewingORE Part 1

A bitewing radiograph taken to assess proximal caries in a 17-year-old shows severe overlap of the premolar contacts, while the occlusal plane and exposure are otherwise acceptable. The receptor was placed correctly but the X-ray tubehead was angled from too far mesially. What is the most likely cause of the contact overlap?

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Correct answer: D — Incorrect horizontal angulation

Correct answer: B. Proximal contact overlap on bitewings results directly from horizontal (mesial–distal) angulation error. When the X-ray beam is directed from too far mesially, the tubehead angle deviates from the perpendicular bisector of the interproximal space, causing the radiographic images of adjacent tooth crowns to overlap. Research shows a linear relationship between beam angulation deviation and overlap width; small changes in horizontal angle produce measurable overlap changes. The stem confirms receptor positioning is correct (eliminating film position as cause) and occlusal plane is acceptable (indicating vertical angulation is correct). Vertical angulation errors affect bone level perception and crest sharpness, not contact overlap. Exposure, cone cutting and fogging are unrelated to the described mesial tubehead positioning.

Reference: Sewerin I. Investigation into the relationship between deviations in X-ray angulation and images of proximal overlapping on bite-wing radiographs. Community Dentistry and Oral Epidemiology. 1983;11(5):284–289. https://pubmed.ncbi.nlm.nih.gov/6589108/