Cone cut radiographic error — ORE Part 1 MCQ

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EasyDental RadiologyCone cut radiographic errorORE Part 1

A periapical radiograph of a lower premolar shows a sharply defined unexposed crescent at one edge. Image density and tooth length are otherwise acceptable. The rectangular collimator was not centred over the receptor. What is the most likely cause?

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Correct answer: B — Misalignment of beam and receptor

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

E is correct. A cone cut results when a restricted X-ray beam, particularly with rectangular collimation, does not fully cover the image receptor. The receptor area outside the beam is unexposed, producing the characteristic sharply defined crescent or peripheral clear area. The stated failure to centre the collimator is the decisive finding. Patient movement causes image unsharpness or double outlines, not an unexposed margin. Excessive processing temperature produces a general density or fogging fault. Excessive vertical angulation causes foreshortening, while inadequate kilovoltage changes penetration and contrast across the whole image. None explains a local, sharply bounded unexposed area.

Reference: Evaluation of radiation exposure with Tru-Align intraoral rectangular collimation system using OSL dosimeters. PubMed, 2011. https://pubmed.ncbi.nlm.nih.gov/21678866/