Periodontal Grade Calculation — ORE Part 1 MCQ
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Correct answer: D — Divide the percentage bone loss at the worst affected site by the patient's age in years
Explanation lettering: B = shown as A · E = shown as B · A = shown as D · D = shown as E
The correct answer is A. In the UK implementation of the 2017/2018 periodontal classification, grading estimates susceptibility/rate of periodontal bone loss using the ratio of maximum percentage radiographic bone loss at the worst affected site to the patient's age in years. Ratios are Grade A below 0.5, Grade B from 0.5 to 1.0, and Grade C above 1.0. Option B reverses the ratio, producing an inverse value that cannot be interpreted using the grading thresholds. Options C and D apply inappropriate arithmetic operations and do not estimate bone loss relative to age. Option E concerns the extent/distribution of disease—based on the proportion of teeth affected—not the grade. The decisive feature is use of percentage bone loss at the single worst affected site, rather than tooth count or an average across the dentition.
Reference: Scottish Dental Clinical Effectiveness Programme (SDCEP). Prevention and Treatment of Periodontal Diseases in Primary Care: Periodontitis, Grading section, 2026. https://www.periodontalcare.sdcep.org.uk/guidance/diagnosis/establishing-a-periodontal-diagnosis/periodontitis/