Crown Lengthening 3mm Rule — ORE Part 1 MCQ

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HardRestorative DentistryCrown Lengthening 3mm RuleORE Part 1

A 50-year-old patient requires crown-lengthening surgery before definitive restoration of a tooth with a mesial crown-root fracture extending subgingivally. Following osseous recontouring, what minimum distance should be planned between the intended restorative margin and the alveolar bone crest?

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Correct answer: C — 3 mm

The correct answer is C: 3 mm. In conventional surgical crown lengthening for a subgingival restorative margin, the crest is positioned about 3 mm apical to the planned margin. This accommodates the supracrestal tissue attachment and sulcus, allowing periodontal healing without persistent margin encroachment. A 1 mm or 2 mm clearance is insufficient in the standard restorative-periodontal planning model and risks inflammation, attachment disruption or subsequent crestal remodelling. Four and 5 mm may sometimes be selected for case-specific anatomical, aesthetic or restorative reasons, but they exceed the minimum asked for. The key distinction is that the measurement is from the intended restorative margin to the bone crest, not merely the dimensions of the connective-tissue attachment.

Reference: Lanning SK, Waldrop TC, Gunsolley JC, Maynard JG. Surgical crown lengthening: evaluation of the biological width. Journal of Periodontology. 2003;74(4):468-474. https://pubmed.ncbi.nlm.nih.gov/12747451/