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[Effects of the fitness of crown margins on gingivae].

The objective of this investigation is to identify the effects of the marginal fitness of the crowns on the gingival tissues. Ten porcelain-fused-to-gold crowns with different degrees of overhangs were cemented in three clinical cases. The crown contours and their marginal fitness were measured intra-orally with an electronic device. The severity of the gingival inflammation was assessed on the marginal gingivae at the midpoint of the labial aspect of these crowns by (1) a newly developed instrument which can measure the consistency and the volume pulse of the gingivae, (2) by the gingival fluid meter "Periotrona" and (3) by clinical examinations. Based on the results of these experiments, the following conclusions can be made: 1. Subgingival restoration with properly placed and well-fitted margins will not affect the marginal gingivae. 2. The crown margins should not be extended too deeply into the gingival crevice. 3. The overhanging restoration caused deleterious effects on the gingivae, and those effects still remained after the removal of the overhangs. 4. Proper oral hygiene instructions are indispensable for the maintenance of healthy gingivae of the crowned teeth.