Nondestructive, in vitro quantification of crown margins

Statement of problem. It is important that artificial crowns fit the prepar ed tooth accurately, as marginal deficiencies are predisposed to plaque acc umulation and lead to increased risk of periodontal disease. Various method s of evaluation for marginal fit are described in the literature, but most approaches are limited by destructive methods of assessment and/or small po int of measurement. Purpose. This study compared, in vitro, the marginal fit of 4 types of comp lete crown on human premolar teeth with the use of nondestructive profilome try. This method determined whether fit was influenced by type of crown or surface morphology of the tooth, namely, grooved or ungrooved surfaces. Material and methods. Four groups of specimens were prepared for complete c rowns: group BA, bonding alloy with chamfer finish line; group G, gold allo y with chamfer finish line; group PC, porcelain with a chamfer finish line; and group PS, porcelain with a shoulder finish line. Two profiles of groov ed mesial and ungrooved distal surfaces of the teeth were performed: (1) te eth prepared for each type of crown and (2) teeth with crowns seated but no t cemented. Marginal fit (absolute marginal discrepancy) from the finish li ne edge of the tooth preparations to crown edges (CE) and leading edges (LE ) of crowns were measured. Results. A 2-way analysis of variance for crown type and tooth surface morp hology revealed significant differences between crown types for all measure ment parameters, except vertical LE. The effect of surface morphology was n ot significant, except for vertical LE (P < .05). For all parameters, excep t vertical LE, the ranking of marginal fit discrepancies from greatest to l east was as follows: group PC, G, BA, and PS. For vertical LE distances, th e ranking was PS, BA, G, and PC (P < .05). Conclusion. Profilometry was used as a nondestructive, accurate method of e valuating the absolute marginal fit of different types of crowns. Marginal fits varied continuously around the circumference of each crown and made cl inical assessment of fit accuracy subjective and arduous.