Replacement reasons and service time of class-I1 amalgam restorations in relation to cavity design

Jokstad A, Mjor IA. Replacement reasons and service time of class-I1 amalgam restorations in relation to cavity design. Acta Odontol Scand 1991;49:109-126. Oslo. ISSN 0001-6357. Four hundred and sixty-eight class-I1 amalgam restorations were placed in 210 patients. The restorations had been inserted by seven Scandinavian dentists in their clinics, among their regularly attending patients. Impressions of the teeth with cavity preparations had been made, and epoxy casts fabricated. The designs and qualities of the cavities were assessed in accordance with an evaluation system for class-I1 cavities designed for use on models. The restorations were observed yearly and scored in accordance with the USPHS criteria. In case of replacement the reason was recorded, and the service time calculated. The restorations were observed throughout a period varying from 8 to 10 years. At the end of the observation period, 212 restorations had been lost owing to dropout patients, 68 restorations had been replaced, and 188 restorations remained functional. The commonest criteria for replacement were secondary caries ( n = 30) and restoration bulk fractures (n = 24). Using univariate statistics and multi-variate discriminant analyses, the time of service and the reasons for replacement were correlated with different clinical variables, including different indices for the dimensions an