Analyses of long-term clinical behavior of class-II amalgam restorations

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Abstract
The purpose of the study was to estimate the influence of different clinical variables on the replacement rate of class-II amalgam restorations in permanent teeth. The study included 210 patients who had 468 restorations placed by 7 Scandinavian dentists. The observation periods varied between 7 and 10 years. At the time of the last recording 188 restorations remained intact in 88 patients, whereas 68 restorations in 53 patients had been replaced. Eighty-six patients with 212 restorations had dropped out of the study. The most prevalent criteria for replacement were secondary caries (n = 30) and restoration bulk fractures (n = 24). Chi-square analyses of the relationship between the prevalence of replacements and the clinical variables indicated effects of the operator and the patients' age and caries activity (p less than 0.001). Similar results were observed when the functional time of the restorations was related to the clinical variables and analyzed by ANOVA and MCA analyses and by survival analyses using logrank and Wilcoxon tests (p less than 0.001). The survival analyses using the Lee-Desu statistic D showed in addition a slight difference between the restorations in the lower premolars and upper and lower molars. There were no differences in the clinical performance between four non-gamma-2 alloys and one conventional alloy. Furthermore, no differences were noted between the survival rates of MC, DO, and MOD restorations. In a Cox regression model the strongest effects on the estimated survival rates were associated with the patients' age and caries activity covariates (global chi-square = 23.5, df = 2, p less than 0.001), whereas the effects of the operator and the other clinical variables were insignificant.