Posterior bridges retained by resin-bonded cast metal inlay retainers: a report of 60 cases followed for 6 years.

Between May 1989 and July 1994, 60 adhesive fixed partial posterior dentures retained by resin-bonded cast metal inlays were placed under controlled conditions. The influence of various prognostic factors on the event free and overall service duration was investigated with univariate and multivariate analysis. The majority of the failures (16 of 18) were caused by loss of adhesion at the metal cement interface and were observed either as debonding of the restorations completely or dislodgement of a single retainer. The other two failures appeared as secondary caries. Univariate analysis demonstrated that, retainer type, approximal configuration and dentine exposition had no effect on the event free service duration. On the other hand, gingival finishing level and luting agent were found to have an effect. Univariate testing was also conducted for the overall service duration and none of the variables were found to have an effect. Multivariate Cox Regression Analysis was performed to estimate the influence of categorical covariates: type of retainer, approximal preparation modification, gingival finishing level, preparation depth and luting agent on survival rates of event free and overall service duration. Luting agent was found to be the single independent prognostic variate (P < 0.0001) for the event free service duration and the other covariates were rejected. For overall service duration, none of the variables were found to be effective.