THE ANALYSIS OF RESTORATION SURVIVAL-DATA IN SPLIT-MOUTH DESIGNS

Objective. To report methodological difficulties with restoration surv ival data in controlled clinical trials on Class II amalgam restoratio ns using a split-mouth design. The advantages and disadvantages of dif ferent ways of handling these data are described. Methods. Three stati stical methods (Kaplan-Meier estimation, logistic regression with rand om component and Friedman's statistic) are compared using data from a controlled clinical trial in which cavosurface angle (regular or non-s tandard) and cavity wall finish (applied or not applied) determine fou r treatment modalities of New True Dentalloy(R) restorations. Results. In this study logistic regression with a random component yields the best interpretable results. Cavity wall finish in combination with a r egular cavosurface angle is indicated as the worst and cavity wall fin ish in combination with a non-standard cavosurface angle as the best t reatment when the criterion is replacement or not within 15 years. Con clusions. The dependency between restorations within a patient needs t o be taken into account. Logistic regression with a random component m ay be a valuable alternative to very advanced statistical survival mod elling when restricting the research question to replacement within a certain time interval is not a major problem. (C) 1998 Elsevier Scienc e Ltd. All rights reserved.