The life expectancy of dental restorations placed within the General Dental Services in England and Wales
This study measured the distribution of the interval between placement and next intervention on the same tooth for direct restorations of teeth in the General Dental Services of the NHS in England and Wales between January 1991 and December 2002. Three different sets of treatment data covering the period were used, involving over 1.3 million restorations. Standard and modified Kaplan-Meier, and three different cross-sectional techniques were used to estimate empirical survival curves, and Cox-regression was used to model the relationship with risk factors associated with the dentist, the patient, geographical location, time, tooth position and type of restoration and cavity. Overall, median survival was slightly more than eight years from placement to re-intervention. The rates of survival without intervention after one year, five years and ten years were, respectively, 89%, 62% and 46%. Key risk factors associated with survival were type of cavity, tooth position, patient age, patient treatment history and patient attendance history. The underlying baseline function of the Cox-regression analysis was closely modelled by both a Weibull and a cubic function. The robustness of the findings was demonstrated by a full replication of the eleven-year analysis using a completely separate fourth sample from the DPB’s data archive.