The Dental Practice Board has an eleven year database whereby payment claims from dentists operating within the General Dental Services (GDS) in England and Wales form the basis of data on directly placed restoration survival. Objectives: To create a mathematical model to describe the observed survival of directly placed restorations from placement to re-intervention, taking account of known covariates, so that future survival may be predicted. Methods: A representative sample of over 250,000 records of restorations on regularly attending adult patients was created from the main database. Standard Cox-Regression methodology was used to develop a semi-parametric model for the survival time from placement of restoration to the next intervention on the same tooth. A wide range of covariates was used, including patient age, annual treatment volume, tooth position and type of restoration. The resultant baseline survival function was subjected to curve fitting techniques to establish a fully parameterised model. This exercise was repeated on an independent replication sample of similar size. Results: Thirty-two covariates made a statistically significant contribution to restoration survival time. These included patient age, dentist age, tooth position and material used. The hazard ratios for all these variables have been calculated with confidence intervals. The baseline survival curve was satisfactorily modelled by both Weibull and cubic functions. Conclusion: The DPB's GDS treatment database has been successfully used to build and verify a model for the time to re-intervention for a restoration. A proportional hazards model is appropriate to model time to re-intervention for a variety of types of restoration, a Weibull baseline hazard function is a satisfactory addition to the model, and thirty-two covariates have been identified as important factors to take into account when judging the likely survival time of a restoration before needing re-intervention. The support of the Dental Practice Board is acknowledged.

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