MECHANICAL LONGEVITY ESTIMATION MODEL FOR POST-AND-CORE RESTORATIONS

Objectives. The aim of this study was to integrate existing knowledge of in vitro strength of post-and-cores and masticatory loading to arri ve at longevity estimates for post-and-core restorations when subjecte d to clinically relevant loads. Methods. A biomechanical model was dev eloped to predict the in vivo longevity. This method was applied to di rect post-and-core restorations with amalgam or composite cores. Both experimental laboratory strength values and theoretical clinical stren gth values were used in the model. The restorations made in the labora tory were assumed to be of a higher quality than clinically made resto rations, due to factors such as ease of manipulation, absence of saliv a, etc. Both a high and low level of average masticatory loading were considered, The model was used to estimate the probability of mechanic al failure before 5 x 10(6) load cycles (5 to 15 years) for all combin ations of load range and manufacturing quality. Results. The calculate d failure probability was effectively zero for most combinations excep t for a clinical quality core subjected to loads in the high range. Th ere the probability of mechanical failure before 5 x 10(6) cycles was estimated to be 2 x 10(-5) for amalgam and 5 x 10(-5) for composite co res. These results agree with the overall observed clinical failure ra te of about 1% per year for post-and-core restorations. Significance. The mechanical properties of the post-and-core restorations were adequ ate for clinically relevant loading conditions.