A two-stage shape optimization process for cavity preparation

Abstract

Objectives Clinical data indicate that previously restored teeth are more likely to fracture under occlusal loads. The reason for this is attributed to the high stresses at the tooth-restoration interface, especially following debonding of the restoration from the tooth. This work aims to minimise these interfacial stresses by optimizing the cavity shape using modern shape optimisation techniques. Methods Shape optimisation methods based on the principle of biological adaptive growth were incorporated into a finite element program and used to optimize the design of cavity preparations as previous work had successfully used one such method to minimise stresses at the internal line angles of conventional restorations with defective bonds. The overall shapes of the cavity preparations were maintained while the profiles of the internal line angles were modified. In the present study, the overall shape of the cavity preparation was also subject to modification in the optimization process. A topological optimization method which placed the restorative material according to the stress distribution was first used to obtain a draft design for the cavity shape, assuming perfect bonding at the tooth-restoration interface. The draft shape was then refined using the method employed in the previous study, to allow for deterioration in the interfacial bond strength. These optimization methods were incorporated into the commercial finite element package ABAQUS as a User Material Subroutine (UMAT) to automate the optimization process. Results Compared with the conventional design, the stress level at the tooth-restoration interface in the optimized design was reduced significantly, irrespective of the bonding condition. Conclusions Finite-element based shape optimization methods provide a useful tool for minimizing the interfacial stresses in dental restorations. The longevity of restored teeth using the optimized designs is therefore expected to be prolonged.