Structural Optimization of Fibre-reinforced Composite in a Three-unit Dental Bridge

Objectives: Failures of fixed partial dentures (FPDs) made of fibre-reinforced composites (FRC) have been reported in many clinical and in-vitro studies. The types of failure include debonding at the composite-tooth interface, delamination of the veneering material from the FRC and fracture of the pontic. The design of the FRC substructure, i.e. the position and orientation of the fibres, will affect the fracture resistance of the FPDs. The purpose of this study was to find an optimal arrangement of the FRC substructure, by means of structural optimization, which could minimize the failure-initiating stresses in a three-unit FPD.

Methods: A structural optimization method mimicking biological adaptive growth was developed for orthotropic materials such as FRC and incorporated into the finite element (FE) program ABAQUS. Using the program, optimization of the fibre positions and directions in a three-unit FPD was carried out, the aim being to align the fibre directions with those of the maximum principal stresses. The optimized design was then modeled and analyzed to verify the improvements in mechanical performance of the FPD.

Results: Results obtained from the optimization suggested that the fibres should be placed at the bottom of the pontic. In the connectors linking the teeth and the pontic, the fibre should be placed at an angle to the horizontal axis. FE analyses of the optimized design indicated a reduction of ~30% in the tensile stresses in the veneering composite as compared with the conventional box-shaped design.

Conclusion: The optimized design obtained using FE-based structural optimization can potentially improve the fracture resistance of FPDs by reducing some of the failure-initiating stresses. Optimization methods can therefore be a useful tool to provide sound scientific guidelines for the design of FRC substructures in FPDs.