The biomaterials and biomechanics of dental restorations : property measurement and simulation

The aim of this study was to improve the accuracy of the predicted shrinkage stress in dental restorations by exploring the interrelationships between the shrinkage stress, the material parameters, the polymerisation shrinkage and the filler content of the composite, through a series of numerical simulation and experimental measurements. Firstly, as a preliminary study, the mathematical solution of a 2D axisymmetric model of a Class-I dental restoration during resin polymerization was used, to evaluate the effect of each of the above factors on shrinkage stress. The subsequent sensitivity analysis based on the analytical solution showed that shrinkage is the most important factor in the development of shrinkage stresses, followed by Young's modulus and viscosity. Secondly, experiments were conducted on an experimental composite to express its micro hardness, Young's modulus and viscosity as functions of the volumetric shrinkage. Shrinkage was measured with the digital image correlation method. Thirdly, the effects of the volumetric filler fraction and filler morphology on the material properties of dental composites were considered using finite element micro-structural models. Fourthly, the shrinkage stress produced by the experimental composite in the Bioman shrinkage-stress instrument was simulated using the finite element method. Good agreement between the simulation and experiment indicated that the material properties determined using the above methodology are likely to be representative. Finally, 3D finite element models were employed to calculate the shrinkage stresses in a restored premolar, considering different filler contents in the composite, different filling methods and different cavity shapes. Results showed that the filler content is not the most crucial factor in the development of shrinkage stress in dental restorations, and the incremental filling method can significantly reduce the overall shrinkage stress in dental restoration.EThOS - Electronic Theses Online ServiceGBUnited Kingdo