Benign design for dental restorations.

This work investigates how the behaviour of a tooth containing a restored cervical lesion differs from that of a natural tooth. A hierarchy of 2-D Finite Element Analysis (FEA) models have been constructed, each examining a different aspect of the loads experienced by a human canine tooth in functional behaviour. Thus, the geometry and material property variables of a Class V restoration that adversely influence the performance of restored teeth can be evaluated. A philosophy of design to be employed when restoring cervical lesions can then be conceived. The main conclusions drawn from this study are as follows: The boundary constraints used in the FEA of human teeth are significant; the Periodontal Ligament (PDL) must be modelled to obtain a realistic stress distribution within the tooth. If the displacements of the tooth are of interest, then the bone should also be incorporated into the LEA model. Various linear elastic (LE), non-linear (NL and multi-linear elastic (MLE) models were used to represent the PDL. The material model used does not appear to influence the stress distributions within the tooth under functional loads. However, the stress distribution within the bone is affected by the material model of the PDL used. When the Young’s Modulus (E) of the material was varied, the magnitudes of the stresses induced in the tooth were affected, but the stress distribution within the tooth remained unaffected. The effect of varying the E of the restorative materials used to restore a rounded and a vshaped cervical lesion were investigated. The materials used could be divided into 3 groups; a low-modulus group, a mid-range group, and a high modulus group. The results predicted by the mid-range group corresponded most closely with those predicted by the natural tooth, and are therefore most benign. The low-modulus group materials reduce stress in the restoration but increase stress in the tooth when compared to the natural tooth model. The high-modulus group materials increase stress in the restoration, but reduce stress within the tooth compared to the natural tooth model. A v-shaped restoration causes a stress concentration in the tooth, behind the vertex of the restoration. Filleting the vertex reduces this stress concentration. The stress along the enamelrestoration interface is significantly increased for the rounded restoration, probably due to the an£le at which the interface intersects the enamel. Stresses induced due to thermal loading are smaller than those induced by bite loads; however, they are thought to be significant when considering the fatigue loading of teeth.