A biophysical analysis of the occlusal wear of dental materials
An artificial oral environment was used to clinically simulate the dental wear process and surface friction between opposing maxillary and mandibular elements. Measurement of surface friction between occlusal surfaces of natural premolar teeth demonstrated large variation. High viscosity lubricants and surfactant containing lubricants were capable of reducing the surface friction. The enamel appeared otherwise insensitive to natural and artificial salivary fluids. Orientation of opposing enamel prisms was critical for reduction of interocclusal friction. A critical choice of prosthetic dental materials evaluted for wear included amalgam, porcelain, and composite opposed by a natural third molar palatal cusp. The wear of amalgam was slight (volume loss 0.0307 .0036 mm^3 and depth .072 .0017 mm at 300K masticatory cycles) and wear of the opposing enamel was not measurable. SEM demonstrated smearing between the amalgam and the enamel cusp, thus supporting an adhesive wear mechanism. The wear of porcelain (volume .165 .037 mm^3, depth .127 .02 mm at 300K masticatory cycles) demonstrated a ploughing effect on the surface supporting an abrasive wear mechanism. The composite wear was intermediate(volume .046 .007 mm^3, depth .059 .01 mm). Posterior composites are thought to wear by an abrasive as well as fatigue mechanism. The artificial mouth demonstrated a high correlation (0.98) with clinical studies.Wear of enamel opposed by enamel demonstrated a degree of variability. The physiologic occlusal orientation between enamel pairs appeared important. A finite element model of a natural and crowned premolar tooth was developed consisting of 586 triangular elements and 343 nodes using ANSYS and IFECS finite element analysis software. Validation of the model was achieved via a physical model of a natural premolar tooth with strain gages. A new full coverage restoration design employing layering of composite restorative materials was proposed and tested. The model predicted a problem of fatigue crack propagation through the restoration which was confirmed in preliminary clinical trials. This provided further evidence for the fatigue mechanism of wear in composite restorations. On the basis of the wear studies conducted, recommendations for restorative treatment design were presented.