Influence of pH values and aging time on the tribological behaviour of posterior restorative materials

Besides the complexity of the contact between teeth, the mouth is also a very specific service environment. Dental restorative materials, and teeth, are subjected to very specific service conditions, wide-ranging temperatures, contact loading, loading rates, sliding conditions and pH variation. Several studies have established that an exposure of resin composites to aqueous environments lowers their mechanical properties. Due to changes in the structure of these materials, softening of the resin matrix and/or bond failure in the outer layer of the filler and in the filler–matrix interface region reduce the mechanical and tribological performance. During the day, the mouth presents different values of pH, and thus it is important to determine the effect of pH on the composites’ tribological behaviour. The main objective of this study is the determination of the nature of the dependency between the tribological behaviour of commercial composites and the influence of values of pH and aging time. Seven commercial resin composites, condensable and suitable for posterior restoration, have been characterized. Each material composite was aged during a period of 3, 6 and 22 months at a temperature of 37 °C, and considering three values of pH: 3, 7 and 9. The tribological behaviour was evaluated in a reciprocating contact against glass spheres. At the end of the tests, the wear was assessed on the composite and also on the counterface. The removal mechanisms enclosed in the wear process are discussed, taking into account the systematic SEM observations to evaluate the failure modes.