In vitro wear device for determining posterior composite wear

An in vitro device has been developed to predict the long-term clinical performance of posterior composite resins. In contrast to most systems, it is based on three-bodied wear--the type of wear generated by food bolus during mastication.

The authors wear-tested two groups of materials that included posterior composite resins, a castable ceramic, an amalgam and an unsalinated composite resin. After the wear-testing device concluded 400,000 cycles, the authors evaluated replicas of restoration surfaces for material loss. They used scanning electron microscopy to determine the mechanism of wear.

The authors detected considerable differences in wear among the various materials included in the study. All of the differences, however, fell within the range of results obtained from the positive and negative controls (unsilanated composite resin and ceramic, respectively). A comparison of the in vitro wear values with the wear values obtained from a series of ongoing clinical studies at the same institution revealed a high level of agreement. Furthermore, replicas of the laboratory-tested composite resin samples revealed the same wear patterns as those generated from clinical restorations. The variation coefficients for the in vitro data generally did not exceed 5 percent, whereas those for the clinical data commonly averaged 20 percent.

Based on the results of this study, the authors conclude that the in vitro testing device is reliably capable of predicting long-term clinical wear values. The results obtained after 92 hours of wear testing correlated closely with those obtained after three years of clinical testing.

Long-term clinical studies are both time-consuming and expensive. Reliable in vitro wear-testing techniques allow manufacturers to develop or modify composite resin systems in considerably shorter periods.