Properties of posterior composites: Results of round robin testing for a specification

• Objectives. Seven sites participated in the round robin testing of five dental composites in order to evaluate specific testing protocols for use in a specification for posterior composites. • Methods. The flexure strength, flexure modulus, solubility in water, and opacity after soaking in water and ethanol, were evaluated for five commercial dental composites at the seven different sites. Samples were either aged for one day or seven days before testing. • Results. Although they were not without problems, the results were supportive of including in a specification a test for solubility in water as well as one for flexural strength and flexural modulus. The specification would be similar to that described by ISO 4049, but based upon the results of this study, an increase in the acceptable values for two of these tests was suggested. The results of this study also demonstrated that despite following an identical protocol and using materials from identical batches, significant variations in absolute values were obtained among the Test sites. However, there was generally good agreement among the sites in the relative ranking of the materials. • Significance. These results provide a strong rationale for the inclusion of one or two standard materials in a specification designed to evaluate composites suggested for use in posterior teeth.