The effect of resin formulation on the degree of conversion and mechanical properties of dental restorative resins

The goal of this study was to determine the effects of resin formulation variables, such as diluent concentration, catalyst type and concentration and cure mode, on the degree of conversion of carbon double bonds and mechanical properties of dental restorative resins. Diametral tensile strength, compressive strength, hardness, flexural modulus and strength, and dynamic mechanical properties were tested, and the results were correlated to the degree of conversion results obtained by infrared analysis. The results showed a significant correlation between increased mechanical properties and higher degrees of conversion. Enhanced conversions were achieved by incorporating higher diluent and lower inhibitor concentrations into the resins. Ambient temperature properties were similarly enhanced by lower inhibitor concentrations, but were not enhanced by higher diluent concentration. Dynamic mechanical properties testing at oral and elevated temperatures elucidated possible differences in resin microstructure and network quality. The storage moduli decreased over the dental temperature range and was lower at all temperatures for resins with lower conversions. The glass transition temperature was also lower in resins with poorer conversions, suggesting that these resins may be more unstable at oral temperatures than more highly converted resins. Dynamic mechanical properties were most closely correlated to degree of conversion in these polymeric systems.