The Polymerization Stress of Flowable Composites

Objective: It is well known that composites exhibit volumetric shrinkage upon curing which results in stress on tooth structure. This effect has limited the ability for bulk placement of methacrylate based restorative materials. A unique Stress Decreasing Resin (SDR) technology has been used to develop a flowable composite with very low residual polymerization. The purpose of this study is to compare volumetric shrinkage, modulus and shrinkage stress, and elucidate the mechanisms of stress development in composite systems. Methods: SureFil SDR Flow, as well as 6 universal/posterior resin composites and 6 flowable resin composites were selected. Volume shrinkage was determined by Helium Pycnometer. The densities of cured and uncured composites were measured. Flexural modulus was determined according to ISO 4049. Polymerization stress was evaluated by NIST/ADA tensometer. Pastes were injected into a 2.25x6mm cell (C-factor 1.33) and light cured at an intensity of 300-400mw/cm² for 60 seconds. Stress was recorded 60 minutes post-cure. Results: The volumetric shrinkage of the test composite was 3.5%, which was found to be higher than that of universal composites and slightly lower than that of flowable composites. The flexural modulus of test composite was found in the range of flowable composites (3000 – 8000 MPa). The polymerization stress was 1.49 MPa, which was significantly lower than that of other resin composites tested, ANOVA (p< 0.05). Conclusion: This study indicates that while volumetric shrinkage and flexural modulus of the test composite were similar to other flowable composites, polymerization stress was lower for this material than other resin composites.