Low Shrinkage Bisphenol A Free Microhybrid Composite

Objective: This study was conducted to evaluate the potential of a novel low shrinkage, multifunctional carbamate-methacrylate monomer as a replacement for bisphenol A derivatives found in the majority of commercial restorative materials. Methods: New BPA free monomer was synthesized by reacting aliphatic isocyanates with aromatic methacrylate-alcohol utilizing dibutyl tin dilaurate as the catalyst. Experimental composite formulations were based on a resin system containing a mixture of the new monomer and 1,6-hexanediol dimethacrylate in the following composition 80:20 (Exp1); 78:22 (Exp 2) and 75:25 (Exp 3) wt%.  The experimental composites contain camphorquinone/ethyl-4-dimethylamino benzoate as a photoinitiator and 75 to 80wt% of inorganic microhybrid fillers.  The composites were prepared using a high speed mixing machine and tested for degree of conversion and volume shrinkage. Additionally, mechanical testing, depth of cure, water absorption and water solubility were carried out according to ISO 4049. The data obtained for the experimental composite material were compared to microhybrid commercial materials based on Bis-GMA/TEGDMA such as ELS (Saremco), Alert (Pentron Clinical Technologies) and Image (Septodont). Statistical analysis was performed using ANOVA and the Student-Newman-Keuls test (p<0.05). Results: The results are shown in Figure 1.

Conclusion: Although high conversion generally coincides with higher volumetric shrinkage, we were able to significantly raise the conversion and keep adequate mechanical strength while maintaining volumetric shrinkage values significantly lower than the commercial samples.  The combination of high polymerization and low shrinkage found makes this monomer an ideal alternative to traditional materials based on Bis-GMA.