Different shades and curing modes of dual-cure resin cements

Abstract

Purpose: Thio-urethane additives increase conversion and strength, particularly fracture toughness, while significantly reducing polymerization stress (PS) in unfilled resins (Pfeifer 2012). This study evaluates the efficacy of such additives in reducing stress/shrinkage and increasing conversion in heavily filled dental composites. Methods and materials: Oligomers (TU) were synthesized by combining 1,6-hexanediol-diissocyante (aliphatic), 1,3bis(1-isocyanato-1-methylethyl)benzene (aromatic) or 4,4′methylenebis(cyclohexyl isocyanate (cyclic) with pentaerythritol tetra-3-mercaptopropionate (PETMP) or trimethyloltris-3-mercaptopropionate (TMP), at 1:2 isocyanate:thiol, leaving pendant thiols. Oligomers were added at 20wt% to BisGMA-UDMA-TEGDMA (1:1:1), camphorquinone/ethyl4-dimethylaminobenzoate (photoinitiators, 0.2/0.8wt%) and di-tert-butyl hydroxytoluene (inhibitor, 0.3wt%). 70wt% silanated inorganic fillers were added (85% Barium glass, 0.4 m; 15% OX-50, 50nm). Polymerization stress (PS) was measured on the Bioman, degree of conversion (DC) was measured with near-IR, and volumetric shrinkage (VS) was measured using the bonded disk technique. Materials were photoactivated for 60 s (BluePhase, 800mW/cm2). Results were analyzed with two-way ANOVA/Tukey’s test (a=5%). Results: Results in the table with the same superscript are statistically similar. In general, conversion and shrinkage values achieved with the TU-modified composites were similar to the control, while the stress values were all significantly reduced – in some cases, by up to 56%. Stress reduction was a function of TU structure. Previous studies have demonstrated the maintenance or improvement of modulus with the addition of up to 20wt% TU (Pfeifer 2012), so stress reduction is likely due to delayed gelation. Future studies will concentrate on dynamic mechanical analysis and gelation/vitrification characterization. Conclusion: Thio-urethane oligomers were able to favorably modify conventional dimethacrylate networks with minimal disruption to existing curing chemistry, reducing polymerization stress in heavily filled resin composites by up to 56%. Support: NIH/NIDCR-1R15-DE023211-01A1.