Methods: Oligomers (TU) were synthesized by combining 1,3-bis(1-isocyanato-1-methylethyl)benzene (aromatic) with trimethylol-tris-3-mercaptopropionate (TMP), at 1:2 isocyanate:thiol, leaving pendant thiols. Oligomers were added at 20wt% to BisGMA/TEGDMA 70/30 wt%, combined with camphorquinone/EDMAB (0.2/0.8 wt% - initiators) and di-tert-butyl hydroxytoluene (inhibitor, 0.3wt%). Silanated inorganic fillers (85% Barium glass, 0.4 microns; 15% OX-50, colloidal silica) were added at 25, 40 or 70 wt%. Near-IR was used to follow methacrylate conversion (DC) and rate of polymerization (RP) during photoactivation. Flexural strength (FS) was measured in three-point bending (2x2x25 mm). Fracture toughness (FT) was assessed in notched specimens (2x5x25 mm). A QTH light source (400-500 nm, 400mW/cm2) was used in all experiments. Results were analyzed with two-way ANOVA/Tukey’s test (α=5%).
Results: Results in the Table with the same superscript in the same row are statistically similar. Conversion increased by 7-14%, likely an effect of delayed gelation/vitrification. FS and FT increased for the lower filler concentrations, but no effect was noticed for the 70wt% filler loading. The oligomers are also expected to reduce shrinkage and stress, which will be evaluated in future studies.
Filler concentration (wt%) |
25 |
40 |
70 |
|||
TU concentration (wt%) |
0 |
20 |
0 |
20 |
0 |
20 |
DCmax (%) |
71.3±0.2b |
78.2±0.3a |
65.6±0.1c |
79.1±0.2a |
71.2±0.4b |
80.4±0.2a |
FS (MPa) |
28.2±1.9d |
55.8±3.6bc |
20.2±1.8d |
61.4±5.8a |
52.4±4.8c |
55.0±5.0bc |
FT (MPa) |
0.7±0.2b |
1.1±0.2a |
1.0±0.2a |
1.1±0.1a |
1.1±0.3a |
1.3±0.2a |
Conclusions: Thio-urethane oligomers were shown to favorably modify conventional dimethacrylate networks with minimal disruption to existing curing chemistry, in filled materials.
Funded by NIH/NIDCR 1R15DE023211-01A1