Methods: SSQs were prepared by acid-catalyzed condensation of 3-mercaptopropyltrimethoxysilane or allyltrimethoxysilane in either pentaerythritol tetrakis(3-mercaptopropionate) (PETMP) or 1,3,5-triallyl-1,3,5-triazine-2,4,6(1H,3H,5H)-trione (TATATO), respectively. The resulting SSQ-containing mixtures were incorporated into 60:40 wt% methacrylate:thiol-ene resins of bisphenol A ethoxylate dimethacrylate (BisEMA) with PETMP and TATATO. Resins were prepared with Irgacure 819 initiator and Q1301 inhibitor. Comparably formulated 70:30 wt% BisEMA:TEGDMA and 60:40 wt% BisEMA:PETMP/TATATO resins were included as controls. Near IR Fourier-transform infrared spectroscopy (FTIR) was employed to monitor photopolymerization behavior and measure cured resin conversions. A MATLAB-based protocol, which fit overlapping peaks as Gaussian curves, was used to resolve individual functional group conversions of convoluted peaks. An Instron MTS with three-point bending fixtures was used for FM/FS measurements.
Results: SSQ-containing resin formulations demonstrated rapid polymerization and high methacrylate functional group conversions (SH-SSQ: 95±1% and allyl-SSQ: 99±1%), comparable to the unmodified BisEMA:PETMP/TATATO control (98±1%) and significantly enhanced over BisEMA/TEGDMA (72±3%). Furthermore, SSQ incorporation provided statistically significant (α=0.05) increases in FS (SH-SSQ: 73±1MPa and allyl-SSQ: 65±1MPa) relative to unmodified BisEMA:PETMP/TATATO (62±2MPa). The BisEMA/TEGDMA control FS (90±3MPa) was higher than all other samples, although its FM (2.23±0.08GPa) was matched by the SSQ-containing resins (SH-SSQ: 2.22±0.04GPa and allyl-SSQ: 2.10±0.04GPa).
Conclusions: This work demonstrates that SSQ addition to methacrylate:thiol-ene formulations is a viable approach to enhance flexural properties for use in dental resins. SSQ-containing resins demonstrate improved FS & FM properties relative to their unmodified ternary counterpart, while maintaining high methacrylate functional group conversions.
This work was supported by NIH Grants DE018233-0142 and F32DE019072, and the I/UCRC Photopolymerization Center.