Thiol-Ene Based Composites as Dental Restorative Materials

Aesthetic alternatives to mercury amalgams are increasingly of interest for dental restorative applications. Accordingly, resin-based composites (RBCs) have been developed to meet this need. Many commercial RBCs have been based on bisphenol A glycerolate dimethacrylate (BisGMA) or bisphenol A ethoxylate dimethacrylate (EBPADMA), with a reactive diluent, triethylene glycol dimethacrylate (TEGDMA). This work investigates new monomers, including thiol and ene components to replace TEGDMA, in an effort to improve biocompatibility, decrease risk of premature failure due to shrinkage stress, and optimize initiator system ratio and overall concentration. 

Objectives: This research investigated the polymerization kinetics, mechanical properties, and shrinkage stress of methacrylate-thiol-ene compositions with different visible light initiator concentrations.

Methods: Mixtures of EBPADMA or BisGMA, pentaerythritol tetrakis(3-mercaptopropionate) (PETMP), and 1,3,5-triallyl-1,3,5-triazine-2,4,6(1H,3H,5H)-trione (TATATO) were prepared with Q1301 inhibitor and a camphorquinone/ethyl-4-dimethylaminobenzoate (CQ/E4DB) initiating system. Additionally, (EBPADMA or BisGMA)/TEGDMA samples with comparable initiator and Q1301 loadings were prepared as controls. RBCs contained 25 wt% resin and 75 wt% glass filler (95 wt% 0.4 micron and 5 wt% 0.05 micron particles). Polymerization kinetics of both resins and composites were determined by real-time Fourier-transform infrared spectroscopy (FTIR). An MTS universal testing system was used to measure the flexural modulus and strength of cured composites. Shrinkage stress was measured using a cantilever beam-based tensometer.

Results: FTIR experiments indicated that concentration of the initiating system must be optimized to maximize functional group conversion. Flexural strength and modulus values for the methacrylate-thiol-ene composites were lower than the control composites, but within acceptable limits for dental restorative applications. Preliminary shrinkage stress data demonstrates lower stress than the controls and potential for further reductions.

Conclusions: This research demonstrates that EBPADMA/PETMP/TATATO resins are promising alternatives to EBPADMA/TEGDMA mixtures for dental restorative materials, with an appropriate concentration of the initiating components.

Funding provided by Septodont.