The effect of a dithiol spiroorthocarbonate on mechanical properties and shrinkage of a dental resin

A novel spiroorthocarbonate with two thiol groups (SOC DITHIOL) was synthesized. This monomer was formulated with dimethacrylate monomers used in dental resins and photopolymerized with an LED dental lamp. The presence of the thiol groups in the monomer enabled it to react with the double bonds of the dimethacrylate monomers by means of the thiol-ene mechanism. Additionally, the SOC DITHIOL underwent cationic ring-opening polymerization, producing the corresponding poly(ether-carbonates). SOC DITHIOL was added to a formulation of a conventional acrylic resin, which includes a mixture of dimethacrylate monomers [glycerolate bisphenol A dimethacrylate (BIS-GMA)/urethane dimethacrylate (UDMA)/triethyleneglycol dimethacrylate (TEGDMA)] in 50/30/20M ratio). Concentration of the prepared SOC was varied in the above dimethacrylate formulation in the range of 5-30mol%. Kinetics of photopolymerization were determined by means of real time Fourier transform infrared spectroscopy, finding that increasing concentrations of the SOC DITHIOL in the formulations, not only did not affect the photopolymerization rate of the acrylic resins, but it helped to increase the final conversion of the methacrylate groups. It was also found that the presence of SOC DITHIOL increased the elastic modulus of the resulting cross-linked polymer. The addition of 30% of SOC DITHIOL reduced shrinkage 59% in comparison with a sample without the SOC.