Properties of methacrylate–thiol–ene formulations as dental restorative materials

Abstract

Objectives-The objective of this study was to evaluate ternary methacrylate-thiol-ene systems, with varying thiol-ene content and thiol:ene stoichiometry, as dental restorative resin materials. It was hypothesized that an off-stoichiometric thiol-ene component would enhance interactions between the methacrylate and thiol-ene processes to reduce shrinkage stress while maintaining equivalent mechanical properties.Methods-Polymerization kinetics and functional group conversions were determined by Fourier transform infrared spectroscopy (FTIR). Cured resin mechanical properties were evaluated using a three-point flexural test, carried out with a hydraulic universal test system. Polymerization shrinkage stress was measured with a tensometer coupled with simultaneous real-time conversion monitoring.Results-The incorporation of thiol-ene mixtures as reactive diluents into conventional dimethacrylate resins previously was shown to combine synergistically advantageous methacrylate mechanical properties with the improved polymerization kinetics and reduced shrinkage stress of thiol-ene systems. In these systems, due to thiol consumption resultant from both the thiol-ene reaction and chain transfer involving the methacrylate polymerization, the optimum thiol:ene stoichiometry deviates from the traditional 1:1 ratio. Increasing the thiol:ene stoichiometry up to 3:1 results in systems with equivalent flexural modulus, 6 -20 % reduced flexural strength, and 5 -33 % reduced shrinkage stress relative to 1:1 stoichiometric thiol:ene systems.Significance-Due to their improved overall functional group conversion, and shrinkage stress reduction while maintaining equivalent flexural modulus, methacrylate-thiol-ene resins, particularly those with excess thiol, beyond the conventional 1:1 thiol:ene molar ratio, yield superior dental restorative materials compared with purely dimethacrylate resins.

Characterization of methacrylate-based composites containing thio-urethane oligomers

“…The covalent interaction of the thio-urethane with the methacrylate occurs through chain-transfer to the pendant thiol functionalities on the backbone of the oligomer. Those chain-transfer reactions delay the gelation/vitrification to higher degrees of conversion [37,38] while at the same time reducing stress development and improving network homogeneity and fracture toughness [25–27]. For all of those reasons, the incorporation of thio-urethane oligomers into methacrylate networks used for dental materials applications is very promising.…”

Micro-Raman spectroscopic analysis of the degree of conversion of composite resins containing different initiators cured by polywave or monowave LED units

“…19 More recent studies have shown no significant changes in DC over 48 h post-irradiation 20 and a plateau in polymerization kinetics within minutes postirradiation. 21,22 Truffier-Boutry et al 20 suggested that postpolymerization changes in material properties should not be associated with ''a simple chemical process'' of continued polymerization and proposed that polymers physically shrink The same superscript letters indicate no statistically significant difference between time intervals in each group ( p > 0.05). due to excess of free volume, bringing free radicals closer which may result in limited propagation and termination.…”

Optimizing the concentration of 2,4,6-trimethylbenzoyldiphenylphosphine oxide initiator in composite resins in relation to monomer conversion

“…Wet polishing was applied since it has been shown to have no effect on DC values 20) . Micro-Raman analysis was done within 10 min post-polymerization since studies on polymerization kinetics of various resin models and RBCs have shown a plateau in conversion within minutes of the start of polymerization [21][22][23] . The present results have shown a logarithmic relationship between the amount of Lucirin ® TPO and the resultant DC for both unfilled and filled resins.…”