Thiol–ene–methacrylate composites as dental restorative materials

Abstract

Objectives The objective of this study was to evaluate composite methacrylate-thiol-ene formulations with varying thiol:ene stoichiometry relative to composite dimethacrylate control formulations. It was hypothesized that the methacrylate-thiol-ene systems would exhibit superior properties relative to the dimethacrylate control resins and that excess thiol relative to ene would further enhance shrinkage and conversion associated properties. Methods Polymerization kinetics and functional group conversions were determined by Fourier transform infrared spectroscopy (FTIR). Volume shrinkage was measured with a linometer and shrinkage stress was measured with a tensometer. Flexural modulus and strength, depth of cure, water sorption and solubility tests were all performed according to ISO 4049. Results All of the methacrylate-thiol-ene systems exhibited improvements in methacrylate conversion, flexural strength, shrinkage stress, depth of cure, and water solubility, while maintaining equivalent flexural modulus and water sorption relative to the dimethacrylate control systems. Increasing the thiol to ene stoichiometry resulted in further increased methacrylate functional group conversion and decreased volume shrinkage. Flexural modulus and strength, shrinkage stress, depth of cure, water sorption and solubility did not exhibit statistically significant changes with excess thiol . Significance Due to their improved overall functional group conversion and reduced water sorption, the methacrylate-thiol-ene formulations are expected to exhibit improved biocompatibility relative to the dimethacrylate control systems. Improvements in flexural strength and reduced shrinkage stress may be expected to result in composite restorations with superior longevity and performance.

Impact of thio-urethane additive and filler type on light-transmission and depth of polymerization of dental composites

“…In concordance with the results found in measurement of polymerization kinetics, addition of chain-transfer thio-urethane increase the DC even close to surface, demonstrating this improvement on DC was not related to modifications on light-transmission. The presence of thiol pedants on thio-urethane structures promotes chains transference on polymerization reaction, delaying the gelation/vitrification stages, which occurs when the material presents higher DC [31, 34]. Considering that these stages represent phases when the mobility reactional is reduced and henceforth few increasing on DC can be observed, delaying the gelation/vitrification results in increased final DC [8].…”

Assessments of antibacterial and physico-mechanical properties for dental materials with chemically anchored quaternary ammonium moieties: Thiol–ene–methacrylate vs. conventional methacrylate system

“…Thiol-ene photopolymerization proceed via a radical mediated stepgrowth polymerization mechanism in which propagation and chain transfer take place alternatively. [14][15][16]20,46]. In an ideal thiol-ene photopolymerization each double bond reacts with just one thiol-containing monomer.…”

“…The step growth addition mechanism of thiol-ene system result in delayed gelation and consequently significant reduction in shrinkage stress as compared with conventional methacrylate analogous [13,[16][17][18][19]. Lower shrinkage stress and enhanced fracture toughness of the thiol-ene system causes significant reduction in crack development in dental composites [2,20].…”

Microstructural Features of Current Resin Composite Materials

“…This can be accomplished with the use of thiol-enes or thiol-methacrylate formulations, in which chain-transfer reactions of the thiol to the vinyl effectively work to delay the point in conversion at which stiffness starts to develop, hence delaying and significantly reducing polymerization stress [27•, 53, 54]. By judiciously choosing the comonomer systems, these materials can also present mechanical properties comparable to the conventional dimethacrylate materials, but with higher conversion and lower stress [54,55]. Drawbacks with this technology that have delayed its commercial implementation include the foul odor and stability concerns (shelf-life) associated with thiol-containing materials.…”