Ester-free thiol–ene dental restoratives—Part B: Composite development

Abstract

Objectives To assess the performance of thiol-ene dental composites based on selected ester-free thiol-ene formulations. Further, to point out the benefits/drawback of having a hydrolytically stable thiol-ene matrix within a glass filled composite. Methods Composite samples containing 50–65 wt% of functionalized glass microparticles were prepared and photopolymerized in the presence of a suitable visible light photoinitiator. Shrinkage stress measurements were conducted as a function of the irradiation time. Degrees of conversion were measured by FT-IR analysis by comparing the double bond signals before and after photopolymerization. Mechanical tests were carried out on specimens after curing as well as after extended aging in water. Dynamic mechanical analysis was employed to track the changes in storage modulus near body temperature. The properties of the thiol-ene composites were compared with those of the BisGMA/TEGDMA control. Results Depending on the resin type, similar or higher conversions were achieved in thiol-ene composites when compared to the dimethacrylate controls. At comparable conversions, lower shrinkage stress values were achieved. Although exhibiting lower initial elastic moduli, the thiol-ene composite’s flexural strengths were found to be comparable with the controls. Contrary to the control, the mechanical properties of the ester-free thiol-ene composites were shown to be unaffected by extensive aging in water and at least equaled that of the control after aging in water for just five weeks. Significance Employing non-degradable step-growth networks as organic matrices in dental composites will provide structurally uniform, tough materials with extended service time.

Ester-free thiol–ene dental restoratives—Part A: Resin development

“…Some selected thiol-ene compositions, DVS-based and neat monomeric mixtures, are therefore assessed as resin matrices in filled composites as detailed in a subsequent report [39]. …”

Enhanced reduction of polymerization-induced shrinkage stress via combination of radical ring opening and addition fragmentation chain transfer

“…Thiol-ene chemistry is a good approach to obtain polymers with defined network architectures. Although thiol-ene reactions are highly efficient they are limited in the stability of the final formulation, 20 often exhibit objectionable odor 21 and they commonly suffer from softness and low T g because of their thio-ether bridges, 22 which has motivated research to strive for alternative solutions. Alternatively, addition fragmentation chain transfer (AFCT) reagents 23,24 can be applied to obtain a well-defined network structure of the final photopolymers.…”

Effects of Photodegradable o‐Nitrobenzyl Nanogels on the Photopolymerization Process

“…The accumulated stress in resin can lead to many issues that include polymer and substrate warping, internal and interfacial defects, reduced toughness, and fatigue resistance among others . There have been many efforts to control the polymerization shrinkage and stress, including the design of novel initiators, monomers or oligomers, the reduction of initial reactive group concentration by inorganic or organic fillers, particles, and nanogels, as well as multiphase generation based on thermodynamically driven demixing, optimization of photocuring protocols, utilization of step‐growth polymerization, or ring‐opening polymerization reaction mechanisms, and the formation of covalent adaptable networks (CANs) …”