RESUMO
Although self-adhesive resin cements are convenient and less technique-sensitive materials for dental clinicians, they exhibit a lower degree of conversion due to acidic components in their composition. Supplementation of the initiator, accelerator, and activator in self-adhesive resin cements has been suggested to compensate for the lower degree of conversion. This study aimed to evaluate the effects of different combinations of self-curing initiators, self-curing activators, and accelerators on the degree of conversion (DC) of self-adhesive resin cements. A dual-cured self-adhesive resin was prepared using six combinations of initiators, activators, and accelerators. The change in the DC over time was evaluated with and without light curing. The film thickness, flow properties, and cytotoxicity of each formulation were assessed. The results showed that all supplemental components had an effect on increasing the DC, but a greater increase in the DC was observed in the following order: activator, accelerator, and initiator. The cytotoxicity of the resin cements was related to the DC values, as resin cements with lower DC values exhibited higher cytotoxicity. The film thickness met the ISO standards for all groups. The results suggest that utilizing an activator is the most effective approach to enhance the DC in self-adhesive resin cement and that cytotoxicity tended to increase with lower DC values, whereas film thickness and flow properties demonstrated no correlation with DC values.
RESUMO
Bisphenol A (BPA) is regarded as an endocrine disruptor associated with negative health effects in animals and humans. Laccase from white-rot fungus can enable BPA oxidation and auto-polymerization to circumvent its biotoxicity, but the work concerning the effect mechanisms of divalent and trivalent metal ions (MIs) on BPA polyreaction have rarely been reported. Herein, Trametes versicolor laccase-started BPA conversion within 1 h followed pseudo-first order kinetics, and the rate constant (kprcs) and half-life were respectively 0.61 h-1 and 1.14 h. The presence of Ca2+, Mg2+, Cu2+, Pb2+, Cd2+, Zn2+ and Al3+ exhibited insignificant impact on BPA removal, whereas Fe2+, Fe3+ and Mn2+ had a strong inhibiting effect. Compared with MI-free, the kprcs values of BPA respectively lowered 34.4%, 44.3% and 98.4% in the presence of Fe2+, Fe3+ and Mn2+. Enzymatic activity and differential absorption spectrum disclosed that the inhibitory actions were accomplished by two different mechanisms. One is Fe2+ was preferentially oxidized into Fe3+ that restrained laccase activity at the initial stage of reaction, and subsequently, the formed Fe3+ complex bound with laccase T1-Cu site and thus impeded the single-electron transfer system. The other is Mn2+ was instantly oxidized by laccase to generate Mn3+-citrate complex, which completely consumed the dissolved O2 in solution and consequently terminated BPA removal. Considering environmental bioremediation, T. versicolor laccase-enabled auto-polymerization is a simple and convenient candidate to eliminate BPA in enzymatic wastewater treatment, however the effects of Fe2+/Fe3+ and Mn2+ on BPA decontamination should be cautiously assessed.