Minimize Polymerization Stress Using a pH-sensitive Compound
Objectives: Polymerization stress of methacrylate dental resin composites is a major concern for dental restorations due to its destructive effects that may lead to tooth fracture and microleakage, which is one of the leading causes for secondary caries. Our objective is to reduce polymerization stress using a pH-sensitive quaternary pyridinium salt (pH-QPS) as an additive to the resin-network. This pH-QPS has a pH-responsive, acid-enhanced antimicrobial efficacy that can selectively inhibit the acid-producing bacteria in a multispecies microbiome.
Methods: A mixture of bisphenol A-glycidyl methacrylate (Bis-GMA) with triethylene glycol dimethacrylate (TEGDMA), 7:3 ratio by mass, was used as a control resin. The resin was mixed with photo-initiators camphorquinone/amine (CQ/amine). The capability of pH-QPS at 1 wt% to reduce polymerization stress was evaluated and compared with the low polymerization generated by a composition-controlled copolymerization of equimolar urethane dimethacrylate (UDMA) and triethyleneglycol divinylbenzyl ether (TEG-DVBE) using the same initiators. Tensometer and near infrared spectrometer were used to simultaneously evaluate the polymerization stress and degree of vinyl conversion (DC) of the dental resin composites.
Results: Experimental results showed that adding pH-QPS to the Bis-GMA/TEGDMA control reduced polymerization stress by approximately 55% ± 3%. In addition, the composition-controlled photo polymerization of UDMA/TEG-DVBE only produced approximately 1/3 of the stress in comparison to the control. Adding pH-QPS to UDMA/TEG-DVBE further reduced the polymerization, also increased the DC by approx. 9 %.
Conclusions: These results suggest that the addition of pH-QPS significantly reduced polymerization stress. Considering its pH-responsive antimicrobial efficacy, the pH-QPS has great potentials in design and producing new dental resin composites to replace the traditional ones.