Effect of combined application with glycolic acid and pyridoxal 5-phosphate on the long-term durability of dentin bonding

Objectives This study focused on assessing the impact of combined with glycolic acid (GA) and pyridoxal 5-phosphate (PLP) on the strength and stability of dentin bonding. Methods GA with 37% concentration was prepared as acid etch, and PLP of varying doses (0.5 wt%, 1.5 wt%, and 2.5 wt%) was used as a primer. Additionally, the demineralization ability of phosphoric acid (PA) and GA on the dentin surface was detected using scanning electron microscopy (SEM). Fourier transform infrared spectroscopy (FTIR) was used to analyze the cross-linking effect of PLP with demineralized dentin collagen, and the effect of PLP on the single bond universal’s degree of conversion. The adhesion property of dentin was assessed using testing micro-tensile bond strength (μTBS), endogenous matrix metalloproteinase (MMPs) activity, nanoleakage, and the morphology at the resin-dentin bonding interface, following 10,000 thermal cycles. Results SEM observation demonstrated that etching with 37% GA for 30 s could effectively demineralizing the dentin surface and the adhesive strength was equivalent to that of the PA group ( p > 0.05). In addition, adhesive strength after aging increased relative to the PA group ( p < 0.05). The FTIR analysis results exhibited that 1.5% PLP improved the conversion rate of adhesive and the effect of chemical binding with collagen fibers. The GA+1.5% PLP group significantly enhanced the bonding interface μTBS, effectively reducing the nanoleakage and activities of MMPs, with no significant difference before and after aging ( p > 0.05), demonstrating excellent aging resistance. Conclusions GA can effectively replace PA as an acid etching agent for treating the dentin surface. The bonding strength of the PA group and the nanoleakage results showed a significant decrease after aging. The combination of 37% GA+1.5% PLP not only demineralizes dentin rapidly but also facilitates cross-linking of collagen fibers to reduce degradation and enhance the bonding quality of the hybrid layer. Clinical significance Compared with the traditional PA etching method, the combined application of 37% GA with 1.5% PLP has made better improvements in maintaining the long-term durability of the bonding interface, providing a potential solution for etching and biologically modifying the dentin substrates.