| Objectives:The previous group successfully applied the 5wt% collagen-reactive functional monomer-4-formylphenyl acrylate primer in combination with ethanol wet bonding to enhance the durability of dentin bonding.In this study,we aimed to omit the ethanol wet bonding step and investigate the effect of functional monomer 4-formylphenyl acrylate(FA)primers,containing different ratios of ethyl acetate(EAC),and ethanol(ET)on the bonding durability of two universal commercial adhesives All-Bond Universal(ABU)and Single Bond Universal(SBU)in etch-and-rinse mode,with a view to developing new approaches for enriching the application of FA primers.Methods:1.FA was prepared from p-hydroxybenzaldehyde by the acyl chloride reaction.5wt% FA primer was prepared from the solvent ethyl acetate and ethanol in the ratio of7:3,6:4,5:5 and 4:6 respectively.2.The Degree of Conversion of All Bond Universal(ABU)and Single Bond(SBU),two universal adhesives,were determined by Fourier transform infrared spectrum(FTIR)after treatment with 5 wt% FA primers in different solvent ratios of ethyl acetate and ethanol(7:3,6:4,5:5,4:6).The primer was applied to the demineralized dentin surface for 60 s for each group separately,and the control group was left untreated to prepare the resin-dentin microtensile bond strength test samples for the ABU and SBU groups.After 10,000 thermal cycles,microtensile test pieces of ABU and SBU commercial bonding agents were fabricated to test the microtensile bond strength at the resin-dentin interface,and fracture patterns were analysed using a stereomicroscope.Finally,the hydrophobicity of the demineralised dentin surface after treatment with different solvent ratios was examined by means of contact-angle of water,and the best ratio of EAC and ET for FA was selected.3.The resin-dentin bonding interface of control group and FA primer group with optimal solvent ratio(EAC:ET-4:6)was observed by using Confocal Laser Scanning Microscope(CLSM).The overall morphology of the resin rag was observed by fluorescence technique to evaluate the permeability of the adhesive,and the matrix metalloproteinase activity at and around the bonding interface was detected by in situ enzyme profiling.Scanning Electron Microscope(SEM)was utilized to further evaluate the immediate and ageing nanoleakage and resin rag patterns at the resindentin bonding interface,and to analyse the reasons for the improved bond durability and stability of the two universal commercial adhesives with the FA primer in ethyl acetate to ethanol solvent ratio.4.The degree of conversion and water contact angle,microtensile bond strength and degree of nanoleakage for ABU and SBU were analysed by ANOVA with multiple comparisons between groups using Tukey’s test(α = 0.05).Results:1.When the solvent EAC:ET of 5 wt% FA primer was 7:3 or 4:6 significantly improved degree of conversion and microtensile bond strength of ABU and SBU(p <0.05),especially when EAC:ET-4:6 was more remarkable,the microtensile bond strength of immediate and aging groups were statistically significantly different from other test groups(p < 0.05),the difference between the other experimental groups immediate and aging test groups was non-significant(p > 0.05).The fracture pattern of every group was dominated mainly by adhesive interfacial fracture,while the interfacial fracture sites were focused on the bottom of the hybrid layer.Static water contact angle tests indicated that the hydrophobicity of the demineralized dentin surface was effectively enhanced(p < 0.05)by the 5 wt% FA primer in each test group,especially at EAC:ET-4:6.2.CLSM and SEM observed the bonding interface of two commercial adhesives,where the application of a 5 wt% FA primer with an EAC:ET of 4:6 resulted in a noticeable inhibition of matrix metalloproteinase activity in the hybrid layer(p < 0.05),a considerable improvement in the infiltration of both adhesives(p < 0.05),as well as a remarkable decreased nanoleakage(p < 0.05).Conclusions:1.The introduction of ethyl acetate and ethanol in different ratios into the solvent system of the FA primer has replaced the ethanol wet bonding step,effectively reducing the clinical operation steps and time.2.When EAC:ET was 4:6,the resin-dentin bonding interface had optimal stability after 5 wt% FA primer treatment,which dramatically enhanced the bond strength of both ABU and SBU universal commercial adhesives.In summary,the FA in the primer chemically binds to the dentin collagen matrix,and the ethanol in the solvent also guides the resin matrix to penetrate deeper into the dentin,improving the hydrophobicity of the interface and the penetration of the adhesive,enhancing the sealing of the dentin bonding interface,reducing nanoleakage at the bonding interface and improving the bonding durability and stability. |
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