Effect Of Cavity Disinfectants On Dentin-resin Bond Strength

Objective:In this study,micro-shear tests,failure mode analysis and scanning electron micro-scope(SEM)observations were used to compare the effects of four different cavity disinfectants on dentin-resin bond strength,besides that,the result can provide a scientific basis for cavity disinfection before resin-filling in clinic.Methods:30 freshly extracted and noncarious human third molars were selected.The occlusal enamel was removed to expose middle flat surfaces of dentin.The teeth were randomly divided into five groups(n=6): control group(distilled water group),ethanol group(75% ethanol),chlorhexidine group(2% CHX),sodium hypochlorite group(1% NaClO)and EDTA group(19% EDTA).Different disinfection methods were used to treat the surface of dentin for 1 min and then the occlusal dentin surfaces were made.20 samples were made into 75 stick specimens(n=15)with cross section of 1.0 mm ×1.0 mm and length of 8 mm,respectively,after bonding Z250 composite resin with 3M Single Bond Universal,for microshear bond strength(MSBS)testing.The failure modes at the dentin-resin interface were observed using a stereomicroscope.Another 10 samples(n=2)were observed dentin surface structure with SEM.Results:1.The MSBS of control group,CHX group,ethanol group,NaClO group,EDTA group were:(26.92±11.07)MPa,(26.78±7.81)MPa,(31.46±11.74)MPa,(36.95±7.81)MPa,(41.88±11.10)MPa,respectively.One-way ANOVA revealed that the influence of cavity disinfectant types on MSBS of dentin-resin was statistically significant(P<0.05).Compared with the MSBS of control group,there were significant differences in EDTA group and NaClO group(P<0.05),but no significant differences in CHX group and ethanol group(P>0.05);there were statistically significant differences between CHX group,EDTA group and NaClO group(P<0.05),but no statistically significant differences between CHX group and ethanol group(P>0.05);there was a statistically significant difference between ethanol group and EDTA group(P<0.05),but no statistically significant difference between the ethanol group and NaClO group(P<0.05);there was no significant difference between EDTA group and NaClO group(P >0.05).2.The fracture mode was mainly mixed failure,accounting for 71%,the failure of dentin or composite resin,namely cohesive fracture accounted for 20%,the failure of adhesive interface accounted for 9% and there was no significant difference between the groups(P>0.05),suggesting that the difference of the fracture mode was not related to the disinfection method.3.The SEM results were as follows: the dentin surface of control group was covered with obvious smear layer and the dentin tubules were invisible;the smear layer of CHX group was thinner,but dentin tubules were rarely open;the smear layer of ethanol group was rough and irregular,and dentin tubules were partly open;the smear layer of NaClO group was significantly thinner,most of the dentin tubules were open and some of the peritubular dentin was demineralized;EDTA group had no smear layer,the dentin tubules were open and most of the peritubular dentin was demineralized.Conclusion:After four kinds of cavity disinfectants treated dentin surface for 1min respectively,19% EDTA and 1% NaClO thinned the smear layer,most of the dentin tubules were open,the peritubular dentin was demineralized and can significantly improve the dentin-resin bond strength;75% ethanol and 2% CHX thinned the smear layer,but the dentin tubules were less open and there was no significant effect on the dentin-resin bond strength.