Effect of different etching methods on shear bond strength of resin infiltrated sound and demineralized enamel

The aim of this in-vitro study was to determine the influence of resin infiltrant application on the shear bond strength of different etching methods on sound and demineralized enamel. 180 extracted human upper incisor's enamel surfaces were used in the study. Half of the specimens were artificially demineralized (14 days, acidic buffer, pH 4.8), other half remained sound. Sound and demineralized samples (n=90) were divided first into 2-subgroups (n=45): Resin Infiltrated Group (Icon, DMG) (I) and No Resin Infiltrated Group (IY). Then, these groups were also divided into three according to the etching procedures (n=15): 35% Phosphoric Acid (FA), %9 Hydrofluoric Acid (HFA), Er,Cr:YSGG laser (L). The caries infiltrant applicated groups were thermocycled (5000X, 5°-55°C) before the etching procedures. Following different etching procedures, a micro hybrid composite (Filtek Z250, 3M ESPE) was applied on enamel surfaces by using an etch-and-rinse adhesive system (Adper Single Bond 2, 3M ESPE). All specimens were analyzed after thermocycling on a shear bond strength testing machine at a crosshead speed of 1mm/min. The values were recorded at the time of failure of composite resins. The failed samples were examined under a stereomicroscope at X20 magnification to determine the mode of failure. The data were statistically analyzed by three-way Anova and multiple comparisons were made by Bonferroni test at 5% significance level. The results revealed that in I groups; FA showed significantly higher shear bond strength value than other etching groups both in sound and demineralized enamel (p<0,05), but L showed higher bond strength than HFA in sound enamel (p<0,05), while it had similar value with HFA in demineralized group (p>0,05). In IY groups; LA and HFA showed similar values in both sound and demineralized enamel (p>0,05), but FA showed higher bond strength value than other etching groups in sound enamel viii (p<0,05), and similar value with L (p>0,05) and higher value than HFA (p<0,05) in demineralized enamel. In I groups; HFA etched sound enamel group showed lower bond strength value than demineralized enamel group (p<0,05). In both FA and L etched groups, there was no statistically significant difference between sound and demineralized groups (p>0,05). In IY groups; HFA and L etched demineralized enamel groups showed higher bond strength than sound enamel groups (p<0,05). FA etched sound enamel group showed higher bond strength values than demineralized enamel group (p<0,05). Among HFA and L etched sound enamel groups; resin infiltrated groups (I) showed higher bond strength values (p<0,05). Among FA etched sound enamel groups, IY group showed higher bonding strength than (I) group (p<0,05). In demineralized enamel; I groups showed higher bond strength than IY groups irrespective of the etching procedures (p<0,05). In conclusion, 35% phosphoric acid can be used on resin infiltrated enamel without impairing the bond strength.