The Effect of a Deproteinizing Pretreatment on the Bonding Performance and Acid Resistance of a Two-step Self-etch Adhesive on Eroded Dentin
This study evaluated how deproteinization using sodium hypochlorite (6% NaOCl) or hypochlorous acid (50 ppm HOCl) with or without the subsequent use of an arylsulfinate salt-containing agent (Clearfil DC Activator; DCA; Kuraray Noritake Dental) affects the micro-tensile bond strength (μTBS) and formation of an acid-base resistant zone (ABRZ) of a two-step self-etch adhesive on eroded dentin. Coronal dentin surfaces of sound human molars were exposed to 48 cycles of demineralization (1% citric acid; 5 minutes) and remineralization (buffer solution with pH=6.4; 3.5 hours). They were then assigned to experimental groups according to the pretreatment used: none (negative control), NaOCl, NaOCl+DCA, HOCl, and HOCl+DCA. Sound dentin surfaces with no pretreatment were used as a positive control. The dentin surfaces were bonded with Clearfil SE Bond 2 (Kuraray Noritake Dental), and μTBS was measured either after 24 hours or 20,000 thermal cycles (TC). The μTBS data were statistically analyzed using a mixed-model analysis of variance (ANOVA) and t-tests with Bonferroni correction. Failure mode was determined with scanning electron microscopy (SEM), which was also used for the observation of ABRZ. Among experimental groups, there was no significant difference between the negative control, HOCl, and HOCl+DCA after 24 hours, but the HOCl-pretreated groups exhibited significantly higher μTBS than the negative control after TC (p<0.01). Pretreatment with NaOCl and NaOCl+DCA resulted in significantly higher μTBS (p<0.001), but the highest μTBS was measured on sound dentin (p<0.001). TC decreased μTBS significantly in all groups (p<0.001) except for sound dentin and NaOCl+DCA (p>0.05). Adhesive failures prevailed in eroded groups, whereas cohesive failures were predominant on sound dentin. ABRZ was recognized in all groups but marked morphological differences were observed. The combined use of 6% NaOCl and the arylsulfinate salt-containing agent partially reversed the compromised bonding performance on eroded dentin, while the effect of 50 ppm HOCl was negligible.SUMMARY
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Distribution of failure modes (%). Abbreviations: 24 h, 24-hour water storage; TC, 20,000 thermal cycles.
Representative SEM images of an adhesive failure and a mixed failure. Resin side of the beam is displayed on the left, dentin side on the right. The presented images were taken at magnification 90× (view of the entire surface) and 1000× (detailed view). Adhesive failures were identified by the presence of grooves produced by the SiC papers and/or the presence of dentinal tubules filled with the adhesive. In mixed failures, dentin was identified by the presence of open dentinal tubules and the composite resin by the presence of filler particles. Abbreviations: CR, composite resin; A, adhesive; D, dentin.
Representative SEM images of the adhesive interfaces after acid-based challenge at magnification 1000×. (a) Sound dentin – control; (b) eroded control with no pretreatment; (c) Eroded dentin pretreated with 6% NaOCl; (d): eroded dentin pretreated with 6% NaOCl and DCA; (e) eroded dentin pretreated with 50 ppm HOCl; (f): eroded dentin pretreated with 50 ppm HOCl and DCA. The white triangles point at the hybrid layer (HL), white arrows point at the acid-base resistant zone ABRZ. Abbreviations: CR, composite resin; OL, outer lesion; A, adhesive; D, dentin.
Representative SEM images of the adhesive interfaces after acid-based challenge at magnification 3500×. Please refer to the legend of Figure 3 for explanation.
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