Acid Etching with Modified Phosphoric Acid to Increase the Longevity of the Bonded Interface

Purpose: To evaluate the effect of three phosphoric acids modified with chlorhexidine (CHX), benzalkonium chloride (BAC), or proanthocyanidins (PRO) and one conventional phosphoric acid (CON) on the immediate (24 h; IM) and 1-year composite-dentin microtensile bond strength (μTBS) and nanoleakage (NL), using an etch-and-rinse adhesive. Materials and Methods: A flat dentin surface was exposed on 28 caries-free extracted molars, which were then randomly assigned to four groups (n = 7). After etching and rinsing with one phosphoric acid per group, the adhesive (Adper Single Bond 2) was applied on a moist dentin surface. Composite buildups (Filtek Z350) were constructed incrementally and bonded stick specimens (0.8 mm2) were prepared and submitted to the microtensile test (0.5 mm/min) immediately (24 h) or after 1 year of water storage. For nanoleakage, 2 bonded sticks from each tooth at each storage period were immersed in 50 wt% ammoniacal silver nitrate, polished, and analyzed by SEM in backscattered mode. Data were submitted to a two-way ANOVA and Tukey's test (α = 0.05). Results: After 1 year, stable μTBS values were observed only for the modified phosphoric acids (CHX, BAC, and PRO). Also, NL was more evident in the CON group than in the CHX, BAC and PRO groups (p 0.05) after 1-year water storage. Conclusions: Compared to the control, the phosphoric acid etchants which contained protease inhibitors (CHX, BAC and PA) promoted the stability of composite-dentin microtensile bond strength and showed less nanoleakage after 1 year of water storage. They represent an effective way of prolonging the stability of the composite-dentin bonds without creating an additional bonding step. Keywords: chlorhexidine, benzalkonium chloride, proanthocyanidins, metalloproteinases, phosphoric acid, longevity, acid etching, cross-linking agents