Impact of fluoride-releasing orthodontic adhesives on the shear bond strength of orthodontic brackets to eroded enamel following different surface treatment protocols

PURPOSE: To assess the impact of enamel surface treatment protocols and the types of adhesive materials on the shear bond strength (SBS) of brackets to eroded enamel substrate. MATERIALS AND METHODS: Eighty extracted premolars were randomly assigned to four main groups in which group C (no treatment) was the control group. The remaining groups were exposed to an erosion challenge through short-term acidic exposure to HCl solution (0.01 M, pH 2.3) for 30 s, with an agitation speed of 50 rpm at an environmental temperature of 25°C. The eroded enamel surface within each group was treated as follows: group N received no treatment; in group P, the eroded enamel was treated with 35% phosphoric acid (Ultradent Products, South Jordan, UT, USA) for 15 s, followed by a rinse for 10 s; and in group F, the eroded enamel was treated with fluoride gel (Bifluorid 12; Voco-GmbH, Cuxhaven, Germany) for 4 min. The brackets were bonded with either a resin composite adhesive (Transbond XT; light-cure adhesive, 3M Unitek, CA, USA) or resin-modified glass ionomer cement (Fuji Ortho LC-GC Corporation, Japan). The specimens were tested for SBS, and the bond failure was assessed according to the adhesive remnant index (ARI). Analysis of variance (ANOVA) and Tukey's post-hoc tests (P < 0.05) were used to compare the SBS of the groups. The ARI values between the groups were recorded. RESULTS: Statistically significant differences were found among the tested variables (P < 0.05). Group P showed the highest mean SBS values regardless of the type of adhesive used, and the difference was statistically significant (P < 0.05). The application of the fluoride gel showed no statistically significant improvement in SBS values. The failure mode distribution among the test groups indicated that failures at the adhesive–bracket interface were predominant in group C compared with the other study groups. CONCLUSIONS: Fluoride pretreatment, which was used to remineralize the eroded enamel surfaces before bonding, resulted in a decrease in the SBS of the orthodontic brackets in vitro compared with the other treated groups. The use of fluoride-releasing adhesive also enhances bonding to the eroded enamel surfaces.