Dentin Bonding Performance, Nanoleakage, and Micromorphological Characteristics of Universal Adhesives in Self-etch Mode: Comparative Evaluation

Abstract The current study aimed to evaluate and compare the microtensile bond strength (µTBS), nanoleakage, and micromorphological characteristics of six universal adhesives (UAs) applied in self-etch (SE) mode to dentin. The occlusal one-third of 60 freshly extracted intact human molars was removed, and the exposed surfaces were treated with one of the six UAs (Gluma Bond [GB], Zipbond Universal [ZB], Scotchbond Universal Plus [SB + ], Single Bond Universal [SB], Futurabond U [FB], or OptiBond eXTRa Universal [OB]) in SE mode (n = 10). After resin composite build-up (Tetric N Ceram Bulk-Fill), specimens were subjected to 5,000 thremocycles and stored in artificial saliva in an incubator for 24 h. For each group, composite resin–dentin beams were prepared (n = 56) from seven specimens and the µTBS test was performed. The failure patterns of the debonded specimens were investigated using a stereo binuclear microscope (x = 30). Data were analyzed using one-way ANOVA and Tukey's significant difference (HSD) tests at a significance level of p < 0.05. The remaining specimens from each group (n = 3) were sectioned in mesio-distal direction. Buccal sections were immersed into ammoniacal silver nitrate followed by a photodeveloper under a fluorescent light and then investigated using scanning electron microscope (SEM) in backscattered mode. Lingual sections were used for assessing the micromorphological pattern of adhesive–dentin interface using SEM in secondary electron mode. One-way ANOVA test indicated a significant difference in the microtensile bond strength among the types of the tested adhesives (p < 0.05). SB+ demonstrated the highest bond strength among all tested adhesives (p < 0.05). SB also showed significantly higher bond strength compared with the other tested adhesives, except for OB (p = 0.317). No statistically significant differences were observed among FB, GB, ZB, and OB (p > 0.05). Regarding nanoleakage patterns, GB showed the highest degree while the lowest nanoleakage pattern was exhibited in OB. Resin–dentin interface exhibited the highest massive amount of resin tags in SB+ and the least amount of resin tags in FB followed by ZB. Based on the extracted results, UA bonding performance was material dependent. The number and depth of resin tags were found to correlate with bond strength, whereas nanoleakage patterns showed no such correlation.