Effect of different adhesive application approaches on bond strength in over-etched dentin

To investigate the effect of over-etching and subsequent use of different adhesive application approaches including active, double, preheated, and ultrasonic application on dentin bond strength.

Dentin specimens from sound human third molars were prepared and allocated into six groups (n= 10 per group). In Group 1 (negative control), the dentin specimens were over-etched with phosphoric acid for 30 seconds, and a two-step etch-and-rinse adhesive (Prime & Bond XP; Dentsply Sirona) was applied for 20 seconds according to the manufacturer's instructions. In test Groups 2-5, the application of the adhesive varied: In Group 2, the adhesive was actively rubbed into the dentin surface, whereas in Group 3, a second adhesive layer was applied after light-curing of the first one. In Group 4, the adhesive was heated to 68°C prior to application, and in Group 5, the adhesive was ultrasonically activated. Acid-etching for 15 seconds and adhesive application for 20 seconds was performed in the positive control group (Group 6) according to the manufacturer's instructions. After light-curing and composite build-up [Ceram.x Spectra ST (HV); Dentsply Sirona], microtensile bond strength and fracture types were determined. Data were statistically analyzed by Kruskal-Wallis rank test, followed by post-hoc pairwise comparisons using Conover tests and P-value adjustment according to Holm (α= 0.05).

Active, double, preheated, or ultrasonic adhesive application showed no significant effect on dentin bond strength when compared to the control groups. Predominantly adhesive failures were observed in all groups.

A modification of adhesive application by using active, double, preheated, or ultrasonic application does not improve bonding to accidentally over-etched dentin.