In vitro evaluation of dentin bond strength and adhesive layer thickness of new generation two-bottle universal adhesive

Objective: Although universal adhesive systems have many advantages, there are concerns about the longevity of bond strength and adhesive layer thickness. This study aimed to evaluate the short and long-term bond strength and adhesive layer thickness of G2- Bond, a new generation two-bottle universal adhesive. Materials and Methods: This study used 30 extracted human lower molars. The teeth were randomly divided into 3 groups of adhesive agents (G- Premio Bond, G2-Bond Universal, Clearfil SE Bond). Adhesive agent and composite resin (Solare-X, GC, Tokyo, Japan) were applied to the teeth with exposed dentin surfaces according to their groups, respectively. The specimens to be used in the microtensile bond strength test were prepared with a precision cutting device. Then, all adhesive and application protocol groups were divided into two subgroups according to the aging method applied (24 hours, 6 months soaking in water). The rod specimens were subjected to microtension bond strength test in a universal testing machine and fracture types were evaluated under stereomicroscope. To observe the thickness of the adhesive layer, 3 rods from each tooth were observed by SEM at ×5000 magnification. Statistical analyses of the data were performed using SPSS v.26 software (SPSS Inc, IBM Corp, IL, USA). Two-way Analysis of Variance (ANOVA) and Tukey HSD tests were used to evaluate the bond strength. One-way ANOVA and Tukey HSD were used to evaluate the adhesive layer thickness and the relationship between adhesive layer thickness and bond strength was evaluated by correlation test (p<0.05). Results: Significant differences were found between the dentin bond strengths and adhesive layer thicknesses of the adhesives used (p<0,05). Soaking and ageing did not cause a statistically significant difference in the bond strength of the adhesives. In the SE Bond post-aging group, a significant negative correlation was observed between adhesive layer thickness and bond strength (p<0.05). There was no significant correlation between adhesive layer thickness and bond strength of the other groups. Conclusion: The two-step adhesive systems used in the study showed better bond strength than the one-stage universal adhesive system. Soaking in water had no significant effect on the bond strength of the adhesives to dentin. Keywords: Adhesive, bond strength, adhesive layer thickness