Microtensile bond strength evaluation to dentin of new universal adhesive systems

Introduction: Since Buonocore (1955), enamel adhesion remains consistent with high bond strength values [ 1 ]. On the contrary, adhesion to dentin remains unpredictable due to collagen presence in its composition. This reason has led to successive modifications of adhesive systems in the last decades in order to allow better performances and higher bond strengths [ 2 , 3 ]. The aim of this study was to evaluate the adhesion resistance to dentin by microtensile bond strength of the universal adhesives studied, in the etch-and-rinse and self-etch approach. Material and Methods: This work was approved by the IUEM Ethics Committee. 18 healthy molar teeth were extracted for orthodontic or periodontal reasons and were randomly divided into 6 groups (n = 3): OC - Octobond LC (Clarben SA, Siauliai, Lithuania), etch-and-rinse; SE - Clearfil SE BOND 2 (Kuraray Noritake Dental Inc, Tokyo, Japan), self-etch; GPE - G-Premio BOND (GC Corporation, Tokyo, Japan), universal in the etch-and-rinse approach; GPS - G-Premio BOND (GC Corporation, Tokyo, Japan), universal in the self-etch approach; AdhE - Adhese Universal (Ivoclar Vivadent, Schaan, Liechtenstein), universal in the etch-and-rinse approach; AdhS - Adhese Universal (Ivoclar Vivadent, Schaan, Liechtenstein), universal in the self-etch approach. Adhesive systems were applied according to manufacturer's instructions and resin composite build-ups were obtained with 20/20 composite resin (A3 color)(Henry Schein Inc, NY, USA)) (2 mm increments; total height: 6-8 mm). Samples were then sectioned in the X and Y directions to obtain 1 ± 0,2 mm 2 beams. Finally, beams were fixed to a jig using a cyanoacrylate adhesive (Zapit, Dental Ventures of America) and submitted to stress until failure in a universal testing machine at 0.5 mm/minute. After failure, the cross-sectional area was measured using a digital calliper. Failure mode and MPa adhesive forces were recorded. For the statistical analysis, since repeated measurements were performed in the same experimental unit, linear mixed model has been used with identity matrix, the best covariance structure suggested by the data. This method produced the same results of the traditional one-way ANOVA model, at the 5% significance level. Results: No significant differences were observed in microtensile bond strengths between groups. Discussion and conclusions: The previous acid conditioning of dentin didn't affect the adhesive strengths for all the tested universal adhesives. Being