Adhesive interface and microtensile bond strength evaluation of four adhesive systems to primary dentin

Objectives: The aim of this study was to evaluate the microtensile bond strength and the adhesive interface of four adhesive systems to primary dentin. Methods: Sixteen sound human primary molars were ground flat to expose dentin and randomly divided into four experimental groups according to the different adhesive material evaluated: three self-etching systems (Clearfil(TM) Protect Bond, Clearfil(TM) S-3 Bond Plus and Futurabond (R) U) and one etch-and-rinse system (Prime & NT). The adhesives were applied under manufacturer's instructions and the crowns "restored" with a composite resin (Synergy (R) D6). The "restored" teeth were then cross-sectioned to obtain sticks. Each stick was evaluated using a microtensile test in a universal testing machine. Additionally, eigh-teen dentin samples from four temporary molars were prepared for dentin conditioning and interface morphology evaluation using scanning electron microscopy. The bond strength results were analyzed using one-way ANOVA and a Tukey HSD test (confidence level of 95%). Results: ClearfilTMS(3) Bond Plus (47,28 MPa), Prime & NT (43.11 MPa) and Clearfil(TM) Protect Bond (40.33 MPa), presented the highest adhesion values without statistical differences. Futurabond (R) U bond strengths (35.16 MPa) was statistically similar to Clearfil(TM) Protect Bond (p = 0.271) but significantly lower from Prime & NT (p = 0.022) and ClearfiF S-3 Bond Plus (p < 0.001). An ultra-morphological evaluation showed marked differences in smear layer dissolution, depth of dentin demineralization and thickness of the hybrid layer promoted by the different adhesive strategies evaluated. Conclusions: Considering the limitations of this in vitro study, some self-etch adhesives may be capable of producing high bond strengths to primary dentin, similar to the etch-and-rinse adhesive evaluated. (C) 2016 Sociedade Portuguesa de Estomatologia e Medicina Dentaria. Published by Elsevier Espana, S.L.U.