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

ObjectivesThe aim of this study was to evaluate the microtensile bond strength and the adhesive interface of four adhesive systems to primary dentin.MethodsSixteen 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™ Protect Bond, Clearfil™ S3 Bond Plus and Futurabond® U) and one etch-and-rinse system (Prime&Bond® NT). The adhesives were applied under manufacturer's instructions and the crowns “restored” with a composite resin (Synergy® 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, eighteen 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%).ResultsClearfilTMS3 Bond Plus (47,28MPa), Prime&Bond® NT (43.11MPa) and Clearfil™ Protect Bond (40.33MPa), presented the highest adhesion values without statistical differences. Futurabond® U bond strengths (35.16MPa) was statistically similar to Clearfil™ Protect Bond (p=0.271) but significantly lower from Prime&Bond® NT (p=0.022) and Clearfil™ S3 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.ConclusionsConsidering 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