Microtensile bond strength evaluation of self-etch adhesives to primary dentin

Abstract

Introduction: A considerable research of adhesive systems is responsible for many publications about the behavior of these materials. While the dentin bond strength of permanent teeth is assessed quite often, a significantly smaller number of researches was carried on aiming to test the dentin bond strength of primary teeth. Although there are substantial microstructural differences between permanent and primary dentin, knowledge about permanent teeth is usually and merely adapted to primary teeth. Current self-etch adhesive systems may represent an attractive addition in pediatric dentistry because, besides their efficacy, they simplify the adhesive protocol reducing operative time and making the technique less sensitive. Purpose: The aim of this study was to evaluate the adhesive interfaces of four adhesive systems to primary dentin. Materials and methods: Sixteen sound human primary molars were ground flat to expose dentin randomly divided into four experimental groups, according to the different adhesive materials evaluated: ClearfilTM Protect Bond, Prime&Bond NT, ClearfilTM S3 Bond Plus and Futurabond U. The adhesives were applied under manufacturer’s instructions and the crowns restored with a composite resin. Then, the restored teeth were cross-sectioned to obtain sticks (1,2mm x 1,2mm x 9 mm). Each stick was evaluated by a microtensile test in a universal testing machine, with a crosshead speed of 0,5mm/minute. The fracture modes were examined and classified with an optical microscope (40x magnification). Primary dentin disks were additionally obtained aiming samples preparation for interface´s morphology characterization by SEM (scanning electron microscopy). The bond strengths data were analyzed using one-way ANOVA and Tukey HSD test. All statistical tests were applied at a confidence level of 95%. Results: ClearfilTM S3 Bond Plus presented the highest values (47,28MPa), followed by Prime&Bond NT (43,11MPa), ClearfilTM Protect Bond (40,33MPa) and FuturabondU (35,16MPa). ClearfilTM S3 Bond Plus, Prime&Bond NT and ClearfilTM Protect Bond showed statistically comparable results. Futurabond® U bond strengths was statistically similar to ClearfilTM Protect Bond but significantly lower from Prime&Bond® NT and ClearfilTM S3 Bond Plus. SEM evaluation of hybrid layer showed that ClearfilTM S3 Bond Plus and Futurabond® U (one-step adhesive systems) have produced a thinner hybrid layer compared to Prime&Bond NT and Clearfil™ Protect Bond (two-step adhesive systems). Conclusions: Concerning the limitations of this in vitro study, self-etch adhesives may be considered as a suitable alternative to etch-rinse adhesives in Pediatric Dentistry.