Long-term stability of dental adhesive incorporated by boron nitride nanotubes

Objective. The aim of this study was to evaluate physicochemical properties, long-term microtensile bond strength and cytotoxicity of methacrylate-based adhesive containing boron nitride nanotubes (BNNTs) as fillers. Methods. A dental adhesive was formulated using BisGMA/HEMA, 66/33 wt% (control). Inorganic BNNT fillers were incorporated into the adhesive at different concentrations (0.05, 0.075, 0.1 and 0.15 wt%). Analyses of degree of conversion (DC), polymerization rate [Rp.(s(-1))], contact angle (CA) on dentin, after 24 h and 6 months microtensile bond strength (mu TBS-24 h and 6 months) were assessed. Cytotoxicity was performed through viability of fibroblast cells (%) by sulforhodamine B (SRB) colorimetry. Results. DC and max. polymerization rate increased (p < 0.05) after incorporating 0.075 and 0.1 wt% BNNT. The contact angle on dentin increased (p < 0.05) after incorporating 0.15 wt% BNNT. The mu TBS-24 h showed no changes (p > 0.05) after incorporating up to 0.15 wt% BNNT comparing to control. After 6 months, mu TBS decreased (p < 0.05) for control and 0.15 wt% BNNT and BNNT groups up to 0.15 wt% showed higher mu TBS than control (p < 0.05). No difference of fibroblast growth was found among adhesives (p > 0.05) and up to 19% of cell viability was found comparing 0.05 wt% BNNT to positive control group (100%). Significance. Incorporating boron nitride nanotubes up to 0.1 wt% into dental adhesive increased the long-term stability to dentin without decreasing viability of fibroblast cell growth. Thus, the use of BNNTs as filler may decrease failure rate of current dentinal adhesives. (C) 2017 The Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.