NaOCl degradation of a HEMA-free all-in-one adhesive bonded to enamel and dentin following two air-blowing techniques

Objective: Phase-separation within HEMA-free all-in-one dental adhesives may result in the entrapment of droplets within the adhesive resin. Strongly air-blowing prior to polymerization, can remove most of these droplets. The objective of this study was to evaluate the effect these droplets may have on the resistance of the adhesive-tooth interface to NaOCl degradation. Methods: The micro-tensile bond strength (mu TBS) to enamel and dentin was determined when a HEMA-free all-in-one adhesive was applied either following a mild or strong air-blowing technique. The bonds were also exposed to an aqueous sodium hypochlorite (NaOCl) solution for 1 h, following a recently introduced methodology to mimic in vivo bond degradation. Results: This study revealed that strong air-blowing of the adhesive only resulted in a significantly higher micro-tensile bond strength (mu TBS) to dentin, but not to enamel. Likewise, NaOCl only reduced the mu TBS to dentin for both the mild and strong air-blowing technique, but again not the mu TBS to enamel. Failure analysis by SEM clearly revealed that strong air-blowing is less effective in droplet removal when the adhesive was applied in small and narrow class-I cavities, as compared to when it was applied to flat surfaces. Conclusions: NaOCl did preferentially dissolve the hybrid layer at dentin, and more for the mild than for the strong air-blowing technique. A strong air-blowing procedure resulted in a more NaOCl-resistant hybrid layer, so that it can be concluded that a HEMA-free one-step adhesive definitely benefits from a strong air-blowing technique. (C) 2006 Elsevier Ltd. All rights reserved.