Detection of the hybrid layer biodegradation initiation factor with a scanning electron microscope

The purpose of this study was to elucidate the origin of initiation of hybrid layer biodegradation. Ninety caries-free human third molars were divided into three surface groups: enamel, dentin, and NaOCl-treated dentin. (n = 30/group) Each group was divided into three subgroups (n = 10/group) of luting resin materials with etch-and-rinse; self-etch and self-adhesive systems. Resin composite blocks and sticks were fabricated and adhered onto dentin and enamel surfaces. The bond strength values were evaluated with micro shear test and statistical analysis were made. On the other hand, teeth were sectioned with a slow-speed saw into multiple beams. After thermocycling, samples were kept in 50% silver nitrate solution. Samples were analyzed with SEM in back-scattered mode. According to the micro-shear bond tests, higher bond strength values were observed in etch-and-rinse system. Bond strength values in self-adhesive and etch-and-rinse groups were significantly higher than self-etch groups in dentin surface and dentin surface treatment with NaOCl. Back-scattered scanning electron microscope results showed that, different degradation mechanism was observed. The present study indicates that, due to the acid etching in dentin, collagen biodegradation was observed within the hybrid layer. On the enamel surfaces, resin degradation was related with resin monomers in adhesive systems.