Physiochemical interactions at the interfaces between self-etch adhesive systems and dentine

The purpose of this study is to provide direct and comprehensive information regarding morphology, quality and chemistry of the interfaces between three self-etching primers/adhesives and dentine.

The occlusal one-third of the crown was removed from 18 unerupted human third molars. The prepared dentine surfaces were randomly selected for treatment with one of three commercial self-etching bonding agents according to manufacturers' instructions. One two-step self-etching adhesive (Clearfil SE Bond) and two one-step self-etching adhesives (One-Up Bond F and Prompt L-Pop) were selected. Five-micron-thick sections of adhesive/dentine interface specimens were cut and stained with Goldner's trichrome for light microscopy. Companion slabs were analysed with micro-Raman spectroscopy and scanning electron microscopy (SEM).

It was shown that the difference in aggressiveness of these three contemporary self-etching systems produced different thickness of hybrid layer. Staining technique showed a distinct coloured line/zone at the adhesive/dentine interfaces for all three bonding systems. The width of this line varied, and was approximately 1, 1-2, 2-3 microm for Clearfil SE Bond, One-Up Bond F and Prompt L-Pop, respectively. The colour differences in the stained interface sections, which is reflected by the extent to which the adhesive encapsulates the demineralised dentine matrix, indicated that collagen fibrils at the interfaces were not totally encased in all three self-etching adhesives. Raman results showed that Prompt L-Pop is the most aggressive systems in this study. It almost totally demineralised the 2-microm deep subsurface dentine, while Clearfil SE is mild, only partially demineralised the first micron deep dentine.

The complementary techniques, i.e. SEM, staining and micro-Raman spectroscopy, hold considerable promise for comprehensive physicochemical characterisation of self-etching adhesive/dentine interfaces. In comparison with two-step self-etching system, the aggressive one-step system produces more complex interfaces.