Methods: Bonding effectiveness was assessed by microtensile bond strength test and scanning electron microscopy (SEM). A three-step etch-and-rinse adhesive (OptiBond FL; Kerr, USA) or a two-step self-etch adhesive (Clearfil SE Bond; Kuraray Medical, Japan) was bonded to three groups of dentine surfaces: no treatment; 5 minutes or 5 days CPP-ACP application. The microtensile test was performed and bond strength data were analysed using ANOVA and Tukey-Kramer post hoc test. Etching characteristics on respective dentine surfaces and resin-dentine interfaces were observed under SEM.
Results: Bond strengths of Clearfil SE Bond to dentine were similar for all tested groups. OptiBond FL; however, showed lower bond strengths following the application of CPP-ACP, Tooth MousseTM, for both time periods. Under SEM observations, the CPP-ACP treated dentine displayed a layer of residue or precipitate attached to the surfaces after the phosphoric acid treatment. The sectioned specimens also showed up the resin-dentine interface with less intertubular linking of resin tags, which could mean some mineralisation of these channels, hence preventing resin infiltration.
Conclusion: The presence of CPP-ACP on the dentine surface may compromise bonding effectiveness of etch-and-rinse adhesive system. However, CPP-ACP application may be beneficial to the dentine bonding of self-etch system, as the chemical interactions between calcium and functional monomers of the adhesives might be enhanced to some degree.