Bonding of resin luting cements to dentine after casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) treatment

Objective To determine whether the application of casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) in the proprietary paste to dentine would affect the subsequent bonding of resin-based adhesive luting cements. Methods Flat mid-coronal occlusal dentine surfaces of extracted human molars were prepared and randomly divided into three groups with different treatment periods of CPP-ACP-containing paste, Tooth Mousse^TM, i.e., no treatment; 5 min; or 5 days. Resin composite blocks were luted using either Variolink N, Panavia F2.0, Rely X U100, or Clearfil SA Luting, following the manufacturers instructions. After storage in 100% relative humidity condition at 37 °C for 24 h, the bonded assemblies were sectioned perpendicular to the interface in x and y directions, obtaining stick-shaped specimens, to assess the adhesion using a microtensile bond strength test. Fractography and micromorphology of resin cement-dentine interface were examined under a SEM. Results Dentine bond strengths of Variolink N and Rely X U100 appeared to be similar for all tested groups. Clearfil SA Luting showed a decrease of bond strength with a strong tendency for adhesive failure between resin cement and dentine following the CPP-ACP application. An increase of bond strength was observed for Panavia F2.0 bonded to CPP-ACP-treated dentine. Micromorphological evaluation revealed intimate interfacial contact and formation of pronounced resin tags for Variolink N and Panavia F2.0, regardless of CPP-ACP treatment. For the self-adhesive luting materials tested, no distinct interaction zone between the resin cements and dentine could be observed and fewer resin tags were formed. Voids at the interface were detected for Clearfil SA Luting bonded to dentine following the treatment of CPP-ACP for both application times. Conclusions Prior application of the CPP-ACP-containing paste to dentine compromised the bonding effectiveness of self-adhesive resin cements. However, with separate pretreatment steps to the tooth surface, dentine adhesion of conventional resin cements seemed not to be negatively influenced by CPP-ACP application.