One-day bonding effectiveness of new self-etch adhesives to bur-cut enamel and dentin

Self-etch adhesives try to solve difficulties commonly associated with the clinical application of etch-and-rinse adhesives. Their application procedure is considered less time-consuming and, more importantly, less technique-sensitive. The main objective of this study was to determine the bonding effectiveness to and the interaction with enamel/dentin of three contemporary one- and two-step self-etch adhesives by microtensile bond strength testing (microTBS), Fe-SEM and TEM when compared to a control two-step self-etch and a three-step etch-and-rinse adhesive. The one-step self-etch adhesive, Adper Prompt (3M ESPE), scored the lowest microTBS of all experimental and control adhesives tested. Conversely, the two-step self-etch adhesives Clearfil SE (Kuraray) and OptiBond Solo Plus Self-Etch (Kerr) approached the values obtained by the three-step etch-and-rinse control (OptiBond FL, Kerr) when bonded to enamel and dentin. Ultramorphological characterization showed that interfacial morphology and the pH of the self-etch primer/adhesive are strongly associated. The interaction with dentin varied from the formation of a submicron, hydroxyapatite-containing hybrid layer for the "mild" self-etch adhesive Clearfil SE to a 3-5 microm thick, hydroxyapatite-depleted hybrid layer for the "strong" self-etch adhesive Adper Prompt. The two-step self-etch adhesives AdheSE and OptiBond Solo Plus Self-Etch presented with a hybrid layer with a hydroxyapatite-depleted top part and a hydroxyapatite-containing base part and were therefore classified into a new group of self-etch adhesives, namely "intermediary strong" self-etch adhesives.