Influence of nano-hydroxyapatite containing desensitizing toothpastes on the sealing ability of dentinal tubules and bonding performance of self-etch adhesives

Objectives: To evaluate the dentinal tubular occlusion of nano-hydroxyapatite (nHAp) containing desensitizing toothpastes and their influence on the resin-dentin bonding performance of two mild self-etch adhesives. Materials and methods: Mid-coronal dentin specimens were prepared from obtained intact human third molars. They were immersed in 1% citric acid for 20 s to expose the dentinal tubules to simulate sensitive teeth and then randomly divided into four groups. The control group received no desensitizing treatment. Experimental groups were treated with two commercial nHAp containing desensitizing toothpastes (Biorepair and Dontodent) and an experimental pure nHAp paste respectively. Each group was further divided into two subgroups and bonded with either G-Bond or Clearfil S³ Bond. The micro-tensile bond strength was tested and failure mode distribution was analyzed. Moreover, the effect of desensitizers on dentinal tubular occlusion was observed by the field-emission scanning electron microscope (FESEM). Resin infiltration of the adhesives labeled by fluorescent Rhodamin B was evaluated under confocal laser scanning microscopy (CLSM). Results: FESEM revealed that all the desensitizers noticeably occluded the dentinal tubules, and the extents were completer after application for 7 days. The majority of the occlusion still preserved even after acid challenge with cola or adhesive. CLSM demonstrated shorter resin tags were produced in the desensitized groups. When bonding with G-Bond, the pure nHAp group showed comparable bond strength to the control group, while Biorepair and Dontodent treatment decreased the bond strength. For groups bonded with Clearfil S³ Bond, all the desensitizers reduced the bond strengths compared to the control and no significant difference was found among the three groups. Conclusion: Nano-hydroxyapatite containing desensitizing toothpastes could occlude dentinal tubules effectively with a certain degree of acid resistance, which contributes to the relief of dentin hypersensitivity. While, the application of these nHAp desensitizers comprised the resin infiltration of G-Bond and Clearfil S³ Bond, resulting in decreased bond strengths of the resin-dentin bonding.