Effect Of Nano-amorphous Calcium Phosphate-containing Self-etch Adhesive On The Dentin Micro-tensile Bond Strength

[Objectives]The aim of the study was to incorporate nanoparticles of amorphous calcium phosphate (NACP) into a self-etch adhesive (Clearfil S3Bond, Kuraray Co., Japan), and investigate its influence on pH value, dentin micro-tensile bond strength and surface morphology of dentin treated with the adhesives containing with/without NACP.[Methods]Eight freshly extracted human third non-caries molars were used in this study within one month after extraction. Flat mid-coronal dentin surfaces were exposed with a low-speed saw (Isomet1000, Buehler, lake Bluff, IL, USA) under copious running water and wet-ground with320-grit silicon carbide paper for45s. The NACP was prepared by mixing100mL of20mmol/L CaCl2solution,100mL of12mmol/L Na2HPO4solution and100μL of lmol/L NaOH solution. After the suspension was centrifuged at the speed of6000rpm for2min (GL-22M, Saite Hunan Co., China), the supernatant was replaced by100%of ethanol to halt the chemical reaction. Then, the suspension was centrifuged at the speed of6000rpm for2min, again. After the supernatant was decanted, the precipitate was heated at40℃under vacuum (DZF-6020, Jinghong Shanghai Co., China). Subsequently, the dried precipitate was analyzed by Fourier Transform Infrared Spectroscopy (FTIR) for NACP identification. The NACP were mixed with an adhesive Clearfil S3Bond (Kuraray Co., Japan) at NACP/(NACP+Clearfil S3Bond) mass percentages of0%,5%,10%, and20%. The pH values of the four adhesives were measured with short-range pH indicator strips (0-7, Lohand Biological Co., China). The dentin surfaces were applied with the adhesives for20s, thoroughly air-dried for5s and light-cured for10s, respectively. Subsequently, two2-mm increments of composite resin (Clearfil AP-X, Kuraray Co., Japan) were placed on the treated dentin, and light-cured for20s for each increment. After water storage at37℃for24h, the specimens were cut into micro-beams about0.8×O.8×8mm with the low-speed saw under running water. The dentin micro-tensile strength was performed with a Micro Tensile Tester (Bisco, USA) at a crosshead speed of1mm/min until fracture. Another41-mm thick dentin pieces were prepared from one molar and treated with the adhesives as the same as above-mentioned, thoroughly water-sprayed, dried with a series of alcohol solutions and critical point dried (Hitachi HCP-2, Japan), before they were gold-sputtered and analyzed by an SEM (Scanning Electron Microscope)(Ultra55, Germany).[Results]The pH value was2.5for Clearfil S3Bond,3.0for the5%NACP-incorporated Clearfil S3Bond,3.5for the10%NACP-incorporated Clearfil S3Bond, and4.0for the20%NACP-incorporated Clearfil S3Bond. Incorporation of5%NACP into Clearfil S3Bond did not decrease the micro-tensile bond strength (p>0.05), while Incorporation of10%NACP into Clearfil S3Bond caused a bond strength reduction compared to the control (p<0.05). Incorporation of20%NACP into Clearfil S3Bond resulted in pre-testing failure of all specimens SEM finding revealed that application of Clearfil S3Bond resulted in partial exposure of dentinal tubules and partial dentin demineralization while dentin demineralization was reduced to some degrees with the increase of NACP-incorporated into the adhesives. [Conclusion]Direct incorporation5%NACP into Clearfil S3Bond did not influence the dentin bond strength, while direct incorporation of more than10%NACP into Clearfil S3Bond would significantly decrease the dentin bond strength. Incorporation of NACP into Clearfil S3Bond reduced the demineralization of dentin surfaces with the mass increase of NACP.