Acid neutralizing and remineralizing orthodontic adhesive containing hydrated calcium silicate

Objectives: The objective of this study was to evaluate an orthodontic adhesive containing hydrated calcium silicate (hCS) in terms of its bond strength with the enamel surface and its acid-neutralization and apatite-forming abilities. Methods: The experimental orthodontic adhesives were composed of 30 wt.% resin matrix and 70 wt.% filler, which itself was a mixture of silanized glass filler and hCS in weight ratios of 100% glass filler (hCS 0), 17.5% hCS (hCS 17.5), 35% hCS (hCS 35.0), and 52.5% hCS (hCS 52.5). The degree of conversion (DC) and shear bond strength (SBS) of bovine enamel surfaces were tested. pH measurements were performed immediately upon submersion of the specimens in a lactic acid solution. The surface precipitates that formed on specimens immersed in phosphate-buffered saline (PBS) were analyzed by scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) and Raman spectroscopy after 15, 30, and 90 days. Results: The experimental groups exhibited no significant differences in DC and had clinically acceptable SBS values. The hCS-containing groups showed increasing pH values as more hCS was added. hCS 52.5 produced Ca- and P-containing surface precipitates after PBS immersion, and hydroxyapatite deposition was detected after 15, 30, and 90 days. Conclusions: These results suggest that orthodontic adhesives containing hCS are effective for acid neutralization. Furthermore, hCS has an apatite-forming ability for enamel remineralization. Clinical significance: The novel orthodontic adhesive containing hCS exhibits a potential clinical benefit against demineralization and enhanced remineralization of the enamel surface around or beneath the orthodontic brackets.