Effect of Phosphate on Enamel-Adhesion Forces of Calcium Silicate

Objectives: To investigate the effect of sodium phosphate (SP) salt on the adhesion forces of single calcium silicate (CS) microparticles on human tooth enamel.
Methods: The adhesion forces were directly measured using an atomic force microscope (AFM) with a liquid cell. A single CS microparticle was glued on a tipless cantilever to form a colloidal AFM probe. Three colloidal probes were made. A slice of polished human enamel was fixed on the bottom of the liquid cell and immersed in either deionized (DI) water or SP solution. The force-displacement curve between single CS microparticle and tooth enamel, under AFM contact mode, were recorded. For each probe, force curves were measured 6 times on each of randomly selected five sampling points on the enamel surface, with 30-second time interval. Scanning electron microscope (SEM) was applied to confirm the intactness of the modified cantilever before and after the force measurement on each sampling point.
Results: Mean (S.D.) adhesion forces calculated from force curves are shown in table.

For all three colloidal probes, the enamel-adhesion forces of single CS microparticles, with the size of approximately 4 mm, were significantly larger in SP solution than in DI water (t-test). These in vitro results indicate that sodium phosphate could facilitate the deposition of calcium silicate onto the enamel surface.
Conclusions: Conclusions: The adhesion between calcium silicate and enamel surface increased with the addition of sodium phosphate.