Surface free energy, interaction, and adsorption of calcium and phosphate to enamel treated with trimetaphosphate and glycerophosphate

Abstract

This study aimed to evaluate the surface ( s) and interaction ( Giwi) free energy and calcium (Ca2+) and phosphate (PO43-) adsorption to dental enamel treated with sodium trimetaphosphate (TMP) or calcium glycerophosphate (CaGP) that had or had not been exposed to CaPO4-containing solutions. Bovine enamel blocks (n = 192; 24 blocks/group) were treated (2 mL/block; 2 min) with TMP (0%, 1%, 3%, and 9%) and CaGP (0, 0.25, 0.5, and 1%), or exposed to a CaPO4-containing solution. The adsorption of these compounds by enamel was assessed before and after treatment. The s and Giwi and their apolar ( sLW and GiwiLW) and polar ( sAB and GiwiAB) components, and acid-base interactions ( s+/ s.) were determined by the contact angles. The data were subjected to ANOVA, followed by the Student-Newman-Keuls test (p < 0.05). The adsorption of TMP was dose-dependent (p < 0.001), and it reduced s and sAB and increased GiwiAB ( Giwi >0) and s. when compared with the group without TMP (p < 0.001). The immersion in CaPO4-containing solution increased s and sAB and reduced GiwiAB ( Giwi >0) and s. (p < 0.001). There was a correlation between the adsorption of TMP and Ca2+ (r = 0.916; p < 0.001) and PO43- (r = 0.899; p < 0.001). The adsorption of CaGP on the enamel was dose-dependent (p < 0.001), reducing s, GiwiAB ( Giwi < 0), sLW, and s. when compared to the group without CaGP (p < 0.001). When exposed to the CaPO4-containing solution, there was an increase in GiwiAB ( Giwi >0), sLW and s., and a decrease in sAB (p < 0.001) without adsorption of Ca2+ by enamel. It may be concluded that TMP and CaGP were adsorbed onto the enamel, producing hydrophilic and hydrophobic surfaces, respectively. TMP produces electron donor sites that induce Ca2+ adsorption, while CaGP releases Ca2+ into the medium.