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 (γ_s) and interaction (ΔG_iwi) 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. γ_s and ΔG_iwi and their apolar (γ_s^LW and ΔG_iwi^LW) and polar (γ_s^AB and ΔG_iwi^AB) components and acid-base interactions (γ_s⁺/γ_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 γ_s and γ_s^AB and increased ΔG_iwi^AB (ΔG_iwi > 0) and γ_s⁻ when compared with the group without TMP (p < 0.001). The immersion in CaPO₄-containing solution increased γ_s and γ_s^AB and reduced ΔG_iwi^AB (ΔG_iwi > 0) and γ_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 γ_s, ΔG_iwi^AB (ΔG_iwi < 0), γ_s^LW, and γ_s⁻ when compared to the group without CaGP (p < 0.001). When exposed to the CaPO₄-containing solution, there was an increase in ΔG_iwi^AB (ΔG_iwi > 0), γ_s^LW, and γ_s⁻ and a decrease in γ_s^AB (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.