Apatite-like calcium phosphate deposition and physicochemical properties of an aspartic acid–functionalized hydraulic cement

Objectives This study evaluated the effects of aspartic acid modification on the physicochemical properties and phosphate-associated surface response of a hydraulic calcium silicate cement. Materials and methods White mineral trioxide aggregate (MTA) was mixed using 0%, 25%, 50%, 75%, or 100% (v/v) of a 4 g/L aspartic acid stock solution. Final setting time, solubility, pH, and Ca²⁺ concentration in the immersion solution were evaluated after seven days in deionized water ( n = 10). Surface roughness, morphology, elemental composition, and phosphate- and carbonate-associated spectral features were assessed after 30 days of storage in deionized water or phosphate-buffered saline (PBS). The Ap/C spectral ratio was calculated from the integrated ATR-FTIR band areas. Data were analyzed using one- or two-way ANOVA followed by Tukey’s test (α = 0.05). Results The 25% formulation showed the shortest setting time, whereas the 100% formulation showed the longest ( p < 0.001). All aspartic acid-containing formulations exhibited greater solubility and lower Ca²⁺ concentrations than the control ( p < 0.05), and the 50%, 75%, and 100% formulations exceeded the recommended solubility limit. The 25% formulation had the lowest pH, whereas the control, 75%, and 100% formulations maintained similar alkaline values. Surface roughness was lowest for the 25% formulation and highest for the 100% formulation, with no significant effect of storage medium. EDS detected negligible surface phosphorus after storage in deionized water but marked phosphorus content after PBS storage. Ap/C analysis showed significant main effects of cement formulation and storage medium, without a significant interaction. The 25%, 50%, and 75% formulations exhibited higher marginal Ap/C ratios than the 0% and 100% formulations. Conclusions Aspartic acid produced non-linear and formulation-dependent changes in the evaluated properties. Higher Ap/C ratios reflected differences in relative spectral composition but did not confirm increased apatite formation or a crystalline apatite phase. Ca–P-rich surface deposition depended on phosphate supplied by the storage medium, and no formulation improved all evaluated outcomes.