Strontium and enamel hydroxyapatite stability: Exploring strontium potential as a food supplement

• Hydroxyapatite (HAP) is less soluble than strontium-substituted apatite (SrHAP) • SrHAP and HAP dissolution are exothermic and endothermic, respectively • Deprotonation of phosphoric acid increased its calcium/strontium binding ability • Sr protects against Ca loss from enamel for acidic condition via ion exchange • Findings suggest Sr supplements and Sr enriched foods could improve dental health Strontium in food and drinking water may positively affect skeletal health, but the mechanisms behind such protection remain unclear, limiting the broader application of strontium supplements. This study explored strontium interaction with hydroxyapatite (HAP), the main tooth and bone component, to clarify such mechanisms. Strontium was found to influence HAP characteristics through ion exchange with calcium, forming the hydroxyapatite analog SrHAP. Despite SrHAP exhibits higher solubility across varying conditions than HAP with ∆ H 0 diss = −4.0 kJ∙mol −1 , ∆ S 0 diss = −78 J∙mol −1 ∙K −1 for SrHAP versus ∆ H 0 diss = 2.6 kJ∙mol −1 , ∆ S 0 diss = −73 J∙mol −1 ∙K −1 for HAP dissolution, strontium was found to protect against calcium loss from enamel under acidic conditions, explained by a decrease in the rate for calcium release by the presence of strontium. The positive effect of strontium on enamel may be attributed to effects on the kinetics of dissolution rather than to effects on equilibration solubility. The negative ∆ S 0 diss for HAP and SrHAP agrees with an ordering of water structure upon dissolution. The findings supported by Density Functional Theory calculations highlight the significance of strontium as a trace element in human nutrition for dental health, suggesting that strontium supplements and strontium-fortified foods could be valuable for improving public dental health, particularly in regions with insufficient strontium intake.