It replaces hydroxide ions between phosphates in the calcium hydroxyapatite crystal structure of the enamel. This reduces the loss of calcium due to the mild s

It replaces hydroxide ions between phosphates in the calcium hydroxyapatite crystal structure of the enamel. This reduces the loss of calcium due to the mild solubility of the mineral and neutralization reaction of the hydroxide with acids. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7339990/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7339990/