> Dental enamel consists primarily (almost 97 percent by weight) of a calcium phosphate mineral in the form of carbonated hydroxyapatite (CHA). CHA is insoluble in an alkaline medium. However, its solubility increases with a decrease in the oral pH. This effect was first noted as a result of direct contact of the tooth surface with acids from extrinsic sources such as beverages. Unlike dental caries, where the demineralization is caused by an acidic environment in GERD is due to the reflux of hydrochloric acid from the stomach (Figure 8.).