The chemical dissolution of dental tissue can be caused by acid that is extrinsic, coming from items that are ingested, such as acidic food and beverages; or intrinsic, coming from hydrochloric acid produced by the parietal cells in the stomach. Hydrochloric acid can have a pH as low as 1, so its destructive capabilities are especially severe, and significantly more so than dietary acid.16
However, regardless of the origin of the acid, the effect is the same: a low pH environment in the oral cavity. The initial reaction is that enamel first undergoes softening, the loss of mineral from a layer extending a few micrometers below the surface. As softening progresses over time, dissolution can completely remove portions of enamel, or the whole enamel layer, exposing the dentin underneath. When dentin is exposed to acid, first there is dissolution at the junction of the peritubular and intertubular dentin. Next, there is loss of the peritubular dentin and widening of the tubule lumina. Finally, there is formation of a demineralized collagenous mix that provides some protection of the underlying tissue. However, this layer is also vulnerable to damage and can ultimately be eroded away as well.17
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