In caries, after the initial lesion of enamel by an external agent—indicated by the brown spot—there follows dissolution of mineral components in the corresponding sector of dentin. The brown spots on interstitial surfaces of teeth, at cavities, seem to be produced by solvent action of phosphoric acid from the cavities. Caries begins at predilectionous points on teeth, where food particles can remain. Aqueous extracts of bread respond to tests for phosphoric acid, which can dissolve crystals of hydroxylapatite in enamel.
Aqueous extracts of deeper layers of carious dentin are of ten acid (bromcresolpurple), but tests for lactic acid or calcium lactate in these extracts have been negative—acidity was due to phosphoric acid. These facts demonstrate that in carious dentin, hydroxylapatite is resolved into its components. Since the qualitative test for lactic acid is not specific, is also given by other substances, and the intensity of the test does not increase in a fermenting saliva-sugar mixture, lactic acid does not appear to be a factor in the progress of caries.
Pulverized dentin contains fluorine, magnesium and phosphoric acid in hydro‑soluble forms. In aqueous extract of Aspergillus oryme containing phosphatase, apatite of dentin is hydrolyzed at pH 7 into phosphoric acid and soluble calcium salt. Phosphatase may be transported in the circulation to dental pulp, which may then contain phosphatase. Since soluble fluorine salts inhibit the action of phosphatase and magnesium salts favor it, these two kinds of substance are probably in equilibrium in normal dentin. In carious or decalcifying processes, the action of magnesium probably predominates. The optimal p1–1 for the action of phosphatase is low, whereas the pH values that follow are high : normal pulp, 7.44; pulp of carious teeth, 7.34-7.14; pulp in pulpitis, 5.76, 6.64, 6.51. Normal and also pathologic pulps have high buffer powers. It would be desirable to determine (and compare) the quantities of soluble fluorine and magnesium in caries-resistant and in non-resistant teeth, and in bone, where the same biochemic conditions prevail ; also, the influence of nutrition on the equilibrium of soluble fluorine and magnesium in the dental hard-tissues, and the probable relation to resistance to caries.
References: Paradentium, 1936, 1937; Rev. Ital. Stour., 1938.