Effect of Different Acids on Character of Demineralization of Enamel Surfaces

¹ Eastman Dental Dispensary, Rochester, New York

A study was made to assess the effect of the addition of certain acid anions to background buffers of acetic and lactic acids on the demineralization of intact enamel surfaces at pH 4.5 and 5.5. The acid anions tested were categorized, on the basis of previous results with powdered enamel, as being "accelerators" or "inhibitors" of the decalcifying action of the background buffers. The lesions produced were subjected to microradiographic and polarized-light analysis. It was found that different patterns of enamel demineralization were produced, depending on the type of acid added.

Type A.—"White-spot" subsurfaced demineralization with a minimum of surface demineralization characteristic of slow rates of demineralization, as with "inhibiting" acids.

Type B.—Both surface and subsurface demineralization of about equal intensity, resulting in an in-depth band of demineralization characteristic of a moderate rate of demineralization or as an advanced state of the Type A lesion. This type of lesion was obtained consistently with citric acid addition only at pH 5.5.

Type C.—Cavitation resulting from surface demineralization, along with little or no concomitant in-depth subsurface demineralization. This lesion was characteristic of a fast rate of demineralization, as with "accelerating," strong, calcium-complexing anions and by agitation of the buffer solutions.

Agitation of the acid buffer solutions transcended the influence of all other factors in determining the type of lesion produced, and this was evidenced from the findings that in agitated systems only Type C or erosion-like lesions were produced. With non-agitated systems, the chemical composition of the demineralizing media was more influential than pH in determining the type of lesion produced. This was indicated by the finding that the addition of certain acids to the background buffers resulted in different patterns of demineralization than those obtained with the latter at the same pH.