Abstract
1) Comparison of demineralization patterns by different pH of acidic gelatin (Fig. 1): The buccal and lingual enamel surfaces of 291 young premolars were painted with varnish leaving a ‘window’. They were placed in acidic gelatin (Silverstone) at pH 3.5, 4.5, and 5.5, for 11-415 days. The piano-parallel ground sections were microradiographed. pH 3.5 produces very intense and deep demineralization lesions with thin remineralized surface layer (Figs. 2 and 3). pH 4.5 and 5.5 produce lesions which can be divided into 5 layers from surface to bottom, (a) highly remineralized narrow surface layer, (b) demineralized layer, (c) highly remineralized narrow layer, (d) narrow demineralized layer, (e) narrow hypermineralized layer (Figs. 4-9). Radiolucency and depth of lesions are pH 3.5>4.5>5.5.
2) Effect of changing pH during demineralization (Fig. 1): pH 3.5→4.5, pH 3.5→5.5, pH 4.5→5.5 The upper layer of lesions shows characteristic lower pH type demineralization, however, lower layer shows higher pH type changes (b-e layers)(Figs. 11-15). pH 4.5→3.5, pH 5.5→3.5 pH 4.5 or 5.5 type changes (a-d layers) are observed at the upper level of lesions and pH 3.5 type intense demineralization is seen at the lower level (Figs. 16-18). pH 3.5→4.5→3.5 At the bottom of deep pH 3.5 type lesion, narrow pH 4.5 type changes (b-d layers) with narrow intensely demineralized deeper layer can be observed (Figs. 19 and 20). pH 4.5→3.5→4.5 pH 3.5 type lesion is sandwiched the bylayers showing pH 4.5 type changes (Fig. 21).
The results of present study indicate that lesions produced by preceding demineralization by higher pH shows very high acid resistance for subsequent demineralization by lower pH and that the influence of changing pH appears mainly at the bottom of lesions rather than at the upper level.
