pH and depth of gingival crevices in different areas of the mouths of fasting humans.

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Abstract
The pH and depth of gingival crevices in eighteen different regions of the human mouth were determined in 19 subjects who had not brushed their teeth for 3 days and had not eaten for at least 12 hours. The pH was measured with antimony micro‐electrodes and crevice depths were estimated simultaneously from markings along the side of the material insulating the electrodes. The crevice pH followed a similar intra‐oral pattern to that observed previously for supragingival plaque except that crevice readings averaged 0.64 pH units above corresponding plaque readings. When the crevice pH for each location was plotted against crevice depth, the pH increased up to a depth of approximately 0.7 mm and then decreased with increasing depth. A similar plot of the supragingival plaque pH (data from an earlier study) against crevice depth showed a direct linear relationship, not the rise and fall relationship observed for crevice pH. It was therefore postulated that the factors responsible for the variation in supragingival plaque pH are also responsible for the variation in crevice pH but, in the deeper crevices, fluid entering the crevices from underlying tissue favours the lowering of the crevice pH.