Powdered charcoal placed under the tongue spreads through the oral cavity within a few minutes6, but regional differences exist in the deposition, distribution and clearance of drugs which are dissolved in saliva7. This is of great importance if local treatment of the entire mucosa is required or the drug is absorbed preferentially from certain sites. Studying the pattern of fluoride concentration in the mouth arising from a slowly dissolving fluoride tablet revealed that when the tablet was placed in the lower mandibular sulcus, fluoride concentrations increased markedly in the region of the tablet, but there was no appreciable increase in salivary levels8. Relatively little had migrated to the opposite side of the mouth suggesting that the lower mandibular sulci are quite isolated from the remainder of the mouth. However, when the tablet was placed in the upper sulcus the fluoride migrated some distance from the site of administration. Glucose behaves in a similar fashion9. The pattern of fluoride distribution and the fluoride concentration are fairly consistent for any one subject, but a 20-fold intrasubject variation was observed. It is believed that the site specific differences are due to saliva movement and dilution of the test substance rather than the nature of the substance. The thickness of the salivary film will vary from place to place depending upon the proximity to the ducts of the major and minor salivary glands, separation of mucosal layers during speaking and mouth breathing.
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