A METHOD FOR DETERMINING THE DISTRIBUTION OF FLUORIDE IN HUMAN DENTAL PLAQUE in vivo AND THE EFFECT OF SOME FACTORS ON THE FLUORIDE DISTRIBUTION

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A method for the determination of the fluoride and mineral profiles within dental plaque formed in vivo has been developed. Plaque samples were repeatedly collected using special devices from the same subject, before a single 900 ppm fluoride rinse and, 10min and 24h after the rinse, and also after immersed in an experimental solution containing 3% of urea and 100 ppm fluoride twice a day on 4 days. The samples were freeze-dried and then embedded in a methacrylate mixture and were sliced from the surface towards the enamel into 3 mum or 6 mum thick sections using an ultra microtome. The thicker sections were collected in several layred plaque samples for the chemical analysis, and the thinner sections were used for determination of plaque volume. Each plaque sample was placed in chloroform to extract the methacrylate. Fluoride, calcium and phosphorus were extracted from the sediment into an acid buffer solution (pH5.2). Fluoride was determined using a fluoride electrode, and concentrations of calcium and phosphorus were determined by sectroscopical and colorimetrical techniques respectively. Results were expressed per unit of plaque volume. The present method allowed examination of fluoride, calcium and phosphorus distribution in plaque along its entire thickness of plaque. Fluoride content significantly increased throughout the sample 10min after rinsing, indicating that fluoride had rapidly penetrated into the plaque. The elevated fluoride concentrations diminished almost to baseline levels within 24 h. A high significant correlation was found between fluoride and minerals in the plaque exposed to the fluoride solutions. Correlation between calcium and phosphorus was significantly higher in the urea treated plaque than the sample exposed fluoride without urea. It is conclued that this technique will be useful for evaluating the fluoride and mineral behavior in the plaque/enamel interface, and the anti-caries efficacy of the fluoride application.