THE MINERAL DISTRIBUTIONS AND THEIR PROMOTION OF FLUORIDE RETENTION IN TH EPLAQUE in vivo EXPOSED TO A MINERAL ENRICHING MOUTHRINSE

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The aim of this study was to clarify the mineral (Ca and P) distributions and their promotion of fluoride retention in the plaque in vivo exposed to a mineral enriching mouthrinse and then to estimate factors, which have an influence on the promotion of fluoride retention in the plaque. 11 subjects consenting (20-31 years), had sampling devices containing plaque receptacles (2mm in diameter) to buccal surfaces of upper molars. After plaque had formed over 3 days, subjects were instructed to rinse with one of five rinsing solutions three times a day on 4 consecutive days. Each solution was made by excluding some ingredients out of a mineral enriching mouthrinse (urea 500mM, CaCl_2 20mM, Na_2HPO_4 12mM, Na_2PO_3F(MFP) 5mM, pH_5). Plaque collections were repeated at intervals using different solutions. Plaque samples exposed to a placebo solution with no ingredients served as control. 24 hours after the last rinsing, the sample was freeze-dried and then embedded in a methacrylate mixture. A series of plaque sections parallel with the tooth surface (4 at 6mum then 2 at 3mum) were repeatedly cut from the outer plaque surface towards the enamel, using an ultramicrotome. The thinner sections were used for area measurement to evaluate sample volume. The thicker sections were collected into several congruous specimens. Fluorides and mineral distributions in plaque were analyzed by a method reported by Kato et al. Archs oral Biol. 42 : 521-525, 1997. Fluoride retention increased except in the deeper plaque layers. Fluoride concentrations (0.5-3.6nmol/mm^3) significantly rose in the samples exposed to solutions containing both MEP and minerals, this tendency being greater in the full mouthrinse. Both calcium and phosphorus levels significantly increased only in the plaque exposed to the mineral enriching mouthrinse. However, ANOVA indicated a difference between subjects would be a stronger factor than the type of mouthrinse for fluoride retention in plaque.