Stability of fluoride levels in surface layer of normal enamel during a 21-month fluoride mouthrinsing program

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Abstract
A 21 mo. trial of the caries-preventive effect of a 0.2% NaF mouthrinse included monitoring changes in the concentration of F in normal enamel. Subsamples of 25 children were randomly selected from groups receiving normal dental treatment (Control group); additional fortnightly professional prophylaxes (Test group) or prophylaxes plus fortnightly 2-min fluoride rinses (Test + F group). At the start of the trial the sound labial surface of tooth 24 (occasionally 23 or 22) was etched with 2 N HCL and the etchant analyzed for F, Ca and phosphate. The contralateral tooth was sampled at the end of the trial. The caries increments (DFS [diseased filled surface]) for the 3 groups over 21 mo. were Control, 2.88; Test, 2.51 and Test + F, 1.77, the last being significantly less than the others (P < 0.05). The average sound enamel surface F concentrations were similar for the 3 groups at the start and the end of the trial. F parameter calculations showed that all differences were nonsignificant. Thus this factor could not explain the reduced caries increment due to F mouthrinsing. F biopsies for the purpose of predicting likely clinical effectiveness of neutral 0.2% NaF mouthrinsing will find little application in public healthy dentistry.