The amounts of fluorine and tin taken up from the fluoride solution and/or toothpaste by the intact blocks of enamel were determined by radioactivity measurements, and their protective effects against acid attack were determined in vitro.
¹⁸F-labelled sodium fluoride (Na¹⁸F) and ¹¹³Sn-labelled stannous pyrophosphate (¹¹³Sn₂P₂O₇) were used. The composition of fluoride solution and toothpaste were as follows: - (a): 0.2% NaF soln. (pH 7), (b): 0.2% NaF-0.1M·H₃PO₄ soln. (pH 4.2, 3.5 and 3.0), (c): toothpaste form of (b) (pH 4.2), (d) 0.2% NaF-0.1M·H₃PO₄-1% Sn₂P₂O₇ soln. (pH 4.2). The paste form in (c) and (e) contained IMP (Insoluble sodium metaphosphate) as abrasive.
The uptake of fluorine was highly increased with lowering the pH of the solution of 0.2% NaF-0.1M·H₃PO₄. The fluorine uptake was evidently higher in case of 0.2% NaF-0.1M·H₃PO₄ soln than the case of 0.2% NaF-0.1M·1-H₃PO₄-1% Sn₂P₂O₇ soln., but the protective effect against acid attack in the latter case was superior than the former. When the enamel surface was treated with the aged solution or toothpaste containing Sn₂P₂O₇, the tin uptake was decreased as compared with the fresh one. The fluorine and tin uptake on the enamel surface from the toothpaste were less than from the solution of the same composition. The repetition of the treatment to enamel increased the uptake amount so far as tested, i. e. five consecutive applications.

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