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Acid-etched surfaces of enamel were given topical applications of neutral NaF, acid NaF, APF, and SnF 2 solutions (about 1% F in each). After a four hour delay following topical application, the surfaces were mineralized in a calcium phosphate solution and then subjected to acid dissolution. Fluoride released from the enamel surfaces was measured during mineralization and subsequent acid dissolution. Results of both processes, and the fluoride released during both processes, indicate that a neutral NaF gave the best results.
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Jeansonne et al. (1972) studied this question.
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