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SEM and microprobe analysis of enamel, pre-treated with polyvalent metals followed by APF application, showed the presence of surface coatings, but very little penetration of fluoride or metal into the subsurface enamel. However, in vitro caries-like lesion formation in the pre-treated enamel was retarded to a greater extent than in APF-only treated enamel.
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Clarkson et al. (1981) studied this question.
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