Abstract： Objective To evaluate casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) and several fluoride products in inhibiting enamel demineralization.Methods Seventy healthy premolars extracted before orthodontic treatment were divided into seven groups (A: CPP-ACP; B:CPP-ACP + fluoride mouth rinses; C:fluoride mouth rinses; D:fluoride glass ionomer protection; E:fluoride resin binder; F:fluoride varnish; G:control group).There were ten samples in each group. The teeth were dipped into an artificial caries solution ten minutes at a time,then applied separately with CPP-ACP,CPP-ACP + fluoride mouth rinses,fluoride mouth rinses,fluoride glass ionomer protection,fluoride resin binder and fluoride varnish on labial enamel.The samples were dipped into an artificial saliva solution ( 37 ℃ ).Then all samples were examined with atomic force microscope ( AFM ) at the end of first,second and third monthes.Results At the end of the first month,surface roughness in group D [ ( 114 ±1 ) nm] was significantly lower than that in group G[ ( 172 ±9) nm].At the end of the second month and the third month,significant difference was found in surface roughness between group G and the rest of groups (P ＜ 0.05 ) ; between group B and the rest of groups ; and between group C and groups ( D,E and F).Conclusions CPP-ACP and fluoride could both inhibit enamel demineralization in vitro. Solid fluoride (groups D,E and F) had better results than liquid fluoride (group C).