Objective To investigate the demineralizing effect of Coca Cola versus Iced Black Tea on permanent tooth enamel in vitro

and also compare the effects of complex of casein phosphopeptide and amorphous calcium phosphate（CPP-ACP）versus Duraphat in remineralizing the demineralized tooth enamel in vitro.Methods A total of 120 permanent teeth removed for orthodontic reasons at Stomatological Hospital of Chongqing Medical University from June to September

2015 were randomly divided into two groups to receive acid etching with Coca Cola or Iced Black Tea

60 samples in each group.After 5days

40 samples were randomly selected from each group and then randomly allocated into two subgroups to receive remineralizing treatment with CPP-ACP or Duraphat

20 samples in each subgroup.All samples received another 5-day acid etching with their respective drinks（Coca Cola or Iced Black Tea）

including the remaining 20 control samples in each group.For each group

the calcium ion concentration in Coca Cola or Iced Black Tea was determined before and after the initial acid etching as well as 5days after remineralization.Results The calcium concentration was higher in Coca Cola（0.913±0.142）mmol/L than that in Iced Black Tea（0.212±0.011）mmol/L.After acid etching

the calcium level was significantly increased in both groups（P<0.05）.After remineralization

in Coca Cola group or Iced Black Tea group

the calcium levels of both CPP-ACP and Duraphat subgroups were significantly lower compared with their respective controls（P<0.05）;the calcium level in CPP-ACP subgroup was significantly lower than that in Duraphat subgroup（P<0.05）.Conclusion Both CPP-ACP and Duraphat can remineralize the demineralized tooth enamel

but CPP-ACP seems to have a stronger remineralizing effect than Duraphat.