Objective    To compare the inhibitory effect of fluoride-releasing resin sealant and glass ionomer sealant on enamel demineralization in vitro.     Methods    Thirty noncarious human third molars extracted were randomly divided into 3 groups with 10 in each.Cavity was placed on buccal surfaces of the molars

then filled with fluoride-releasing resin sealant (Clinpro

TM

sealant)

glass ionomer sealant (Fuji Ⅸ GP) or non-fluoride-releasing resin sealant (Co

ncise).After thermocycling for 300 cycles

the surface microhardness of sound enamel 1 mm away from sealant-filled cavities in each group was measured. Then after the treated molars were placed in an artificial demineralizing solution for a week

their surface microhardness was detected again.     Results    The mean reduction of surface microhardness was (87.30±23.84) HV for Clinpro

TM

sealant group

(76.90±27.75) HV for Fuji Ⅸ GP group and (147.67±46.42) HV for Concise group. There was a significant difference (P0.01) between the fluoride-releasing materials and the non-fluoride-releasing material

but no significant difference between Clinpro

TM

sealant group and Fuji Ⅸ GP group (P0.05).     Conclusion    Both the fluoride-releasing resin sealant and glass ionomer sealant can effectively reduce the amount of enamel demineralization adjacent to the materials. Fluoride ion released from the sealants protects the adjacent enamel against in vitro demineralization to some extent.