Abstract: Objective After the teeth were etched with 35% phosphoric acid,the first permanent molars were sealed by 3M flowable composite resin and common pit and fissure sealant so as to compare the retention rate and caries prevalence rate of dental caries by the two kinds of sealing material.Methods 240 permanent mandibular first molars with deep fissures and with no caries among 120 children of 7-9 years old were selected.The self export control method was used.According to the result of coin tossing,one side was chosen as the phosphoric acid +3M flowable resin group,and the other side the phosphoric acid etching +3M pit and fissure sealant group.After 3 months,6 months,12 months,and 24 months,pit and fissure sealant retention and caries rates were respectively examined.Results In the 3rd and 6th months,pit and fissure sealant retention,and caries decrease rate between two groups were different with no statistical significance （P>0.05）.In the 12th and 24th months,retention and caries decrease rates in the flowable composite resin group were higher than those in the pit and fissure sealant group,while caries incidence rate was lower than that in the pit and fissure sealant group.The differences were statistically significant （P<0.05）.Conclusions The clinical effect of the phosphoric acid etching combined with flowable composite resin is better than that of phosphoric acid etching combined with pit and fissure sealant.The former method can increase retention rate of sealing materials,thus lowering prevalence rate of dental caries.

Key words: phosphoric acid etching, flowable composite resin, pit and fissure sealant, retention rate, caries prevalence rate