Effect of 40% chlorhexidine varnish on mutans streptococci counts in pits and fissures of permanent first molars

Abstract Objectives This study aimed to test the following hypotheses: (1) a carry-over effect of EC40 does not occur in a split-mouth model, (2) two consecutive applications of EC40 varnish with an interval of 3 months per year has a better inhibiting effect on mutans streptococci in pit and fissure plaque of permanent first molars of 6–7-year olds than a repeated application at each 6 months and (3) EC40 exerts an inhibiting effect on mutans streptococci for at least a 6-month duration. Methods Using a split-mouth design, test molars received EC40 on fissures and pits and control molars remained without treatment. One group of test molars received EC40 at baseline, 6, 12 and 18 months and another group at baseline, 3, 12 and 15 months. Plaque samples were taken from pits and fissures of test and control molars at baseline, 6, 9, 12 and 24 months. A mixed ANOVA model was used to analyze the data. Results The first hypothesis was accepted, the second rejected and the third accepted. Conclusions Twice a year EC40 application on pits and fissures of permanent first molars of 6–7-year-old children can significantly reduce mutans streptococci numbers for a 6-month period, but the reductions were small.