Effect of an antibacterial varnish on lactic acid production in plaque adjacent to fixed orthodontic appliances

The effect of an antibacterial varnish on lactic acid concentration in suspensions of early supragingival plaque collected adjacent to fixed orthodontic brackets was evaluated in 25 adolescents using a double-blind split-mouth design with a placebo varnish control. The test varnish contained 1% chlorhexidine and 1% thymol as active ingredients. Both varnishes were applied on two occasions within 3 days and plaque was subsequently collected at 3, 7 and 30 days after the first treatment. The samples were evaluated for total viable counts (TVC) and the proportion of mutans streptococci. Acid fermentation in suspensions was induced by glucose and L(+)-lactic acid concentrations were determined enzymatically after a 30-min incubation period. The test varnish did not affect TVC but reduced the proportion of mutans streptococci significantly at the 7-day follow-up (P<0.05). The concentration of lactic acid was reduced by approximately 20% on the 3- and 7-day follow-ups (P<0.05). The results suggest that the chlorhexidine/thymol-containing varnish may to some extent reduce the viability and metabolic activity of susceptible oral bacteria in suspensions of early supragingival plaque.