Influence of Variation of pH of Chlorhexidine Mouth Rinses on Oral Retention and Plaque-Inhibiting Effect

Two clinical trials have been performed. In the first series the oral retention of chlorhexidine after mouth rinses of various pH values was determined, employing 14C-ring-labelled chlorhexidine for quantitation. The amount of chlorhexidine retained in the mouth was found to be considerably less when the mouth rinses were adjusted to low pH values (1.5 and 3.0) than when the pH was neutral or alkaline (6.4 and 9.0). In another series the plaque formation during a 3-day period without oral hygiene was estimated, employing chlorhexidine mouth rinses of various pH values. The plaque-inhibiting capacity of chlorhexidine was almost eliminated by lowering the pH of the mouth rinses to 1.5 or 3.0. Bacteriologic in vitro tests, employing a cariogenic streptococcus as the target bacteria, failed to demonstrate differences between the bactericidal effect of the drug at low and high pH. The findings that both the plaque-inhibiting property of chlorhexidine and the retention of the drug in the oral cavity were pH-dependent support the hypothesis that the drug’s clinical effect is related to its retention in the mouth.