Transient reduction of Streptococcus mutans interdentally by chlorhexidine gel

Chlorhexidine gel was applied interproximally with the intent to reduce Streptococcus mutans at these sites. Bacterial samples were obtained using toothpicks, which were inserted in each interproximal space and then immediately pressed against agar plates, selective for S. mutans. Duplicate bacterial samples of non-treated subjects showed that this method gave reproducible results. Using a split mouth technique, 10 subjects were exposed to short term chlorhexidine exposures of varied intensity. At the baseline sampling about 90% of the sites showed growth of S. mutans. One week after the chlorhexidine applications about 55% were infected. After 40 d S. mutans were back to about baseline levels except for the most intensively treated interproximals, which showed 75% infected sites. Thus, at many sites the reduction of S. mutans was only transient. Four subjects with more than 1 million S. mutans per ml saliva participated in a study where salivary and interproximal levels of S. mutans were compared after a rinsing period with chlorhexidine lasting for 2 weeks. The effect of the rinses varied individually, but it was noted that several interproximal spaces could be infected even if the saliva numbers did not reach detectable levels of S. mutans.