Effect of Chlorhexidine Varnish on Actinomyces naeslundii Genospecies in Plaque from Dental Fissures

This study describes the effects of varnish containing 40% chlorhexidine diacetate on Actinomyces naeslundii populations in plaque from human molar fissures. In each of 15 subjects two dental fissures with high levels of mutans streptococci were selected. The experimental treatment consisted of the single application of a small amount of chlorhexidine varnish onto the selected fissures. The varnish was removed 15 min after application. One month after varnish application a significant increase was observed in A. naeslundii counts while the number of mutans streptococci had decreased significantly compared with preexperimental levels. From 85 randomly selected Actinomyces isolates taken from blood agar plates before varnish application, 44% belonged to A. naeslundii genospecies 1 and 56% to A. naeslundii genospecies 2. From 106 isolates taken 1 month after chlorhexidine varnish application, 42% belonged to A. naeslundii genospecies 1 and 58% to A. naeslundii genospecies 2. At baseline 28% of A. naeslundii genospecies 1 strains were catalase-positive, but 1 month after varnish application 4% of the strains were catalase-positive (p < 0.05). It is concluded that chlorhexidine varnish application caused an increase of A. naeslundii in dental plaque, but induced no significant changes in the distribution of the two A. naeslundii genospecies.