PLAQUE COMPOSITION, FLUORIDE TOLERANCE AND ACID PRODUCTION OF MUTANS STREPTOCOCCI BEFORE AND AFTER THE SUSPENSION OF THE USE OF FLUORIDE TOOTHPASTES

Although fluoride toothpastes are widely used for caries prevention, l ittle is known about the impact of fluoride dentifrices on plaque comp osition. Also the issue of adaptation of mutans streptococci to grow i n vivo in a fluoride environment has received little attention. Such a n adaptation may be of interest as it has been suggested that adapted mutans streptococci may show reduced glycolytic activity thereby being less cariogenic. In the present experiments the impact of the suspens ion of the use of fluoride toothpastes on plaque composition, fluoride tolerance and acid production of mutans streptococci was studied. Poo led plaque samples from the lingual surfaces of the lower incisors wer e collected from individuals (n = 13) just before and 7 weeks after th ey had replaced their fluoride toothpastes (0.1-0.15% F) with a non-fl uoride one. The samples were analysed for fluoride and the numbers and proportions of streptococci, Streptococcus mutans, Streptococcus sobr inus, Actinomyces species, and lactobacilli, respectively. The fluorid e tolerance of the mutans streptococci was estimated by culture of the plaque samples on TYCSB agar supplemented with of 0, 1, 2, 3, 4, and 5 mmol/l fluoride (NaF) at pH 7.2. From each plaque sample six S. muta ns strains were isolated for the measurement of the rate of acid produ ction (Vap) at pH 7 in the presence of 0, 5, and 10 mmol/l F. The over night final pH was measured in cultures of the S, mutans strains with excess of glucose and 0, 5, and 10 mmol/l F. The results showed that t he removal of the fluoride pressure from plaque did not affect the num bers or proportions of the various species and genera of bacteria. The fluoride tolerance of the mutans streptococci, and the Vap or the ove rnight final pH of the isolated strains had not changed. These results suggest that the use of fluoride toothpaste had not affected plaque c omposition, nor fluoride tolerance or acidogenicity of mutans streptoc occi. Probably the amount of fluoride delivered by fluoride dentifrice s to dental plaque is too low to induce such adaptations.