The long-term effects of daily rinsing with stannous fluoride or sodium fluoride on bacteria in dental plaque.

Microbial parameters were studied in the plaque of 88 subjects between the ages of 14 and 17 years who had rinsed daily with either 0.1% stannous fluoride or 0.05% sodium fluoride for 28 months. Plaque was collected from specific sites, dispersed, diluted, and cultured to estimate total numbers of plaque organisms and proportions of streptococci, Streptococcus mutans and Veillonella. While prior studies had indicated that rinsing with stannous fluoride would decrease numbers of S. mutans and increase numbers of Veillonella compared to those in subjects rinsing with sodium fluoride, no significant differences were observed in this study. In addition to its caries-preventive effects, stannous fluoride has been shown to reduce plaque formation. Inhibitory effects on plaque were first demonstrated in rats by K6nig (1959) and later confirmed by Shern et al. (Shern and Couet 1977; Shern et al, 1978). Short-term human studies have shown that stannous fluoride mouthrinses reduce plaque formation. ~ Of particular interest is the demonstration of a significant reduction in numbers of Streptococcus mutans in dental plaque, in view of the important role that this organism plays in the etiology of dental caries. Such an effect was demonstrated in a small group of subjects with high caries activity who rinsed twice daily with stannous fluoride for two years (Klock et al. 1985). In a similar group subjects in the same study who rinsed with sodium fluoride, there was no change in S. mutans levels in plaque. Veillonella are commonly found in plaque, constituting about one-third of total viable organisms (Mays and Johnson 1977), and have been found in higher numbers in children with low caries activity who consumed water containing excessive (i.e., 3-21 ppm) amounts fluoride (Kilian et al. 1979). ~ Andres et al. 1974; Svatun et al. 1977; Tinanoff et al. 1980; Leverett et al. 1981; Svanberg and Rolla 1982; Tinanoff et al. 1983. The present investigation was designed as a crosssectional study to compare the levels of S. mutans and Veillonella in plaque after long-term daily rinsing with stannous fluoride or sodium fluoride having similar fluoride concentrations. Material and Methods Subjects for this study were selected from a larger population of children who rinsed daily under supervision on school days with either a 0.05% aqueous NaF solution (226 ppm F) or a 0.1% aqueous SnF2 solution (242 ppm F). A total of 175 subjects in the NaF group and 176 subjects in the SnF2 group had maintained this regimen for 28 months. Details of this study have been reported earlier (Leverett et al. 1981, 1984). The subjects for whom data now are being reported were selected from these larger groups according to two criteria. 1. They had to have been "regular rinsers" as evidenced by records that they had actually rinsed under supervision on at least 75 % of all possible rinse days during the 28-month period. 2. They had at least one active carious lesion at the time of final examination. A total of 46 children in the SnF2 rinse group and 42 in the NaF group met these two criteria. Their ages ranged from 14 to 17 years at the time of the examination at the end of 28 months of rinsing. Plaque was collected from the buccal aspect of the proximal surfaces of the lower right molar and premolar teeth with sterile Jacquette ® scalers. The plaque samples were placed in cold reduced transport medium (Loesche et al. 1973), capped tightly, and kept at 10° C until delivery to the laboratory. On arrival, they were brought to 20 ml and dispersed by sonication (3 bursts of 10 sec duration each). Serial 10fold dilutions then were made with the transport medium and agar plates were spotted with 20 ~tl of each dilution by the method of Westergren and Krasse (1978). Blood agar, veillonella agar, mitis salivarius agar, and m. salivarius agar with bacitracin (MSAB 10 EFFECT OF SNF2 AND NAF ONPLAQUE BACTERIA: McHUGH ET AL. Gold et al. 1973) were used for enumeration of total viable flora, Veillonella, and S. mutans. The plates were incubated anaerobically for 48 hr at 37° C and colonies counted with a binocular microscope. Blood agar plates were incubated for an additional 24 hr before counting. As reported previously, Plaque Index, Gingival Index, Stain Index, and DMFS scores were recorded for each subject at baseline and after four, 16, and 28 months (Leverett et al. 1981, 1984, 1986).