Alteration in salivary and plaque S. mutans in adults brushing with 0.4% SnF2 gel once or twice a day.

Two clinical trials were performed to investigate the antibacterial effects of SnF2 and to explore the apparent selective reduction of salivary S. mutans. In the first clinical trial, subjects were followed through baseline periods interposed between periods of either once or twice daily brushing with 0.4% SnF2. At weekly intervals, salivary samples from each subject were quantitated for S. mutans and total colony-forming units. SnF2 reduced salivary S. mutans more than the total CFU, and twice daily brushing was found more effective than brushing once a day. The second trial sampled both plaque and saliva in the same subjects to investigate whether the selectivity of SnF2 against S. mutans was the result of a site-specific effect. Similar percentage reductions in S. mutans were found in both saliva and plaque, suggesting that the effect of SnF~ against S. mutans must be due to something other than SnF2 affecting primarily the bacteria on teeth. Caries reduction by fluoride traditionally has been ascribed to its physicochemical interaction with enamel. Recent research, however, also has been directed at the effect that different fluoride compounds have on bacterial growth and plaque formation. It appears that one fluoride compound, SnF2, has greater antimicrobial properties than other commonly used fluoride compounds. 1 The antimicrobial properties of SnF2 appear to affect S. mutans, the bacterium associated with dental caries, more than other nonpathogenic bacteria in the mouth. This "selective" reduction of S. mutans by SnF2 first was observed in a study of 22 rampant caries subjects who rinsed twice a day with either NaF or SnF2. Those subjects rinsing with SnF2 had significant reduction of salivary S. mutans, while salivary total colony-forming units (CFU) and salivary lactobacilli were not affected by the SnF 2 rinsing. 2 Subsequently, there have been at least 5 reports showing selective reduction of S. mutans by SnF 2 using various concentrations, frequency of use, and delivery systems. 3-7 Several theories have been proposed to explain the selectivity of SnF2 against S. mutans. One explanation is that SnF2 inhibits acid formation in plaque for several hours, and the increase in plaque pH may create an ecologic disadvantage for S. mutans.3 Another theory is that tooth surfaces disinfected with an antimicrobial agent such as SnF2 are recolonized more easily with S. sanquis because of its greater oral reservoir. 4 It also seems possible that the noted selective reduction of salivary S. mutans is an artifact of the sampling procedure. If an antimicrobial agent primarily affected bacteria adhering to teeth, then the number of tooth-associated bacteria shed to the saliva could appear to be selectively reduced compared to the rest of the salivary flora. This paper reports on 2 clinical trials, using similar methodologies, to examine a delivery system for SnF2 and to further explore the reported selective reduction of S. mutans by SnF2. The first clinical trial used a time series approach to explore the effects on bacterial reduction caused by varying the intervals of application of SnF2. As a result of the frequent recovery periods in this approach, the authors also were able to examine the data for possible carry-over effects of SnF2 past the treatment intervals, and for possible bacterial adapatations to SnF2. The second trial sampled both plaque and saliva in the same subjects to determine whether a reduction in the number of sites on the teeth that seed S. mutans into saliva causes the apparent salivary reduction of S. mutans by SnF 2. 180 $. MUTANS/BRUSHING WITH Snl:2: Tinanoff and Zameck Methods and Materials The subjects of this study consisted of 17 adults, 20-39 years old, having greater than 2 x 105 S. mutans/ ml saliva, selected from 27 employees of the University of Connecticut Health Center who were screened for sufficient salivary S. mutans levels. During the 22 weeks of the study, subjects were sampled weekly to monitor their total CFU and S. mutans levels, while they participated in a time series experiment.8 A time series experiment follows the same subjects through intervals of baseline periods interposed between a progression of experimental periods. This specific time series consisted of an initial 2week baseline period in which subjects gave weekly salivary samples, but no modification of the subject’s oral hygiene habits or dentifrice took place. After this initial baseline period, the subjects were asked to brush their teeth, once daily in the evening for 1 min with a 0.4% SnF2 gel a for the next 2 weeks (weeks 3-4). nonfluoride toothpaste b also was given to the subjects for their use ad libitum. Weeks 5, 6, and 7 consisted of a nontherapeutic period in which subjects used only the nonfluoridated toothpaste. On weeks 8-9, the use of the 0.4% SnF2, once a day, was repeated again followed by a 3-week nontherapeutic period. The same experimental approach was used to test twice daily brushing with SnF2. During weeks 13-14 and 18-19, subjects were instructed to brush twice a day with SnF2, while weeks 15, 16, 17, and 20, 21, 22 were interposed nontherapeutic periods where subjects brushed only with nonfluoridated toothpaste. For the microbiologic sample, subjects provided 1 ml of saliva, stimulated by chewing on a piece of paraffin. Each saliva sample was vortexed, sonicated, serially diluted in 0.05M phosphate buffer (pH 7.0), and 25 ~1 of each dilution was spread onto thirds of a 10% sheep blood agar plate for estimates of the total aerobic bacteria, and Mitis Salivarius ® agar plates containing 0.2 units/ml Bacitracin ® for estimates of S. mutarls. 9 Total CFU were counted with the aid of 20x magnification after 24-hr incubation in a CO2-enriched environment (candle jar) at 37°C. After incubating the MSB agar plates for 96 hr in candle jars, those colonies with morphologic characteristics of S. mutans were counted. The means of the total CFU and S. mutans for each time interval were calculated and further reduced to total means for treatment periods. Although traditional statistical tests with a time series experiment Gelkam-1030 ppm F-, 2950 ppm Sn÷ ÷; Scherer Laboratories: Dallas, TX. NASAdent-Scherer Laboratories: Dallas, TX. are questionable due to lack of double blindness, changes of baselines, and potential carry-over effects; paired t-tests still were performed between treatment adjacent nontherapeutic periods to enable more than visual inspection of the data. Reductions in Plaque Versus Saliva The subjects of this study were 10 adults, 20-39 years old, who had more than 2 x 104 S. mutans/ml saliva. Each subject’s saliva and plaque were sampled weekly during a 3-week baseline period and a subsequent 3-week experimental period. No modification of the subjects’ oral hygiene habits or dentifrice took place during the baseline period. In the experimental period, the subjects were asked to brush their teeth unsupervised, twice daily for 1 min with the 0.4% SnF2 gel. The sampling, sonicating, diluting, and plating of saliva for estimation of total CFU and S. mutans/ml saliva were performed as in the previous study. After the saliva samples were acquired from each patient, a pooled dental plaque sample was obtained from each patient by scraping the gingival margins of the teeth with a large dental cleoid carver until the end was covered with plaque (3 mg). The end of the carver containing the plaque then was placed in 4.5 ml of phosphate buffer and the carver was shaken until the bacterial mass was dislodged. The plaque in the buffer then was vigorously sonicated for 20 sec using a sonicator equipped with a microtip. The dispersed bacteria then were diluted further and plated in the same way as the saliva samples. The mean percentage of S. mutans per total flora was calculated for plaque and saliva samples in order to compare the potential reductions in both ecologic niches due