Short-term Effect of NaF-mouthrinse on Glucose-induced pH Fall in Plaque

Objective: Fluoride is known to inhibit acid production by oral streptococci in vitro. However, it was reported that NaF-mouthrinse with 250-ppm could not inhibit acid production by plaque which was obtained over 30-min after the rinse. Thus, this study aimed to evaluate the short-term effect of a single fluoride-mouthrinse containing different concentrations of NaF on glucose-induced pH fall, and fluoride retention within dental plaque.

Methods: After informed-consent was obtained, 9 volunteers (27±5 years) were asked to accumulate plaque for 24-h without oral prophylaxis, and rinsed with 10-mL NaF solution (250, 500 or 900-ppm F^-) for 1-min. Supragingival plaque (ca. 7.0-mg wet weight) of each volunteer was collected before (control), 15 or 30-min after the rinse. These samples were suspended in 27-µl of 1-mM potassium phosphate buffer (pH 7.0), incubated with 10-mM glucose and the pH fall was monitored for 25-min with a portable pH meter. The fluoride-ion retention within the plaque samples were also determined at pH 5.0 with a fluoride-ion electrode.

Results: The mean minimum pH value (n=2) of the control was 4.4, while those at 15-min after the rinse with 250, 500 and 900-ppm were increased to 4.9, 5.3 and 5.7, respectively. Similar results were obtained for the plaque taken 30-min after the rinse except for the pH value with 250-ppm rinse, which returned to the control level. Amounts of fluoride retention at 15-min after the rinse with 250, 500 and 900-ppm (n=3) were 5.3±2.3, 6.3±5.1 and 8.7±5.3-ppm, respectively, and were higher than that of the control (3.9±0.9-ppm). Similar results were obtained for the plaque taken 30-min after the rinse.

Conclusion: This study revealed that NaF-mouthrinse can inhibit the acid production by plaque for short-term, probably because of the fluoride retention in plaque, suggesting that fluoride inhibits plaque acidogenicity in vivo. Supported by MHLW-Grants (MSTA-43) and MEXT-Grants (17791350).