Microdiffusion Analysis of Fluoride Release Into Saliva From Different Varnishes

Objectives: Recently, we showed that 5%NaF varnishes with different ingredients can increase levels of fluoride in saliva differently based on direct analysis of saliva supernatant. To investigate whether fluoride was chemically bound or otherwise unavailable as previously measured, samples were further analyzed for total fluoride.
Methods: Four varnishes, 5%NaF, 5%NaF+TCP, 5%NaF+ACP, and placebo containing no fluoride, were used. During each round of treatment, adult subjects (n=15) had ~ 0.3 g of varnish applied to buccal surfaces of all teeth. Treatments were in random order with intervening 2-week wash-out periods. Unstimulated whole saliva was collected at baseline, and at 1, 4, 6, 26, and 50 hrs following varnish application. For comparison to the previous data, samples were analyzed for total fluoride using a modified microdiffusion method. Linear mixed effects models were used to evaluate the effects of varnish and time on whole saliva fluoride (5% significance level).
Results: For time periods 1, 4, 6, and 26 hrs, treatment with all fluoride varnishes resulted in higher concentrations of fluoride than placebo varnish. Other significant differences include: after 4 hrs 5%NaF+TCP was higher than 5%NaF+ACP, after 6 hrs 5%NaF was higher than 5%NaF+ACP, and after 26 hrs both 5%NaF and 5%NaF+TCP were higher than 5%NaF+ACP. Among the varnishes, 5%NaF+ACP showed more variability in results between the two methods, with more fluoride detected by microdiffusion without centrifugation. By direct measurement of supernatant, 5%NaF+ACP was lower than the other two F-varnishes at 1, 4, 6 and 26 hrs; however the results of microdiffusion reduced those differences, particularly at 1 hr when no significant difference was observed.
Conclusions: These results have confirmed that varnishes having equal fluoride content but different composition can increase levels of fluoride in saliva differently. They also showed that some varnishes release substantial levels of fluoride in compounds that are removed by centrifugation.