Systemic Fluoride Absorption Following Fluoride Gel Application

One of the most frequently used modes of topical fluoride application is via acidulated gels. The fluoride concentration of these gels varies between 0.5-1.2 percent. Each application delivers 35 ml gel using trays individually adapted to the dental arch. The patient is thus exposed to as much as 60 mg fluoride for four-five minutes. Since most of these gels are both acidulated (pH 3.5) and flavored, they stimulate salivation. This enhances swallowing of excess saliva and gel during application. Adverse reactions following gel application such as nausea have been reported (Beal and Rock, Brit Dent J 140:307-310, 1976). Since children in particular are, in this way, exposed to relatively high amounts of fluoride in terms of mg per kilogram bodyweight, it seems important to examine these products from a pharmaco-kinetic standpoint. This involves plasma fluoride studies. In the present study the plasma fluoride concentration was investigated after a single application of 5 ml 1.23 percent fluoride gel (LurideR) using trays. Three subjects aged 25, 38 and 42 years, respectively, were examined. Following 12 hours of fasting, two trays-one for the upper jaw and one for the lower-were each filled with 5 ml gel and inserted for a period of four minutes. During this period the subjects were not allowed to rinse or spit. Finger tip capillary blood samples were collected immediately before application and 0.25, 0.5, 0.75, one, two, three, four, five, six, seven, eight, and 14 hours thereafter. Plasma samples (0.5 ml) were analyzed for fluoride concentration using an ion-specific electrode following acetate buffering (pH 4.9). The method is presented elsewhere (Ekstrand, Calcif Tiss Res 23:225228, 1977). After removal of the trays, the patients were allowed to spit. The Figure demonstrates the fluoride plasma concentration in the 25year-old subject (body weight 54 kg). For 30 minutes, the plasma fluoride level was 51.6 ,AM. For the next two hours, the plasma concentration remained over 46 ,M. The concentration then decreased comparatively rapidly during the next four hours and more slowly thereafter. After 14 hours, the plasma concentration was about ten times higher than the base line level. A similar pattern was found in the other two subjects. One of the subjects experienced nausea and slight dizziness. The amount of gel remaining in the oral cavity was checked by weighing and found to be about 3 ml (36 mg fluoride). The plasma fluoride levels are close to those reported to give a reduction in maximum urine concentration ability. (Mazze et al., Anesthesiology 4: 265-271, 1977). Consequently, since the use of fluoride gels is increasing, and twice daily application at home has been recommended even for small children (W. J. Loesche and T. Pink, IADR Progr & Abst. 58:No. 815, 1979), the findings of the present experiment should be taken into account when doses of fluoride are discussed (as in the case of small children). Finally, this study stresses the importance of similar investigations on children.