Introduction 4 6 14 21 25 2 5 14 16 17 24 8 13 23 26 12 3 11 26 13 18 22 The above-mentioned studies had made clear that fluoride-treated tooth surfaces and salivary fluoride levels are increased after administering local fluoride regimes. Besides these effects, it may be speculated that fluoride applications also lead to fluoride uptake at tooth surfaces that were not directly treated or covered with fluoridation agents such as varnishes. This fact could especially be important for demineralized surfaces, which were inaccessible to direct fluoride application such as inter-proximal areas. Due to toxicological and practical reasons, application of fluoride varnishes is mostly limited to some sites of the dentition. Therefore, the aim of the present study was to determine fluoride transfer from fluoride-varnished enamel surfaces to demineralized enamel surfaces located at various distances from the fluoridation site. Materials and methods Enamel samples 1 According to this procedure, each two enamel samples were prepared from 30 bovine incisors and each four samples were gained from additional 120 incisors. One sample from each tooth was used for the determination of baseline fluoride content of the respective tooth. The remaining samples of the 30 bovine incisors were later treated according to series 1–3. The remaining samples of the 120 bovine incisors were used for the determination of intra-oral fluoride transfer and acquisition. Set-up of the study The study was designed and conducted according to the guidelines of Good Clinical Practice. Ethical approval of the study was granted by the Ethics Committee of the University of Göttingen (2/9/01). Ten panellists (aged 21 to 29 years) participated in the study. They were all residents of Göttingen (fluoride content in domestic water: <0.2 ppm F). The subjects had been instructed to avoid fluoride uptake. The participants had a stimulated salivary fluoride rate within the normal range of 1.0–5.0 ml/min. Further inclusion criteria were that they had at least 20 teeth, no faulty dental restorations, no glass ionomer fillings and no current dental caries activity. Intra-oral, lower jaw appliances with two buccal aspects were worn by ten volunteers in three series of 6 days each. In each series, one enamel sample was placed for 6 days in one buccal aspect of the appliance after treatment according to the respective series (=central, fluoridated sample). With each five of the participants, the fluoridated samples were placed in the right buccal aspect; with the remaining subjects, the fluoridated samples were fixed in the left aspect of the appliance. A washout phase of 1 week elapsed between the three series. ® ® 1 Table 1 ® ®   ® ® Fluoride content 0.12% 2.26% Fluoride form Sodium fluoride Sodium fluoride Cetylaminehydrofluoride  Bis N  pH 4.6 Neutral Solvent Solvent-free alcohol (33.14%) Base Water-soluble polymer Natural resins (colophonium, mastix, shellac) Other ingredients – Wax, saccharine, flavour Manufacturer Hager & Werken, Duisburg, Germany  Colgate-Palmolive, Hamburg, Germany Each three unfluoridated samples were placed into each appliance at different sites (a–c): (a) directly neighboured to the central, fluoridated specimen (=next), (b) at 1-cm distance (=1 cm) and (c) in the opposite buccal aspect of the appliance (=opposite). These three samples were replaced after 1, 3 and 5 days by new unfluoridated samples, which were removed after 1 day intra-oral exposition. Thus, each one sample was worn at the respective site for the following periods: days 0–1, days 1–2, days 3–4 and days 5–6. The central samples, which were fluoridated on day 0, were not removed from the appliances before completion of the experiment. ® Fluoride analysis 15 9 Statistics 20 7 2 3 P Results 2 Table 2 a     − 1st Layer (0–30 μm) 2nd Layer (31–60 μm) Period Site Mirafluorid (%) Duraphat (%) Control (%) Mirafluorid (%) Duraphat (%) Control (%) Mirafluorid (%) Duraphat (%) Control (%) 0–6 Central 90 100 0 10 100 10 10 100 0 0–1 Next 10 60 0 0 30 0 0 30 0 0–1 1 cm 10 30 0 0 50 0 0 10 0 0–1 Opposite 0 0 0 0 10 0 0 0 0 1–2 Next 20 10 0 10 10 0 0 0 0 1–2 1 cm 20 0 0 0 0 0 0 0 0 1–2 Opposite 10 0 0 0 0 0 0 0 0 3–4 Next 10 0 0 0 10 0 0 0 0 3–4 1 cm 10 0 0 0 0 0 0 0 0 3–4 Opposite 10 0 0 0 0 0 0 0 0 5–6 Next 0 0 0 0 0 0 0 0 0 5–6 1 cm 10 0 0 0 0 0 0 0 0 5–6 Opposite 0 0 0 0 0 0 0 0 0 a 2 3 3 P P P Table 3 Mean ± standard deviation (median; minimum–maximum) of KOH-soluble fluoride and structurally bound fluoride (in 1st and 2nd layer) given for the experimental groups with more than 50% of the respective measurements above detection limit     − 2 3 3 Period Site Mirafluorid Duraphat Duraphat Duraphat 0–6 Central a a,c b b 0–1 Next –* c –* –* *Less than 50% readings above detection limit a − b − c Discussion Introduction 10 10 24 2 19 1 Under clinical conditions, a varnish is often applied onto more sites, which might elevate salivary fluoride to a presumably higher extent as in the present study, where the varnishes were applied to a single site only. Due to the results of the present study, it could be concluded that within the first day after application, intra-oral fluoride release from the tested fluoride varnish Duraphat leads to KOH-soluble fluoride uptake only in demineralized enamel samples, which are located in close vicinity to the fluoridation site. Owing to the negligible transfer of fluoride from the varnish to more remote sites, this finding means, for the clinical situation, that all sites in the oral cavity requiring fluoridation have to be directly treated with the varnish.