Fluoride uptake and retention following combined applications of APF and stannous fluoride in vitro.

This study compared the original, more concentrated acidulated phosphate fluoride (APF) and stannous fluoride (SnG) regimens and one of the commercial products with respect to the stability of the fluoride deposited from the treatments in vitro. Specimens of human enamel were treated with two-step sequential applications or mixtures of APF and SnF2 and subsequently were exposed to one of three washing procedures of varying intensity. Data obtained from successive acid-etch biopsies were used to construct fluoride-by-depth profiles for each treatment. The sequential application of the more concentrated 1.23% APF followed by 0.5% SnG was the only treatment which produced elevated enamel fluoride levels compared to untreated controls following the most rigorous wash. ride (F) concentrations than those tested in the previously cited studies. The use of the lower F concentrations apparently is based upon the results of a separate in vitro study by Shannon and Edmonds 6 which showed no difference in ESR when the F concentration of the APF was lowered to 0.25%. The manufacturers of these commercial products also suggest that a two-min application period be used for their APF/SnF2 mixture as opposed to the four-min treatment time employed in the studies by Shannon and Crall. The objective of this study was to compare two of the commercial APF/SnF2 topical regimens with the previously tested regimens in terms of their ability to deposit F in enamel in a relatively stable form in vitro. Controlled clinical trails have shown that semiannual applications of 8-10% stannous fluoride (SnF2) or 1.23% acidulated phosphate fluoride (APF) can reduce the incidence of caries in children, especially in nonfluoridated areas. 1 As a result, these agents have been used independently as part of caries prevention programs in dental offices for many years. The results of laboratory studies of enamel solubility reduction (ESR) by Shannon et 2;3 and ar tificial ca ries in hibition by Crall et al. 4,5 have suggested that combined applications of 1.23% APF and 0.5% SnF2, either by a two-step sequential regimen or as a mixture, might have the potential to provide greater protection aga~st caries than if either agent waa uaed alone. Commercial firms have developed and promoted treatment packages containing APF and SnF~ for combined application in the derlfal office. ~,b However, the APF and SnF 2 solt~fi0~$ recommended for topical application in these pa¢l~ag~ have lower fluo~ " Gel-Kam, Scherer Lab0i’at0rie~; in¢~ Dallas, i~X~ b Omni, Dunhall Phai~¢0ufi¢~ls~ li~c., G¢~vetfe, AR. Methods and Materials The study was designed to minimize the effect of the variability which exists in baseline enamel fluoride levels between teeth without physically altering the enamel prior to the fluoride application (as is done in some analytical techniques, ie., ESR). To accomplish this, three separate experiments were performed. The same six treatment regimens were used in each experiment, but three different washing procedures of varying duration were employed to assess the stability of the F deposited as a result of each regimen. The treatment regimens examined in this study are outlined in Table 1. Regimen 1 served as a control; the apecimens assigned to this group were exposed ~0 deioni~ed distilled water fo~ 4 min Regimen 2 consisted of a 4~min exposure to a conventional 1.23% APF solution, * Regimens 3 and 4 were the sequential and mixture treatments originally tested by Shannon et aL and al~o by the author~, Regimen~ 5 and 6 em~ Karldiurn, Lotvi¢ Cotp~, ~t~ Louis, MO. 226. COMBINED A~FIS~I:~ AlsPLiI~A~’IONsi Ccall ~nd Bjei~ga ployed commercially available APF/SnF2 products d using the manufacturer’s recommended application times for sequential and mixture treatments. Extracted, macroscopically caries-free human molars were sectioned to provide multiple specimens of buccal enamel from each tooth. A total of 168 specimens were obtained for study. The specimens were assigned to the various treatment groups using a stratified random distribution and a balanced incomplete blocking design. Each specimen was labeled according to tooth, treatment regimen, and washing procedure and subsequently was covered with an acid-resistant varnish except for a circular window of exposed enamel (area = 4.1 mm2). The specimens then were treated with the appropriate regimens as outlined in Table 1. Following the topical applications, the specimens from each treatment regimen were divided into three groups corresponding to one of three washing procedures. All specimens were washed in an inorganic solution at 25°C with constant stirring for 18 hr (wash 1) or 24 hr (washes 2 and 3) with solution changes outlined in Table 2. The inorganic wash solution contained 1 mM Ca, 3 mM P, and 20 mM NaHCO3 at pH 7.0. 7 In addition, the specimens assigned to washTABLE 1. Treatment Regimens Application Agent F Concentration Time (%) (min) 1. dd H20 0 4 2. APF 1.23 4 APF 1.23 2 3. + (sequential) SnF2 0.12 2 APF 4. + (mixture) 0.92 4