Enamel fluoride uptake from a new APF foam.

There is concern that the ingestion of fluoride (F) from topical application of 1.23% APF gel may cause gastric irritation and other side effects. In this in vitro study, a newly developed APF-based foam was tested. Sound human enamel was treated for 4 rain with APF foam or a conventional APF gel (Nupro®), both containing 1.23 % F. Enamel biopsies were obtained using the acid-etch technique. There was a significant increase (P < 0.001) in F uptake from the two F agents compared with their untreated controls. The uptake of F from the new foam and Nupro gel in the outer 15 ~tm enamel were 1736 and 2596 ppm, respectively. The difference in F uptake from the foam and gel preparations at 5 ~tm depth was not statistically significant (P = 0.074). Clinically, the amount foam needed for full-mouth treatment is less than I g, whereas for APF gel it is nearly 4 g. The topical application of acidulated phosphate fluoride (APF) gels has been demonstrated by clinical studies to reduce dental caries to an average of 25% (Clarkson and Wei 1982; Mellberg and Ripa 1983). The Accepted Dental Therapeutics (1984) listed 22 APF gels accepted by the American Dental Association (ADA). Most of these gels contain 1.23% F (as NaF and HF), phosphoric acid and carboxymethyl cellulose as the gelling base. The pH is usually between 3.0 and 4.5 and the viscosity of 7000 to 20,000 centipoises. Fluoride gels have the advantage of being used in trays, enabling the entire mouth to be treated in a single application. Because the F gels are viscous, the use of a well-fitting tray is essential to facilitate the flow of the gel into the interproximal surfaces of teeth. Concern has been expressed recently about the potential risk of excessive F ingestion following application of 1.23% APF gels. Ekstrand et al. (1981) reported that an average of 78% (31.2 mg F) of topically applied 1.23% APF gels was ingested when vacuum-molded trays were used on children 5-16 years of age. LeCompte and Whitford (1981) reported that the average amount of F retained by children approached 14 mg or 54% of the applied dose using the cotton-roll isolation technique. However, the amount of F ingested was greatly reduced when suction was applied and when better fitting trays were used (LeCompte and Doyle 1985). The ingested from APF gels may cause side-effects such as nausea, vomiting, and gastrointestinal pain. Recently, in vitro evidence indicated that there is no direct relationship between the F content of APF gels and their ability to reduce enamel solubility, (Shannon and Edmonds 1978; Hattab 1984), increase enamel uptake, (Dijkman et al. 1982; Naleway 1985), and decrease the carious lesion depth (Sluiter and PurdellLewis 1984). Based on these findings and the concern for the potential risk of overdosage, suggestions have been made to lower the F concentration in gels and/or to use a well controlled application technique. In an attempt to minimize the risk of F overdosage and to maintain the efficacy of topical F treatment, a new foam-based APF agent has been developed. The aim of the present study was to determine whether a foam-based APF agent is effective in producing enamel F uptake to concentrations attained by conventional APF gels. Because the foam is considerably lighter than gels, it will fill a topical application tray with a much smaller weight of the agent and hence the total amount of F ingested could potentially be less. This will be the subject of a subsequent study. Materials and Methods A total of 40 premolars, extracted for orthodontic reasons, free of defects and showing no signs of caries or hypoplastic lesions on the buccal aspects, were utilized in this study. The teeth were cleaned with an aqueous slurry of pumice and washed with water. Two round adhesive disks 4ram in diameter were placed on the mesial and distal aspects of the buccal surface. The disks were burnished onto the enamel surface to assure a good peripheral seal and all tooth surfaces were covered with acid-resistant nail varnish. The mesial and distal enamel circles covered with the disks were chosen at random to serve as test (F-treated) or control (F-untreated) surfaces. In this way each tooth served as its own control. Pediatric Dentistry: June, 1988 Volume 10, Number 2 111 Treatment Procedure and Enamel Biopsy The disk covering the control area was removed leaving behind a varnish-free enamel surface window of 12.6 mm2. Acid-etch biopsies were carried out using F-free cotton pellets. The pellet was saturated with 0.1 ml of 0.5 M HC104 and held with forceps against the window for 15, 30, and 30 sec consecutively. Immediately after each etching, the etchant was buffered by directly pipetting onto the enamel 0.4 ml of 0.5 M citrate buffer followed by 0.5 ml of deionized water. The residual solution left on the tooth surface was aspirated with a microsampling pipette and small pieces of F-free filter paper and transferred to the original sample solution. The biopsied control window was covered with nail varnish and the disk of the test area then was removed. The test windows were treated with one of the following: APF foama containing 1.23% F, sucrose esters, and nonionic surfactant (pH 3.5); or Nupro® gelb, an APF gel containing 1.23% F from sodium fluoride and hydrogen fluoride (batch 5M5823). The windows were exposed for 4 rain to the F agents at room temperature in a relative humidity of 100%. Immediately after F treatment, the enamel surfaces were washed for 30 sec under running tap water and for I min under running deionized water. Chemical Analysis and Data Evaluation The F concentrations in the solutions containing the biopsied enamel were determined using combination Fion electrodes c coupled to a digital ionalyzer, d The phosphate concentrations in the samples were determined by a double-beam spectrophotometer ~ using the malachite green method (Hattab and Linden 1984). The mass of enamel in each sample was calculated by assuming that enamel contains 17.5% phosphorus. The thickness of the biopsied enamel layers was estimated from the following formula: Layer Mass of enamel (~g) Thickness (l~m) = Biopsy area (mm2) x Density of enamel Because the thicknesses of the biopsied layers are not totally controllable and because of the very steep F gradient in the outer enamel, the mean F concentrations were adjusted to standardized depths of 5,10, and 15 ~tm from enamel F profile (Hattab 1987). The paired t-test was used to evaluate the differences in enamel F concentrations between the test and control windows of each F treatment and between the two treatments (APF gel and APF foam). Block Drug Co Inc; Jersey City, NJ. Johnson & Johnson Dental Products Co; East Windsor, NJ. Orion model 960900 -Orion Research Inc; Cambridge, MA. Orion model 901 -Orion Research Inc; Cambridge, MA. Shimadzu model UV-150-02 -Shimadzu; Tokyo, Japan. Results Measurements of phosphate allowed the determination of the relationship between etch depth and F concentration. The mean (+ SD) thickness of enamel layers removed after 15, 30, and 30-sec etching were 3.16 + 0.40, 5.30 +_ 0.44, and 5.76 + 0.64 ~tm, respectively. There were no significant differences in the thickness of enamel layers removed from the control and F-treated groups. The total thickness of the three layers was 14.22 ~tm. The precision of the enamel biopsy was 11.7% (N = 240). The mean concentration of F found at standardized depth of the control and test (F-treated) groups are shown in the Table. The data are graphically presented in the Figure. With the control group, the F concentraTABLE. Mean Fluoride Concentrations at Standarcl Enamel Depths Before (Control) and After 4-min Treatment With 1.23% APF Foam or Conventional Nupro® Gel. F Concentration (ppm) at Standardized Depths (mean + SD) Topical Agent 5 #m 10 I~m 15 I~m