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Biological Rat Assay for Total Fluoride Availability in Foods1

Juan M. Navia, Hady Lopez and Edwin L. Bradley

Institute of Dental Research and Biostatistics Department, School of Dentistry, University of Alabama in Birmingham, University Station, Birmingham, AL 35294

A fluoride (F) bioassay procedure based on the method of standard additions and using weanling rats was designed and tested. Rats were distributed between a control (C) group fed MIT 200 diet (F conc. < 0.5 ppm) and an experimental (E) group fed this diet plus 1% dehydrated instant tea used as a model test food. Both groups were further divided into subgroups fed the C or E diets, but supplemented with 0, 5, 10, 20 or 40 ppm F as NaF, and offered deionized water for a period of 10 days. Rats were then killed and femur (fm) and tibia (tb) dissected. Bone samples were treated in a closed system with HCl (6 N) and later with sodium citrate (30%) to determine F concentration using a specific ion electrode. F values (y) for fm and tb were plotted against F amounts added to the diets (xt). Weighted regression equations describing the linear relationship between the two variables were used to calculate the available F content of dehydrated tea which was 830 ± 43 ppm F (using fm data) and 836 ± 67 ppm (using tb data). Chemical assay of the dehydrated tea used as a test food gave a F concentration of 887 ± 16 ppm or 93.5 ± 5.1% availability. This rat bioassay to determine total available fluoride in a dried food can be combined with a chemical assay to obtain a measure of percent availability of F.

KEY WORDS: • fluoride bioassay • bioavailability

1 Supported by NIH-NIDR grants DE 02670 and 07020.

Manuscript received 10 September 1980.




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