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Effect of the Period of Citrus Beverage Exposure on the Fluoride Concentration of the Molar Surfaces of Rats

A previous study showed that administration of a commercial grapefruit beverage (pH, 3.1 to 3.5) as the only drinking fluid for four weeks, followed by drinking water fluoridated to 2.0 ppm fluoride (F) for an additional four weeks, resulted in a significant increase in the F content of the surfaces of the molars of rats. Because of the ability of citrate to complex calcium and because of the low pH of the citrus beverage, intercrystalline tooth spaces were opened and permitted an increased uptake of F (LEHMAN, GEDALIA, and WESTREICH, unpublished results). In the present study a commercial orange beverage of a similar pH was administered to determine the F uptake of the surfaces of the molars in rats after shorter exposure to the eroding fluid. Thirty white laboratory rats of the strain Sabra (Hebrew University) were separated into three groups of ten rats each. The groups received a commercial orange beverage (pH, 3.1 to 3.5) that contained less than 0.1 ppm F for 3 (group A), 7 (group B), and 14 (group C) days. Drinking water containing 2 ppm F was given for one month after the period of beverage administration. The rats then were killed. Maxillary and mandibular bone segments were dissected out and the molar surfaces were exposed to 0.25 N HCl for 30 minutes to remove the surface layer for F analysis (WEATHERELL and HARGREAVES, Adv Fluor Res 4:181-191, 1965). The tooth segments were weighed before and after exposure to HCl under standardized conditions of drying with CaCl2. The difference between the weights represented the amount of tooth substance removed. F was analyzed in the HCO solutions, with a combined fluoride electrode.* A previously studied group of rats that received only fluoridated water containing 2 ppm F for four weeks served as a control group. We also will refer to the findings in rats that received grapefruit beverage for 30 days followed by water containing 2 ppm F for four weeks; this is group D. We assumed that commercial orange and grapefruit beverages have the same erosive effect because both contain citric acid and have the same pH. The mean F content of the molar surfaces increased gradually with increased exposure period to the erosive beverage. In the maxillary teeth it rose from 14.7 ppm (control) to 25.0 ppm (group A), 34.3 ppm (group B), 33.9 ppm (group C) and up to 44.0 ppm (group D). In the mandib-