Comparative study on fluoride accumulation in hard tissues of rats with chronic drinking-water-borne fluorosis / 环境与职业医学

ABSTRACT

Background A large number of studies on fluoride-induced systemic bone damage have been reported previously, but there is little understanding of the characteristics of fluoride accumulation in jawbone. Jawbone is homologous to the other bone tissues in the body, and is an indispensable and important frame structure in the oral cavity. Objective To study fluoride accumulation and its change trends in teeth, jawbone, and femur of SD rats with chronic drinking-water-borne fluorosis. Methods A total of 144 three-week-old SD rats, half male and half female, were randomly divided into two groups, a normal control group and a fluoride group. The rats in the normal controlgroup drank purified water disinfected and filtered from Guizhou, and the water contained 0.08 mg·kg−1 fluoride which was lower than the national water quality standard at 1 mg·kg−1. The rats in the fluoride group were fed with sodium fluoride (NaF) solution with a concentration of 150 mg·L−1. At 3, 5 and 7 months of the fluoride exposure, the levels of fluoride in urine, blood, teeth, jawbone, and femur were measured by fluoride ion electrode method. Results There was no sex difference in fluoride content in different biological samples of rats in the fluoride group and the normal control group (all P>0.05). After 3 months of fluoride exposure, the rats in the fluoride group showed dental fluorosis of grade II, and higher levels of fluoride ion in blood and urine than the normal control group (all P<0.05), indicating that the rat model of fluoride drinking-water-borne chronic fluorosis was successfully replicated. In the normal control group, the levels of fluoride in femur remained stable; at the end of 3 months, the levels of fluoride in jawbone and teeth were (1097.36±470.34) and (453.09±173.43) mg·kg−1 respectively, and at the end of 7 months, the levels of fluoride in jawbone and teeth were (2113.18±634.49) and (1604.80±160.43) mg·kg−1 respectively. Both jawbone and teeth showed a positive temporal effect of increasing fluoride accumulation (P<0.05). After continuous fluoride feeding, the fluoride levels in jawbone, teeth, and femur of rats in the fluoride group were (3145.02±765.82), (1550.20±77.73), and (3640.55±699.42) mg·kg−1 after 3 months, and (8420.36±1728.56), (4702.08±1417.06), and (6091.99±1384.97) mg·kg−1 after 7 months. The three kinds of hard tissues all showed a positive temporal effect of increasing fluoride accumulation (P<0.05), and the cumulative increas was large than that in the normal control group. Among them, jawbone fluorine increased most. At the end of 5 months, the levels of fluoride in jawbone, femur, and teeth were (6485.02±2141.98), (4914.99±1529.41), and (3365.21±1462.27) mg·kg−1 respectively, and the levels of fluoride in jawbone was much higher than those in femur and teeth (P<0.05). Conclusion Hard tissues such as bones and teeth are fluorine sensitive tissues. Compared with femur, jawbone showed significantly high fluoride accumulation, while teeth show relatively lagging fluoride accumulation.