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Fluoride Reduces Bone Strength in Older Rats

Department of Orthopaedic Surgery, Indiana University, Indianapolis, Indiana 46202

K. Hasegawa

Department of Anatomy of the School of Medicine, Indiana University, Indianapolis, Indiana 46202

W. Zhang

Department of Oral Health Research Institute of the School of Dentistry, Indiana University, Indianapolis, Indiana 46202

M. Wilson

Department of Oral Health Research Institute of the School of Dentistry, Indiana University, Indianapolis, Indiana 46202

Y. Li

Department of Oral Health Research Institute of the School of Dentistry, Indiana University, Indianapolis, Indiana 46202

A.J. Dunipace

Department of Oral Health Research Institute of the School of Dentistry, Indiana University, Indianapolis, Indiana 46202

In response to recent concerns about the effect of water fluoridation on hip fracture rates, we studied the influence of fluoride intake on bone strength. Four groups of rats were fed a low-fluoride diet ad libitum and received 0, 5, 15, or 50 ppm of fluoride in their drinking water. Animals were euthanized after 3, 6, 12, or 18 months of treatment. Mechanical strength of the right femur was measured by three-point bending. Fluoride content for the left femur was measured, and static histomorphometric measurements were made on a lumbar vertebra. Femoral failure load was not significantly decreased in rats treated for 3 and 6 months, but was decreased as much as 23% in rats treated 12 and 18 months at 50 ppm fluoride. Extrapolation from regression equations predicted that older rats lose 36% of femoral bone strength when bone fluoride content is increased from 0 to 10,000 ppm, while younger rats will lose only 15%. Thus, the decreased strength appeared to be due to the combined effects of fluoride intake and age on bone tissue and was not associated with a decrease in bone density or mineralization defects. There were only small effects of fluoride on bone histomorphometry. Fluoride intake at high levels had no negative effects on bone mineralization. Fluoride intake was associated with slight increases in trabecular bone volume and trabecular thickness, but these effects could not be demonstrated consistently. The mechanism by which large amounts of fluoride affect bone strength more severely in older animals is unknown.

Key Words: rats • fluoride • bone • biomechanics

Journal of Dental Research, Vol. 74, No. 8, 1475-1481 (1995)
DOI: 10.1177/00220345950740080701


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