The effects of fluoride on the periosteal and endosteal surfaces of the rat femur. A scanning electron microscope study

Anorganic preparations of the femoral diaphyses of male rats given 150 ppm fluoride in the drinking water for 10 weeks were examined by scanning electron microscopy and compared to similar preparations from control, untreated rats. In fluoride-treated rats, the surface features of the periosteum were characteristic of woven bone formation. Apposition areas appeared uneven and frayed, consisting of bunches of poorly-defined needles. The mineralized segments varied in size with wide gaps in between, suggesting a delay in the rate of mineralization at the periosteum. The uneven surface was a reflection of the underlying irregular orientation of the collagen fiber bundles. Numerous osteocyte lacunae buried at various depths were evident, and the lacunar walls were irregular with mineralized segments running in all directions. These features were in contrast to the ordered arrangement of both the collagen fiber bundles and osteocytes seen in typical lamellar bone formation of the untreated animals. On the endosteal surfaces, apposition areas as well as fully mineralized areas appeared similar in both groups. However, well-defined resorption areas were decreased in the fluoride-treated rats. The few Howship's lacunae present on the endosteal surfaces were shallow and poorly formed. These observations of the femoral diaphyses indicate that the ingestion of fluoride for 10 weeks in the rat results in an increase in matrix and bone formation at the periosteum with a concomitant decrease in resorptive activity at the endosteum.