Abstract

OBJECTIVE: to study qualitative and quantitative changes of bone tissue and articular cartilage in rats exposed to sodium fluoride.

MATERIALS AND METHODS: 75 female Wistar cats, each weighing about 200 g, were divided equally into three groups. Animals in Groups 1 and 2 received daily doses of 0.5 mg and 5 mg of NaF, respectively, through intraperitoneal administration, whereas those in Group 3 (controls) received physiological saline solution only. The experiments were run for a period of 3 mo11ths. Histological and histochemical studies were carried out on adjoining bones, femur and tibia, and lumbar venebrae m-V of the animals. The materials used for histological studies were fixed in a 10% formaldehyde solution, decalcified at room temperature in a solution composed of 24 ml 85% formic acid, 5O ml 55% HCl, and 126 ml distilled water. Sections were stained with haematoxylin and eosin (H·E), picrosirius red F3BA, and exposed to toluidine-blue at pH 6 an d pH 3.5. The ultrastructural chan.ges of bone tissue and articular cartilage were investigated by polarization optical methods. The fluoride content of bone tissue was determined by ion selective analysis. The fluorapatite crystals were identified by electron diffraction.

RESULTS: The bone tissue mass, the osteoid surface and osteoid volume increased, the enchondral ossification and the mineralisation of osteoid were delayed, and the proportion of newly formed woven bone increased in correlation with th.e administered dose of fluoride. A sporadic, scattered necrosis of osteocytes and chondrocytes, and a progressive disorientation in the bone and articular cartilage, were shown in rats exposed to NaF. Compared with the
controls, the specimens obtained from NaF-treated animals showed marked decreases in orientation of capsular and intercapsular collagen fibers and glycosaminoglycans in the preexisting bone tissue and articular cartilage.

The structural changes were correlated with the dose of administered NaF, and with the fluoride content of bone tissue (in Group 1: 1.10 mgF/g, in Group 2: 1.44 mgF/g. and in Group 3 (control): 0.423 mgF/g). The fluorapatite crystals, in spite of decalcification, could still be identified in the animals of Group 2.

CONCLUSIONS AND INTERPRETATION: The quantity of bone tissue increased and the quality diminished with increase in NaF levels administered. The enlarged bone mass may be caused by increased bone formation and/or by
decreased bone resorption. The augmented bone (osteoid) formation can be caused by either the relatively or absolutely greater number, increased activity, or longer life span, of osteoblasts. The cause of diminished bone resorption may be due to absolutely or relatively reduced number, decreased activity or shoner life span of osteoclasts. The reduced solubility of fluorapatite may play an important role also. According to our interpretation the increased bone and osteoid volume is caused by decreased bone resorption. The ultrastructural disorientation of bone tissue and articular cartilage are connected to the necrosis of osteocytes and chondrocytes, and may be accepted as a toxic effect of fluoride.

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