Experimental Osteo-fluorosis in the Domestic Pig: A Histomorphometric Study of Vertebral Trabecular Bone

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Abstract
The experiment aimed at describing effects of fluoride on structure and remodeling of vertebral trabecular bone in pigs. Eight animals receiving a supplement of 2 mg F /kg b. w. per day from age eight to 14 mo were compared with eight controls. Plasma fluoride increased from 0.7 ± 0.1 μM/1 to 12.7 ± 2.0 μM/1 in pigs receiving fluoride. At slaughter, the concentration of fluoride in dry fat-free bone was 149.3 ± 10.5 mM/kg for fluorotic animals and 9.5 ± 0.9 mM/kg for controls. Morphologic changes were assessed in un-decalcified specimens of the fourth lumbar vertebra by quantitative histology using fluorochromes as intra-vital tissue time markers. The volume of trabecular bone tissue (bone + marrow) was unchanged in fluorotic animals, but the volume density of bone was increased by 17%. Surface densities of cancellous bone were almost unchanged, whereas the thickness of trabeculae increased in fluorosis. Fluoride enhanced remodeling of trabecular surfaces: The fraction of surface occupied by resorption lacunae increased 40%, and the formative surface approximately 30%. No changes were demonstrated at surface points undergoing formation: Osteoid thickness, calcification rate, lamellar thickness, and completed wall thickness were normal. It is concluded that the observed findings cannot be explained by fluoride-induced changes in a single cell. Fluoride appears to affect all cells involved in remodeling by direct or indirect mechanisms.