Abstract
When growing rabbits are given drinking water which contains 225 or 500 parts per million sodium fluoride, they develop gross osteofluorosis if treatment is continued for up to 200 days. Long bones initially show narrowing of endochondral cartilage, thinning of the metaphysis and occasional fractures at the metaphyseal-epiphyseal junction. Then the plate of cartilage becomes wider than normal and later the hypertrophic zone calcifies intermittently, forming a wide dense chalk-white mass from which a new, slightly thicker metaphysis forms. As animals age, the cartilaginous plate and metaphysis in fluoride-treated animals become narrower although remaining wider than normal. These changes are seen best in the radius and ulna. There is an associated and rapid thickening of bones at sites of normal appositional growth or an effect which may lead to gross enlargement and increased radio-opacity of the bones. Both formation and resorption of bone are increased in some bones but not others. The sites of bone change show a consistent pattern for individual bones, the pattern being modified by the dose and duration of fluoride ingestion and by the degree of inhibition of longitudinal growth, as well as being complicated by variations in the rate of remodelling, which seem unrelated to the health of the animals. The changes are better shown with 225 p.p.m. fluoride than with 500 p.p.m. For the higher dose, the sequence of changes may be obscured by inhibition of longitudinal growth and remodelling. It is concluded that the development of osteofluorosis is associated initially with delayed mineralization and increased resorption, followed by rapid proliferation and subsequent remodelling of diaphyseal bone.