Naturally occurring compounds of fluorinemdash;fluoridesmdash;have been of medical interest because of their toxicity and their effect on dental enamel.1Sodium fluoride (NaF) is widely distributed in soil worldwide, but the content varies greatly from one location to another. Animals, including man, obtain fluoride from plants and water but not appreciably from other animals. Fluoride gains access to the atmosphere in the burning of soft coal and in the manufacture of superphosphate and refining of aluminum, steel, lead, copper, and nickel, and it can be absorbed from the respiratory tract. Incidental sources of fluoride in the diet come from food additives, such as baking powder that has been contaminated with fluoride. Additional sources of fluoride are rodenticides and insecticides, and it is from the ingestion of these agents that most cases of acute toxicity result.Sodium fluoride is highly soluble in water and is readily absorbed from the gastrointestinal tract. Once absorbed, fluoride is deposited in the skeleton and teeth. It is also concentrated in the thyroid gland, aorta, and possibly kidneys. The amount of fluoride stored in bone depends on intake and age. The greater the intake, the greater is the accumulation in bone. More fluoride is deposited in growing bone than in mature bone. Once deposited, fluoride is slowly mobilized from bone. Some ingested fluoride passes through the gastrointestinal tract in insoluble complexes with calcium and iron. Fluoride is excreted from the plasma through the kidneys; however, about 90percnt; of fluoride filtered through the glomeruli is reabsorbed in the renal tubules. Small amounts of fluoride are excreted in sweat, from the lactating breast, and into the gastrointestinal tract.Fluoride inhibits several enzyme systems, including utilization of glucose by red blood cells. It reduces tissue respiration and anaerobic glycolysis.Fluoride is accumulated in the aorta with age, and the increasing concentration with age probably results from the calcification that occurs in the aorta. In bone, fluoride causes replacement of hydroxyapatite with the denser fluoroapatite. Prolonged ingestion of excess fluoride causes increased osteoblastic activity. The density and calcification of bone increase, and with accumulation of excess fluoride over time, fluorosis or osteosclerosis results. The cortex of long bones becomes thickened, numerous exostoses occur throughout the skeleton and ligaments, tendons and muscle attachments to bone become calcified. The exostoses can occur in the spinal canal and result in neurologic deficits. In its severest form, osteosclerosis is a disabling disease known as crippling fluorosis. The histologic appearance of osteosclerosis is similar to that of the mature, highly calcified, acidophilic bone of inactive otosclerosis.
展开▼
