Fluorosis-Like Effects of Acidosis, but Not NH4<sup>+</sup>, on Rat Incisor Enamel

Abstract

Previous studies have shown that chronic acidosis induced by NH4Cl is associated with disturbances in enamel mineralization that resemble severe fluorosis and increased fluoride concentrations in both soft and hard tissues. It has not been shown whether these effects are due to acidosis per se or exposure to high levels of NH+4. This 42-day study with rats fed a low-fluoride diet was done to identify the etiological factor. Two control groups received deionized water or water containing NaCl. Two groups received NH+4-containing compounds that did not produce acidosis (NH4HCO3 or HN4 acetate). Two other groups were rendered acidotic by exposure to NH4Cl in the drinking water (metabolic acidosis) or to an atmosphere containing 10% CO2 (respiratory acidosis). The femur epiphysial fluoride concentrations were elevated in the NH4Cl and NH4 acetate groups, and the magnesium concentrations were elevated in the groups exposed to NH+4 compounds and in the 10% CO2 group. Microradiographic analysis revealed severe disturbances in the mineralization pattern of incisor enamel in both acidotic groups, but normal enamel in the other groups. Enamel fluoride and magnesium concentrations were highest in the acidotic groups. The enamel fluoride concentrations were low (8-14 ppm) and not regarded as the cause of the defective mineralization. It was concluded that the effects on structure and composition of enamel were due to acidosis and not to exposure to high levels of NH+4.