Renal impairment in children is associated with tooth defects that include enamel pitting and hypoplasia. However, the specific effects of uremia on tooth formation are not known. In this study, we used rat mandibular incisors, which continuously erupt and contain all stages of tooth formation, to characterize the effects of uremia on tooth formation. We also tested the hypothesis that uremia aggravates the fluoride (F)-induced changes in developing teeth. Rats were subjected to a two-stage 5/6 nephrectomy or sham operation and then exposed to 0 (control) or 50 ppm NaF in drinking water for 14 days. The effects of these treatments on food intake, body growth rate, and biochemical serum parameters for renal function and calcium metabolism were monitored. Nephrectomy reduced food intake and weight gain. Intake of F by nephrectomized rats increased plasma F levels twofold and further decreased food intake and body weight gain. Uremia affected formation of dentin and enamel and was more extensive than the effect of F alone. Uremia also significantly increased predentin width and induced deposition of large amounts of osteodentin-like matrix-containing cells in the pulp chamber. In enamel formation, the cells most sensitive to uremia were the transitional-stage ameloblasts. These data demonstrate that intake of F by rats with reduced renal function impairs F clearance from the plasma and aggravates the already negative effects of uremia on incisor tooth development.
In summary, these studies show that tooth development is disturbed under uremic conditions. The effects of uremia are primarily in the dentin but also occur in enamel, resulting in hypoplasia and pitting of the enamel surface. The crown portion of human central incisors (the most aesthetically visible teeth) forms up to approximately 4 years of age, with the second permanent molars forming by about 8 years of age. Therefore, children who present with renal insufficiency before the age of 8 years are at risk for tooth defects. These effects will be more severe in the presence of F, and ingestion of F by young children with renal failure (i.e. F supplements or swallowing F-containing toothpaste) is contraindicated, as suggested previously.