The effect of chronic renal insufficiency on orthodontic tooth movement in rats.

The purpose of this study was to determine the effects of impaired renal function on the amount of orthodontic tooth movement (OTM) in a rat model of renal insufficiency (RI). The animals were divided into three groups: a control unoperated group in which only OTM was done, a sham-operated group, and an RI group. OTM was done two weeks after performance of the sham operation or the surgery to induce RI. Renal failure was induced by electrocoagulation of one kidney cortex followed by contralateral nephrectomy. A fixed orthodontic appliance consisting of a 5 mm length of nickel-titanium closed-coil spring was ligated between the maxillary right incisor and first molar to deliver an initial mesial force of 60 g. Four weeks after RI induction, the amount of tooth movement was estimated by measuring the space created between the first and second molars on a stone cast. Bone density was measured by optical densitometry on radiographs and serum parathyroid hormone (PTH) was measured with a radioimmunoassay method. The results showed that induction of RI significantly increased both OTM (P < .05) and PTH levels (P < .01), although there was no significant difference in bone density by optical densitometry between the unoperated, sham-operated, and RI groups four weeks after RI induction. The results suggest that an increase of bone-remodeling activities, as evident from a significantly higher level of PTH, may be responsible for increase in tooth movement.