Effects of continuous infusion of PTH on experimental tooth movement in rats

Development of new methods for accelerating orthodontic tooth movement has been strongly desired for shortening of the treatment period. The rate of o rthodontic tooth movement is dependent on the rate of bone resorption occur ring in the compressed periodontium in the direction of orthodontic farce a pplied to the tooth. In the present study, we examined the effects of conti nuous infusion of parathyroid hormone (PTH) on tooth movement, Male rats we ighing 350-400 g sere treated with subcutaneous infusion of vehicle or hPTH (1-84) at 1-10 mu g/100 g of body weight/day. When the upper right first mo lar (M-1) was moved mesially for 72 h by the insertion of an elastic band b etween the first and second molars, M-1 movement was accelerated by PTH inf usion at 10 mu g PTH infusion caused a 2- to 3-fold increase in the number of osteoclasts in the compressed periodontium of M-1, indicating that such treatment accelerated tooth movement by enhancing bone resorptive activity induced in the compressed periodontium. When M-1 was moved mesially by an o rthodontic coil spring ligated between upper incisors and M-1 for 12 days, PTH(1-84) infusion at 10 mu g caused a 2-fold increase in the rate of M-1 m ovement. PTH(1-34) infusion at 4 mu g had an effect comparable to that of P TH(1-84). However, intermittent injection of PTH(1-34) did not accelerate M -1 movement, PTH infusion for 13 days did not affect either bone mineral me asurements or the serum calcium level. These finding suggest that continuou s administration of PTH is applicable to accelerate orthodontic tooth movem ent.