The effect of corticosteroid-induced osteoporosis on orthodontic tooth movement.

The purpose of this research was to study the effect of corticosteroid-induced osteoporosis on orthodontic tooth movement and relapse. Sixteen 3-month-old New Zealand white rabbits were divided into four equal groups, two treatment and two control. All treatment rabbits were administered daily injections of 15 mg/kg cortisone acetate for 4 days before and during the experimental period. An orthodontic appliance delivering a mesial force of 4 ounces was placed on the maxillary left first molar of all animals. For all groups, measurements of active tooth movement were made after 4, 7, 11, and 14 days. For two of the groups, appliances were removed on day 14, and additional measurements of relapse were made through day 21. With the use of radiodensitometric readings of the humerus bone and histology of the maxilla, osteoporosis was demonstrated in the treatment animals. Mean incremental and cumulative active tooth movement was three to four times greater (p < 0.0001) in the treatment rabbits than in the controls. The treatment group in which relapse was measured demonstrated 100% relapse on day 18, whereas the control group relapsed at a much lesser rate through day 21 and never achieved 100% relapse. Histologic findings appeared to support tooth movement results. In conclusion, the results of this study indicate that rabbits subjected to corticosteroid-induced osteoporosis undergo significantly more rapid orthodontic tooth movement and subsequent relapse than control animals.