Effect of compressive forces on a bone modelling surface

The work presented herein, is an experimental study on the effect of an orthodontic appliance with a helicoidal spring designed to exert force toward palatine--i.e. in the opposite direction to the natural vestibular drift--on a bone remodelling surface. The appliance consists of two stainless steel molar bands, with a horizontal bracket tube welded to their palatal aspect through which the arms of the helicoidal spring are passed. Wistar rats, 250 g body weight, were fitted with the device for 48 and 96 hours. One group of rats was administered two doses of tetracycline hydrochloride prior to device placement, in order to label mineralizing fronts. Histomorphometric studies of the periodontal wall of the palatine alveolar bone showed a marked increase of bone resorption at both experimental time points together with an increase in the number of osteoclasts, and no tetracycline labelling after 48 hours. The results show that compressive forces are capable of stimulating resorption, even on bone modelling surfaces. The pressure applied would stimulate osteoblasts to send out signals for osteoclast recruitment and activity.