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.

An original orthodontic appliance for experimental mesial movements in rats.

The design of an original appliance to achieve mesial movement of the first upper molar on one side in rat is presented. The appliance is constructed in 0.4 mm stainless steel wire forming a parallelepiped 3 mm in width in its anterior sector, 4 mm in width in its posterior sector and 12 mm in length in its lateral branches. In addition a central longitudinal bar is welded to the structure. The lateral branches of the appliance slide freely through the tubes welded to the palatal aspect of the molar bands, cemented in turn to both first molars. A wire 2 mm in length is welded in the anchorage area to the mesial side of the molar tube at 3 mm from the anterior end of the appliance, which acts as a butt. A pre-formed nickel-titanium open coil spring 0.23 mm thick, lumen 0.60 mm and 5.00 mm in length is placed distal to the molar tube. The spring is compressed by 1 mm of its original length, the final force being approximately 50 g. The movement achieved was measured on plaster casts obtained from pre and postoperative impressions, and afforded values of 0.250 mm +/- 0.790 mm on the active side and 0.012 +/- 0.011 mm on the passive side. The histologic studies showed an extensive erosive area on the pressure side of the alveolar wall. The appliance presented will be useful to achieve models of experimental movements of only one molar towards mesial with a force of known magnitude.

Uranium inhibits bone formation in physiologic alveolar bone modeling and remodeling.

The toxic effect of uranium (U) on bone modeling and remodeling was studied by performing histomorphometric measurements in the periodontal cortical bone of rats. Two different single intraperitoneal doses of uranyl nitrate (238U) were administered to two sets of rats respectively (2 and 0.8 mg/kg body wt). Rats treated with the first dose were killed 14 days postinjection (PI) and those treated with the second were killed 14, 30, and 60 days PI. The results revealed a decrease in bone formation in rats treated with uranium. On the remodeling side the decrease in bone formation was coupled to an increase in bone resorption on the 14th day PI. On the modeling side no bone resorption was observed and the decrease in bone formation was linked to an increase in resting bone zones. Bone formation depression as a key event in U intoxication is stressed.