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.