Study on Deformation of Fixation Devices of RED System in Maxillary Distraction Osteogenesis

Abstract

Le Fort I osteotomy followed by distraction osteogenesis using the Rigid External Distraction (RED) system has been a useful method for facial and occlusal improvement of maxillary hypoplasia. Although an arch wire jointed to the stainless steel traction rod has been commonly fixed to the upper teeth in the RED system, some disadvantages, such as drifting of the teeth, have been pointed out in this method. Recently, the Leipzig retention plate, which is directly fixed to the maxilla, was reported and we also have been using this plate in our department. However, distraction osteogenesis using the RED system with these devices sometimes takes a long distraction time to get the expected amount of distraction because of the difference in the actual and expected amounts of maxillary advancement. One of the causes of this difference may be the deflection of the devices caused by the traction force.
In this study, we examined the deformation of the devices caused by the traction force. The bending stiffness of the stainless steel rod of the teeth-fixing wire and the square rod of the Leipzig retention plate were determined by a three-point bending test. The elastic modulus of the stainless rod was lower than that of the square rod. On another examination of the deflection of the stainless steel rod and the square rod, which were bent into a U-shape, the deflection-load ratio of the stainless steel rod was higher than that of the square rod.
We next studied the deformation of the teeth-fixing wire and Leipzig retention plate fixed to the dental arch model. Furthermore, the vertical rod and Halo frame of the RED system were fixed to the cranial model and their deformation was evaluated. We found that the teeth-fixing wire showed a greater deformation than the Leipzig retention plate on the dental arch model. The deformation of the vertical rod plus Halo frame was not observed when the traction force was less than 40N.
These results indicated that the Leipzig retention plate was more useful than the teeth-fixing wire in the RED system because of the lower extent of deformation as well as the lack of teeth drifting. In addition, our results indicated that the deformation of the external fixation devices of the RED system could be negligible.