Mandible distraction using internal device: mathematical analysis of the results.

For many years, surgeons have sought a method to treat severe facial deformities without using bone grafts and extensive surgery. Distraction osteogenesis offers this promise. The technique used in mandibular hypoplasia follows the basic principles proposed by Ilizarov which states that the device must be elongated 1 mm per day to create optimal bone production. Despite the widespread implementation of this recommendation to include the 1-mm/day separation, doubt still exists as to whether this is the optimal treatment regimen. Intraoral devices with percutaneous activator pins were used in 16 patients with hypoplastic mandibles. The results of distraction were documented by panorex and cephalogram of the mandible. The length of the ramus as well as multiple mandible dimensions and facial angles were measured. The panorex and cephalogram of the mandible were effective in demonstrating the significant increase in length of the mandible and ramus, as well as the entire mandible, but there was no correlation between the stretching obtained by the distraction device and that measured by the radiographic studies. The S-N-B angle was the only facial angle in which there is a statistically significant increase measured and this appeared to be related to a mandible rotation. It is concluded that the mandible distraction (using an intraoral device and an external activator pin) was effective in increasing the ramus length and both the panorex and the cephalogram were effective in demonstrating this morphologic change. There was no correlation between the clinical result and the radiographic studies demonstrating that the clinical judgment still has a significant role in controlling mandible distraction.