Background

            Distraction osteogenesis is an endogenous form of tissue engineering that simultaneously generates new bone and lengthens soft tissues by the application of controlled mechanical strain. However, accurate preoperative planning is necessary for predictable outcomes.

 Objectives

To determine the vectors of distraction for optimal three dimensional advancement/movement of the mandible (unilateral and bilateral) and midface.

 Methods

Individual retrospective clinical and radiographic studies were conducted of all patients who underwent unilateral mandibular distraction, bilateral mandibular distraction and midface distraction. Only patients with adequate pre- and post-distraction clinical and cephalometric data (n=45) were included in the study; CT data were also used to corroborate the above. Cephalometric tracings were made and anatomic landmarks identified on pre-activation and post-activation films. The vector was recorded as an angle between the position of the distraction device and the maxillary occlusal plane. The direction and magnitude of skeletal change/movement were recorded. All studies were conducted by two senior orthodontists in a blinded fashion.

 Results

In unilateral mandibular distraction, a horizontal vector (relative to the maxillary occlusal plane) resulted in minimal increase in the ramal height but a marked shift of the mandible toward or beyond the craniofacial midline. A vertical vector resulted in significant vertical ramal lengthening but minimal midline shift of the mandible.

In bilateral mandibular distraction, a horizontal vector resulted in minimal counterclockwise rotation of the symphyseal plane, greater downward vertical translation of the symphysis and minimal closure of an anterior open bite. A vertical vector, however, yielded greater counterclockwise rotation, horizontal projection of the symphysis and closure of an anterior open bite.

In midface distraction there was forward translation with minimal rotation of the Le Fort III segment if the vector is applied along a plane parallel to the maxillary occlusal plane and at a location that is 55% between occlusal plane and nasion.

 Conclusions

Craniofacial distraction should be planned preoperatively as carefully as orthognathic surgery. Among the most important variables is the vector of distraction – i.e. the placement of the distraction device relative to the occlusal plane. With proper planning the distracted skeletal segment can be moved three dimensionally through space to the desired goal.