Biomechanical considerations in distraction of the osteotomized dentomaxillary complex.

The completely osteotomized dentomaxillary complex is essentially a free body constrained only by its soft tissue attachments. Therefore the line of action and point of application of any protractive force(s) used during distraction osteogenesis must be considered relative to its center of mass. This is in contrast to the nonsurgically separated dentomaxillary complex, which is a constrained body, and therefore the application of protractive force(s) must be considered relative to its center of resistance. These two centers are not coincident. With knowledge of the location of the center of mass, predictable protraction of the dentomaxillary complex can be achieved. In this study, the center of mass of an adult maxillary specimen osteotomized to emulate a Le Fort I osteotomy was determined. Protractive force(s) through the center of mass will produce linear advancement along its line of action. Protractive movement of the dentomaxillary complex can be adjusted downward and forward or upward and forward by locating the protractive force(s) line of action superior or inferior to the center of mass. A cleft patient is described wherein the surgically separated dentomaxillary complex is protracted downward and forward with a force vector superior to its approximate center of mass. This results in a predictable increase in overbite and overjet with negligible mandibular rotation.