Molding of the Regenerate in Mandibular Distraction: Part 1: Laboratory Study

Distraction osteogenesis has evolved as a mainstream surgical technique for lengthening and augmentation of the hypoplastic mandible. As clinical experience accumulated, there developed the need to "mold" the bony regenerate to avoid the development of postdistraction malocclusion and to achieve the desired craniofacial form. Although the potential to mold the regenerate has important clinical implications, the safety and efficacy of such an acute manipulation of the bony regenerate form have not yet been investigated in the laboratory. The purpose of this study was to determine if the distraction regenerate could be molded and result in a bony union. Four adult female dogs underwent bilateral mandibular distraction with an external multiplanar device (Stryker, Osteonics). After a latency period of 5 days, the mandibles underwent linear (anteroposterior) and angular (superoinferior) distraction to produce an anterior open bite of approximately 30 degrees. At the conclusion of the distraction procedure, the distraction sites were molded to close the open bite. In two dogs, the maneuver was performed over 3 days by changing the angulation of the devices (gradual molding), and in the other two dogs, molding was achieved with a single movement (acute molding). In the latter, the distraction devices were adjusted and reapplied to allow for anatomical fixation during the consolidation period of 49 days. According to the research protocol, the mandibles were assessed serially by cephalograms and computed tomography (CT) scans. All dogs survived the study without complications. The bony regenerate was easily molded in both groups to close the surgically created open bite. After molding, all the regenerates showed CT scan evidence of solid bone (consolidation), which was classified as "extended" on the Hamanishi scale. After the dogs were killed and soft tissue was removed, the regenerate seemed to be robust on gross examination without any evidence of fibrous nonunion. In addition, histological study of the regenerate confirmed the bony union. The study demonstrates that the mandible can be successfully molded into a desired anatomical position immediately after distraction without producing a fibrous union. Furthermore, it has been demonstrated that the bony regenerate is sufficiently malleable before consolidation to undergo either acute or gradual angular molding without disturbing osteogenic potential. The ability to mold the regenerate without the fear of creating a fibrous union or destroying bony potential provides the surgeon the capability to optimize the dental occlusion and mandibular form as part of the distraction treatment process.