Distraction Osteogenesis of the Mandible Treatment & Management

The orthodontist and the surgeon must have frequent communication throughout the entire planning process, and must share the same treatment objectives.

After the workup is completed, the placement of the osteotomy and the selection of the distraction device should be determined. Either an internal (intraoral) device or an external device is used, though most routine cases can be done intraorally. Patients accept internal devices better than external ones, but the former are difficult to use in patients with small bones. External devices offer flexibility and vector selection but often cause scarring of the skin.

On the basis of the mandibular defect, the surgeon must determine where to place the osteotomy. As a general rule, if the mandible is defective in a ramus height, the osteotomy should be placed superior to the angle on the ramus, with a distractor placed in a vertical plane. If the mandible is deficient in body length, the osteotomy should be placed anterior to the angle, with the distractor device placed across the defect in a horizontal plane. If the mandible has a combination of defects, the device needs to be placed in an oblique plane. As an alternative, the surgeon may use an external multivector device with 2 osteotomies, 1 anterior and 1 superior to the angle, and 3 pins placed to obtain a multivector advancement.

The patient receives prophylactic antibiotics and nasoendotracheal general anesthesia. An incision is made in the facial vestibule of the mandible, perpendicular to the osteotomy site. A subperiosteal plane is carefully developed to expose the osteotomy site, while an intact periosteal layer is maintained. The osteotomy is placed in the predetermined position on the basis of the findings on the preoperative workup.

Depending on the surgeon's preference, a reciprocating saw or a fissure bur can be used to perform the osteotomy, staying clear of the inferior alveolar nerve bundle by 3-5 mm. Lateral, superior, and inferior aspects of the mandible are cut, leaving the mid portion of the lingual cortex intact, as depicted in the 1st image below. Care should be taken to preserve as much osteogenic tissue as possible, including periosteal and endosteal blood supply. The intraoral distraction device is now secured to the mandible with screw fixation, as depicted in the 2nd image below. The osteotomy is then completed by using a series of osteotomes on the inferior and superior borders and on the lingual aspect. At this point, activation is attempted to ensure movement of the proximal and distal segments. The device is then returned to its starting position. The tissue is carefully closed over the device.

When mandibular symphyseal osteotomy is performed, access is obtained through the usual genioplasty incision. The osteotomy is started through the body of the mandible with a saw. The device is secured in position, and a thin osteotome is then used to complete the bony cut through the alveolar process and between the teeth, attempting to maintain the integrity of the soft tissue and avoid damaging teeth.

When a continuity defect of the mandible is encountered, the surgeon can use distraction osteogenesis or, more specifically, transport osteogenesis (instead of a bone graft) to address this problem. An osteotomy is performed on either the proximal segment or the distal segment, resulting in a transport disk of bone at least 1.5-2 cm in thickness. After the latency period, this disk is transported across the mandibular defect, following the usual rate and rhythm protocol. After the entire defect has been traversed with the disk, the surgeon allows for consolidation. On occasion, a small bone graft is placed at the interface of the disk and on the opposite side, where consolidation is not always complete.

The traditional latency period is 5-7 days. Young children have an increased bone metabolism and may have a latency period as short as 24-48 hours, without affecting ultimate consolidation. Waiting too long increases the risk of bony union; waiting 7 days is advised if the periosteum is excessively traumatized. In addition, if both hard tissue and soft tissue are less than ideal in quality or quantity, increasing the latency period may be considered.

As mentioned before and according to most study results, the recommended rate of distraction is 1 mm per day. A slower rate could result in premature bony union, whereas a faster rate could result in a fibrous union. The inferior alveolar nerve seems to tolerate a distraction rate of 1 mm/d. Ilizarov recommended a continuous rhythm for distraction; however, this is not feasible in the clinical setting, so a rhythm of 1-2 times per day is recommended. The surgeon or a responsible adult should activate the appliance. During a bilateral mandibular advancement, an anterior open bite tends to develop; this can be corrected at the end of advancement with orthodontic elastics.

The consolidation phase is typically 8 weeks, although some adults may require up to 12 weeks of consolidation. During this phase, the fixation must be rigid enough to prevent the formation of fibrous tissue but not too rigid to prevent physiologic loading of the new bone. The formation of the regenerate can be monitored with serial radiographs or CT scans.

These procedures can often be performed on an outpatient basis, although some patients may require 1-2 days of hospitalization for postoperative care. After the consolidation phase is complete, the device can be removed using intravenous sedation and local anesthesia. Orthodontic detailing of the occlusion can begin 3-6 months after the consolidation phase.

In bilateral expansion of the mandible, the patient should be distracted until a slight class III dental occlusion exists (edge-edge incisal relationship). In a unilateral expansion, a slight overcorrection of the mandibular midline is recommended to overcome the deficient soft tissue envelope.

During the distraction phase, the patient is examined every 2-3 days to monitor the advancement and to detect potential occlusal discrepancies. During the consolidation phase, the patient should be seen on a weekly basis to monitor healing and ossification of the regenerate.

See Postoperative details.

With experience, the overall complication rate is low. Complications include the following: fibrous nonunion or premature union of bone, infection that may hinder osteogenesis, noncompliant patient with treatment failure, scarring of the skin with external devices, hardware failure, and malocclusion because of improper vectors.

Distraction osteogenesis of the mandible has become a commonplace procedure with the flexibility to allow the surgeon to address a wide variety of mandibular defects. The sophistication of the distraction devices has increased in the last few years, allowing multivector movement of the mandible. A high percentage of patients accept intraoral distraction with a small, low-profile distraction device.

Although traditional mandibular osteotomy, such as bilateral sagittal split osteotomy, will always have a role, distraction osteogenesis allows a surgeon to treat patients who are unable or unwilling to undergo traditional osteotomy. Distraction osteogenesis is a highly predictable and reliable method of increasing the bone in a deficient mandible.

With technologic advancements, distraction devices have become smaller and more sophisticated than early versions. Distraction osteogenesis may even be teamed with endoscopic techniques to allow the placement of these devices with minimal surgery.

Preliminary studies of rabbits have shown that distraction performed in the presence of recombinant human bone morphogenetic protein placed into the distraction site accelerates bone formation.

Distraction osteogenesis is showing great promise in the treatment of OSA. Although traditional combined maxillary and mandibular osteotomy are effective in treating mild-to-moderate OSA, the results are disappointing in patients with severe OSA (RDI >60) and/or a high BMI (>28). This is likely because traditional mandibular osteotomy has a physiologic limit of about 10 mm of advancement, which may be insufficient to open the airway for effective relief of the obstruction in the obese patient or in those with severe disease.

Distraction osteogenesis allows for advancement of up to 25 mm by using a specially designed distraction device, as depicted in the image below. In effect, the amount of distraction is individualized for each patient by performing polysomnography (PSG) after about 15-18 mm of advancement. If the PSG demonstrates a normal RDI, distraction is stopped to allow for consolidation. If the RDI is still elevated, distraction continues for the full 25 mm.

As part of this treatment protocol, the patient undergoes a LeFort I osteotomy with down fracture and then placed in intermaxillary fixation to allow the distraction device to move the maxilla and mandible as a unit and maintain the preexisting dental occlusion. In addition, the patient receives elective tracheotomy for airway protection. During PSG, the tracheotomy is occluded to avoid confounding the results.

When the distraction phase is completed, the cannula is removed. The consolidation phase is approximately 4 months, after which the device is removed. In 1 case series, this protocol was highly effective in the management of severe OSA. Patient selection and compliance are important for the success of this procedure.

One controversy involves the use of distraction osteogenesis instead of traditional bilateral sagittal split osteotomy. Some authors have stated that bilateral sagittal split osteotomy is an obsolete procedure with no role in current practice. In reality, traditional mandibular osteotomies will always have a role; however, distraction osteogenesis gives the surgeon another option in treating a wide variety of mandibular deficiencies.