Mandibular body osteotomy (Dingman)

A mandibular body ostectomy is an osteotomy with a segmental resection of a defined section of the mandibular body.

The inferior alveolar nerve typically crosses the osteotomy sites and the bony piece which has to be resected. In order to avoid damage to that nerve it is recommended to free and mobilize it from the inferior alveolar canal before the osteotomies and the resections are performed.

This osteotomy can only be used to shorten the mandibular body.

For a detailed description of how to plan orthognathic surgery, please click here.

In dentate patients some surgeons extract the tooth/teeth in the segment which is going to be resected before performing the osteotomies.

A transoral surgical approach is routinely used.

The inferior alveolar nerve can be identified and mobilized after removing the lateral cortical bone overlying the nerve. This can be facilitated by the use of a piezoelectric cutting device.

After the alveolar nerve is identified and mobilized, two parallel vertical osteotomy lines are marked with a pen or drill on the bone surface. The lingual mucoperiosteal layer is detached from the bone with a periosteal elevator. The osteotomy is then performed with either a saw, drill or piezoelectric saw.

While performing the osteotomies care must be taken to protect the nerve, for instance with a freer elevator.

After completion of both osteotomies the segment of bone is removed.

After bilateral resection, the anterior segment of the mandible is moved posteriorly into the preplanned position.

Mandibulo-maxillary fixation is performed to position the mandibular segments to the desired relationship with the maxilla. A prefabricated surgical splint (or wafer) may be used to facilitate this.

Internal fixation is usually performed with two straight miniplates one above and one below the inferior alveolar nerve. The plate placement and drilling is usually performed from the transoral route.

After completion of osteosynthesis on both sides, the MMF is released and the resulting occlusion is checked against the pre-planned position. The splint may be fixed to the maxillary teeth with a few thin wires and left in place during the healing phase to allow for neuromuscular adaption and position control.

If MMF screws or Temporary Anchoring Devices (TADs) are used intraoperatively, they are removed at the end of surgery if not further needed for elastic traction. If a final splint was used, it may be fixed to the orthodontic devices (brackets) of the upper jaw to assure the planned occlusion and to serve as guidance for the neuromuscular adaption during functional training for about 2 weeks postoperatively.

To reduce swelling, the application of ice-packs or cooling devices during the early post-operative phase is advice. Intravenous steroids should also be continued for a short period postoperatively for the same purpose.

Antibiotic prophylaxis is continued for 1-5 days depending on the nature, complexity, and duration of the surgical procedure.

Especially in two-jaw surgery, the airway control is of major importance. An individual decision has to be taken if the patient can be extubated or should remain intubated until it is clear that safe airway can be established.

Early post-operative x-rays are obtained to verify correct segment position. Additional postoperative imaging is performed as needed.

Regular follow up examinations to monitor healing and the postoperative occlusion are required. If an occlusal problem is present in the early postoperative phase, the surgeon must determine its etiology. If the malocclusion is secondary to surgical edema or muscle detachment/disorders, training elastics may be beneficial. The elastics are only used for guidance, because active motion of the mandible is desirable. Patients should be instructed how to place and remove the elastics using a hand mirror. If the malocclusion is secondary to a bone problem due to inadequate fragment positioning, displaced or failed hardware, or condylar displacement during surgery, elastic training will be of no benefit. The patient must be rescheduled for revision surgery.

At each appointment, the surgeon must evaluate the patient's ability to perform adequate oral hygiene and wound care and should provide additional instructions if necessary.

Postoperatively, patients will have to follow three basic instructions:

1. Diet
In orthognathic surgery the internal fixation devices usually do not allow for full functional load. A soft diet should be used up to 6 weeks, starting with liquids for the first 3-4 days. Elastics can be removed during eating.

2. Oral hygiene
Patients with intraoral wounds must be instructed in appropriate oral hygiene procedures. The presence of orthodontic appliances, the splint, and elastics makes this a more difficult task. A small soft toothbrush with toothpaste should be used.Any elastics are usually removed for oral hygiene procedures. Additionally, antiseptic rinses can be used in the early postoperative period. An oral irrigator (eg, Waterpik) is a very useful tool to help . If a Waterpik is used, care should be taken not to direct the jet stream directly over intraoral incisions to prevent wound dehiscence in the early postoperative phase.

3. Functional training/physiotherapy
The patient is instructed how to perform functional training (opening and excursive exercises) as soon as possible. The progress should be monitored by the surgeon. If available and needed, a physiotherapist can support the functional rehabilitation. An undisturbed mouth opening of minimum 35 mm interincisal jaw opening should be attained by 4 weeks postoperatively.

In case of undisturbed healing, the postoperative orthodontic treatment can usually start 2 to 6 weeks after surgery depending on the case.