Preservation of the mandible in the management of cancer of the oral cavity

The proximity of the soft tissue of the oral cavity to the mandible requires evaluation of the potential involvement of the bony structure by contiguous spread of the tumor. Marchetta et al and Carter et al have demonstrated that cancer spreads to the mandible by direct invasion rather than through lymphatic spread. Thus, preservation of the entire mandible or partial resection of the mandible is oncologically feasible (Figure 2).

In the dentate mandible, invasion of the bone takes place mainly through the occlusal surface via the dental interstices. Thus, fixation of the tumor to the cortex of the mandible and direct invasion are unusual. Conversely, when the mandible is grossly eroded by tumor, a segmental resection is required. Another indication for segmental mandibulectomy is the patient who has received radiation to the oral cavity. In these patients, when the oral cancer abuts the previously radiated mandible, histological examination often shows multifocal involvement of the bone by the tumor. Thus, a segmental mandibulectomy is indicated.^{,  ,} 

Thus, in patients who have had previous radiation and present with cancer that abuts or is fixed to the mandible, preservation of the mandible is not oncologically feasible. Tumors that directly invade the mandible, as evidenced by preoperative radiographic evaluation, are also not candidates for conservation procedures.

Many techniques and skin incisions have been used for this procedure. These range from lazy-c incisions to z-plasties. All incisions heal well and result in excellent cosmesis. We routinely use a straight-line incision from the lip inferiorly down the chin. The only place that requires specific attention is the vermilion border. This must be realigned exactly or a noticeable cosmetic defect will be present. We score this to facilitate closure at the end of the case. A lip-splitting incision is used. Once the lip has been divided, we elevate cheek flaps bilaterally off the anterior symphysis. The soft tissue of the chin is elevated from the anterior aspect of the mandible. Care must be taken to preserve the mental nerve. Once the cortex is exposed, the proposed osteotomy is outlined with either cautery or a marking pen. Two-millimeter plates with two screws on either side of the proposed osteotomy site are positioned and holes drilled. Two plates are used (Figure 3A). The plates are tagged to allow proper orientation at the end of the case. The osteotomy is then performed in a step fashion. This allows for preservation of the genioglossal attachment to the genioglossal tubercle. It also prevents superior and inferior movement of the mandibular segment after plating. The mandible is divided with an oscillating saw and copious irrigation for temperature control. Once the mandible is divided, the two segments are retracted laterally, and an incision is made in the mucosa of the floor of the mouth (Figure 3B). Adequate mucosa is left attached to the mandible to reconstruct the soft tissue (Figure 3C,D). At the end of the procedure, reconstruction of the mandible is undertaken with the two previously measured and bent plates. These are fixed to the mandible with 8-mm, 2.0 monocortical screws (Figure 3E). We do not place the patient in intermaxillary fixation or restrict diet in the immediate postoperative period. Eating and chewing is more limited by the tumor resection and reconstructive technique than by the repair of the mandible.

Marginal mandibulectomy has proved to be an efficacious procedure in the oncologic management of oral cavity carcinoma. The local regional recurrence rate is low, and the maintenance of mandibular continuity with native mandible facilitates oral rehabilitation.