Introduction
Mandibular defects can range from isolated segmental deficiencies to large extensive areas of bone loss involving the entire jaw. These defects can result from trauma, infection, and/or resection of benign and malignant tumors. Many options are available for mandibular reconstruction, including reconstruction plates, particulate bone grafts, block grafts, and free tissue transfer such as a tibular graft. Each of these techniques carries with it significant morbidity.

Distraction osteogenesis (DO) is a new option for correcting height of deficient alveolar bone as an alternative to antral bone grafting. It has proven also to be a reliable method for reconstructing missing segments of resected bone.1 Distraction osteogenesis is an excellent treatment option because both hard and soft tissues are reconstructed at the same time using the same procedure.

Recently a new type of distractor became available for reconstructing segmental mandibular defects that meet distraction osteogenesis objectives. In this technique, a plate-guided distraction device (PGD) is attached to a standard reconstruction bar, and the palate intimately follows the shape of the plate and the mandibular contour during distraction. This allows for three dimensional vector control during the distraction process.2,3 This internal DO device may obviate the need for more major surgery.

Three patients underwent transport distraction osteogenesis using the PGD for reconstructing discontinuity mandibular defects. The size of the defects ranged from 4 to 7 centimeters and involved the angle, body, and symphysis regions. The defects resulted from excision of squamous cell carcinoma (SSCA) fibrosarcoma, and ameloblastoma. One of the cases is reported here.

Report of one case
A 50-year-old hispanic female presented with a mandibular lesion which was biopsied and found to be fibrosarcoma. A complete mandibular resection (hemi-mandibulectomy) was performed to remove the lesion and a reconstruction plate was placed. After 8 months the patient had distraction osteogenesis using the new PGD to restore the missing mandibular tissue involving the angle and body of her mandible.

An osteotomy was made to provide for the transport segment of bone. Care was taken to minimally disrupt the periosteal blood supply to the segment.

The PGD was placed and secured to the plate proximally and to the transport segment distally. The device was activated to ensure uniform distraction between the host mandible and the transport segment (Fig. 1).

After a 7-day latency period the device was activated at a rate of 0.5 mm twice per day. The distraction continued until the transport segment docked against the host bone (see Fig. 2,3).

The device was left in place for 12 weeks and subsequently removed. A bone graft harvested from the metaphysis of the proximal tibia was used to ensure union between the transported bone segment and the proximal mandible (Fig. 3) facial symmetry has been restored along with full function (Fig. 4).

Animal research in distraction osteogenesis
Recent research has involved the use of bone inductor cytokines to facilitate the bone reconstruction process in distraction osteogenesis. Since distraction osteogenesis is dependent upon the slow movement of the bone segments, it would be advantageous if rapid osseous repair of the distracted segment could be effected by the addition of bone-inducting cytokines.

To evaluate this theory: (1) the posterior edentulous ridges of Macaca fascicularis monkeys were elevated bilaterally by a distraction osteogenesis device, and (2) a BMP cytokine was injected on one side into the distracted area using a collagen carrier.

On the opposite side the collagen carrier with no BMP inductor was injected. It was found after eight weeks that the distracted segment having the BMP carrier showed an accelerated bone healing process as opposed to the control.

This opens the way to new research and clinical application of two synergistic techniques of increasing the height of alveolar ridges as well as other areas involving osseous defects of the mandible and maxilla (Fig 5).