Size and Location of Mandibular and Soft Tissue Defects

Mandibular segmental defects involving the symphysis and parasymphysis are the most significant in terms of aesthetic and functional morbidity. Failure to reconstruct this part of the mandible results in the Andy Gump deformity and loss of the tongue-anchoring and masticatory platform functions of the anterior arch. The anterior arch also serves to anchor the hyomandibular muscle complex involved in laryngeal elevation and deglutition. Experience with MRPs has revealed an unac-ceptably high rate (35%) of hardware failure, mainly from plate exposure and breakage due to the pulling forces of the geniohyoid and digastric muscles attached to the remaining soft tissues surrounding the plate (6) (Fig. 1). This effect is compounded by gravity and the use of regional myocutaneous flaps pedicled inferiorly (e.g., the pectoralis flap).

Two common issues with regard to microvascular mandibular replacement are the type of fixation needed to secure the bone graft in place and the method used to size and shape the bone graft accurately to match the resected segment closely. Rigid fixation is required to secure the bone graft to the mandibular stumps. Either simple -g mandibular plates fixed to either end of the bone graft to the mandibular stumps or a |

continuous microvascular reconstruction plate can be used. Wire fixation should be »

avoided as excessive movement may impede osseous union. The mandibular plates are each secured with three screws in the native mandible and two screws in the graft.

A continuous microvascular plate is thinner than the typical MRP and the newer plates are locking screw-type with smaller holes and screws. With regard to the sizing and shaping of the bone graft, a microvascular plate can be adapted to the native mandible prior to resection and the bone graft fit to it ex vivo. As an alternative, §

the resected specimen is inspected and the bone graft is osteotomized and sized to

Figure 1 An MRP alone was used to reconstruct an anterior arch defect. This patient experienced both plate breakage (a) and exposure (b) approximately 2 years postoperatively.

approximate the size and shape of the resected bone. If possible, it is helpful to place the patient in temporary maxillary-mandibular fixation during placement of the bone graft and application of hardware. Often the bone graft lacks the height of the native mandible. In these cases, the graft should be aligned with the superior aspect of the native mandible to minimize the required height of osseointegrated implants and to eliminate any step-offs that may interfere with a tissue-borne denture. In some cases, a template-driven method for sizing and shaping the bone graft is lacking and a stereolithographic model may be of use. Using computed tomography (CT) data, a three-dimensional model is created using computer-aided design (CAD) software. This model is then used to create custom reconstruction plates that can be used as a template for the bone graft and to secure the graft into place

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