Mandibular Defects

Malignant tumors associated with the lower gum, floor of mouth and adjacent structures also represent a difficult challenge for the prosthodontist with regard to rehabilitation after treatment. The disabilities resulting from such resections would include impaired speech articulation, difficulty in swallowing, deviation of the mandible during functional movements, and poor control of salivary secre-tions.33 Cosmetic disfigurement also can be present. These patients present a far more difficult rehabilitation problem than do patients with maxillary sur

Figure 20-11. A, Subtotal glossectomy—microvascular radial free flap reconstruction. B, Palatal augmentation prosthesis. C, Palatal augmentation prosthesis allowing contact of residual tongue against junction of hard and soft palate for swallowing and [k,g] phoneme improvement.

gical defects, particularly if a significant portion of the tongue is also resected.

Recently, advances in the reconstruction of such defects by means of microvascular free flaps have allowed the maxillofacial prosthodontist to rehabilitate these patients more effectively. With proper multidisciplinary pretreatment planning and postoperative treatment, osseointegrated implants can be strategically placed in patients with reconstructed mandibles to restore occlusal and masticatory functions.34-40

For the mandibular resection patient, most emphasis previously has been placed on the amount of mandible resected and the number of teeth remaining in the non-resected portion of the mandible. Equally important are the quantity and position of adjacent structures lost, including tongue, floor of mouth, and the buccal and lingual vestibules. The degree to which mastication is affected depends somewhat on the amount of mandible removed, but equally significant is the status of the tongue in function.41 The tongue must be able to place the food bolus on the occlusal surface of the teeth for mastication to take place. The tongue—which, in many instances has limited mobility and strength—is also required to balance the position of these removable prostheses.

Following segmental mandibulectomy an un-restored mandible becomes retruded and deviates toward the surgical site.42 When the mandible opens and closes, previous vertical movements are replaced by an oblique or diagonal motion controlled by the unilateral temporomandibular joint apparatus. Loss of one temporomandibular joint leads to less precise movements of the mandible. Loss of muscles of mastication in the resected side also forces the mandible to rotate upward upon closure if the coronoid process is present owing to the pull of the temporalis musculature. The severity and permanence of this mandibular deviation are unpredictable. Loss of the adjacent soft tissue and primary closure of the defect without flap reconstruction contribute to severe functional disability.

Closure of composite resections with soft-tissue flaps or grafts is desirable. Musculocutaneous flap closure can decrease the deviation of the mandible, making mandibular guide therapy more effective.

Traditionally, if mandibular continuity is not restored surgically, mandibular guide appliances, hemidentures, or palatal ramps on maxillary pros-theses are used to decrease mandibular functional disabilities. Sometimes these prosthetic appliances are cumbersome and do not provide a presurgical degree of functional mastication.

If mandibular continuity is not restored, a number of methods can reduce the degree of mandibular deviation. These methods include intermaxillary fixation (IMF) at the time of surgery, mandibular guidebar restorations, and palatal-based guidance restorations. If IMF is not employed, the patient should be placed into an exercise program as early as possible after surgery. On maximum opening, the mandible is displaced by hand as forcefully as possible toward the non-resected side. These movements tend to lessen scar contracture, reduce trismus and improve maxillomandibular relationships. Exercises should be carefully demonstrated to the patient and notes made periodically to record the degree of progress (via Boley gauge). The earlier the mandibular guidance is initiated, the more successful is the result.

If the patient is dentulous in the non-resected maxillary and mandibular quadrants, a cast mandibular resection prosthesis is appropriate. This prosthesis consists of a removable partial denture framework with a metal flange extending 7 to 10 mm laterally and superiorly on the buccal aspects of the maxillary bicuspids and molars on the unre-sected side. The non-resected quadrants of the maxilla and mandible must be periodontally stable and caries-free and should have enough bony support to absorb diagonal forces. The guide flanges engage the maxillary buccal bicuspid and molar surfaces during initial mandibular opening and closure, thereby directing the mandible to an appropriate intercuspal position. In the postoperative setting, mandibular guidance appliances are usually delayed until healing is complete (2 to 3 months).

Because many patients receive radiation therapy after mandibular resections, the oral mucosa is usually atrophic and fragile, predisposing it to soft-tissue irritation. Chronic alcohol abuse and poor nutrition may further compromise oral mucous membranes. The diminished output and thick muci-nous nature of saliva after radiation can impair retention and may be inadequate to lubricate the denture-mucosal interface. Deviation of the mandible can create abnormal maxillo-mandibular relationships that may prevent ideal placement of the denture teeth and flanges over their supporting structures.44 In the resected mandible patient, most consequential is the impairment of the motor and sensory control of tongue, lip, and cheek, limiting the ability of the patient to control dentures during function. The integrated neuromuscular balance between tongue, lips, and cheeks contributes to limited success of edentulous resection appliances. Microvascular free-flap mandibular reconstruction via a fibula has a success rate of 95 percent.43 By use of free-flap mandibular reconstruction followed by osseointegrated implants on selected patients, occlusal function can be restored.

Thus, as one readily can appreciate, osseointe-grated implant-supportive resection appliances can overcome many of the aforementioned difficulties, particularly those associated with compromised retention, stability, or support. Osseoimplants in the resected reconstructed irradiated mandible in selected patients, both with and without hyperbaric oxygen, have proven to be successful45 (Figure 20-12; see also Figures 19-6, D and E).

Osseointegrated implants are strategically placed in the fibula approximately 1 year after completion of all cancer therapy (Stage I). Using placement and surgical techniques described by Branemark and colleagues, 4 to 6 months for osseointegration is suggested prior to abutment placement (Stage II).

Figure 20-12. Osseointegrated fixed implants prosthesis in fibula free-flap mandibular reconstruction (6 years after surgery).

Bicortical integration is required, utilizing at least 10 mm implants into the fibula. A variety of occlusal schemes can be utilized with attention focused on providing maximum tongue movement for efficiency of mastication.

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