2017-18 HSC Section 3 Green Book

Volume 137, Number 1 • Hybrid Maxillomandibular Fixation System

Fig. 2. ( Above ) Pantomogram of a patient with multiple missing teeth with right parasymphysis fracture of the mandible. ( Below ) Pantomogram of the same patient after placement of hybrid maxil- lomandibular fixation to establish the vertical dimension and open reduction and internal fixation with two miniplates.

placing an average of seven screws per arch for a total of 14 screws. The number of screws can likely be decreased to five screws per arch and still have enough rigidity because of the inherent rigidity of the titanium alloy of the SMARTLock system. If five screws are used per arch (10 screws total), this would potentially decrease the time of placement of the SMARTLock system to 10.3 minutes. Removal of the system was simple. Patients were able to tolerate removal without local anes- thesia if there was no mucosal overgrowth of the screws. The most common complication associ- ated with the system was mucosal overgrowth, which occurred in 38 percent of patients (Fig. 4). Overgrowth of the mucosa did not seem to have any unwanted effect except for making removal more difficult. When there was mucosal over- growth, local anesthesia was administered and a stab incision with a no. 15 blade was made to access the screws. Proper use of the screw spacer instrument will create space between the mucosa, and improper spacing will increase the chance of mucosa migrating over the screws. Other complications associated with the SMARTLock system included screw loosening, which accounted for 10 screws (3.1 percent) in four patients (17 percent). One patient had

one missing screw. The stability of screws can be increased by inserting the screws orthogonal to the bone. Four patients (17 percent) reported lip irritation. The lugs on the SMARTLock system are larger than the traditional Erich arch bars, which may lead to more lip irritation. This can be man- aged by bending the lugs inward with an instru- ment and providing the patient with orthodontic wax to place on the lugs. One patient had wound dehiscence, which may have been affected by the proximity of the screw holes to the incision used to access the mandibular fracture. Modifying the mucosal incision may be necessary when using the SMARTLock system to prevent the incision from being too close to the screw holes. Radiographic analysis of tooth root damage showed that 7.5 percent of screws caused dentin injury, pulp injury, or root fracture (Table 10). A majority of the screws (92.5 percent) either were completely in bone or encroached on the peri- odontal ligament but did not cause root damage. The incidence of radiographic tooth involve- ment on cone-beam computed tomography was 7.5 percent. Root damage can be prevented by using preoperative panoramic radiographs to plan placement of screws and by bending the screw holes away from room prominences. All screws

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