Complete bony ankylosis of the TMJ is a significant problem for patients as well as doctors. When the total joint reconstruction surgery with alloplastic materials is planned, it would be necessary to combine the advantages of stock TMJ prosthesis and custom-made TMJ prosthesis: a single-stage approach, low-cost, more precise surgical outcome, and less operation time-consuming.
There are several considerations for accurate placement of the stock TMJ prosthesis. First, since the stock TMJ prosthesis does not fit perfectly to the resection site due to straight design, leading to difficulty in properly positioning the condylar component medio-laterally. As a solution for this problem, the fossa component of the stock TMJ prosthesis system was fixated, followed by fixation of the condylar component and adjustment of its medio-lateral position by controlling the depth of the fixation screws.
Second, because the tissue surface of the condylar component of the stock TMJ prosthesis is flat, it is difficult to get a perfect adaptation onto the resection site. Therefore, the frontal ramus inclination of the condylar component of the stock TMJ prosthesis should be meticulously investigated. In the frontal view, if the lower margin of the condyle components of the stock TMJ prosthesis at the mandibular angle area is located medial to the glenoid fossa, the condyle head portion of the condyle components of the stock TMJ prosthesis may be positioned too laterally. In contrast, if the lower margin of the condyle components of the stock TMJ prosthesis at the mandibular angle area is located lateral to the glenoid fossa, opposite situation may arise. By controlling the insertion depth of fixation screws, such problems can be overcome. The insertion depth of fixation screws can be controlled while observing the relationship between the condyle head portion of the condyle component and the glenoid fossa. For example, if the frontal ramus inclination of the condylar component of the stock TMJ prosthesis is inclined to inward, the upper fixation screws for the condyle components can be inserted loosely, while the lower fixation screws can be inserted to their full depth.
The advantage of the system we used is that the cutting condyle and positioning TMJ prostheses can be determined according to the patient’s anatomy before surgery. Therefore, the need to perform the staged operation in two times is reduced, the operation time can be shortened, and using stock prostheses is cheaper than customized TMJ prostheses. In disadvantage, it’s less accurate than customized. The three-dimensional position can be grossly positioned the same as the surgical plan, but because the adaptation of prostheses is not accurate, minor differences such as the frontal ramal angle may occur. In order to overcome this drawback, the condyle prostheses should be placed first, and then the condylar part can be positioned more accurately. Another disadvantage of this system is that when condyle cutting, prediction of medio-lateral depth is not possible, so the perception of the safety zone toward the cranial base must be present before surgery.
In this case with recurrent bony TMJ ankylosis in both sides, all treatment objectives of total joint reconstruction surgery including improvement of mouth opening, correction of deformity, pain relief, and prevention of re-ankylosis were met with the use of 3D virtual surgical planning, CAD/CAM-fabricated surgical guides, and stock TMJ prostheses. However, it is necessary to increase the sample size and longitudinal long-term follow-up for evaluating possible complications.