Fixation Methods for Mandibular Advancement and Their Effects on Temporomandibular Joint: A Finite Element Analysis Study.

OBJECTIVES: Bilateral sagittal split osteotomy (BSSO) is a common surgical procedure to correct dentofacial deformities that involve the mandible. Usually bicortical bone fixation screw or miniplates with monocortical bone fixation screw were used to gain stability after BSSO. On the other hand, the use of resorbable screw materials had been reported. In this study, our aim is to determine first stress distribution values at the temporomandibular joint (TMJ) and second displacement amounts of each mandibular bone segment. METHODS: A three-dimensional virtual mesh model of the mandible was constructed. Then, BSSO with 9 mm advancement was simulated using the finite element model (FEM). Fixation between each mandibular segment was also virtually performed using seven different combinations of fixation materials, as follows: miniplate only (M), miniplate and a titanium bicortical bone fixation screw (H), miniplate and a resorbable bicortical bone fixation screw (HR), 3 L-shaped titanium bicortical bone fixation screws (L), 3 L-shaped resorbable bicortical bone fixation screws (LR), 3 inverted L-shaped titanium bicortical bone fixation screws (IL), and 3 inverted L-shaped resorbable bicortical bone fixation screws (ILR). RESULTS: At 9 mm advancement, the biggest stress values at the anterior area TMJ was seen at M fixation and LR fixation at posterior TMJ. The minimum stress values on anterior TMJ were seen at L fixation and M fixation at posterior TMJ. Minimum displacement was seen in IL method. It was followed by L, H, HR, M, ILR, and LR, respectively. CONCLUSION: According to our results, bicortical screw fixation was associated with more stress on the condyle. In terms of total stress value, especially LR and ILR lead to higher amounts.

Does fixation method affects temporomandibular joints after mandibular advancement?

PURPOSE: Sagittal split ramus osteotomy (SSRO) is a standard procedure in which miniplates and screws are used to achieve stabilization. Although the titanium plate and screw fixation system is stable, resorbable fixation systems are also used. There is currently no consensus on the ideal fixation technique for SSRO procedures and its effect on the condyle. We aimed to evaluate the stress distribution on temporomandibular joints (TMJ). METHODS: A 3D finite element model of a hemimandible was designed and 5 mm advancement was simulated on a computer model. Four different fixation techniques were applied: inverted-L shaped bicortical screws, L-shaped bicortical screws, miniplate with monocortical screws, and miniplate with monocortical screws and bicortical screw. Computer models were prepared twice for resorbable and titanium material. Load of 600N and muscle forces were applied. In the finite element analysis, computer models simulated and analyzed stress distribution of bone, fixation materials and condyle. RESULTS: Bicortical screws increase the total stress on TMJ, and the stress is located more on the posterior part than the anterior. Miniplates decrease the stress, and the forces are located more on the anterior aspect of the TMJ. CONCLUSION: According to our analysis, the use of bicortical screws increases the stress amount on the condyle. For the patients with a tendency toward temporomandibular disorders, using miniplate fixation techniques may decrease the forces around the condyle. These findings should be useful for oral surgeons when deciding on the most appropriate fixation technique in patients with a tendency toward temporomandibular joint disorders.