Abstract
The aim of this study was to evaluate the stress and dislodgement resistance by finite element analysis of different types of fixation in mandibular orthognathic surgery. A 3D solid finite element model of a hemi-mandible was obtained. A bilateral sagittal split osteotomy was simulated and the distal segment was advanced 5 mm forward. After the adjustment and superimposing of segments, 9 different types of osteosynthesis with 2.0 miniplates and screws were simulated: A, one 4-hole conventional straight miniplate; B, one 4-hole locking straight miniplate; C, one 4-hole conventional miniplate and one bicortical screw; D, one 4-hole locking miniplate and 1 bicortical screws; E, one 6-hole conventional straight miniplate; F, one 6-hole locking miniplate; G, two 4-hole conventional straight miniplates; H, two 4-hole locking straight miniplates; and I, 3 bicortical screws in an inverted-L pattern. In each model, forces simulating the masticatory muscles were applied. The values of stress in the plates and screws were checked. The dislodgement resistance was checked at the proximal segment since the distal segment was stable because of the screen at the occlusal tooth. The regions with the lowest and highest displacement were measured. The offset between the osteotomized segments was verified by millimeter intervals. Inverted-L with bicortical screws was the model that had the lowest dislodgment and the model with the lowest tension was the one with two conventional plates. The results suggest that the tension was better distributed in the locking miniplates, but the locking screws presented higher concentration of tension.
Highlights
The bilateral sagittal split osteotomy of the rami (BSSO) is recognized as a standard procedure for treatment of certain mandibular discrepancies
The bone stabilization progressed from osteosynthesis by steel wire with maxillomandibular intermaxillary block (MMI) to the rigid internal fixation with titanium miniplates and screws
Some disadvantages related to methods of rigid fixation should be remembered, like displacement of the condyle, irreversible nerve injuries related to compression caused by screws or miniplates, difficulty in cases of reintervention and occlusal changes [4]
Summary
The bilateral sagittal split osteotomy of the rami (BSSO) is recognized as a standard procedure for treatment of certain mandibular discrepancies. The bone stabilization progressed from osteosynthesis by steel wire with maxillomandibular intermaxillary block (MMI) to the rigid internal fixation with titanium miniplates and screws. The stable internal fixation is the standard procedure used to stabilize the BSSO in oral and maxillofacial surgery [3]. Different methods of internal fixation have been used to allow quick mobility and the return to function after BSSO. Some disadvantages related to methods of rigid fixation should be remembered, like displacement of the condyle, irreversible nerve injuries related to compression caused by screws or miniplates, difficulty in cases of reintervention and occlusal changes [4]
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