Evaluation of the effect of mandibular length and height on the sagittal split ramus osteotomy rigid internal fixation techniques: A finite element analysis

Biomechanical Evaluation of Seven Fixation Methods for Sagittal Split Ramus Osteotomy with Four Advancement Levels by Finite Element Analysis

Background

Mandibular sagittal split ramus osteotomy (SSRO) is a routine surgery to correct mandibular deformities, such as mandibular retrusion, protrusion, deficiency, and asymmetry. However, nonunion/malunion of the fragments and relapse caused by fixation failure after SSRO are major concerns. Rigid fixation to maintain postosteotomy segmental stabilization is critical for success. Additionally, understanding the biomechanical characteristics of different fixation methods in SSRO with large advancements is extremely important for clinical guidance. Therefore, the aim of the present study was to evaluate the biomechanical characteristics of different SSRO methods by finite element analysis.

Methods

SSRO finite element models with 5-, 10-, 15-, and 20-mm advancements were developed. Seven fixation methods, namely, two types of bicortical screws, single miniplate, dual miniplates, grid plate, dual L-shaped plates, and hybrid fixation, were positioned into the SSRO models. Molar and incisal biomechanical loads were applied to all models to simulate bite forces. We then investigated the immediate postoperative stability from four aspects, namely, the stability of the distal osteotomy segment, osteotomy regional stability, stress distribution on the mandible, and implant stress performance.

Results

The stability of the distal osteotomy segment and osteotomy region decreased when the advancement increased. All seven fixation methods displayed favorable biomechanical stability under minor advancement (5 mm). With large advancements, bicortical screws, dual miniplates, and grid plates provided better stability. The von Mises stress was concentrated around the screws close to the osteotomy region for the proximal segment for all fixation methods, and the von Mises stress on implants increased with larger advancements. With small advancements, five fixation methods endured tolerable maximum stresses of <880 MPa. A single miniplate and dual L-shaped plates generally suffered high stresses using larger advancements. The biomechanical characteristics were similar under molar and incisal loads.

Conclusions

The current study investigated the biomechanical properties of seven fixation devices after SSRO under molar and incisal loads. Generally, bicortical screws, grid plates, and dual miniplates provided better biomechanical stability using finite element analysis.

Evaluation of different fixation methods with finite element analysis in total mandibular subapical osteotomy

PURPOSE

The purpose of the study was to evaluate the stress distribution in various miniplates that were used in cases that underwent advancement with total mandibular subapical osteotomy (TMSO) using finite element analysis (FEA).

MATERIAL AND METHOD

Cone beam computed tomography (CBCT) images of a patient with appropriate bone tissues were used as a reference for the modeling of the mandible. In all mandibular models, horizontal TMSO was performed in a region 5 mm away from the apex of the teeth and vertical TMSO was performed in the retromolar region, 10 mm posterior to the second molar tooth. After TMSO, the dentoalveolar segment was advanced 3 mm and miniplates were placed symmetrically at four points for fixation. Four different miniplates with 2.0 mm thickness were used. Three different forces were applied to the models. Stress distribution on the models was evaluated using maximum von Mises stress values.

RESULTS

The maximum von Mises stress occurred in Y + I and Y + L models following the application of 300 N force from the incisal. An evaluation of posterior unilateral force indicated that the stress was remarkably high in the models with a posterior I-plate. The stress in the Y + I model was higher under unilateral force compared to the stress in other models. Under posterior bilateral force, the maximum von Mises stress values ​​occurred in the I-plates of T + I, Y + I, and L + I models (1006, 1012, and 1004 MPa, respectively).

CONCLUSION

Within the limitations of our study, we found that the ideal stress distribution was in the T + L and L + L plate combinations in the plates used for fixation after advancement with TMSO.