Finite Element Evaluation of Stable Fixation in Combined Mandibular Fractures

Comparative Study of Miniplate vs Reconstruction Plate in the Management of Bilateral Parasymphysis Mandible Fracture: FEM Analysis

Aim and Objective

The present study compared the stability of fracture fragments in the management of bilateral parasymphysis mandible fracture with Miniplate fixation and Reconstruction plate fixation using finite element analysis.

Material and Method

3D FE Mandible model was created using CT scanner. Two bilateral parasymphysis mandible fracture models were created. Model 1 was fixed with Miniplates, and Model 2 was fixed with Reconstruction plate. Loading forces of 120 N at molar region and 62.5 N at incisor region were applied. These two models were imported to ANSY'S Workbench Software.

Result

Miniplate fixation model showed comparatively reduced gap between fragments than Reconstruction plate. But the gap values of both the models were within the physiologic limit of healing under this specific loading. Analytically Miniplates were superior to Reconstruction plate in the management of bilateral parasymphysis fracture.

Conclusion

Analytically Miniplates are superior to Reconstruction plate in the management of bilateral parasymphysis fracture. As the masticatory forces were reduced during fracture healing period, both fixations provide satisfactory healing. So both Miniplate and Reconstruction plate can be considered as fixation method for bilateral parasymphysis mandible fracture.

Biomechanical assessment of different fixation methods in mandibular high sagittal oblique osteotomy using a three-dimensional finite element analysis model

With modern-day technical advances, high sagittal oblique osteotomy (HSOO) of the mandible was recently described as an alternative to bilateral sagittal split osteotomy for the correction of mandibular skeletal deformities. However, neither in vitro nor numerical biomechanical assessments have evaluated the performance of fixation methods in HSOO. The aim of this study was to compare the biomechanical characteristics and stress distribution in bone and osteosynthesis fixations when using different designs and placing configurations, in order to determine a favourable plating method. We established two finite element models of HSOO with advancement (T1) and set-back (T2) movements of the mandible. Six different configurations of fixation of the ramus, progressively loaded by a constant force, were assessed for each model. The von Mises stress distribution in fixations and in bone, and bony segment displacement, were analysed. The lowest mechanical stresses and minimal gradient of displacement between the proximal and distal bony segments were detected in the combined one-third anterior- and posterior-positioned double mini-plate T1 and T2 models. This suggests that the appropriate method to correct mandibular deformities in HSOO surgery is with use of double mini-plates positioned in the anterior one-third and posterior one-third between the bony segments of the ramus.

Finite Element Analysis of Two- and Three-Dimensional Fixation in Treating Mandibular Symphyseal Fracture Combined With Bilateral Condylar Intracapsular Fractures

ABSTRACT

The aim of this study was to compare through finite element analysis two- and three-dimensional (2D and 3D) fixation in the treatment of mandibular symphyseal fracture combined with bilateral condylar intracapsular fractures. The authors created 2 fixation models for the above fracture, and analyzed the stress and displacement in the mandible and fixation materials under 3 loading conditions. The von Mises stress of the mandible and plates peaked during lateral occlusion, and was lowest during central occlusion. In all conditions, stresses in the fixation materials did not exceed the yield stress of titanium. The inferior border of the symphyseal fracture segments showed opposing displacements, and the mandible tended to widen in the 2D fixation model. However, the fracture displacement did not exceed 150 μm for either fixation method. The results suggested that after well reduction and fixation of condylar intracapsular fractures, either 2D or 3D fixation for symphyseal fracture can provide adequately strong fixation. Compared with 2D fixation, 3D fixation has more advantages in controlling the mandibular width and preventing the fixation materials from enduring excessive stress.

Biomechanical Analysis of Various Reconstructive Methods for the Mandibular Body and Ramus Defect Using a Free Vascularized Fibula Flap

Several different methods exist for reconstructing the mandibular body and ramus defect with the use of a free vascularized fibula flap, but none have adequately addressed the long-term mechanical stability and osseointegration. The aim of this study is to compare the biomechanics of different surgical methods and to investigate the best approach for reconstructing the mandibular body and ramus defect. Five finite element models based on different reconstructive methods were simulated. Stress, strain, and displacement of connective bone sections were calculated for five models and compared. The models were printed using a 3D printer, and stiffness was measured using an electromechanical universal testing machine. The postoperative follow-up cone beam computed tomography (CBCT) was taken at different time points to analyze bone mineral density of connective bone sections. The results showed that the “double up” (DU) model was the most efficient for reconstructing a mandibular body and ramus defect by comparing the mechanical distribution of three sections under vertical and inclined loading conditions of 100 N. The stiffness detection showed that stiffness in the DU and “double down” (DD) models was higher compared with the “single up” (SU), “single down” (SD), and “distraction osteogenesis” (DO) models. We used the DU model for the surgery, and postoperative follow-up CBCT showed that bone mineral density of each fibular connective section increased gradually with time, plateauing at 12 weeks. We conclude that a free vascularized fibula flap of the DU type was the best approach for the reconstruction of the mandibular body and ramus defect. Preoperative finite element analysis and stiffness testing were shown to be very useful for maxillofacial reconstruction.

Stress distribution in mandibular donor site after harvesting bone grafts of various sizes from the ascending ramus of a dentate mandible by finite element analysis

PURPOSE

Harvesting bone from the ascending ramus of the mandible is a common procedure. However, mandibular fracture may occur after grafting bone blocks. This study aimed to investigate the resulting force distribution of stress and strain in the mandibular donor site after harvesting bone grafts of different sizes and various loadings.

METHODS

Finite element analysis was performed for virtual harvesting of bone blocks of nine different sizes between 15 × 20 and 25 × 30 mm and three different chewing loads (incisal, ipsilateral and contralateral). von Mises stress and first principal stress distributions were measured.

RESULTS

von Mises stress was distributed between 35.01 (10 × 15 mm graft, incisal load) and 333.25 MPa (30 × 20 mm graft ipsilateral load), whereas first principal stress distributions were between 48.27 (10 × 15 mm graft, incisal load) and 414.69 MPa (30 × 20 mm graft ipsilateral load). In general, the least stress was observed with incisal load followed by ipsilateral load and finally contralateral load. The critical value of 133 MPa was found after removing almost all grafts with a width of 20 or 30 mm.

CONCLUSIONS

Incisal loading led to less stress compared with contralateral and ipsilateral loads. Increasing graft size led to increasing weakness of the donor site. Graft width exerted a greater influence on stress development than its height.

CLINICAL RELEVANCE

Ipsilateral chewing and increasing width of the bone graft result in maximum stress in the mandibular donor side, and critical values regarding to the possibility of fractures are already to expect from a graft size of 20 × 15 mm.

Integrity of a Single Superior Border Plate Repair in Mandibular Angle Fracture: A Novel Cadaveric Human Mandible Model

PURPOSE

The purpose of this study was to compare the integrity of human mandibular angle fracture after fixation with a single titanium plate along the upper lateral border with that of the native human mandible.

MATERIALS AND METHODS

This cross-sectional anatomic study involved the left hemimandibles of 16 human cadavers. They were selected and divided in 2 groups by remaining dental status. Additional predictor variables, such as height of the left mandibular body and gender, were noted. Left hemisected native mandibles were mounted at the condyle and loaded on an Instron 5565 mechanical unit (Instron Corp, Norwood, MA) until fracture. Fractured left hemimandibles were fixated with a titanium miniplate and screws. After plate fixation, each hemimandible was reloaded on an Instron 5565 until fracture. Data pertaining to primary outcomes of load application were recorded in newtons at displacement values of 3.0, 5.0, and 7.0 mm and at displacement at fixation failure. Primary outcomes of maximum load and displacement at maximum load were recorded in newtons and millimeters, respectively. Descriptive statistics were used to summarize sample characteristics. Statistical comparisons were performed using t test, χ² (or Fisher exact) test, and linear regression. Pearson correlation was used to examine relations between select biomechanical measurements.

RESULTS

The study sample was composed of 12 female and 4 male cadaveric hemimandibles. Donors' age at time of death ranged from 54 to 95 years (mean age, 78.94 yr). The mean maximum load in native and plated hemimandibles was 943.56 and 292.57 N, respectively (P < .0001).

CONCLUSION

Key clinical findings of this study include the inability of single plate mandible fixation to restore the mandible to preinjury levels and verification that gender, dental status, and height of the mandible do not alter the stability of a single plate fixated mandible.