Biomechanical effects of surgical cut direction in unilateral mandibular lengthening by distraction osteogenesis using a finite element model

The Stress Concentration and Biomechanical Properties of the Intra-oral Distractors and the Extra-oral Distractors Used in Treatment of Post Ankylosis Facial Asymmetric Patients: A Finite Element Analysis Study

ABSTRACT

Assessment of stress and micromotions using finite element analysis along both the intraoral and the extraoral distractors devices used in the mandibular distraction of post temporomandibular joint ankylosis deformed mandible patients. The process of finite element analysis was carried out to assess distraction models. The first model was an extraoral mandibular distraction model and the second model was an intraoral mandibular distraction model. To analyze the stress state, 2 vertical loads were applied on the defective and normal side respectively by a 3D finite element ball model. The intraoral system observed lower stress (4.5 MPa) in the mandibular bone compared to the extra-oral system (11.5 MPa). The results revealed that the intraoral system observed higher stress on the distractor fixing points (392.21 MPa) compared to the extra-oral fixing points (12.62 MPa). The results revealed that the extra-oral system reflected higher displacement on the bone surrounding the screws of about 3720 μm compared to the intraoral system 1414.6 μm. Internal devices give better shielding to the bone and induce fewer stresses over the mandibular, so it is more advisable to be used. The external devices permit greater distraction length because the pins and the distractor main body are subjected to fewer stresses.

The Stress Concentration and Biomechanical Properties of the Intraoral Distractors and the Extraoral Distractors Used in Treatment of Hemifacial Microsomia Patients: A Simulation Finite Element Analysis Study

THE AIM OF THE STUDY

Finite element analysis of the stresses subjected to both the intraoral and the extraoral distractors devices used in the mandibular distraction of hemifacial microsomia patients.

METHODOLOGY

Two models were included in the current study. The first model was an extraoral distractor and the second model was an intraoral distractor model. To generate the results in the simulated models; 2 vertical loads were applied (222.7 and 137.78 N) on the defective and normal side, respectively.

RESULTS

The intraoral system observed lower stress (6.85 MPa) in the mandibular bone compared to the extraoral system (13.21 MPa). The intraoral distractor had a higher stress concentration on the distractor fixing screws (352 MPa) compared to the extraoral distractor fixing pins (15 MPa). The extraoral distractor had a higher displacement effect on the mandibular bone around the pins of 263.35 μm in comparison to the intraoral distractor effect which was 77.87 μm.

CONCLUSIONS

Internal oral distractor provides a sort of stress shielding to the distracted bone and less displacement, so it is more advisable to be used in general. The external devices are advised only in extralong distraction distance because the distractor is subjected to lower stresses compared to intraoral counterparts.

The relations between the stress in temporomandibular joints and the deviated distances for mandibular asymmetric patients

The study aimed to compare the difference of stress distributions in temporomandibular joints (TMJs) between the patients with mandibular asymmetry and asymptomatic subjects and find the relations between deviated distance and biomechanical stress using three-dimensional finite element method, to give guidance to dentists for correction of mandibular asymmetry. Ten facial symmetric subjects without symptoms of temporomandibular disorders (TMD) and 10 mandibular asymmetric patients were recruited and assigned as the Control and Case group respectively. The FE models of the mandible and maxilla were reconstructed from cone-beam computed tomography (CBCT) images. Muscle forces and boundary conditions were applied to the two groups corresponding to centric and anterior occlusions. The simulation manifested significant differences in stresses of the TMJs between the non-deviated and deviated sides in the Case group under the centric and anterior occlusions. The stresses in the Case group were significantly greater than those in the Control group, especially on the non-deviated side. Besides, there were weak and moderate correlations between the third principal stresses and deviated distances for the patients under centric and anterior occlusions. The excessive stresses in the TMJ of patients with mandibular asymmetry were associated with temporomandibular disorders.

Biomechanical analysis of a curvilinear distractor device for correcting mandibular symphyseal defects

PURPOSE

The local mechanical environment is a determinant of successful transport disc distraction osteogenesis. This study assessed the biomechanics of a curvilinear distractor device for correcting mandibular symphyseal defects.

MATERIALS AND METHODS

The finite element method was used to analyze an intact mandible, mandibular distractor bodies with different rail thicknesses (4, 6, 8, and 10 mm), and mandibular distractor bodies with rails and auxiliary lingual brackets.

RESULTS

Rail thickness was positively correlated with maximum von Mises stress in the distractor and negatively correlated with maximum displacement of the mandibular distractor bodies. The maximum von Mises stress occurred at the junction of the rails and fixed arms. It also exceeded the yield strength of the titanium material. Compared with the maximum displacement of the intact mandible, that of the mandibular distractor bodies was visibly increased.

CONCLUSION

An auxiliary lingual bracket can effectively decrease stress in such devices and displacement of mandibular distractor bodies. Rail fixation alone cannot achieve stability for distraction osteogenesis. Using an auxiliary lingual bracket effectively prevents distractor breakage and exposure.