OBJECTIVES: The objective of this study is to measuring the morphology and position of bilateral temporomandibular joints in patients with unilateral and bilateral molar scissor bite and simulating the deformation of the mandible during occlusion, in order to provide thesis for the diagnosis of temporomandibular joint disease in patients with unilateral and bilateral molar scissor bite. METHODS: This study was a retrospective study. A total of 10 patients with unilateral molar scissor bite (the unilateral molar scissor bite group) and 10 patients with bilateral molar scissor bite (the bilateral molar scissor bite group) were selected as the experimental group, and 20 adult patients with classⅠ of angle classification of similar ages were selected as the control group. All patients underwent cone beam computed tomography scans, by measuring the width of the fossa, height of the fossa, articular eminence inclination, long axis of the condyle, minor axis of the condyle, horizontal angle of the condyle and the space of the temporomandibular joint, compare temporomandibular joint morphology and position. The three-dimensional finite element analysis of the mandible morphology was carried out to evaluate the force and deformation of the mandible by using software to simulate the occlusion of the patients. It was further explored the relationship between the force of the mandible morphology and the possible temporomandibular joint disorder symptoms of the patients. RESULTS: Intergroup comparisons for the unilateral molar scissor bite group and left sides of the other groups revealed that the superior articular space in the group with unilateral molar scissor bite was shorter than that in the control group (P<0.05); the long axis of the condyle in the unilateral and bilateral molar scissor bite group were both shorter than that of the control group (P<0.05); among which the unilateral group was larger than the bilateral group, and the minor axis of the condyle in bilateral molar scissor bite group was smaller than in the control group (P<0.05), and the unilateral and bilateral condylar groups were larger than the control group (P<0.05); and the condylar horizontal angle in the unilateral and bilateral groups were larger than that in the control group (P<0.05). The normal sides of the unilateral molar scissor bite group and right sides of the other groups had smaller superior articular space than the control group (P<0.05); and the condylar long-axis in bilateral group was smaller than the control group (P<0.05); and the normal side of the condylar short-axis unilateral group was larger than that of the bilateral condylar group. Three-dimensional finite element analysis: the condyle of patients with molar scissor bite was a concentrated area of deformation during the bite of the mandible, when the first molar occlusion of the scissors bite side was simulated, the maximum deformation was located in the condyle in the X-axis and Z-axis directions. The amount of deformation was greater than that of the scissor bite side in the X-axis direction, while in the Z-axis direction, the normal side was greater than the scissor bite side. The maximum sites of local deformation in the X-axis direction were located in anterior and posterior the transverse crest of scissor bite side, and the minimum sites of local deformation was at 1/3 of the anterior slope of the inner pole of the normal side, the maximum local deformation sites in the Z-axis direction were located in the outer pole and below the outer pole of the normal side. The X-axis deformation value was the largest in the molars occlusion on the normal side, the Y-axis deformation value was in the premolars occlusion on the normal side, and the Z-axis deformation value was the largest in the centric occlusion, the deformation value of the condyle was not most significant in molar scissor bite. CONCLUSIONS Unilateral and bilateral molar scissor bite resulting in a short condyle morphology, and the bilateral group had a shorter condylar morphology than the unilateral group. The condyle of the patient with molar scissor bite is a concentrated area of poor occlusal deformation, and the largest sites of deformation are distributed near the transverse ridge of the inner and outer poles of the condyle. Different occlusion conditions have an effect on condylar deformation values, but do not indicate whether there is a clear association between them.
Humans ; Finite Element Analysis ; Retrospective Studies ; Temporomandibular Joint/pathology* ; Cone-Beam Computed Tomography ; Mandible/pathology* ; Imaging, Three-Dimensional ; Adult ; Temporomandibular Joint Disorders/diagnostic imaging* ; Mandibular Condyle/diagnostic imaging* ; Female ; Male ; Molar

OBJECTIVES: This study aims to analyze the biomechanics of three kinds of rigid internal fixation methods for condylar head fractures. METHODS: A three dimensional finite element model of the normal mandible was constructed. It was then used to prepare condylar head fracture finite element model and three kinds of rigid internal fixation finite element model (unilateral tension screw, bilateral tension screw, tension screw+titanium plate). The mechanical characteristics and changes of the mandible condyle under the same mechanical conditions were compared among the three different rigid internal fixation methods. RESULTS: The maximum equivalent stress and displacement of the non-free end of condyle under the rigid internal fixation method of unilateral tension screw were 71.03 MPa and 4.72 mm, respectively. The maximum equivalent stress and displacement of the free end of condyle were 78.45 MPa and 4.50 mm, respectively. The maximum stress of fracture suture was 3.27 MPa. The maximum equivalent stress and displacement of the non-free end of condyle under the rigid internal fixation method of bilateral tension screw were 70.52 MPa and 4.00 mm, respectively. The maximum equivalent stress and displacement of the free end of condyle were 72.49 MPa and 3.85 mm, respectively. The maximum stress of fracture suture was 2.33 MPa. The maximum equivalent stress and maximum displacement of the non-free end of condyle under the rigid internal fixation method of tension screw+titanium plate were 67.26 MPa and 2.66 mm, respectively. The maximum equivalent stress and maximum displacement of the free end of condyle were 69.66 MPa and 2.50 mm, respectively. The maximum stress of fracture suture was 2.18 MPa. CONCLUSIONS The tension screw+titanium plate rigid internal fixation method is the most conducive to biomechanical distribution for condylar head fractures.
Fracture Fixation, Internal/instrumentation* ; Mandibular Condyle/surgery* ; Biomechanical Phenomena ; Bone Screws ; Finite Element Analysis ; Humans ; Mandibular Fractures/surgery* ; Bone Plates ; Titanium ; Stress, Mechanical

OBJECTIVE: To compare the biomechanical properties of four internal fixation methods in a lower cervical spine injury model using the finite element method. METHODS: Cervical CT data of a 28-year-old healthy adult male were utilized to establish a finite element model of the normal cervical spine and a lower cervical spine three-column injury model. Four internal fixation methods were then applied to the three-column injury model, resulting in four groups:Group A, anterior cervical locked-plate(ACLP) fixation system model(anterior approach);Group B, posterior cervical pedicle screw fixation model (posterior approach);Group C, combined anterior and posterior cervical pedicle screw fixation model; Group D, Novel composite anterior cervical internal fixation model. A 75 N axial compressive load and a 1.0 N·m pure moment were applied to the upper surface of the cervical spine model to simulate flexion, extension, rotation, and lateral bending movements. The intervertebral range of motion(ROM) and stress distribution of the internal fixators under different motion conditions were compared across all models. RESULTS: Compared with the normal model, the reductions in overall intervertebral ROM for each group under flexion, extension, rotation, and lateral bending were as follows:Group A, 24.04°, 23.12°, 6.24°, and 9.06°;Group B, 24.42°, 24.34°, 6.48°, and 9.20°;Group C, 25.43°, 25.29°, 7.17°, and 9.57°;Group D, 24.75°, 25.5°, 6.71°, and 9.12°. The peak stress values of the internal fixators in each group were:Group A, 53.9 MPa, 79.9 MPa, 61.4 MPa, and 80.3 MPa;Group B, 218.3 MPa, 105.4 MPa, 206.6 MPa, and 186.8 MPa;Group C, 40.8 MPa, 97.2 MPa, 47.1 MPa, and 39.4 MPa;Group D, 93.0 MPa, 144.0 MPa, 64.8 MPa, and 106.3 MPa. CONCLUSION The biomechanical properties of the novel composite anterior cervical internal fixation method are similar to those of the combined anterior-posterior fixation method, and superior to both the anterior cervical ACLP plate-screw fixation and posterior cervical pedicle screw fixation methods.
Humans ; Finite Element Analysis ; Cervical Vertebrae/physiopathology* ; Male ; Biomechanical Phenomena ; Adult ; Fracture Fixation, Internal/methods* ; Range of Motion, Articular

PURPOSE: To judge the injury mode and injury severity of the real human body through the measured values of anthropomorphic test devices (ATD) injury indices, the mapping relationship of lumbar injury between ATD and human body model (HBM) was explored. METHODS: Through the ATD model and HBM simulation, the mapping relationship of lumbar injury between the 2 subjects was explored. The sled environment consisted of a semi-rigid seat with an adjustable seatback angle and a 3-point seat belt system with a seatback-mounted D-ring. Three seatback recline states of 25°, 45°, and 65° were designed, and the seat pan angle was maintained at 15°. A 23 g, 47 km/h pulse was used. The validity of the finite element model of the sled was verified by the comparison of ATD simulation and test results. ATD model was the test device for human occupant restraint for autonomous vehicles (THOR-AV) dummy model and HBM was the total human model for safety (THUMS) v6.1. The posture of the 2 models was adjusted to adapt to the 3 seat states. The lumbar response of THOR-AV and the mechanical and biomechanical data on L1 - L5 vertebrae of THUMS were output, and the response relationship between THOR-AV and THUMS was descriptive statistically analyzed. RESULTS: Both THOR-AV and THUMS were submarined in the 65° seatback angle case. With the change of seatback angle, the lumbar spine axial compression force (F_z) of THOR-AV and THUMS changed in the similar trend. The maximum F_z ratio of THOR-AV to THUMS at 25° and 45° seatback angle cases were 1.6 and 1.7. The flexion moment (M_y) and the time when the maximum M_y occurred in the 2 subjects were very different. In particular, the form of moment experienced by the L1 - L5 vertebrae of THUMS also changed. The changing trend of M_y measured by THOR-AV over time can reflect the changing trend of maximum stress of L1 and L2 of THUMS. CONCLUSION The F_z of ATD and HBM presents a certain proportional relationship, and there is a mapping relationship between the 2 subjects on F_z. The mapping function can be further clarified by applying more pulses and adopting more seatback angles. It is difficult to map M_y directly because they are very different in ATD and HBM. The M_y of ATD and stress of HBM lumbar showed a similar change trend over time, and there may be a hidden mapping relationship.
Humans ; Lumbar Vertebrae/injuries* ; Finite Element Analysis ; Biomechanical Phenomena ; Manikins ; Spinal Injuries/physiopathology*

PURPOSE: Hand-sewn anastomosis as the gold standard of vascular anastomosis cannot fully meet the requirements of vascular anastomosis in speed and quality. Various vascular couplers have been developed to ameliorate this situation. Most of them are mainly used for venous anastomosis rather than arterial anastomosis. Although it is generally acknowledged that in almost all operations involving vascular reconstruction, it is the arteries that need to be anastomosed faster and more accurately and not the veins. A dedicated device is needed for creating arterial anastomosis in an easy, timesaving, less damaging but reliable procedure. Therefore, we plan to develop a novel arterial coupler device and test pre-clinical safety and effectiveness. METHODS: In this cohort study, the rationality of this novel arterial coupler was preliminarily tested by finite element analysis before it was manufactured. Several factors restrict the use of vascular couplers in arterial anastomosis, such as arterial eversion, fixation, etc. The manufactured arterial couplers underwent in vitro and in vivo experiments. In vitro, isolated arteries of beagles were anastomosed with the assistance of an arterial coupler, and the anastomosed arteries were evaluated through anti-traction tests. In animal experiments, the bilateral femoral arteries of 5 beagles served as a control group. After dissection, the femoral artery on one side was randomly selected to be anastomosed with a quick arterial coupler (QAC) (QAC group), and the femoral artery on the other side was anastomosed by the same person using an end-to-end suture technique with a 6-0 Prolene suture (suture group). The bilateral femoral arteries of 5 beagles were used for coupler-assisted anastomosis and hand-sewn anastomosis in vivo, respectively. Success rate, blood loss, anastomotic time, clamp time, total operation time, and patency rate were recorded. The patency of anastomosed arteries was assessed using vascular Doppler ultrasound, electromagnetic flowmeter, and pathological examination (6 weeks after surgery). RESULTS: As a novel arterial coupler, QAC was successfully designed and manufactured by using poly lactic-co-glycolic acid raw materials and 3-dimensions printing technology. Its rationality was preliminarily tested through finite element analysis and related mechanical analysis methods. The isolated arteries were successfully anastomosed with the assistance of QAC in vitro testing, which showed good anti-traction properties. In animal studies, QAC-assisted arterial anastomosis has superior profiles compared to hand-sewn anastomosis in anastomotic time (7.80 ± 1.41 vs. 16.38 ± 1.04 min), clamp time (8.80 ± 1.41 vs. 14.14 ± 1.57 min), and total operation time (46.64 ± 2.38 vs. 51.96 ± 3.65 min). The results of electromagnetic flowmeter, vascular Doppler ultrasound, and pathological examination showed that QAC-assisted anastomotic arteries were superior to hand-sewn arteries in terms of postoperative blood flow (16.86 ± 3.93 vs. 10.36 ± 0.92 mL/min) and vascular patency in 6 weeks after surgery. CONCLUSION QAC is a well-designed and easily maneuverable device specialized for end-to-end arterial anastomosis. Application of this device may decrease thermal ischemia time and improve the patency of anastomotic arteries, thus, improving outcomes.
Animals ; Anastomosis, Surgical/instrumentation* ; Dogs ; Femoral Artery/surgery* ; Vascular Surgical Procedures/instrumentation* ; Finite Element Analysis

Prosthesis loosening is the leading cause of postoperative revision in unicompartmental knee arthroplasty (UKA). The deviation of medial and lateral translational installation of the prosthesis during surgery is a common clinical phenomenon and an important factor in increasing the risk of prosthesis loosening. This study established a UKA finite element model and a bone-prosthesis fixation interface micromotion prediction model. The predicted medial contact force and joint motion of the knee joint from a patient-specific lower extremity musculoskeletal multibody dynamics model of UKA were used as boundary conditions. The effects of 9 femoral component medial and lateral translational installation deviations on the Von Mises stress of the proximal tibia, the contact stress, and the micro-motion of the bone prosthesis fixation interface were quantitatively studied. It was found that compared with the neutral position (a/A of 0.492), the lateral translational deviation of the femoral component significantly increased the tibial Von Mises stress and the bone-prosthesis fixation interface contact stress. The maximum Von Mises stress and the maximum contact stress of the fixation interface increased by 14.08% and 143.15%, respectively, when a/A was 0.361. The medial translational deviation of the femoral component significantly increased the bone-prosthesis fixation interface micro-motion. The maximum value of micromotion under the conditions of femoral neutral and medial translation deviation was in the range of 20-50 μm, which is suitable for osseointegration. Therefore, based on considerations such as the micromotion range suitable for osseointegration reported in the literature, the risk of reducing prosthesis loosening, and factors that may induce pain, it is recommended that clinicians control the mounting position of the femoral component during surgery within the safe range of 0-4 mm medial translation deviation.
Humans ; Arthroplasty, Replacement, Knee/methods* ; Finite Element Analysis ; Biomechanical Phenomena ; Knee Prosthesis ; Tibia/surgery* ; Femur/surgery* ; Stress, Mechanical ; Prosthesis Failure ; Knee Joint/surgery* ; Prosthesis Design

Transcranial temporal interference stimulation (tTIS) is a novel non-invasive transcranial electrical stimulation technique that achieves deep brain stimulation through multiple electrodes applying electric fields of different frequencies. Current studies on the mechanism of tTIS effects are primarily based on rodents, but experimental outcomes are often significantly influenced by electrode configurations. To enhance the performance of tTIS within the limited cranial space of rodents, we proposed various electrode configurations for tTIS and conducted finite element simulations using a realistic mouse model. Results demonstrated that ventral-dorsal, four-channel bipolar, and two-channel configurations performed best in terms of focality, diffusion of activated brain regions, and scalp impact, respectively. Compared to traditional transcranial direct current stimulation (tDCS), these configurations improved by 94.83%, 50.59%, and 3 514.58% in the respective evaluation metrics. This study provides a reference for selecting electrode configurations in future tTIS research on rodents.
Animals ; Transcranial Direct Current Stimulation/instrumentation* ; Electrodes ; Mice ; Computer Simulation ; Finite Element Analysis ; Brain/physiology*

Clinical trials have demonstrated that kilohertz-frequency transcutaneous spinal cord stimulation (TSCS) can be used to facilitate the recovery of sensory-motor function for patients with spinal cord injury, whereas the neural mechanism of TSCS is still undetermined so that the choice of stimulation parameters is largely dependent on the clinical experience. In this paper, a finite element model of transcutaneous spinal cord stimulation was used to calculate the electric field distribution of human spinal cord segments T ₁₂ to L ₂, whereas the activation thresholds of spinal fibers were determined by using a double-cable neuron model. Then the variation of activation thresholds was obtained by varying the carrier waveform, the interphase delay, the modulating frequency, and the modulating pulse width. Compared with the sinusoidal carrier, the usage of square carrier could significantly reduce the activation threshold of dorsal root (DR) fibers. Moreover, the variation of activation thresholds was no more than 1 V due to the varied modulating frequency and decreases with the increased modulating pulse width. For a square carrier at 10 kHz modulated by rectangular pulse with the frequency of 50 Hz and the pulse width of 1 ms, the lowest activation thresholds of DR fibers and dorsal column fibers were 27.6 V and 55.8 V, respectively. An interphase delay of 5 μs was able to reduce the activation thresholds of the DR fibers to 20.1 V. The simulation results can lay a theoretical foundation on the selection of TSCS parameters in clinical trials.
Humans ; Spinal Cord Stimulation/methods* ; Nerve Fibers/physiology* ; Finite Element Analysis ; Spinal Cord/physiology* ; Computer Simulation ; Spinal Cord Injuries/physiopathology* ; Lumbosacral Region ; Lumbar Vertebrae ; Transcutaneous Electric Nerve Stimulation/methods* ; Models, Neurological

This article aims to compare and analyze the biomechanical differences between wing-shaped titanium plates and traditional titanium plates in fixing acetabular anterior column and posterior hemi-transverse (ACPHT) fracture under multiple working conditions using the finite element method. Firstly, four sets of internal fixation models for acetabular ACPHT fractures were established, and the hip joint stress under standing, sitting, forward extension, and abduction conditions was calculated through analysis software. Then, the stress of screws and titanium plates, as well as the stress and displacement of the fracture end face, were analyzed. Research has found that when using wing-shaped titanium plates to fix acetabular ACPHT fractures, the peak stress of screws decreases under all working conditions, while the peak stress of wing-shaped titanium plates decreases under standing and sitting conditions and increases under forward and outward extension conditions. The relative displacement and mean stress of the fracture end face decrease under all working conditions, but the values are higher under forward and outward extension conditions. Wing-shaped titanium plates can reduce the probability of screw fatigue failure when fixing acetabular ACPHT fractures and can bear greater loads under forward and outward extension conditions, improving the mechanical stability of the pelvis. Moreover, the stress on the fracture end surface is more conducive to stimulating fracture healing and promoting bone tissue growth. However, premature forward and outward extension rehabilitation exercises should not be performed.
Titanium ; Bone Plates ; Humans ; Acetabulum/surgery* ; Fracture Fixation, Internal/methods* ; Biomechanical Phenomena ; Finite Element Analysis ; Bone Screws ; Fractures, Bone/surgery* ; Stress, Mechanical ; Working Conditions

Alveolar bone reconstruction simulation is an effective means for quantifying orthodontics, but currently, it is not possible to directly obtain human alveolar bone material models for simulation. This study introduces a prediction method for the equivalent shear modulus of three-dimensional random porous materials, integrating the first-order Ogden hyperelastic model to construct a computed tomography (CT) based porous hyperelastic Ogden model (CT-PHO) for human alveolar bone. Model parameters are derived by combining results from micro-CT, nanoindentation experiments, and uniaxial compression tests. Compared to previous predictive models, the CT-PHO model shows a lower root mean square error (RMSE) under all bone density conditions. Simulation results using the CT-PHO model parameters in uniaxial compression experiments demonstrate more accurate prediction of the mechanical behavior of alveolar bone under compression. Further prediction and validation with different individual human alveolar bone samples yield accurate results, confirming the generality of the CT-PHO model. The study suggests that the CT-PHO model proposed in this paper can estimate the material properties of human alveolar bone and may eventually be used for bone reconstruction simulations to guide clinical treatment.
Humans ; Tomography, X-Ray Computed/methods* ; Porosity ; Alveolar Process/physiology* ; Bone Density ; Computer Simulation ; Elasticity ; X-Ray Microtomography ; Stress, Mechanical ; Finite Element Analysis ; Models, Biological