Comportamiento Mecánico de un Premolar Humano Sano Sometido a Fuerzas Funcionales y Disfuncionales en un MEF / Mechanical Behavior of a Healthy Human Premolar Subjected to Functional and Dysfunctional Forces in a FEM

El propósito de este estudio fue analizar el comportamiento mecánico de la estructura dental sana de un primer premolar inferior humano sometido a fuerzas funcionales y disfuncionales en diferentes direcciones. Se buscó comprender, bajo las variables contempladas, las zonas de concentración de esfuerzos que conllevan al daño estructural de sus constituyentes y tejidos adyacentes. Se realizó el modelo 3D de la reconstrucción de un archivo TAC de un primer premolar inferior, que incluyó esmalte, dentina, ligamento periodontal y hueso alveolar considerando tres variables: dirección, magnitud y área de la fuerza aplicada. La dirección fue dirigida en tres vectores (vertical, tangencial y horizontal) bajo cuatro magnitudes, una funcional de 35 N y tres disfuncionales de 170, 310 y 445 N, aplicadas sobre un área de la cara oclusal y/o vestibular del premolar que involucró tres contactos estabilizadores (A, B y C) y dos paradores de cierre. Los resultados obtenidos explican el fenómeno de combinar tres vectores, cuatro magnitudes y un área de aplicación de la fuerza, donde los valores de esfuerzo efectivo equivalente Von Mises muestran valores máximos a partir de los 60 MPa. Los valores de tensión máximos se localizan, bajo la carga horizontal a 170 N y en el proceso masticatorio en la zona cervical, cuando la fuerza pasa del 60 %. Sobre la base de los hallazgos de este estudio, se puede concluir que la reacción de los tejidos a fuerzas funcionales y disfuncionales varía de acuerdo con la magnitud, dirección y área de aplicación de la fuerza. Los valores de tensión resultan ser más altos bajo la aplicación de fuerzas disfuncionales tanto en magnitud como en dirección, produciendo esfuerzos tensiles significativos para la estructura dental y periodontal cervical, mientras que, bajo las cargas funcionales aplicadas en cualquier dirección, no se generan esfuerzos lesivos. Esto supone el reconocimiento del poder de detrimento estructural del diente y periodonto frente al bruxismo céntrico y excéntrico.

SUMMARY: The purpose of this study was to analyze the mechanical behavior of the healthy dental structure of a human mandibular first premolar subjected to functional and dysfunctional forces in different directions. It was sought to understand, under the contemplated variables, the areas of stress concentration that lead to structural damage of its constituents and adjacent tissues. The 3D model of the reconstruction of a CT file of a lower first premolar was made, which included enamel, dentin, periodontal ligament and alveolar bone considering three variables: direction, magnitude and area of the applied force. The direction was directed in three vectors (vertical, tangential and horizontal) under four magnitudes, one functional of 35 N and three dysfunctional of 170, 310 and 445 N, applied to an area of the occlusal and/or buccal face of the premolar that involved three stabilizing contacts (A, B and C) and two closing stops. The results obtained explain the phenomenon of combining three vectors, four magnitudes and an area of force application, where the values of effective equivalent Von Mises stress show maximum values from 60 MPa. The maximum tension values are located under the horizontal load at 170 N and in the masticatory process in the cervical area, when the force exceeds 60%. Based on the findings of this study, it can be concluded that the reaction of tissues to functional and dysfunctional forces varies according to the magnitude, direction, and area of application of the force. The stress values turn out to be higher under the application of dysfunctional forces both in magnitude and in direction, producing significant tensile stresses for the dental and cervical periodontal structure, while under functional loads applied in any direction, no damaging stresses are generated. This supposes the recognition of the power of structural detriment of the tooth and periodontium against centric and eccentric bruxism.

Development and global validation of a 1-week-old piglet head finite element model for impact simulations / 中华创伤杂志(英文版)

PURPOSE@#Child head injury under impact scenarios (e.g. falls, vehicle crashes, etc.) is an important topic in the field of injury biomechanics. The head of piglet was commonly used as the surrogate to investigate the biomechanical response and mechanisms of pediatric head injuries because of the similar cellular structures and material properties. However, up to date, piglet head models with accurate geometry and material properties, which have been validated by impact experiments, are seldom. We aim to develop such a model for future research.@*METHODS@#In this study, first, the detailed anatomical structures of the piglet head, including the skull, suture, brain, pia mater, dura mater, cerebrospinal fluid, scalp and soft tissue, were constructed based on CT scans. Then, a structured butterfly method was adopted to mesh the complex geometries of the piglet head to generate high-quality elements and each component was assigned corresponding constitutive material models. Finally, the guided drop tower tests were conducted and the force-time histories were ectracted to validate the piglet head finite element model.@*RESULTS@#Simulations were conducted on the developed finite element model under impact conditions and the simulation results were compared with the experimental data from the guided drop tower tests and the published literature. The average peak force and duration of the guide drop tower test were similar to that of the simulation, with an error below 10%. The inaccuracy was below 20%. The average peak force and duration reported in the literature were comparable to those of the simulation, with the exception of the duration for an impact energy of 11 J. The results showed that the model was capable to capture the response of the pig head.@*CONCLUSION@#This study can provide an effective tool for investigating child head injury mechanisms and protection strategies under impact loading conditions.

Effects of Impact Angle on Head Injury in Six-Year-Old Child Pedestrian-Car Collision / 医用生物力学

Objective To explore the influence of child head injury under different impact angles by applying the finite element model of six-year-old child pedestrian as specified in the European New Car Assessment Programme (Euro NCAP). Methods Based on the finite element model of 6-year-old pedestrian with detailed anatomical structure as specified by the Euro NCAP (TB024), four groups of simulation experiments were set up to explore the mechanism of head injury in children under different impact angles. The initial position for head mass center was on the longitudinal center line of the car. The initial speed of the car was 40 km/h. The car contacted with the model from the direction of the right (0°), the front (90°), the left (180°) and the back (270°). The kinematics differences and head impact responses were compared, and injuries of the facial bone and skull were analyzed. Results Through the analysis of head contact force, acceleration of head mass center, resultant velocity of head mass center with the vehicle, head injury criterion (HIC15), facial bone fracture and skull stress distribution, it was found that the risk of head fracture and brain contusion under back impact and front impact was higher than that under side impact. The risk of head fracture and brain contusion was highest under back impact, while the lowest under side impact. Conclusions Child pedestrian head injury was the largest under back impact. The results have important application values for the assessment and development of car-pedestrian collision protection device.

Effects of different alveolar bone finite element models on the biomechanical responses of periodontal ligament / 生物医学工程学杂志

In the study of oral orthodontics, the dental tissue models play an important role in finite element analysis results. Currently, the commonly used alveolar bone models mainly have two kinds: the uniform and the non-uniform models. The material of the uniform model was defined with the whole alveolar bone, and each mesh element has a uniform mechanical property. While the material of the elements in non-uniform model was differently determined by the Hounsfield unit (HU) value of computed tomography (CT) images where the element was located. To investigate the effects of different alveolar bone models on the biomechanical responses of periodontal ligament (PDL), a clinical patient was chosen as the research object, his mandibular canine, PDL and two kinds of alveolar bone models were constructed, and intrusive force of 1 N and moment of 2 Nmm were exerted on the canine along its root direction, respectively, which were used to analyze the hydrostatic stress and the maximal logarithmic principal strain of PDL under different loads. Research results indicated that the mechanical responses of PDL had been affected by alveolar bone models, no matter the canine translation or rotation. Compared to the uniform model, if the alveolar bone was defined as the non-uniform model, the maximal stress and strain of PDL were decreased by 13.13% and 35.57%, respectively, when the canine translation along its root direction; while the maximal stress and strain of PDL were decreased by 19.55% and 35.64%, respectively, when the canine rotation along its root direction. The uniform alveolar bone model will induce orthodontists to choose a smaller orthodontic force. The non-uniform alveolar bone model can better reflect the differences of bone characteristics in the real alveolar bone, and more conducive to obtain accurate analysis results.

Finite element analysis of the effects of periodontal tissue temperature by continuous wave technique / 华西口腔医学杂志

OBJECTIVES@#The safety of root canal filling with 200 °C hot gutta-percha was investigated to study the effect of continuous wave technique combined with high-temperature injectable gutta-percha condensation technique on the surface temperature of periodontal tissue.@*METHODS@#CT technique and Mimics, Geomagic, and Solidworks software were utilized to build the entity models of alveolar bone, dentin and root canal, periodontal ligament, and blood flow, respectively, which were then assembled in Solidworks into a finite element model of tooth with blood flow. By utilizing ABAQUS collaborative simulation platform, fluid-structure coupling was analyzed on the whole process of root canal filling. Consequently, the surface temperature of the periodontal tissue was obtained.@*RESULTS@#In the absence of blood flow, the temperature of the periodontal ligament surface reached 50.048 ℃ during root canal filling with 200 ℃ gutta-percha. Considering blood flow, the temperature of periodontal ligament surface was 39.570 ℃.@*CONCLUSIONS@#The temperature of the periodontal ligament surface increased when the continuous wave root canal was filled with 200 ℃ gutta-percha, and the periodontal tissue was not damaged.

Finite element analysis of determining corneal biomechanical properties in vivo based on Corvis ST / 生物医学工程学杂志

The decrease of corneal stiffness is the key factor leading to keratoconus, and the corneal collagen fiber stiffness and fiber dispersion are closely related to the corneal biomechanical properties. In this paper, a finite element model of human cornea based on corneal microstructure, namely collagen fiber, was established before and after laser assisted in situ keratomileusis (LASIK). By simulating the Corvis ST process and comparing with the actual clinical results, the hyperelastic constitutive parameters and corneal collagen fiber stiffness modulus of the corneal material were determined before and after refractive surgery. After LASIK, the corneal collagen fiber stiffness modulus increased significantly, and was highly correlated with central corneal thickness (CCT). The predictive relationship between the corneal collagen fiber stiffness modulus and the corresponding CCT before and after surgery was: = exp(9.14 - 0.009CCT ), = exp(8.82 - 0.008CCT ). According to the results of this study, the central corneal thickness of the patient can be used to estimate the preoperative and postoperative collagen fiber stiffness modulus, and then a personalized corneal model that is more consistent with the actual situation of the patient can be established, providing a theoretical reference for more accurately predicting the safe surgical cutting amount of the cornea.

Dynamic Response and Damage Analysis of Human Head and Neck in Automobile Rear Impact / 医用生物力学

Objective To establish the precise finite element model of the head and neck based on human anatomical structure, so as to study neck injuries caused by rear impact at different speeds. Methods The model was based on CT scan images of the head and neck of human body. The Mimics software was used to reconstruct the three-dimensional (3D) bone, and the 3D solid ligaments, small joints and other tissues of the neck were improved and meshed by HyperMesh. The generated models included the head, 8 vertebrae (C1-T1), 6 intervertebral discs (annulus, nucleus pulposus and upper and lower cartilage endplates), facet joints (cartilage and joint capsule ligaments), ligaments, muscles, etc. Finally, the model verification and post-collision calculation were completed in the finite element post-processing software. Results The simulation results of the models under axial impact, front and back flexion and lateral flexion were compared with the experimental data to verify the effectiveness of the model. Then post-collision simulation at the speed of 20, 40, 60 and 80 km/h was conducted. At the speed of 20 km/h, there was no damage to the neck. At the speed of 40, 60 and 80 km/h, the ligament was the first to be damaged. As the speed increased, the stress on tissues of the neck increased continuously. At the speed of 80 km/h, the maximum stresses of the dense bone, cancellous bone and annulus of the cervical vertebrae were 226.4, 11.5, and 162.8 MPa, respectively. When the ligament strain reached the limit, tearing began to occur. Conclusions The finite element model of the head and neck established in this study has high bionics and effectiveness, and can be used for studying neck injury analysis in traffic accidents, which is helpful for the diagnosis, treatment and prevention of cervical spine injury to a certain extent.

The Effect on Head-Neck Injuries of Six-Year-Old Child Occupant by Misusing the Restraint System / 医用生物力学

Objective To explore the effect of restraint system misuse on head-neck injuries for rear occupant of 6-year-old children in frontal impact crashes. Methods Based on the previously validated 6-year-old child occupant finite element model, in terms of ECE R44 testing regulations, the impact crash under right and wrong use of restraint system was simulated in Pam-Crash software. Results The force and moment of the neck were the minimum by merely using booster seat, but the maximum intracranial pressure, the maximum stress and the maximum principal strain were larger than their damage threshold and would cause fatal brain damage in child head. The only use of adult safety belt would cause more serious damage in child neck with larger force and moment. Conclusions Two ways of misusing the restraint system would aggravate head-neck injuries of the 6-year-old child. The proper use of the restraint system can provide the best protective effect for head and neck of the 6-year-old child occupant.

Comparison of finite element models of osteonecrosis of the femoral head based on CT gray-assigned method / 中国组织工程研究

BACKGROUND: Previous studies have reported that femoral head finite element models are mostly modeled with single or few samples for specific biomechanical research, but there is little research on model stability. OBJECTIVE: To compare the models of normal femoral head and osteonecrosis of the femoral head with multiple samples, and to analyze the accuracy and stability of the models through the comparison of stress distribution and mechanical parameters, so as to provide mechanical basis for prevention and treatment of collapse of osteonecrosis of the femoral head. METHODS: Totally 20 sides uncollapsed of osteonecrosis of the femoral head one year of non-surgical treatment were selected as the experimental group, and the healthy side of 20 patients with unilateral osteonecrosis of the femoral head were set as the normal group. The CT data of the femoral head were collected to establish the finite element model. The stress distribution of normal femoral head and osteonecrosis of the femoral head, the maximum equivalent stress and the maximum total deformation at the weight-bearing area of the femoral head were observed and compared. This study was approved by the Medical Ethics Committee of Wangjing Hospital of China Academy of Chinese Medical Sciences. Patients signed the informed consent. RESULTS AND CONCLUSION: (1) The finite element models of normal proximal femur, non-necrotic proximal femur and necrotic bone were established. The number of elements and nodes were 502 568±114 196, 692 608±154 678; 449 954±125 824, 623 311±171 401; 19 133±13 167, 27 577±19 131, respectively. (2) When the load was set by simulating one-foot standing position, the cloud image showed that when 2.5 times body weight applied to the weight-bearing area of the femoral head; the surface stress of the weight-bearing area of the normal femoral head was uniform. The stress was uniformly distributed in the femoral head along the stress trabeculae, and the calcar femorale bears the most. The stress concentration area appeared on the surface of the weight-bearing area and the necrotic area of osteonecrosis of the femoral head. The stress was scattered and distributed on the inner and outer sides of the femoral neck and the femoral head of osteonecrosis of the femoral head produced more deformation than the normal femoral head. (3) The maximum total deformation of the weight-bearing area of the osteonecrosis of the femoral head and the normal femoral head was (4.14±1.31) mm and (1.36±0.22) mm and the maximum equivalent stress was (1.94±0.77) MPa and (0.75±0.19) MPa, respectively, and with statistically significance (P < 0.05). Moreover, two groups of data tend to be concentrated and the models are stable. Through the comparison of multi-sample normal femoral head and osteonecrosis of the femoral head, the CT gray-assigned method reflects the actual mechanical properties of osteonecrosis of the femoral head, and has good accuracy and stability.

Three-dimensional finite element analysis of traction under different lumbar physiological curvatures / 中国组织工程研究

BACKGROUND: In recent years, the finite element analysis of lumbar biomechanics has become a hot topic. Lumbar lordosis is considered to reduce the pressure load on the lumbar intervertebral disc and protect the lumbar spine. OBJECTIVE: To study the biomechanical effects of lumbar traction on L1-L5 lumbar segments in normal physiological curvature, flexion position and maximum overextension position, and to evaluate the optimal physiological curvature of lumbar traction. METHODS: A healthy male volunteer, aged 26 years, with a height of 174 cm and a weight of 60 kg, was selected, who had no history of lumbar spine diseases. With the L3 segment as the traction site, a finite element model of the whole lumbar spine was established based on lateral radiographs of the lumbar spine at the initiation site and during the maximal overextension as photographed by a DR machine. Based on the three-dimensional finite element model of the lumbar spine, the stress values and distributions of the lumbar vertebrae, the intervertebral joints, the intervertebral discs and the anterior longitudinal ligaments of the whole lumbar spine under different physiological curvatures were calculated. The patient was fully informed of the study protocol and signed an informed consent. The study protocol was approved by the Ethics Committee of Rehabilitation Hospital Affiliated to Fujian University of Traditional Chinese Medicine. RESULTS AND CONCLUSION: (1) Under six kinds of simulated working conditions, the range of motion of L1-L2 was 9.31° for flexion and extension, 9.84° for right and left bending, and 4.43° for right and left rotation; the range of motion of L2-L3 was 10.22° for flexion and extension, 12.35° for left and right bending, and 4.57° for left and right rotation; the range of motion of L3-L4 was 11.20° for flexion and extension, 11.63° for left and right bending, and 5.32° for left and right rotation; the range of motion of L4-L5 was 13.16° for flexion and extension, 11.58° for left and right bending, and 5.05° for left and right rotation. Under the normal physiological curvature of the lumbar vertebrae, the stress value of different lumbar spine structures was much greater than the stress value of hyperextension traction. The normal curvature of the anterior longitudinal ligament was 2.47 MPa, and the curvature of hyperextension traction value was 21.20 MPa. The stress value of L3 was the highest, which was four times that of the hyperextension traction. The stress value of the intervertebral joints at L2-L3 and intervertebral disc was highest than that of any other segment of the lumbar spine. These findings indicate that the pressure of lumbar vertebrae, intervertebral joints and intervertebral discs in hyperextension position is less than that in normal physiological curvature traction, and the pressure of anterior longitudinal ligament is always within the safe range. Lumbar traction may have better clinical efficacy and definite security in hyperextension position.

Effects of Dynamic Brain Response under Different Setting of Skull-Brain Interface and Mesh Density Division of Cerebrospinal Fluid / 医用生物力学

Objective To explore the effects of different skull-brain interfaces and mesh density of the cerebrospinal fluid (CSF) on dynamic responses of the brain. Methods The impact kinematics on cadaver head under rotation and translation impacts were reconstructed based on the 50th percentile adult head finite element model. The interfaces between skull and CSF, CSF and brain were modeled with different types of interfaces, which were set as sharing nodes, tied, frictionless sliding, so as to investigate the effect of different interface types on dynamic responses of the brain. Then, the interfaces between CSF, skull and brain were set as sharing nodes, while CSF was divided into single-layer and tri-layer of hexahedral element with the constant thickness of CSF, to study influences of CSF with different mesh density layers on dynamic responses of the brain. Results The intracranial pressure was highly sensitive to the interface types, while the brain response seemed to be relatively insensitive to the variation in CSF layers. Conclusions The research findings provide theoretical references for the construction of CSF and the selection of skull-brain contact interface of the head finite element model.

A numerical analysis of the effects of the lower-limb prosthetic socket on muscle atrophy of the residual limb / 生物医学工程学杂志

Muscle atrophy of the residual limb after lower-limb amputation is a disadvantage of amputees' rehabilitation. To investigate the biomechanics mechanism of muscle atrophy of the residual limb, we built a finite element model of a residual limb including muscle, skeletons and main vessels based on magnetic resonance images of a trans-femoral amputee, and studied the biomechanics effects of the socket of the lower-limb prosthesis on the soft tissue and vessels in the residual limb. It was found that the descending branch of the lateral femoral circumflex artery suffered the most serious constriction due to the extrusion, while that of the deep femoral artery was comparatively light. Besides, the degree of the constriction of the descending branch of the lateral femoral circumflex vein, femoral vein and deep femoral vein decreased in turn, and that of the great saphenous vein was serious. The stress-strain in the anterior femoral muscle group were highest, while the stress concentration of the inferior muscle group was observed at the end of the thighbone, and other biomechanical indicators at the inferior region were also high. This study validated that the extrusion of the socket on the vessels could cause muscle atrophy to some degree, and provided theoretical references for learning the mechanism of muscle atrophy in residual limb and its effective preventive measures.

Biomechanical Effect of Laminectomy on Adjacent Segment after Lumbar Interbody Fusion / 医用生物力学

Objective To study the biomechanical influence of posterior laminectomy with varying extent on adjacent segment after lumbar interbody fusion. Methods Three finite element models of lumbar posterior fusion were developed based on the validated intact lumbar model. These models were: posterior fusion with bi-lateral incision of facet joint (Bi-TLIF），inferior partly incision of laminar (PLIF)，total laminectomy (LAM-PLIF). The range of motion (ROM), intradiscal pressure (IDP), facet joint contact force (FJF) of adjacent segment of fusion models under various loading were compared with the intact model. The follower load of 400 N under 7.5 N·m torque was exerted on superior endplate of L1 segment. The 6-DOF (degree of freedom) of sacroiliac joint surface was constrained during loading. ResultsDuring flexion, obvious biomechanical changes of superior adjacent segment (L3-4) were found in Bi-TLIF, PLIF, LAM-PLIF surgery groups. Compared with the intact model, the ROM in Bi-TLIF, PLIF, LAM-PLIF group increased by 1.0%, 9.3%, 24.5%, respectively, while IDP in the above fusion groups increased by 1.4%, 4.3%, 10.0%，respectively. These changes were not obvious in other postures. For FJF, the Bi-TLIF and PLIF group showed obvious increasing effect on L3-4 segment, while almost had no effect on L5-S1 segment. Conclusions Laminectomy increased ROM, IDP and FJF of adjacent segment (especially superior adjacent segment) after posterior lumbar fusion, which might increase the risk of adjacent segment degeneration. This biomechanical effect was more obvious with the increase in incision range of laminar. Therefore, preserving more posterior complex during decompression has a positive effect on preventing adjacent segment degeneration (ASD) following lumbar fusion surgeries.

Biomechanical Response of Membrane Element and Spring Element for Simulation of Ligament Injury / 医用生物力学

Objective To compare and analyze the effect of membrane element and spring element on biomechanical responses of cervical ligaments. Methods Based on the existing 6-year-old pediatric neck finite element model, the ligaments were simulated by membrane element and spring element, respectively. Then dynamic tensile test of C4-5 vertebrae and tensile test of full cervical spine were conducted. The membrane element model was also used to simulate the bending test, and the simulation results were analyzed. Results In dynamic tensile test of C4-5 vertebral segment, the final failure force of membrane element simulation test and spring element simulation test was 1 207 N and 842 N, respectively, and their difference from the cadaver experiment was 0.6% and 30.6%, respectively. In full cervical tensile test, the difference of peak force from membrane element simulation test and cadaver experiment was 1.8%. The peak force of spring element simulation test was 484 N, and the difference from simulation test and cadaver experiment was large. The simulation result of membrane element bending test was good. Conclusions The spring element had some limitations in force simulation. The membrane element had higher biofidelity and could reflect the biomechanical response of the ligaments.

Research on thorax impact injury of children at different ages based on finite element models / 生物医学工程学杂志

The pediatric cadaver impact experiments were reconstructed using the validated finite element(FE) models of the 3-year-old and 6-year-old children. The effect of parameters, such as hammer size, material parameters and thorax anatomical structure characteristics, on the impact mechanical responses of 3-year-old and 6-year-old pediatric thorax was discussed by designing reasonable finite element simulation experiments. The research results showed that the variation of thorax contact peak force for 3-year-old group was far larger than that of 6-year-old group when the child was impacted by hammers with different size, which meant that 3-year-old child was more sensitive to hammer size. The mechanical properties of thoracic organs had little influence on the thorax injury because of the small difference between 3-year-old and 6-year-old child in this research. During the impact, rib deformation led to different impact location and deformation of internal organs because the 3-year-old and 6-year-old children had different geometrical anatomical structures, such as different size of internal organs. Therefore, the injury of internal organs in the two groups was obviously different. It is of great significance to develop children finite element models with high biofidelity according to its real anatomical structures.

Displacement and stress distribution of the maxillofacial complex during maxillary protraction using palatal plates: A three-dimensional finite element analysis / 대한치과교정학회지

OBJECTIVE: The purpose of this study was to analyze initial displacement and stress distribution of the maxillofacial complex during dentoskeletal maxillary protraction with various appliance designs placed on the palatal region by using three-dimensional finite element analysis. METHODS: Six models of maxillary protraction were developed: conventional facemask (Type A), facemask with dentoskeletal hybrid anchorage (Type B), facemask with a palatal plate (Type C), intraoral traction using a Class III palatal plate (Type D), facemask with a palatal plate combined with rapid maxillary expansion (RME; Type E), and Class III palatal plate intraoral traction with RME (Type F). In Types A, B, C, and D, maxillary protraction alone was performed, whereas in Types E and F, transverse expansion was performed simultaneously with maxillary protraction. RESULTS: Type C displayed the greatest amount of anterior dentoskeletal displacement in the sagittal plane. Types A and B resulted in similar amounts of anterior displacement of all the maxillofacial landmarks. Type D showed little movement, but Type E with expansion and the palatal plate displayed a larger range of movement of the maxillofacial landmarks in all directions. CONCLUSIONS: The palatal plate served as an effective skeletal anchor for use with the facemask in maxillary protraction. In contrast, the intraoral use of Class III palatal plates showed minimal skeletal and dental effects in maxillary protraction. In addition, palatal expansion with the protraction force showed minimal effect on the forward movement of the maxillary complex.

Finite-element analysis of the center of resistance of the mandibular dentition / 대한치과교정학회지

OBJECTIVE: The aim of this study was to investigate the three-dimensional (3D) position of the center of resistance of 4 mandibular anterior teeth, 6 mandibular anterior teeth, and the complete mandibular dentition by using 3D finite-element analysis. METHODS: Finite-element models included the complete mandibular dentition, periodontal ligament, and alveolar bone. The crowns of teeth in each group were fixed with buccal and lingual arch wires and lingual splint wires to minimize individual tooth movement and to evenly disperse the forces onto the teeth. Each group of teeth was subdivided into 0.5-mm intervals horizontally and vertically, and a force of 200 g was applied on each group. The center of resistance was defined as the point where the applied force induced parallel movement. RESULTS: The center of resistance of the 4 mandibular anterior teeth group was 13.0 mm apical and 6.0 mm posterior, that of the 6 mandibular anterior teeth group was 13.5 mm apical and 8.5 mm posterior, and that of the complete mandibular dentition group was 13.5 mm apical and 25.0 mm posterior to the incisal edge of the mandibular central incisors. CONCLUSIONS: Finite-element analysis was useful in determining the 3D position of the center of resistance of the 4 mandibular anterior teeth group, 6 mandibular anterior teeth group, and complete mandibular dentition group.

Analysis of growth plate material property effect on knee injury of six-year-old child occupant / 医用生物力学

Objective To develop the finite element model of six-year-old child occupant lower extremity with higher biofidelity and validate the model of knee joints,as well as analyze the biomechanical responses of growth plate under frontal impact load and injury mechanisms of the knee joint by using this model.Methods The sixyear-old child occupant lower extremity with growth plate was modeled based on children's anatomy and CT images,and corresponding material properties of the lower extremity model were assigned.The model was validated according to biomechanical experiments by Kerrigan et aL and Haut et aL and then was used to analyze the injury results of growth plate with different material properties.Results The model validation was qualified by comparing the curves from the experimental and simulation results.The growth plates at knee regions could change injury patterns of the child occupant lower extremity fracture.The material properties of growth plate could affect threshold of axial damage of the femur as well as relative position of the fracture.Conclusions The validated model can be used for related study and application on biomechanical responses and injury mechanisms of sixyear-old child occupant lower extremities.

Low power consumption structure design of an incus-stimulating middle ear implant based on piezoelectric stack / 医用生物力学

Objective To improve the design plan and get a piezoelectric actuator with displacement magnification structure,so as to reduce power consumption of the existing incus-stimulating piezoelectric actuator for middle ear implant.Methods Based on anatomical structure of human ear,the piezoelectric actuator with displacement magnification structure,and the one only composed of piezoelectric stack were designed,respectively,then the corresponding coupled mechanical models of the middle ear with the piezoelectric actuator were established.By comparing the calculation results from the two types of coupled mechanical models,the hearing compensation property and power consumption of the actuator before and after the implantation with the displacement magnification structure were analyzed.Results After adding the displacement magnification structure,the sound pressure level (SPL) at 1 kHz frequency was increased from 100 dB to 113 dB when the piezoelectric actuator was stimulated by 10.5 V effective voltages.In addition,for the piezoelectric stack,its power consumption at the frequency of 1,2 and 4 kHz were 6.42,1.56 and 0.28 mW,respectively;after introducing the displacement magnification structure,the power consumption at the above-mentioned 3 frequencies decreased to 0.39,0.09 and 0.01 mW,respectively.Conclusions Piezoelectric actuator with displacement magnification structure in this study can improve hearing compensation ability of the incus-stimulating middle ear implant,and effectively reduce the power consumption.The research findings will help to further improve the structure design of middle ear implant,thus achieving better hearing compensation effect.

Analysis of growth plate material property effect on knee injury of six-year-old child occupant / 医用生物力学

Objective To develop the finite element model of six-year-old child occupant lower extremity with higher biofidelity and validate the model of knee joints,as well as analyze the biomechanical responses of growth plate under frontal impact load and injury mechanisms of the knee joint by using this model.Methods The sixyear-old child occupant lower extremity with growth plate was modeled based on children's anatomy and CT images,and corresponding material properties of the lower extremity model were assigned.The model was validated according to biomechanical experiments by Kerrigan et aL and Haut et aL and then was used to analyze the injury results of growth plate with different material properties.Results The model validation was qualified by comparing the curves from the experimental and simulation results.The growth plates at knee regions could change injury patterns of the child occupant lower extremity fracture.The material properties of growth plate could affect threshold of axial damage of the femur as well as relative position of the fracture.Conclusions The validated model can be used for related study and application on biomechanical responses and injury mechanisms of sixyear-old child occupant lower extremities.