Stress distribution in lower second molar mesialization using mini-implants: a pilot study using 3D finite element analysis / Distribuição de tensões na mesialização do segundo molar inferior usando mini-implantes: um estudo piloto usando análise de elementos finitos 3D

Objective: to analyze the stress distribution in a 3D model that simulates second molar mesialization using two different types of mini-implants. Material and Methods: a mandible bone model was obtained by recomposing a computed tomography performed by a software program. The cortical and trabecular bone, a lower second molar, periodontal ligament, orthodontic tube, resin cement and the mini-implants were designed and modeled using the Rhinoceros 4.0 software program. The characteristics of self-drilling orthodontic mini-implants were: one with 7 mm length, 1 mm transmucosal neck section and 1.6 mm diameter and another with 5 mm length and 1.5 mm diameter. A total of 235.161 and 224.505 elements were used for the mesh. These models were inserted into the bone block and then subjected to loads of 200 cN (centinewton). The results were calculated and analyzed by the Ansys 17.0 software program for qualitative verification through displacement and maximum principal stress maps. Results: it was possible to observe that the periodontal ligament presented low displacement and stress values. However, the physiological values presented are among those capable to provide orthodontic movement, with compression and tensile area visualization staggered between 0.1 and -0.1 MPa (megapascal). Conclusion: within the limitations of the study, the mini-implants tested showed similar results where the load on the tooth allowed dental displacement (molar mesialization), with a tendency to rotate it, theoretically allowing the second molar to take the location of the first molar. (AU)

Objetivo: analisar a distribuição de tensões em um modelo 3D que simula a mesialização do segundo molar usando dois tipos diferentes de mini-implantes. Material e Métodos: um modelo de osso mandibular foi obtido por recomposição de uma tomografia computadorizada realizada por um software. O osso cortical e trabecular, um segundo molar inferior, ligamento periodontal, tubo ortodôntico, cimento resinoso e os mini-implantes foram projetados e modelados no software Rhinoceros 4.0. As características dos mini-implantes ortodônticos auto perfurantes foram: um com 7 mm de comprimento, 1 mm de secção transmucosa e 1,6 mm de diâmetro e outro com 5 mm de comprimento e 1,5 mm de diâmetro. Para a malha, foram utilizados 235.161 e 224.505 elementos. Esses modelos foram inseridos no bloco ósseo e então submetidos a cargas de 200 cN (centinewton). Os resultados foram calculados e analisados pelo software Ansys 17.0 para verificação qualitativa por meio de mapas de deslocamento e tensões máximas principais. Resultados: foi possível observar que o ligamento periodontal apresentou baixos valores de deslocamento e tensões. Porém, os valores fisiológicos apresentados são capazes de proporcionar movimentação ortodôntica, com visualização da área de compressão e tração escalonada entre 0,1 e -0,1 MPa (megapascal). Conclusão: dentro das limitações do estudo, os mini-implantes testados apresentaram resultados semelhantes onde a carga sobre o dente permitiu o deslocamento dentário (mesialização do molar), com tendência a girá-lo, permitindo teoricamente que o segundo molar ocupe do lugar do primeiro molar (AU)

Biomechanics of implant-supported restorations / Biomecânica das restaurações implantossuportadas

The rehabilitation of patients with dental implant-supported restorations is an ideal treatment option in contemporary dentistry. The aim of this review was to compile and to demonstrate the mechanical response during loading condition, on the stress distributions of implant-supported prostheses. The findings show that the majority of stresses were concentrated in the cervical region of the implant/abutment interface and that they can be affected by several clinical parameters and loading conditions. Finally, the final prosthetic design should combine superior mechanical response, long-term survival rate and allow patient satisfaction. (AU)

A reabilitação de pacientes com restaurações implanto-suportadas é uma opção de tratamento ideal na odontologia contemporânea. O objetivo desta revisão foi compilar e demonstrar a resposta mecânica durante a aplicação de carga, na distribuição de tensão de próteses implanto-suportadas. Os achados mostram que a maioria das tensões se concentram na região cervical da interface implante/pilar e pode ser afetada por diversos parâmetros clínicos e condições de carregamento. Por fim, o desenho protético final deve combinar uma melhor resposta mecânica, taxa de sobrevida a longo prazo e permitir a satisfação do paciente. (AU)

Influence of the cervical margin relocation on stress distribution - a finite element analysis on lower first molar restored by direct nano-ceramic composite

Aim: Evaluate the influence of the cervical margin relocation (CMR) on stress distribution in the lower first molar restored with direct nano-ceramic composite (zenit). Methods: A 3D model of the lower first molar was modeled and used. Standardized mesio-occluso-distal (MOD) preparation consisted in two models used in this study with mesial subgingival margin in model II. (CMR) was applied in model II using flowable composite or resin glass ionomer (Riva). Both models were restored with nanoceramic composite and then subjected to six runs (2 for the model I and 4 for model II) with load (100N) as two load cases, one at (11º) and other at (45º) from the vertical axis. The stress distributions (FEA) in the final restoration and (CMR) material were analyzed using 3D models. Results: The two models recorded an equivalent Von Mises stress and Total deformation in the final restoration, regardless of the difference in the oblique angle incidence from (11º to 45º) or the type of the material used for (CMR) there was no significant difference in the (FEA) between the model with CMR (model II) and the model without CMR (model I). Conclusions: (CMR) technique seems to be biomechanically beneficial with high eccentric applied stress, (CMR) with resin glass ionomer or flowable composite resin in combination with nanoceramic composite improved the biomechanical behavior of (MOD) cavities extended below cement enamel junction (CMR) with high modulus elasticity material like (Riva) exhibits a more uniform stress distribution

Mechanical behavior of implant-supported full-arch prostheses in different locations in the maxilla: 3D-FEA and strain gauge analysis / Comportamento mecânico de próteses de arco inteiro implanto-suportadas em localizações diferentes na maxila: análise 3D-FEA e strain gauge

The maxillary bone restriction can limit the implants position to support a full-arch prosthesis. Objective:Therefore, this study evaluated the biomechanical behavior of a full-arch prosthesis supported by six implants in different configurations: group A (implants inserted in the region of canines, first premolars and second molars), group B (implants inserted in the region of first premolar, first molar and second molar) and group C (implants in second premolar, first premolar and second molar). Material and Methods: The models were analyzed by the finite element method validated by strain gauge. Three types of loads were applied: in the central incisors, first premolars and second molars, obtaining results of von-Mises stress peaks and microstrain. All registered results reported higher stress concentration in the prosthesis of all groups, with group C presenting higher values in all structures when compared to A and B groups. The highest mean microstrain was also observed in group C (288.8 ± 225.2 µÎµ/µÎµ), however, there was no statistically significant difference between the evaluated groups. In both groups, regardless of the magnitude and direction of the load, the maximum von-Mises stresses recorded for implants and prosthesis displacements were lower in group A. Conclusion: It was concluded that an equidistant distribution of implants favors biomechanical behavior of full-arch prostheses supported by implants; and the placement of posterior implants seems to be a viable alternative to rehabilitate totally edentulous individuals. (AU)

A limitação óssea maxilar totais pode limitar o posicionamento dos implantes para suportar uma prótese de arco total. Objetivo: Sendo assim, este estudo avaliou o comportamento biomecânico de uma prótese de arco total suportada por seis implantes em diferentes configurações: grupo A (implantes inseridos na região de caninos, primeiros pré-molares e segundos molares), grupo B (implantes inseridos na região de primeiro pré-molar, primeiro molar e segundo molar) e grupo C (implantes em segundo pré-molar, primeiro pré-molar e segundo molar). Materiais e métodos: Os modelos foram analisados pelo método de elementos finitos validados por extensometria. Foram aplicados três tipos de cargas: nos incisivos centrais, primeiros pré-molares e nos segundos molares, obtendo resultados de picos de tensão de von-Mises e microdeformação. Todos os resultados registrados mostraram maior concentração de tensão na prótese de todos os grupos, sendo que o grupo C apresentou maiores valores em todas as estruturas quando comparado com os grupos A e B. A maior média de microdeformação também foi observada no grupo C (288,8 ± 225,2 µÎµ/µÎµ), no entanto, não houve diferença estatisticamente significativa entre os grupos avaliados. Em todos os grupos, independentemente da magnitude e direção da carga, as tensões máximas de von-Mises registradas para os implantes e deslocamentos de próteses foram menores no grupo A. Conclusão: Concluiu-se que a distribuição de implantes de forma equidistante favorece o desempenho biomecânico das próteses de arco total suportada por implantes; e o posicionamento de implantes posteriores parece ser uma alternativa viável para reabilitar indivíduos densdentados totais. (AU)

Influence of diameter in the stress distribution of extra-short dental implants under axial and oblique load: a finite element analysis

Aim: This study evaluated the influence of a wide diameter on extra-short dental implant stress distribution as a retainer for single implant-supported crowns in the atrophic mandible posterior region under axial and oblique load. Methods: Four 3D digital casts of an atrophic mandible, with a single implant-retained crown with a 3:1 crown-to-implant ratio, were created for finite element analysis. The implant diameter used was either 4 mm (regular) or 6 mm (wide), both with 5 mm length. A 200 N axial or 30º oblique load was applied to the mandibular right first molar occlusal surface. The equivalent von Mises stress was recorded for the abutment and implant, minimum principal stress, and maximum shear stress for cortical and cancellous bone. Results: Oblique load increased the stress in all components when compared to axial load. Wide diameter implants showed a decrease of von Mises stress around 40% in both load directions at the implant, and an increase of at least 3.6% at the abutment. Wide diameter implants exhibited better results for cancellous bone in both angulations. However, in the cortical bone, the minimum principal stress was at least 66% greater for wide than regular diameter implants, and the maximum shear stress was more than 100% greater. Conclusion: Extra-short dental implants with wide diameter result in better biomechanical behavior for the implant, but the implications of a potential risk of overloading the cortical bone and bone loss over time, mainly under oblique load, should be investigated

Restaurações endocrown em pré-molares: influência das paredes remanescentes da estrutura dentária e materiais restauradores na resistência à fadiga / Endocrown restorations in premolars: influence of remaining axial walls of tooth structure and restorative materials on fatigue resistance

Este estudo teve como objetivo avaliar o efeito da estrutura dentária remanescente e dois materiais diferentes de restauração CAD/CAM no desempenho à fadiga e no modo de falha de pré-molares tratados endodonticamente restaurados por endocrowns. Um total de 90 pré-molares superiores foram tratados endodonticamente e divididos aleatoriamente de acordo com o número de paredes axiais remanescentes, e os materiais restauradores foram divididos em 6 grupos (n = 15); quatro paredes restantes restauradas com zircônia ultratranslúcida 5Y-PSZ (grupo Fo-Z) e dissilicato de lítio (grupo Fo-L), três paredes restantes restauradas com 5Y-PSZ (grupo Th-Z) e dissilicato de lítio (grupo Th-L) e duas paredes restantes restauradas com 5YPSZ (grupo Tw-Z) e dissilicato de lítio (Tw-L). As restaurações foram cimentadas adesivamente e os espécimes foram submetidos a cargas de fadiga gradual em seu longo eixo (carga inicial: 200 N, frequência: 20 Hz). Uma carga incremental de 100 N por 10.000 ciclos foi aplicada com um pistão metálico de Ø 6 mm até a falha. A carga de falha por fadiga (FFL) e o número de ciclos de falha (CFF) no momento da falha foram registrados e analisados estatisticamente por ANOVA 2 fatores e teste de Kaplan-Meier (α = 0,05). Os espécimes fraturados foram examinados em estereomicroscópio em 8× e 25× e os modos de falha foram determinados como reparáveis ou catastróficos. FFL e CFF foram significativamente influenciados pelo material restaurador (p < 0,05). As restaurações de 5Y-PSZ apresentaram FFL (Fo-Z = 1487 N, Tw-Z = 1427 N, Tw-Z = 1533 N) e probabilidade de sobrevivência significativamente maiores quando comparadas com dissilicato de lítio (Fo-L = 1060 N, Th-L = 940 N, TwL = 1000 N). O número de paredes remanescentes não afetou o comportamento de fadiga ou modo de falha dos corpos de prova. Das restaurações de dissilicato de lítio, 51% tiveram falhas reparáveis, enquanto 95% das restaurações de zircônia ultratranslúcida 5Y-ZP tiveram falhas catastróficas. Endocrowns de zircônia apresentaram melhor desempenho em fadiga do que endocrowns de dissilicato de lítio, independentemente do número de paredes remanescentes do eixo. Endocrowns de pré-molares de dissilicato de lítio e 5Y-PSZ apresentaram maior FFL do que as cargas mastigatórias normais (AU)

This study aimed to evaluate the effect of the remaining tooth structure and two different CAD/CAM restoration materials on the fatigue performance and failure mode of endodontically treated premolars restored with endocrowns. A total of 90 maxillary premolars were endodontically treated and divided randomly according to the number of remaining axial walls, and the restorative materials were divided into 6 groups (n = 15); four remaining walls restored with ultratranslucent zirconia 5Y-PSZ (group Fo-Z) and lithium disilicate (group Fo-L), three remaining walls restored with 5Y-PSZ (group Th-Z) and lithium disilicate (Group Th-L), and two remaining walls restored with 5Y-PSZ (group Tw-Z) and lithium disilicate (Tw-L). The restorations were cemented adhesively and the specimens were subjected to stepwise fatigue loading along the long axis (initial load: 200 N, frequency: 20 Hz). An incremental step load of 100 N per 10,000 cycles was applied with a Ø6-mm metallic piston until failure. The fatigue failure load (FFL) and number of failure cycles (CFF) at the time of failure were recorded and statistically analyzed with two-way ANOVA and the Kaplan-Meier test (α = 0.05). Fractured specimens were examined under a stereomicroscope at 8× and 25× and failure modes determined as reparable or catastrophic. FFL and CFF were significantly influenced by restorative material (p < 0.05). 5Y-PSZ endocrowns showed significantly higher FFL (Fo-Z = 1487 N, Th-Z = 1427 N, Tw-Z = 1533 N) and survival probability when compared with lithium disilicate (Fo-L = 1060 N, Th-L = 940 N, Tw-L = 1000 N). The number of remaining walls did not affect the fatigue behavior or failure mode of the specimens. Of the lithium disilicate restorations, 51% had repairable failures, while 95% of ultratranslucent zirconia 5Y-ZP restorations had catastrophic failures. Zirconia endocrowns showed better fatigue performance than lithium disilicate endocrowns, regardless of the number of remaining axis walls. Lithium disilicate and 5Y-PSZ premolar endocrowns showed higher FFL than the normal masticatory loads (AU)

Three-dimensional finite element analysis of cement flow in abutment margin-crown platform switching / 北京大学学报(医学版)

OBJECTIVE@#To analyze the cement flow in the abutment margin-crown platform switching structure by using the three-dimensional finite element analysis, in order to prove that whether the abutment margin-crown platform switching structure can reduce the inflow depth of cement in the implantation adhesive retention.@*METHODS@#By using ANSYS 19.0 software, two models were created, including the one with regular margin and crown (Model one, the traditional group), and the other one with abutment margin-crown platform switching structure (Model two, the platform switching group). Both abutments of the two models were wrapped by gingiva, and the depth of the abutment margins was 1.5 mm submucosal. Two-way fluid structure coupling calculations were produced in two models by using ANSYS 19.0 software. In the two models, the same amount of cement were put between the inner side of the crowns and the abutments. The process of cementing the crown to the abutment was simulated when the crown was 0.6 mm above the abutment. The crown was falling at a constant speed in the whole process spending 0.1 s. Then we observed the cement flow outside the crowns at the time of 0.025 s, 0.05 s, 0.075 s, 0.1 s, and measured the depth of cement over the margins at the time of 0.1 s.@*RESULTS@#At the time of 0 s, 0.025 s, 0.05 s, the cements in the two models were all above the abutment margins. At the time of 0.075 s, in Model one, the gingiva was squeezed by the cement and became deformed, and then a gap was formed between the gingiva and the abutment into which the cement started to flow. In Model two, because of the narrow neck of the crown, the cement flowed out from the gingival as it was pressed by the upward counterforce from the gingival and the abutment margin. At the time of 0.1 s, in Model one, the cement continued to flow deep inside with the gravity force and pressure, and the depth of the cement over the margin was 1 mm. In Model two, the cement continued to flow out from the gingival at the time of 0.075 s, and the depth of the cement over the margin was 0 mm.@*CONCLUSION@#When the abutment was wrapped by the gingiva, the inflow depth of cement in the implantation adhesive retention can be reduced in the abutment margin-crown platform switching structure.

Finite element analysis of PMMA bone cement reinforced screw plate fixation for osteoporotic proximal humeral fracture / 中国骨伤

OBJECTIVE@#With the help of finite element analysis, to explore the effect of proximal humeral bone cement enhanced screw plate fixation on the stability of internal fixation of osteoporotic proximal humeral fracture.@*METHODS@#The digital model of unstable proximal humeral fracture with metaphyseal bone defect was made, and the finite element models of proximal humeral fracture bone cement enhanced screw plate fixation and common screw plate fixation were established respectively. The stress of cancellous bone around the screw, the overall stiffness, the maximum stress of the plate and the maximum stress of the screw were analyzed.@*RESULTS@#The maximum stresses of cancellous bone around 6 screws at the head of proximal humeral with bone cement enhanced screw plate fixation were 1.07 MPa for No.1 nail, 0.43 MPa for No.2 nail, 1.16 MPa for No.3 nail, 0.34 MPa for No.4 nail, 1.99 MPa for No.5 nail and 1.57 MPa for No.6 nail. These with common screw plate fixation were:2.68 MPa for No.1 nail, 0.67 MPa for No.2 nail, 4.37 MPa for No.3 nail, 0.75 MPa for No.4 nail, 3.30 MPa for No.5 nail and 2.47 MPa for No.6 nail. Overall stiffness of the two models is 448 N/mm for bone cement structure and 434 N/mm for common structure. The maximum stress of plate appears in the joint hole:701MPa for bone cement structure and 42 0MPa for common structure. The maximum stress of screws appeared at the tail end of No.4 nail:284 MPa for bone cement structure and 240.8 MPa for common structure.@*CONCLUSION@#Through finite element analysis, it is proved that the proximal humerus bone cement enhanced screw plate fixation of osteoporotic proximal humeral fracture can effectively reduce the stress of cancellous bone around the screw and enhance the initial stability after fracture operation, thus preventing from penetrating out and humeral head collapsing.

Biomechanical analysis of four internal fixations for Pauwels Ⅲ femoral neck fractures with defects / 中国骨伤

OBJECTIVE@#To investigate the biomechanical characteristics of different internal fixations for Pauwels type Ⅲ femoral neck fracture with defect, and provide reference for the treatment of femoral neck fracture.@*METHODS@#Three-dimensional (3D) finite element models of femoral neck fractures were established based on CT images, including fracture and fracture with defects. Four internal fixations were simulated, namely, inverted cannulated screw(ICS), ICS combined with medial buttress plate, the femoral neck system (FNS) and FNS combined with medial buttress plate. The von Mises stress, model stiffness and fracture displacements of fracture models under 2 100 N axial loads were measured and compared.@*RESULTS@#When femoral neck fracture was fixed by ICS and FNS, the peak stress was mainly concentrated on the surface of the screw near the fracture line, and the peak stress of FNS is higher than that of ICS;When the medial buttress plate was combined, the peak stress was increased and transferred to medial buttress plate, with more obvious of ICS fixation. For the same fracture model, the stiffness of FNS was higher than that of ICS. Compared with femoral neck fracture with defects, fracture model showed higher stiffness in the same internal fixation. The use of medial buttress plate increased model stiffness, but ICS increased more than FNS. The fracture displacement of ICS model exceeded that of FNS.@*CONCLUSION@#For Pauwels type Ⅲ femoral neck fracture with defects, FNS had better biomechanical properties than ICS. ICS combined with medial buttress plate can better enhance fixation stability and non-locking plate is recommended. FNS had the capability of shear resistance and needn't combine with medial buttress plate.

Biomechanical characteristics of retinaculum in the treatment of femoral neck fractures / 中国骨伤

OBJECTIVE@#To investigate the biomechanical characteristics of retinaculum in the treatment of femoral neck fractures.@*METHODS@#The CT data of a 75-year-old female volunteer was processed by software to construct an intact femur model and femoral neck fracture model fixed with three cannulated screws, which were divided into models with retinaculum or not. The Von-Mises stress distribution and displacement were compared to analyze the stability differences between the different models to study the mechanical characteristics of the retinaculum in the treatment of femoral neck fractures.@*RESULTS@#In the intact femur, the most obvious displacement appeared in the weight-bearing area of the femoral head, with retinaculum 0.381 37 mm, and without retinaculum 0.381 68 mm. The most concentrated part of the Von-Mises stress distribution was located in the medial and inferior part of the femoral neck, with retinaculum 11.80 MPa, without retinaculum 11.91 MPa. In the femoral neck fracture fixed with three cannulated screws model, the most obvious position of displacement also appeared in the weight-bearing area of the femoral head, with retinaculum 0.457 27 mm, without retinaculum 0.458 63 mm. The most concentrated part of the Von-Mises located at the medical and inferior part of the femoral neck, with retinaculum 59.22 MPa, without retinaculum 59.14 MPa. For the cannulated screws, the Von-Mises force peaks all appeared in the posterior and superior screw, with retinaculum 107.48 MPa, without retinaculum 110.84 MPa. Among the three screws, the Von-Mises stress of the anterior-superior screw was the smallest, which was 67.88 MPa vs 68.76 MPa in the retinaculum and non-retinaculum groups, respectively.@*CONCLUSION@#The complete retinaculum has little effect on the stability of intact femur and femoral neck fractures with anatomical reduction after internal fixation, and cannot effectively improve the stability of the fracture end after the fracture.

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.

Finite element analysis of different reconstruction methods of coracoclavicular ligament for acromioclavicular joint dislocation / 中国骨伤

OBJECTIVE@#This study aims to examine the biomechanical effects of different reconstruction methods, including single-bundle, double-bundle anatomical reconstruction, and double-bundle truly anatomical reconstruction of the coracoclavicular ligament on the acromioclavicular joint using finite element analysis, to provide a theoretical basis for the clinical application of truly anatomical coracoclavicular ligament reconstruction.@*METHODS@#One volunteer, aged 27 years old, with a height of 178 cm and a weight of 75 kg, was selected for CT scanning of the shoulder joint. Three-dimensional finite element models of single-bundle reconstruction, double-bundle anatomical reconstruction, and double-bundle truly anatomical reconstruction of coracoclavicular ligament were established by using Mimics17.0, Geomagic studio 2012, UG NX 10.0, HyperMesh 14.0 and ABAQUS 6.14 software. The maximum displacement of the middle point of the distal clavicle in the main loading direction and the maximum equivalent stress of the reconstruction device under different loading conditions were recorded and compared.@*RESULTS@#The maximum forward displacement and the maximum backward displacement of the middle point of the distal clavicle in the double-bundle truly anatomic reconstruction were the lowest, which were 7.76 mm and 7.27 mm respectively. When an upward load was applied, the maximum displacement of the distal clavicle midpoint in the double-beam anatomic reconstruction was the lowest, which was 5.12 mm. Applying three different loads forward, backward, and upward, the maximum equivalent stress of the reconstruction devices in the double-beam reconstruction was lower than that in the single-beam reconstruction. The maximum equivalent stress of the trapezoid ligament reconstruction device in the double-bundle truly anatomical reconstruction was lower than that in the double-bundle anatomical reconstruction, which was 73.29 MPa, but the maximum equivalent stress of the conoid ligament reconstruction device was higher than that of the double-bundle anatomical reconstruction.@*CONCLUSION@#The truly anatomical reconstruction of coracoclavicular ligament can improve the horizontal stability of acromioclavicular joint and reduce the stress of the trapezoid ligament reconstruction device. It can be a good method for the treatment of acromioclavicular joint dislocation.

Three-dimensional finite element model construction and biomechanical analysis of customized titanium alloy lunate prosthesis / 中国修复重建外科杂志

OBJECTIVE@#To design customized titanium alloy lunate prosthesis, construct three-dimensional finite element model of wrist joint before and after replacement by finite element analysis, and observe the biomechanical changes of wrist joint after replacement, providing biomechanical basis for clinical application of prosthesis.@*METHODS@#One fresh frozen human forearm was collected, and the maximum range of motions in flexion, extension, ulnar deviation, and radialis deviation tested by cortex motion capture system were 48.42°, 38.04°, 35.68°, and 26.41°, respectively. The wrist joint data was obtained by CT scan and imported into Mimics21.0 software and Magics21.0 software to construct a wrist joint three-dimensional model and design customized titanium alloy lunate prosthesis. Then Geomagic Studio 2017 software and Solidworks 2017 software were used to construct the three-dimensional finite element models of a normal wrist joint (normal model) and a wrist joint with lunate prosthesis after replacement (replacement model). The stress distribution and deformation of the wrist joint before and after replacement were analyzed for flexion at and 15°, 30°, 48.42°, extension at 15°, 30°, and 38.04°, ulnar deviation at 10°, 20°, and 35.68°, and radial deviation at 5°, 15°, and 26.41° by the ANSYS 17.0 finite element analysis software. And the stress distribution of lunate bone and lunate prosthesis were also observed.@*RESULTS@#The three-dimensional finite element models of wrist joint before and after replacement were successfully constructed. At different range of motion of flexion, extension, ulnar deviation, and radial deviation, there were some differences in the number of nodes and units in the grid models. In the four directions of flexion, extension, ulnar deviation, and radial deviation, the maximum deformation of wrist joint in normal model and replacement model occurred in the radial side, and the values increased gradually with the increase of the range of motion. The maximum stress of the wrist joint increased gradually with the increase of the range of motion, and at maximum range of motion, the stress was concentrated on the proximal radius, showing an overall trend of moving from the radial wrist to the proximal radius. The maximum stress of normal lunate bone increased gradually with the increase of range of motion in different directions, and the stress position also changed. The maximum stress of lunate prosthesis was concentrated on the ulnar side of the prosthesis, which increased gradually with the increase of the range of motion in flexion, and decreased gradually with the increase of the range of motion in extension, ulnar deviation, and radialis deviation. The stress on prosthesis increased significantly when compared with that on normal lunate bone.@*CONCLUSION@#The customized titanium alloy lunate prosthesis does not change the wrist joint load transfer mode, which provided data support for the clinical application of the prosthesis.

Establishment of finite element model of varus-type ankle arthritis and biomechanical analysis of different correction models for tibial anterior surface angle / 中国修复重建外科杂志

OBJECTIVE@#To establish the finite element model of varus-type ankle arthritis and to implement the finite element mechanical analysis of different correction models for tibial anterior surface angle (TAS) in supramalleolar osteotomy.@*METHODS@#A female patient with left varus-type ankle arthritis (Takakura stage Ⅱ, TAS 78°) was taken as the study object. Based on the CT data, the three-dimensional model of varus-type ankle arthritis (TAS 78°) and different TAS correction models [normal (TAS 89°), 5° valgus (TAS 94°), and 10° valgus (TAS 99°)] were created by software Mimics 21.0, Geomagic Wrap 2021, Solidworks 2017, and Workbench 17.0. The 290 N vertical downward force was applied to the upper surface of the tibia and 60 N vertical downward force to the upper surface of the fibula. Von Mises stress distribution and stress peak were calculated.@*RESULTS@#The finite element model of normal TAS was basically consistent with biomechanics of the foot. According to biomechanical analysis, the maximum stress of the varus model appeared in the medial tibiotalar joint surface and the medial part of the top tibiotalar joint surface. The stress distribution of talofibular joint surface and the lateral part of the top tibiotalar joint surface were uniform. In the normal model, the stress distributions of the talofibular joint surface and the tibiotalar joint surface were uniform, and no obvious stress concentration was observed. The maximum stress in the 5° valgus model appeared at the posterior part of the talofibular joint surface and the lateral part of the top tibiotalar joint surface. The stress distribution of medial tibiotalar joint surface was uniform. The maximum stress of the 10° valgus model appeared at the posterior part of the talofibular joint surface and the lateral part of the top tibiotalar joint surface. The stress on the medial tibiotalar joint surface increased.@*CONCLUSION@#With the increase of valgus, the stress of ankle joint gradually shift outwards, and the stress concentration tends to appear. There was no obvious obstruction of fibula with 10° TAS correction. However, when TAS correction exceeds 10° and continues to increase, the obstruction effect of fibula becomes increasingly significant.

Biomechanical effects of three internal fixation modes on femoral subtrochanteric spiral fractures in osteoporotic patients by finite element analysis / 中国修复重建外科杂志

OBJECTIVE@#The biomechanical characteristics of three internal fixation modes for femoral subtrochanteric spiral fracture in osteoporotic patients were compared and analyzed by finite element technology, so as to provide the basis for the optimization of fixation methods for femoral subtrochanteric spiral fracture.@*METHODS@#Ten female patients with osteoporosis and femoral subtrochanteric spiral fractures caused by trauma, aged 65-75 years old, with a height of 160-170 cm and a body weight mass of 60-70 kg, were selected as the study subjects. The femur was scanned by spiral CT and a three-dimensional model of the femur was established by digital technology. The computer aided design models of proximal intramedullary nail (PFN), proximal femoral locking plate (PFLP), and the combination of the two (PFLP+PFN) were constructed under the condition of subtrochanteric fracture. Then the same load of 500 N was applied to the femoral head, and the stress distribution of the internal fixators, the stress distribution of the femur, and the displacement of femur after fracture fixation were compared and analyzed under the three finite element internal fixation modes, so as to evaluate the fixation effect.@*RESULTS@#In the PFLP fixation mode, the stress of the plate was mainly concentrated in the main screw channel, the stresses of the different part of the plate were not equal, and gradually decreased from the head to the tail. In the PFN fixation mode, the stress was concentrated in the upper part of the lateral middle segment. In the PFLP+PFN fixation mode, the maximum stress appeared between the first and the second screws in the lower segment, and the maximum stress appeared in the lateral part of the middle segment of the PFN. The maximum stress of PFLP+PFN fixation mode was significantly higher than that of PFLP fixation mode, but significantly lower than that of PFN fixation mode ( P<0.05). In PFLP and PFN fixation modes, the maximum stress of femur appeared in the medial and lateral cortical bone of the middle femur and the lower side of the lowest screw. In PFLP+PFN fixation mode, the stress of femur concentrated in the medial and lateral of the middle femur. There was no significant difference in the maximum stress of femur among the three finite element fixation modes ( P>0.05). The maximum displacement occurred at the femoral head after three finite element fixation modes were used to fix subtrochanteric femoral fractures. The maximum displacement of femur in PFLP fixation mode was the largest, followed by PFN, and PFLP+PFN was the minimum, with significant differences ( P<0.05).@*CONCLUSION@#Under static loading conditions, the PFLP+PFN fixation mode produces the smallest maximum displacement when compared with the single PFN and PFLP fixation modes, but its maximum plate stress is greater than the single PFN and PFLP fixation mode, suggesting that the combination mode has higher stability, but the plate load is greater, and the possibility of fixation failure is higher.

Macroscopic and mesoscopic biomechanical analysis of the bone unit in idiopathic scoliosis / 生物医学工程学杂志

To investigate the effects of postoperative fusion implantation on the mesoscopic biomechanical properties of vertebrae and bone tissue osteogenesis in idiopathic scoliosis, a macroscopic finite element model of the postoperative fusion device was developed, and a mesoscopic model of the bone unit was developed using the Saint Venant sub-model approach. To simulate human physiological conditions, the differences in biomechanical properties between macroscopic cortical bone and mesoscopic bone units under the same boundary conditions were studied, and the effects of fusion implantation on bone tissue growth at the mesoscopic scale were analyzed. The results showed that the stresses in the mesoscopic structure of the lumbar spine increased compared to the macroscopic structure, and the mesoscopic stress in this case is 2.606 to 5.958 times of the macroscopic stress; the stresses in the upper bone unit of the fusion device were greater than those in the lower part; the average stresses in the upper vertebral body end surfaces were ranked in the order of right, left, posterior and anterior; the stresses in the lower vertebral body were ranked in the order of left, posterior, right and anterior; and rotation was the condition with the greatest stress value in the bone unit. It is hypothesized that bone tissue osteogenesis is better on the upper face of the fusion than on the lower face, and that bone tissue growth rate on the upper face is in the order of right, left, posterior, and anterior; while on the lower face, it is in the order of left, posterior, right, and anterior; and that patients' constant rotational movements after surgery is conducive to bone growth. The results of the study may provide a theoretical basis for the design of surgical protocols and optimization of fusion devices for idiopathic scoliosis.

Study on quantitative analysis of bracket-induced nonlinear response of labio-cheek soft tissue during the orthodontic process / 生物医学工程学杂志

In the orthodontics process, intervention and sliding of an orthodontic bracket during the orthodontic process can arise large response of the labio-cheek soft tissue. Soft tissue damage and ulcers frequently happen at the early stage of orthodontic treatment. In the field of orthodontic medicine, qualitative analysis is always carried out through statistics of clinical cases, while quantitative explanation of bio-mechanical mechanism is lacking. For this purpose, finite element analysis of a three-dimensional labio-cheek-bracket-tooth model is conducted to quantify the bracket-induced mechanical response of the labio-cheek soft tissue, which involves complex coupling of contact nonlinearity, material nonlinearity and geometric nonlinearity. Firstly, based on the biological composition characteristics of labio-cheek, a second-order Ogden model is optimally selected to describe the adipose-like material of the labio-cheek soft tissue. Secondly, according to the characteristics of oral activity, a two-stage simulation model of bracket intervention and orthogonal sliding is established, and the key contact parameters are optimally set. Finally, the two-level analysis method of overall model and submodel is used to achieve efficient solution of high-precision strains in submodels based on the displacement boundary obtained from the overall model calculation. Calculation results with four typical tooth morphologies during orthodontic treatment show that: ① the maximum strain of soft tissue is distributed along the sharp edges of the bracket, consistent with the clinically observed profile of soft tissue deformation; ② the maximum strain of soft tissue is reduced as the teeth align, consistent with the clinical manifestation of common damage and ulcers at the beginning of orthodontic treatment and reduced patient discomfort at the end of treatment. The method in this paper can provide reference for relevant quantitative analysis studies in the field of orthodontic medical treatment at home and abroad, and further benefit to the product development analysis of new orthodontic devices.

Strain Analysis in Cementless Hip Femoral Prosthesis using the Finite Element Method - Influence of the Variability of the Angular Positioning of the Implant / Análise da deformação na prótese femoral não cimentada do quadril pelo método de elementos finitos - Influência da variabilidade do posicionamento angular do implante

Abstract Objective The present study aims to evaluate the influence of different positioning of the hip femoral prosthesis on the stress and strain over this implant. Methods A femoral prosthesis (Taper - Víncula, Rio Claro, SP, Brazil) was submitted to a stress and strain analysis using the finite element method (FEM) according to the International Organization for Standardization (ISO) 7206-6 Implants for surgery - Partial and total hip joint prostheses - Part 6: Endurance properties testing and performance requirements of neck region of stemmed femoral components standard. The analysis proposed a branch of the physical test with a +/− 5° angle variation on the standard proposed for α and β variables. Results The isolated +/− 5° variation on the α angle, as well as the association of +/− 5° variation on the α and β angles, presented significant statistical differences compared with the control strain (p= 0.027 and 0.021, respectively). Variation on angle β alone did not result in a significant change in the strain of the prosthesis (p= 0.128). The stem positioning with greatest implant strain was α = 5° and β = 14° (p= 0.032). Conclusion A variation on the positioning of the prosthetic femoral stem by +/− 5° in the coronal plane and/or the association of a +/− 5° angle in coronal and sagittal planes significantly influenced implant strain.

Resumo Objetivo Avaliar a influência da variação do posicionamento da prótese femoral do quadril na tensão e na deformação produzidas neste implante. Métodos Utilizou-se a análise de tensão e de deformação da prótese femoral (Taper, Víncula, Rio Claro, SP, Brasil) pelo método de elementos finitos (MEF) de acordo com a norma ISO 7206-6 Implants for surgery - Partial and total hip joint prostheses-Part 6: Endurance properties testing and performance requirements of neck region of stemmed femoral components. A análise propôs uma ramificação do ensaio físico, com variação da angulação de +/− 5° sobre a proposta normativa das variáveis α e β. Resultados Ao comparar com a deformação controle, houve significância estatística com a angulação isolada de +/− 5° do ângulo α, bem como com a associação de +/− 5° nas angulações α e β (p= 0,027 e 0,021, respectivamente). Já com a variação apenas do ângulo β, não houve variação significativa na deformação da prótese (p= 0,128). A posição da haste com maior deformação no implante foi com α = 5° e β = 14° (p= 0,032). Conclusão A variabilidade de posicionamento da haste femoral protética de +/− 5° no plano coronal e/ou a associação da angulação de +/− 5° nos planos coronal e sagital interferiu de forma significativa na deformação do implante.

Zygomatic implants in intra-sinus versus extra-maxillary approaches for prosthetic rehabilitation in severely atrophic maxillae: finite element analysis / Implantes cigomáticos en abordajes intra sinusal versus extra maxilar para rehabilitación protésica en maxilares severamente atróficos: análisis de elementos finitos

Objetive: To compare the stresses and deformations generated on the surrounding bone of the zygomatic implants when using an intra sinusal and extra-maxillary approach, through the finite element method. Material and Methods: Computer aided designs (CADs) were constructed using SolidWorks Software of a skull with bone resorption to be rehabilitated through a fixed hybrid prosthesis using two zygomatic and two conventional straight implants. For the boundary conditions (load conditions), symmetry in the sagittal plane was assumed and that all the materials were isotropic, homogeneous and linearly elastic. Two zygomatic implantation techniques were simulated: intra sinusal (Is) and extra maxillary (Em). Vertical and lateral loads of 150 N and 50 N were applied to the finite element models to obtain Von Mises equivalent stress and strain (displacement). Results: The average measurement of the Von Mises stress (MPa) recorded were as follows: Approach of the implant body (Is: 0.24- Em: 0.28,) effort of implant body with vertical load: Is: 0.69 - Em: 0.96; effort of peri-implant surface under horizontal load: Is: 2.11 - Em: 0.94. Average displacement under vertical load of peri-implant surface Is: 0.35 - Em: 0.40, and of implant body Is: 1.34 - Em: 2.04. Average total deformation in approach Is: 2.23 mm - Em: 0.80mm, and average total deformation in the implant body under horizontal load was Is: 0.14 - Em: 0.21. Conclusion: The results of this study indicate that despite the differences that occurred in both stress and strain (displacement) between the intra-sinus and extra-maxillary approaches, the static strength of the bone, which is approximately 150 MPa in tension and 250 MPa in compression was not exceeded. Considering the limitations of finite element analysis, there seems to be no biomechanical reason to choose one approach over the other.

Objetivo: Comparar por el método de elementos finitos los esfuerzos y deformaciones generados sobre el hueso circundante de implantes cigomáticos tratados con un abordaje intra sinusal y extra maxilar. Material y Métodos: Se construyeron los diseños asistidos por computadora (CAD) utilizando el Software SolidWorks de un cráneo con una reabsorción ósea para ser rehabilitado, a través de una prótesis híbrida fija, mediante dos implantes cigomáticos y dos rectos convencionales. Para las condiciones de frontera (condiciones de carga) se asumió simetría en el plano sagital y que todos los materiales eran isotrópicos, homogéneos y linealmente elásticos. Se simularon dos técnicas de implantación cigomática: una intra sinusal (Is) y otra extra maxilar (Em). Se aplicaron cargas verticales y laterales de 150 N y 50 N a los modelos de elementos finitos para obtener el esfuerzo equivalente de Von mises y la deformación (desplazamiento). Resultados: La medición promedio del esfuerzo de Von Mises (MPa) registró: abordaje del cuerpo de implante (Is: 0.24-Em: 0.28) esfuerzo del cuerpo de implante con carga vertical: (Is:0.69 ­ Em: 0.96); esfuerzo de la superficie peri implantar ante carga horizontal (lateral):( Is:2.11 ­ Em:0.94). Desplazamiento promedio ante carga vertical de la superficie peri implantar (Is:0.35 ­ Em:0.40) y del cuerpo del implante (Is:1.34 ­ Em:2.04). Deformación total promedio en mm en abordaje (Is: 2.23 ­ Em:0.80) y deformación total promedio en el cuerpo del implante ante carga horizontal (Is:0.14 ­ Em:0.21). Conclusión: Los resultados de este estudio indican que a pesar de las diferencias que se presentaron tanto en el esfuerzo como en la deformación (desplazamiento) entre los abordajes intra sinusal y extra maxilar, la resistencia estática del hueso, que es de aproximadamente 150 MPa en tensión y 250 MPa en compresión no se superó. Considerando las limitaciones de los AEF, parece no haber razones biomecánicas para elegir uno u otro enfoque.

Falhas biomecânicas com uso de mini-implante ortodôntico: análise por elementos finitos / Biomechanical failures with the use of orthodontic mini-implants: finite element analysis

Esta tese foi dividida em três partes, sendo que cada uma consistiu estudo independente, com objetivos próprios. Na parte 1, o objetivo foi avaliar a influência do modo de representar a interface osso-OMI (osseointegrada ou não osseointegrada) sobre a previsão do risco de reabsorção óssea peri-implantar. Foram construídos quatro modelos tridimensionais que representaram o OMI inserido em quatro cilindros de osso de densidades crescentes, diferenciados pela espessura do osso cortical (Ct = 0,5; 1,2; 2,0 e 3,0 mm) e pelo módulo de elasticidade do osso trabecular (TE = 0,2; 1,4; 3,0 e 5,5 GPa). Para cada modelo, foram simuladas duas condições de interface osso-OMI: uma que considerava união perfeita entre osso e OMI (osseointegrado) e outra que considerava a possibilidade de movimentos relativos entre eles (não osseointegrado). Uma força horizontal de 2 N foi aplicada na cabeça do OMI, para simular a retração de dentes anteriores. A avaliação do risco de reabsorção óssea peri-implantar foi baseada no critério de falha da deformação principal maior, assumindo um valor crítico de 3.000 strain, tanto para tração quanto para compressão. Os resultados mostraram que, ao simular a interface osso-OMI como perfeitamente unida, o risco de perda de estabilidade do OMI por reabsorção óssea peri-implantar no osso menos denso fica subestimado. Na parte 2, foram novamente representadas as quatro condições de qualidade óssea, mas com modelos que representavam o contorno anatômico dos ossos correspondentes: maxila pouco densa, maxila controle, mandíbula controle e mandíbula muito densa. A AEF foi conduzida para tentar explicar por que os OMIs colocados na maxila apresentam maior taxa de sucesso em relação aos OMI colocados na mandíbula, apesar da melhor qualidade do osso mandibular. Além da força horizontal de 2 N (cenário clínico), foi simulada uma força horizontal de 10 N (condição de sobrecarga) e a interface osso OMI foi simulada como não-osseointegrada em todos os modelos. A avaliação do risco de reabsorção óssea peri-implantar seguiu o mesmo critério da parte 1 e foi também avaliado o risco de falta de estabilidade imediata, baseado no deslocamento intra-ósseo do OMI. Em todos os casos, o pico de deslocamento do OMI ficou muito abaixo do limiar de 50-100 m, o que sugere que a estabilidade primária seria suficiente mesmo no cenário de maxila de baixa densidade sobrecarregada. De acordo com os dados da deformação principal maior, a maxila está mais sujeita a perder sua estabilidade inicial devido à sobrecarga ortodôntica, especialmente na condição de baixa densidade, em que tanto a deformação de tração quanto a de compressão ultrapassaram o limiar de reabsorção óssea patológica. É provável que essa AEF não conseguiu prever o maior risco de falha de OMI em mandíbula de alta densidade porque não simulou as tensões residuais geradas pela inserção do OMI. Portanto, a simulação da inserção do OMI parece essencial para explicar a contradição que motivou esse estudo. Na parte 3, o objetivo foi comparar, através da AEF, o risco de reabsorção radicular inflamatória induzida ortodonticamente (RRIIO) entre duas mecânicas ortodônticas de intrusão (convencional e com mini-implantes), em situações de diferentes níveis de suporte periodontal. Foram construídos quatro modelos de um pré-molar superior inserido na maxila: controle (CTL) e 2, 4 ou 6 mm de perda óssea horizontal (R2, R4 e R6, respectivamente). Uma força de intrusão de 25 cN foi utilizada para as duas mecânicas em estudo. Nos modelos com mini-implante ortodôntico, a força foi dividida entre as faces vestibular e palatina. Nos modelos sem mini-implantes, a força foi aplicada apenas na vestibular. O índice de risco de reabsorção radicular (iRRR) foi calculado dividindo o pico de tensão hidrostática compressiva no ligamento periodontal pela tensão hidrostática dos capilares (4,7 kPa). A mecânica com mini-implante, além de apresentar iRRR sempre menores (CTL 1,2 e 1,4; R2: 1,4 e 1,7; R4: 1,7 e 2,2; R6: 2,4 e 3,2 - para mecânicas com e sem OMI, respectivamente), gerou apenas uma região com tensão hidrostática acima do valor crítico, próxima ao ápice do dente, para todos os modelos. Na mecânica convencional, houve também uma região com tensão hidrostática compressiva acima de 4,7 kPa na região cervical vestibular do modelo com 6 mm de perda óssea horizontal. O uso de mini-implante na intrusão ortodôntica diminuiu o risco de RRIIO em todos os casos simulados e o risco de reabsorção óssea adicional no modelo em que o dente apresentava uma perda óssea horizontal prévia de 6 mm.