Axially rigid steerable needle with compliant active tip control.

Steerable instruments allow for precise access to deeply-seated targets while sparing sensitive tissues and avoiding anatomical structures. In this study we present a novel omnidirectional steerable instrument for prostate high-dose-rate (HDR) brachytherapy (BT). The instrument utilizes a needle with internal compliant mechanism, which enables distal tip steering through proximal instrument bending while retaining high axial and flexural rigidity. Finite element analysis evaluated the design and the prototype was validated in experiments involving tissue simulants and ex-vivo bovine tissue. Ultrasound (US) images were used to provide visualization and shape-reconstruction of the instrument during the insertions. In the experiments lateral tip steering up to 20 mm was found. Manually controlled active needle tip steering in inhomogeneous tissue simulants and ex-vivo tissue resulted in mean targeting errors of 1.4 mm and 2 mm in 3D position, respectively. The experiments show that steering response of the instrument is history-independent. The results indicate that the endpoint accuracy of the steerable instrument is similar to that of the conventional rigid HDR BT needle while adding the ability to steer along curved paths. Due to the design of the steerable needle sufficient axial and flexural rigidity is preserved to enable puncturing and path control within various heterogeneous tissues. The developed instrument has the potential to overcome problems currently unavoidable with conventional instruments, such as pubic arch interference in HDR BT, without major changes to the clinical workflow.

Finite element analysis relating shape, material properties, and dimensions of taenioglossan radular teeth with trophic specialisations in Paludomidae (Gastropoda).

The radula, a chitinous membrane with embedded tooth rows, is the molluscan autapomorphy for feeding. The morphologies, arrangements and mechanical properties of teeth can vary between taxa, which is usually interpreted as adaptation to food. In previous studies, we proposed about trophic and other functional specialisations in taenioglossan radulae from species of African paludomid gastropods. These were based on the analysis of shape, material properties, force-resistance, and the mechanical behaviour of teeth, when interacting with an obstacle. The latter was previously simulated for one species (Spekia zonata) by the finite-element-analysis (FEA) and, for more species, observed in experiments. In the here presented work we test the previous hypotheses by applying the FEA on 3D modelled radulae, with incorporated material properties, from three additional paludomid species. These species forage either on algae attached to rocks (Lavigeria grandis), covering sand (Cleopatra johnstoni), or attached to plant surface and covering sand (Bridouxia grandidieriana). Since the analysed radulae vary greatly in their general size (e.g. width) and size of teeth between species, we additionally aimed at relating the simulated stress and strain distributions with the tooth sizes by altering the force/volume. For this purpose, we also included S. zonata again in the present study. Our FEA results show that smaller radulae are more affected by stress and strain than larger ones, when each tooth is loaded with the same force. However, the results are not fully in congruence with results from the previous breaking stress experiments, indicating that besides the parameter size, more mechanisms leading to reduced stress/strain must be present in radulae.

Integration of neural architecture within a finite element framework for improved neuromusculoskeletal modeling.

Neuromusculoskeletal (NMS) models can aid in studying the impacts of the nervous and musculoskeletal systems on one another. These computational models facilitate studies investigating mechanisms and treatment of musculoskeletal and neurodegenerative conditions. In this study, we present a predictive NMS model that uses an embedded neural architecture within a finite element (FE) framework to simulate muscle activation. A previously developed neuromuscular model of a motor neuron was embedded into a simple FE musculoskeletal model. Input stimulation profiles from literature were simulated in the FE NMS model to verify effective integration of the software platforms. Motor unit recruitment and rate coding capabilities of the model were evaluated. The integrated model reproduced previously published output muscle forces with an average error of 0.0435 N. The integrated model effectively demonstrated motor unit recruitment and rate coding in the physiological range based upon motor unit discharge rates and muscle force output. The combined capability of a predictive NMS model within a FE framework can aid in improving our understanding of how the nervous and musculoskeletal systems work together. While this study focused on a simple FE application, the framework presented here easily accommodates increased complexity in the neuromuscular model, the FE simulation, or both.

Three-Dimensional Finite Element Analysis and Biomechanical Analysis of Midfoot von Mises Stress Levels in Flatfoot, Clubfoot, and Lisfranc Joint Injury.

BACKGROUND Midfoot deformity and injury can affect the internal pressure distribution of the foot. This study aimed to use 3D finite element and biomechanical analyses of midfoot von Mises stress levels in flatfoot, clubfoot, and Lisfranc joint injury. MATERIAL AND METHODS Normal feet, flatfeet, clubfeet (30 individuals each), and Lisfranc injuries (50 individuals) were reconstructed by CT, and 3D finite element models were established by ABAQUS. Spring element was used to simulate the plantar fascia and ligaments and set hyperelastic coefficients in encapsulated bone and ligaments. The stance phase was simulated by applying 350 N on the top of the talus. The von Mises stress of the feet and ankle was visualized and analyzed. RESULTS The von Mises stress on healthy feet was higher in the lateral metatarsal and ankle bones than in the medial metatarsal bone. Among the flatfoot group, the stress on the metatarsals, talus, and navicular bones was significantly increased compared with that on healthy feet. Among patients with clubfeet, stress was mainly concentrated on the talus, and stress on the lateral metatarsal and navicular bones was significantly lower. The von Mises stress on the fractured bone was decreased, and the stress on the bone adjacent to the fractured bone was higher in Lisfranc injury. During bone dislocation alone or fracture accompanied by dislocation, the von Mises stress of the dislocated bone tended to be constant or increased. CONCLUSIONS Prediction of von Mises stress distribution may be used clinically to evaluate the effects of deformity and injury on changes in structure and internal pressure distribution on the midfoot.

Efeito da elevação da margem gengival e do material restaurador no comportamento em fadiga e distribuição de tensão de molares restaurados com inlays mod / Effect of deep margin elevation and restorative material on the fatigue behavior and stress distribution of molars restored with MOD inlays

Este estudo avaliou o efeito da elevação da margem gengival (DME) e dos materiais restauradores (cerâmica vítrea reforçada por leucita [C] vs. resina composta indireta [R]) no comportamento de fadiga e distribuição de tensão de molares superiores com margens proximais com 2 mm de profundidade restauradas com inlays mesio-ocluso-distal (MOD). Para isso, 52 terceiros molares humanos extraídos foram distribuídos aleatoriamente em quatro grupos (n = 13): C; DME + C; R; e DME + R. Restaurações do tipo inlay foram confeccionados no CAD-CAM e cimentadas adesivamente em todos os dentes. O comportamento em fadiga foi avaliado com o ensaio de vida acelerada stepwise stress (10.000 ciclos/step; step=50 N; 20 Hz; carga inicial=200 N). As cargas e o número de ciclos de falha em fadiga foram analisados com ANOVA de 2 fatores e teste de Tukey (p <0,05), também foram realizados gráficos de sobrevivência de Kaplan-Meier. A distribuição de tensões foi avaliada utilizando a análise por elementos finitos. Os modelos foram considerados isotrópicos, lineares, homogêneos e apresentaram contatos colados. Uma carga axial (400 N) foi aplicada à superfície oclusal. A distribuição de tensões foi analisada com o critério de tensão principal máxima. Para o comportamento em fadiga, não houve diferença para o fator DME (p> 0,05). Para o fator material restaurador, a carga e o número de ciclos para falha foram estatisticamente maiores nos grupos R (p <0,05). A análise por elementos finitos mostrou que os inlays de resina composta concentraram mais tensões na estrutura do dente, enquanto os inlays de cerâmica concentraram mais tensões na restauração. Falhas não reparáveis foram mais frequentes nos grupos de inlays de resina composta. Foi possível concluir que a DME não foi prejudicial para o comportamento em fadiga e na distribuição de tensão. As inlays de resina composta foram mais resistentes ao teste de fadiga, embora o modo de falha tenha sido mais agressivo(AU)

Objectives: This study evaluated the effect of deep margin elevation (DME) and restorative materials (leucite-reinforced glass-ceramics [C] vs. indirect resin composite [R]) on the fatigue behavior and stress distribution of upper molars with 2-mm deep proximal margins restored with MOD-inlay. Methods: Fiftytwo extracted human third molars were randomly assigned into four groups (n=13): C; DME+C; R; and DME+R. Inlays were fabricated in CAD-CAM and bonded to all teeth. The fatigue behavior was assessed with the stepwise stress test (10,000 cycles/step; step=50N; 20 Hz; initial load=200 N). Fatigue failure loads and number of cycles were analyzed with 2-way ANOVA and Tukey's test (p<0.05) and Kaplan-Meier survival plots. The stress distribution was assessed with finite element analysis. The models were considered isotropic, linear, homogeneous, and presented bonded contacts. A tripod axial load (400 N) was applied to the occlusal surface. The stress distribution was analyzed with the maximum principal stress criterion. Results: For fatigue, there was no difference for DME factor (p>.05). For the material factor, the load and number of cycles for failure were statistically higher in the R groups (p<.05). The finite element analysis showed that resin composite inlays concentrated more stress in the tooth structure, while ceramic inlays concentrated more stress in the restoration. Non-reparable failures were more frequent in the resin composite inlays groups. Conclusions: DME was not negative for fatigue and biomechanical behaviors. Resin composite inlays were more resistant to the fatigue test, although the failure mode was more aggressive(AU)

Finite element modeling to compare craniocervical motion in two age-matched pediatric patients without or with Down syndrome: implications for the role of bony geometry in craniocervical junction instability.

OBJECTIVE: Instability of the craniocervical junction (CCJ) is a well-known finding in patients with Down syndrome (DS); however, the relative contributions of bony morphology versus ligamentous laxity responsible for abnormal CCJ motion are unknown. Using finite element modeling, the authors of this study attempted to quantify those relative differences. METHODS: Two CCJ finite element models were created for age-matched pediatric patients, a patient with DS and a control without DS. Soft tissues and ligamentous structures were added based on bony landmarks from the CT scans. Ligament stiffness values were assigned using published adult ligament stiffness properties. Range of motion (ROM) testing determined that model behavior most closely matched pediatric cadaveric data when ligament stiffness values were scaled down to 25% of those found in adults. These values, along with those assigned to the other soft-tissue materials, were identical for each model to ensure that the only variable between the two was the bone morphology. The finite element models were then subjected to three types of simulations to assess ROM, anterior-posterior (AP) translation displacement, and axial tension. RESULTS: The DS model exhibited more laxity than the normal model at all levels for all of the cardinal ROMs and AP translation. For the CCJ, the flexion-extension, lateral bending, axial rotation, and AP translation values predicted by the DS model were 40.7%, 52.1%, 26.1%, and 39.8% higher, respectively, than those for the normal model. When simulating axial tension, the soft-tissue structural stiffness values predicted by the DS and normal models were nearly identical. CONCLUSIONS: The increased laxity exhibited by the DS model in the cardinal ROMs and AP translation, along with the nearly identical soft-tissue structural stiffness values exhibited in axial tension, calls into question the previously held notion that ligamentous laxity is the sole explanation for craniocervical instability in DS.

A GPU-based caching strategy for multi-material linear elastic FEM on regular grids.

In this study, we present a novel strategy to the method of finite elements (FEM) of linear elastic problems of very high resolution on graphic processing units (GPU). The approach exploits regularities in the system matrix that occur in regular hexahedral grids to achieve cache-friendly matrix-free FEM. The node-by-node method lies in the class of block-iterative Gauss-Seidel multigrid solvers. Our method significantly improves convergence times in cases where an ordered distribution of distinct materials is present in the dataset. The method was evaluated on three real world datasets: An aluminum-silicon (AlSi) alloy and a dual phase steel material sample, both captured by scanning electron tomography, and a clinical computed tomography (CT) scan of a tibia. The caching scheme leads to a speed-up factor of ×2-×4 compared to the same code without the caching scheme. Additionally, it facilitates the computation of high-resolution problems that cannot be computed otherwise due to memory consumption.

An investigation into structural behaviors of skulls chewing food in different occlusal relationships using FEM.

OBJECTIVES: This study aims to investigate the effect of different occlusal relationships on skull structural and mechanical behaviors through simulation of chewing food. METHODS: Finite element (FE) skull models of occlusion for Class I, end-on Class II, and full-cusp Class II were generated. End-on Class II and full-cusp Class II were chosen as mild and severe Class II occlusions, respectively. A simplified food bolus was introduced between the upper and lower dentition of the right molars. Chewing food was simulated in the skulls by moving the mandible. An experiment was conducted to measure strains at selective locations and compared them to the analytical results for validation. RESULTS: In the early stages of mandibular movement, masticatory forces predicted from the skull models without food were lower than the skull models with food but increased drastically after occluding teeth full enough. As a result, the relationship between masticatory force and mandible movement shows that there is no significant difference between the skull models with food and without food in the range of human masticatory force, approximately 250 N. In all the cases of skulls including a food bolus, stress was similarly propagated from the mandible to the maxilla and concentrated in the same regions, including the mandibular notch and alveolar bone around the lower molars. CONCLUSION: It is predicted that there is no significant difference of bite force-mandible movement relationships and stress distributions of skull and teeth, between end-on Class II and full-cusp Class II models. When simulating chewing activities on candy and carrot, it is also found that there is no difference of masticatory performance between Class II occlusions, from structural as well as mechanical perspectives.

Comportamento biomecânico de caninos desgastados por atrição frente a diferentes técnicas restauradoras / Canine guide reconstruction with diferente technics: influence on biomechanics properties

O objetivo do estudo foi avaliar o comportamento mecânico de materiais restauradores utilizados na reabilitação da guia canino. O estudo foi dividido em uma etapa in sílico e outra in vitro. Dez modelos 3D de dentes caninos hígidos foram obtidos por engenharia reversa e utilizados como Grupo Controle (n = 10) para o teste in sílico por meio da análise por elementos finitos (FEA). Um desgaste incisal de 2 mm foi simulado em cada amostra 3D e reabilitado com restauração incisal direta de resina composta (Grupo IRC, n = 10) e indireta de cerâmica (Grupo IC, n = 10). Os mesmos modelos também receberam, além do desgaste incisal, um preparo vestibular para faceta laminada, restaurados com os mesmos materiais, compondo os Grupos FRC (faceta de resina composta, n = 10) e FC (faceta cerâmica, n = 10). Os modelos foram exportados para um software de engenharia assistida por computador (CAE) e as geometrias foram transformadas em malhas de elementos tetraédricos, consideradas sólidas, isotrópicas, homogêneas e lineares. Uma carga de 100 N foi aplicada simulando a desoclusão pelo canino para análise mecânica estrutural dinâmica. A deformação total foi mensurada e a tensão máxima principal foi usada como critério de falha. Com base nos resultados da avaliação in sílico, dois tipos de restauração foram selecionados para a fase in vitro, onde realizou-se um ensaio mecânico de fadiga para análise do desgaste. Trinta dentes caninos hígidos foram distribuídos em três grupos: Controle (n = 10), IRC (n = 10) e FC (n = 10). As amostras foram submetidas ao ensaio de fadiga em cicladora mecânica com deslizamento de 2 mm por 240.000 ciclos, carga de 49 N e 4 Hz de frequência, imersas em água em temperatura ambiente. A cada 60.000 ciclos as amostras foram moldadas e seus modelos escaneados para avaliação da quantidade de desgaste através da técnica de correlação por imagem digital, quantificando a perda de estrutura a cada intervalo. As técnicas restauradoras com resina composta sofreram maior deformação total, tendo a cerâmica um comportamento semelhante ao dente hígido. A probabilidade de falha no movimento de desoclusão foi menor na cerâmica. Para o desgaste, não houve diferença significante entre grupos experimentais até 180.000 ciclos. Aos 240.000 ciclos, a resina composta apresentou maior desgaste que a cerâmica (p = 0,02). Todos os grupos provocaram desgaste em seus antagonistas, mas não houve diferença significante entre eles (p < 0,05). Dentro das limitações deste estudo, pode-se concluir que os laminados cerâmicos apresentaram menor desgaste, deformação e probabilidade de falha na restauração da guia canino. Ainda, a anatomia do dente e o tipo de restauração influenciaram o comportamento dos materiais(AU)

The purpose of this study was to evaluate the mechanical behavior of materials restorative used in rehabilitation of canine guide. The study was divided in two parts in silico and in vitro test. Ten 3D models of sound canine teeth were obtained by reverse engineering technique and used as Control Group (n = 10) to in silico test by finite elements analysis (FEA). A 2 mm wear were simulated in each 3D sample and restored according to restorative material; Group IRC (Incisal Composite Resin, n=10) and Group IC (Incisal Ceramic, n = 10). Laminate preparations were modeled and restored with the same materials, Group FRC (Laminate Composite Resin, n=10) and Group FC (Laminate Ceramic, n = 10). All models were exported to Computer Aided Engineering (CAE) software, the geometries were meshed with tetrahydric elements and all contacts were considered perfectly bonded. The load simulated the canine guide (100 N) and the assembly was constrained at the bottom surface to run a structural mechanic dynamic analysis. The Total Deformation was measured and Maximum Principal Stress was used as failure criteria. Thirty sound canine tooth were divided in three groups to in vitro test; Control (n = 10), IRC (n = 10) and FC (n = 10). The samples were subjected to the fatigue test in a wear machine for 240.000 cycles, load of 49 N, frequency of 4 Hz, sliding distance of 2 mm in water at room temperature. The samples were molded every 60.000 cycles and their models scanned to evaluate wear by digital image correlation. Composite resin groups showed higher total deformation and ceramic groups had a more similar behavior to the control group. The probability of failure was lower for the ceramic in the canine guidance. For wear, there was no significant difference between groups up to 180.000 cycles. After 240.000 cycles, the wear was greater in the IRC group (p = 0,02). The wear of the antagonists was not statistically different between groups. Within the limitations of this study, it can be concluded that the ceramic laminates showed less wear, deformation and probability of failure in restoring of the canine guide. In addition, anatomy of the tooth and type of restoration influenced the behavior of the materials(AU)

Avaliação in vitro de carga máxima de fratura em próteses fixas adesivas de resina composta indireta reforçadas com malha de sílica-nylon submetidas ao processo de envelhecimento / In vitro evaluation of maximum fracture load in resin-bonded fixed dental prostheses of indirect composite resin reinforced by silica-nylon mesh submitted to the aging process

O uso de próteses fixas adesivas é uma opção de tratamento reabilitador em casos de ausência dentária. A resina composta é um material com boas características mecânicas e estéticas, mas se faz necessário a utilização de reforços para proporcionar maior resistência ao conjunto. O presente estudo teve como objetivo avaliar a carga máxima de fratura quando da utilização de um sistema de reforço de sílica-nylon em próteses fixas adesivas confeccionadas em resina composta indireta. O estudo in vitro simulou uma prótese fixa adesiva de três elementos anterior (A) e posterior (P). Dessa forma, foram confeccionados 80 espécimes distribuídos em 8 grupos experimentais (n=10), tendo como variáveis a presença do sistema de reforço em sílica-nylon (R) e a ciclagem mecânica da peça protética (C). O processo de envelhecimento foi realizado através da ciclagem mecânica por 106 ciclos a 4 Hz (ERIOS ER-11000 Plus, São Paulo, Brasil). As amostras foram submetidas ao ensaio de resistência à carga máxima de fratura na máquina de ensaio universal (EMIC DL 1000, EMIC, Brasil) com uma célula de carga de 1000 Kgf e foram feitas análises das amostras após a fratura em estereomicroscópio (Discovery V20 CarlZeiss, Jena, Alemanha) e Microscopia Eletrônica de Varredura (Inspect S 50, FEI Company, Brno, República Tcheca). A análise estatística foi constituída pela análise de variância (ANOVA) e teste Tukey 5%. O estudo in silico foi realizado através da Análise em Elementos Finitos (FEA), onde os dentes pilares e as próteses foram escaneados (Ceramill Map 400, Amann Girrbach) e transferidos para o software CAD Rhinoceros (version 4.0SR8; McNeel North America, Seattle, WA), para elaboração do modelo volumétrico 3D e posteriormente a análise foi feita através do Software Ansys 19.3 (ANSYS, Inc. Southpointe, Canonsburg, EUA). Os resultados de resistência à carga máxima de fratura foram (N): A=163,55; AC=184,48; AR=198,81; ARC=192,24; P=539,99; PC=359,61; PR=541,74 e PRC=608,74. Foi constatado que houve diferença estatística na presença do reforço tanto nos grupos da região anterior (p=0,025), quanto da região posterior (p=0,001). Os resultados de tensão máxima principal, obtidos no FEA, foram (MPa): A=53,24/122,40; AR=55,07/117,70; P=33,28/36,18 e PR=28,06/42,87. Concluiu-se que a incorporação da malha de sílica-nylon aumentou a resistência à carga máxima de fratura das próteses fixas adesivas, independente da área em que se encontra, e os resultados obtidos no FEA corroboraram com os encontrados no teste in vitro o que permite concluir que houve validação do teste in silico(AU)

The use of resin-bonded fixed dental prostheses is a rehabilitative treatment option in cases of missing teeth. Composite resin is a material with good mechanical and aesthetic characteristics, but it is necessary to use reinforcements to provide greater resistance to the prosthesis. The present study aims to evaluate the maximum fracture load using a silica-nylon reinforcement system on resin-bonded fixed dental prostheses made of indirect composite resin. In vitro test simulated an anterior (A) and posterior (P) three-element resin-bonded fixed dental prostheses. Thus, 80 specimens were made in 8 experimental groups (n = 10), with variables the presence of the silica-nylon reinforcement system (R) and the mechanical cycling of the prosthesis (C). The aging process was performed through mechanical cycling for 106 cycles at 4 Hz (ERIOS ER-11000 Plus, São Paulo, Brazil). The samples were tested by maximum fracture load in the universal test machine (EMIC DL 1000, EMIC, Brazil) with a 1000 Kgf load cell and analyzed by stereomicroscope (Discovery V20 CarlZeiss, Jena, Germany) and Scanning Electron Microscopy (Inspect S 50, FEI Company, Brno, Czech Republic). Statistical analysis consisted of analysis of variance (ANOVA) and Tukey test 5%. In silico study was performed by Finite Element Analysis (FEA), where the abutment teeth and the prostheses were scanned (Ceramill Map 400, Amann Girrbach) and transferred to the CAD Rhinoceros (version 4.0SR8; McNeel North America, Seattle, WA) for the elaboration of the 3D volumetric model and the analysis test was made in the Ansys Software 19.3 (ANSYS, Canonsburg, PA, USA). The results of resistance to the maximum fracture load were (N): A=163,55; AC=184,48; AR=198,81; ARC=192,24; P=539,99; PC=359,61; PR=541,74 and PRC=608,74. It was found that there was a statistical difference in the presence of reinforcement in both the anterior region (p=0,025) and posterior region groups (p=0,001). The maximum main stress results obtained in the FEA were (MPa): A=53,24/122,40; AR=55,07/117,70; P=33,28/36,18 and PR=28,06/42,87. It was concluded that the incorporation of the silica-nylon mesh increased the resistance to maximum fracture load of the resin-bonded fixed dental prostheses regardless of the area it is located, and the results obtained in the FEA corroborated the results of in vitro test, which allows to conclude that the in silico test was validated(AU)

Anatomically accurate model of EMG during index finger flexion and abduction derived from diffusion tensor imaging.

This study presents a modelling framework in which information on muscle fiber direction and orientation during contraction is derived from diffusion tensor imaging (DTI) and incorporated in a computational model of the surface electromyographic (EMG) signal. The proposed model makes use of the principle of reciprocity to simultaneously calculate the electric potentials produced at the recording electrode by charges distributed along an arbitrary number of muscle fibers within the muscle, allowing for a computationally efficient evaluation of extracellular motor unit action potentials. The approach is applied to the complex architecture of the first dorsal interosseous (FDI) muscle of the hand to simulate EMG during index finger flexion and abduction. Using diffusion tensor imaging methods, the results show how muscle fiber orientation and curvature in this intrinsic hand muscle change during flexion and abduction. Incorporation of anatomically accurate muscle architecture and other hand tissue morphologies enables the model to capture variations in extracellular action potential waveform shape across the motor unit population and to predict experimentally observed differences in EMG signal features when switching from index finger abduction to flexion. The simulation results illustrate how structural and electrical properties of the tissues comprising the volume conductor, in combination with fiber direction and curvature, shape the detected action potentials. Using the model, the relative contribution of motor units of different sizes located throughout the muscle under both conditions is examined, yielding a prediction of the detection profile of the surface EMG electrode array over the muscle cross-section.

A Finite Element Solution of the Forward Problem in EEG for Multipolar Sources.

Multipolar source models have been presented in the context of electro/magnetoencephalography (E/MEG) to compensate for the limitations of the classical equivalent current dipole to represent realistic generators of brain activity. Although there exist several reports accounting for the advantages of multipolar components over single dipoles, there is still no available numerical implementation in fully personalized scenarios. In this paper, we present, for the first time, a finite element framework for simulating EEG signals generated by multipolar current sources in individualized, heterogeneous, and anisotropic head models. This formulation is based on the subtraction approach, guaranteeing the existence and uniqueness of the solution. In particular, we analyze the cases of monopolar, dipolar, and quadrupolar source components, for which we study their performance in idealized and realistic head models. Numerical solutions are compared with analytical formulas in multi-layered spherical models. Such formulas are available in the case of monopolar and dipolar sources, and here derived for the quadrupolar components. We finally illustrate their advantages in the description of extended current generators using a realistic head model. The framework presented here enables further analysis towards the estimation of biophysically principled source parameters from standard E/MEG experiments.

Effect of Statistically Iterative Image Reconstruction on Vertebral Bone Strength Prediction Using Bone Mineral Density and Finite Element Modeling: A Preliminary Study.

Statistical iterative reconstruction (SIR) using multidetector computed tomography (MDCT) is a promising alternative to standard filtered back projection (FBP), because of lower noise generation while maintaining image quality. Hence, we investigated the feasibility of SIR in predicting MDCT-based bone mineral density (BMD) and vertebral bone strength from finite element (FE) analysis. The BMD and FE-predicted bone strength derived from MDCT images reconstructed using standard FBP (FFBP) and SIR with (FSIR) and without regularization (FSIRB0) were validated against experimental failure loads (Fexp). Statistical iterative reconstruction produced the best quality images with regard to noise, signal-to-noise ratio, and contrast-to-noise ratio. Fexp significantly correlated with FFBP, FSIR, and FSIRB0. FFBP had a significant correlation with FSIRB0 and FSIR. The BMD derived from FBP, SIRB0, and SIR were significantly correlated. Effects of regularization should be further investigated with FE and BMD analysis to allow for an optimal iterative reconstruction algorithm to be implemented in an in vivo scenario.

Numerical simulation of transapical off-pump mitral valve repair with neochordae implantation.

BACKGROUND: Transapical off-pump mitral valve (MV) repair is a novel minimally-invasive surgical technique, allowing to correct mitral regurgitation (MR) caused by chordae tendineae rupture. While numerical simulation of the MV structure has proven to be useful to evaluate the effects of the MV surgical repair techniques, no numerical simulation studies on the outcomes of transapical MV repair have been done up to now. OBJECTIVE: The purpose of this study is to evaluate the transapical MV repair using finite element modeling and to determine the effect of the neochordal length on the function of the prolapsing MV. METHODS: The reconstruction of the MV geometry based on the patient-specific data was performed. In order to simulate prolapse, chordae inserted into the middle segment of the posterior leaflet (P2) were ruptured. A total of four virtual transapical repairs using neochordae of different length were performed. The function of the MV before and after virtual repairs was simulated. RESULTS: The evaluation of the effect of the neochordal length on post-repair MV function showed that the length of the implanted neochordae has a significant impact on the correction of MR caused by chordae tendineae rupture. CONCLUSIONS: The presented results can improve the understanding of the effects of transapical MV repair.

Estudo comparativo de diferentes mini-implantes utilizados para mesialização de segundo molar inferior: análise por elementos finitos 3d / Study of different mini-implants used for lower molar mesialização: Analysis by finite elements 3d

A perda do primeiro molar é uma situação comum na rotina do consultório e com isso surgem alternativas de tratamento para reabilitação, sendo uma delas, o fechamento de espaço através da mesialização do segundo molar. O uso de miniimplante proporciona ancoragem máxima, costuma ser bem tolerado pelo paciente e se destaca pela facilidade de instalação e remoção, apresentando dessa maneira desempenho clínico bastante favorável. O objetivo desse estudo foi analisar a distribuição de tensões em modelo que simula a mesialização de molar inferior utilizando diferentes tipos de mini-implantes. Embasado no método dos elementos finitos foi obtido modelo ósseo de mandíbula por recomposição de uma tomografia computadorizada realizada pelo software Invesalius (CTI, São Paulo, Brasil). O desenho do segundo molar foi obtido por técnica de recomposição tomográfica. Elementos de ancoragem auto-perfurantes da marca Neodent e também auto-rosqueantes da marca Titanium Fix foram desenhados e modelados por ferramenta de revolução do perfil desenhado no software Rhinoceros 3D, inseridos ao bloco ósseo e então submetidos a cargas de 200 cN. Os resultados foram calculados e analisados pelo programa Ansys 17.0 para verificação por meio da análise de mapas de deslocamento e tensões máximas principais, principalmente do osso cortical e indicaram que, dentro do modelo experimental, o ligamento periodontal apresentou valores baixos de tensão máxima principal, porém dentro dos valores fisiológicos para prover a movimentação, com visualização de áreas de compressão e de tração com escala entre 0,1 a -0,1 MPa. Concluiu-se que a carga testada permite a deslocamento dentário porém com tendência a giroversão(AU)

The loss of the first molar is a common situation in the routine of the dentist and with this treatment alternatives for rehabilitation arises, one of them being the closure of space through the mesialization of the second molar. The use of miniimplants provides maximum anchorage, is well tolerated by the patient and stands out for ease installation and removal, thus presenting a very favorable clinical performance. The objective of this study was to analyze the stress distribution in a model that simulates the inferior molar mesialization using different types of mini- implants. Based on the finite element method, a mandible bone model was obtained by recomposing a computerized tomography performed by invesalius software (CTI, São Paulo, Brazil). The second molar design was obtained by a technique similar to the tomographic recomposition. Neodent self-piercing anchoring elements and also Titanium Fix self-piercing anchors were designed and modeled by a revolution tool in the Rhinoceros 3D software, inserted into the bone block and then subjected to loads of up to 200 cN. The results were calculated and analyzed by the Ansys 17.0 program for verification by means of the analysis of displacement maps and main maximum stresses, mainly of the cortical bone and indicated that, within the experimental model, the periodontal ligament presented low values of main maximum tension, however within the physiological values to provide the movement, with visualization of areas of compression and traction with scale between 0.1 and -0.1 MPa. It was concluded that the load tested allows dental displacement but with a tendency to gyroversion(AU)

Effects of malalignment angle on the contact stress of knee prosthesis components, using finite element method.

In this paper, the complex 3D virtual model of the prosthetic knee is obtained using embedded applications: DesignModeler and SpaceClaim under ANSYS Workbench 14.5 software package. A number of six cases of prosthetic knee joint assembly, depending on the malalignment angle, are developed. Stress maps and the values of the maximum von Mises stress on the three prosthesis components: polyethylene insert, tibial component and femoral component, for all studied prosthetic knee assemblies were obtained. The results show that as the malalignment angle increases, the values of von Mises stresses increase in all prosthesis components. The parameterized virtual models of the knee prosthesis components allow different changes in shape or dimensions, which can lead to the optimization of the implant and to the improvement of the prosthetic knee biomechanics.

Efeito da graduação do módulo elástico na vida útil e resistência de restaurações cerâmicas / Effect of the elastic modulus graduation on the useful life and resistance of ceramic restorations

O objetivo deste estudo foi avaliar a distribuição de tensão, resistência, confiabilidade e vida útil de diferentes configurações cerâmicas dispostas em multicamadas, compostas por materiais cerâmicos de módulos de elasticidade distintos, comparando-as a modelos monocamadas. Para o delineamento dos modelos teórico e experimental, foram utilizadas as cerâmicas usinadas, com respectivos módulos elásticos: Feldspática (F): 64 GPa; dissilicato de lítio (L): 95 GPa; Zircônia tetragonal policristalina parcialmente estabilizada por ítrio (Y): 209,3 GPa. No estudo teórico foi utilizada a análise de elementos finitos, e foram desenhados dois modelos em 3D de um primeiro molar superior num software CAD para simular uma restauração monolítica (espessura: 1,5 mm) e uma restauração multicamadas (3 camadas cerâmicas de 0,4 mm + 2 camadas de cimento de 0,15 mm, totalizando de 1,5 mm de espessura). Foram preconizados 3 grupos monolíticos: F, L e Y; e 5 grupos multicamadas: FLY (F + L + Y), FFY (F + F + Y), LLY (L + L + Y), LFY (L + F + Y); YLF (Y + L + F), correspondente ao modelo bioinspirado. Foi aplicada uma carga de 150 N em três áreas de contato na fossa central e a tensão máxima principal (MPS) foi calculada em cada camada. O pico de tensão obtido (MPa) em cada camada de cada grupo foi: F: 10,55; Y: 18,48; L: 12,26; LFY: 25,58/3,96/26,82; LLY: 22,07/7,18/24,04; FFY: 22,58/6,26/28,99; FLY: 20,11/9,68/24,98; YLF: 39,44/7,18/5,42. Desta forma, foi possível constatar que a gradação do módulo elástico, com maior E externamente e menor E na região mais interna, proporcionou menor tensão nas camadas internas da restauração. Com o objetivo de validar os achados, foi proposto o modelo experimental simplificado, no qual foram utilizados discos cerâmicos de espessuras 0,3 mm e 1,5 mm. Os discos de 0,3 mm foram dispostos em 4 camadas, cimentados com cimento químico (Multilink N), e os discos de 1,5 mm não receberam nenhum tratamento, de modo que a espessura final dos espécimes fossem 1,5 mm (±0,15 mm). Foram obtidos 6 grupos: F (F: monolítico de 1,5 mm); L (L: monolítico de 1,5 mm); LLFF (L + L + F + F); FFLL (F + F + L + L); YLFF (Y + L + F + F); YLLF (Y + L + L + F). A carga para a fratura foi obtida através do ensaio de flexão biaxial (n=10; 1000 kgf, velocidade 1,0 mm/min) até a ocorrência de falha. Os dados foram analisados através de ANOVA-1 fator e comparações múltiplas de Tukey (5%). O ensaio de flexão biaxial foi também simulado através da análise de elementos finitos para identificar a tensão de tração gerada em cada camada dos grupos. O limite de fadiga (100.000 ciclos; 20 Hz) foi determinado através do método de escada (staircase). A análise de fratura foi realizada através de estereomicroscópio e microscopia eletrônica de varredura. Os resultados mostraram valores de carga para a fratura (N) seguindo a ordem: L (592,88 ± 73,78)D > FFLL (319,78 ± 43,59)C > YLLF (246,75 ± 24,89)B > F (167,13 ± 9,84)A > YLFF (166,51 ± 15,24) A > LLFF (165,46 ± 22,75)A ; e limite de resistência à fadiga (N): L (310,92 ± 26.73)F > FFLL (190,17 ± 8.32)E > F (106,21 ± 2.81)D > YLLF (96,48 ± 5.73)C > YLFF (89,56 ± 2.38)B > LLFF (77,23 ± 6.33)A . Ocorreram falhas em todos os grupos, sendo o local de origem na superfície de tração, coincidente com o local de maior tensão de tração analisado pelo método dos elementos finitos. Desta forma, concluiu-se que o modelo teórico evidenciou melhor desempenho de restaurações bioinspiradas, entretanto, no modelo experimental, a resistência do conjunto foi guiada pelo material na região de tração e a interface adesiva foi um fator limitante, com necessidade de se desenvolver uma estrutura bioinspirada de forma homogênea para validar os achados do modelo teórico(AU)

The aim of this study was to evaluate the strength, reliability and useful life of different ceramic configurations arranged in multilayers, composed of ceramic materials with different elastic moduli, comparing them to monolayer models. For the design of the theoretical and experimental models, machined ceramics were used, with respective elastic modulus: feldspathic (F), 64 GPa; lithium disilicate (L), 95 GPa; and Yttrium-partially stabilized tetragonal zirconia (Y-TZP) (Y), 209.3 GPa. In the theoretical study it was used the Finite Element Analyses, Two 3D upper first molar models were generated in CAD software in order to simulate monolayer (1.5 mm thickness) and multilayer restorations (3 ceramic layers of 0.4 mm + 2 cement layers of 0.15 mm, with a final thickness of 1.5 mm. The following groups were obtained: Monolithic groups: F, L and Y; Multilayer groups: FLY (F + L + Y), FFY (F + F + Y), LLY (L + L + Y), LFY (L + F + Y); and a Bioinspired Multilayer group: YLF (Y + L + F). Maximum principal stress (MPS) was calculated on each layer through a load of 150 N in three contact areas in the central fossa. The tensile strength peaks (MPa) were F: 10.55, Y: 18.48, L: 12.26, LFY: 25.58/3.96/26.82, LLY: 22.07/7.18/24.04, FFY: 22.58/6.26/28.99, FLY: 20.11/9.68/24.98 and YLF: 39.44/7.18/5.42. F and L ceramics did not prevent stress dissipation in the inner layers, and Y provided a decrease in tensile stress in the inner layers when used in the outermost layer in ZLF group. Multilayer ceramics with a larger external E modulus and a smaller internal modulus provided less stress in the innermost layers of the restoration. To validate these findings an experimental simplified model was preconized in order to obtain discs of 0.3 mm and 1.5 mm thickness. The 0.3 mm discs were arranged in 4 layers cemented with chemical cement (Multilink N), and the 1.5 mm discs were not treated, in such a way that the final thickness of all specimens was 1.5 mm (± 0.15 mm). The following 6 groups were obtained: F (F: monolithic); L (L: monolithic); LLFF (L + L + F + F); FFLL (F + F + L + L); YLFF (Y + L + F + F); YLLF (Y + L + L + F). The loads to fracture were obtained using the biaxial flexure strength test (1000 kgf, 1 mm/min) until failure and data were analyzed using ANOVA-1 way and Tukey's multiple comparisons (5%). The biaxial bending test was also simulated through finite element analysis (FEA) to identify the tensile stress generated at each layer of the groups. Mean flexural fatigue limits (100,000 cycles; 20 Hz) were determined under stair case approach. The fracture analysis was performed by stereomicroscope and scanning electron microscopy. The load to fracture (N) were obtained as follow L (592,88 ± 73,78)D > FFLL (319,78 ± 43,59)C > YLLF (246,75 ± 24,89)B > F (167,13 ± 9,84)A > YLFF (166,51 ± 15,24)A > LLFF (165,46 ± 22,75)A ; and the fatigue limit (N): L (310,92 ± 26.73)F > FFLL (190,17 ± 8.32)E > F (106,21 ± 2.81)D > YLLF (96,48 ± 5.73)C > YLFF (89,56 ± 2.38)B > LLFF (77,23 ± 6.33)A . All the groups presented failures and the origin were located at the tension region of the discs, as encountered in FEA. Thus, it was concluded that the theoretical model showed better performance of bioinspired restorations, however, in the experimental model the material under tension was mandatory for the resistance of the restoration, the adhesive interface negatively influenced the biomechanical behavior of the multilayer structures and there is a need to develop a homogeneous bio-inspired structure to validate the findings of the theoretical model(AU)

Distribuição de tensões em um modelo tridimensional de canino e pré-molares superiores sob diferentes carregamentos oclusais: análise pelo método de elementos finitos / Stress distribution in a three-dimensional model of canine and premolars superiors under different occlusal loads: analysis by finite element method

O objetivo desse estudo foi analisar, por meio do Método de Elementos Finitos, a distribuição de tensões na estrutura dentária, no ligamento periodontal (LP) e no osso alveolar em um modelo tridimensional do canino (23), primeiro (24) e segundo pré-molares superiores (25) submetidos à ação de cargas axiais e oblíquas. Além disso, objetivou-se avaliar a influência do ponto de contato proximal na distribuição das tensões no modelo de três dentes (M1), comparado a um modelo unitário do 24 (M2). As propriedades mecânicas bem como as condições de contorno e carregamento foram determinadas no programa de elementos finitos Ansys®. Cargas axiais e oblíquas foram aplicadas nas seguintes simulações: C1) Carga axial nos contatos A e B no dente 24; C2) Contato excêntrico no dente 24; C3) Carga oblíqua de 45N, com inclinação de 45o no contato A do dente 24; C4) Carga oblíqua de 45N, com inclinação de 45o no contato B do dente 24; C5) Cargas axiais simultâneas, de 70N na ponta de cúspide do dente 23, 90N nos contatos A e B do dente 24 e de 105N nos contaos A e B do dente 25. Para estimar a possibilidade de falha no esmalte, as tensões máximas principais foram analisadas e deformações máximas e mínimas principais foram analisadas no LP e no osso alveolar, sendo que ambos foram comparados a valores encontrados em outros estudos com metodologia similar. Em C1, a distribuição de tensões foi mais favorável para as estruturas dente-LP-osso, com picos de tensões semelhantes em M1 e M2. Em C2, tensões deslocaramse para apical, devido ao contato entre os dentes 24 e 23 em M1; os picos de tensões foram maiores em M1 do que em M2 no esmalte e no osso e o inverso ocorreu na dentina e no LP. Em C3, tensões de tração concentraram-se na região cervical do esmalte e na furca do dente 24; os picos das tensões no esmalte, osso e LP foram menores em M1 comparado a M2, mas na dentina ocorreu o contrário (M1>M2). Em C4, ocorreu o maior pico de tensão de tração no esmalte, tensões de tração concentraram-se na furca do dente 24; esmalte e dentina comportaram-se de forma similar (M1>M2) e osso e LP também (M1˂M2). Em C5, tensões de tração se concentraram no osso alveolar do dente 23. Os contatos proximais em M1 permitiram a distribuição das tensões de forma mais homogênea para o LP e osso que em M2. Exceto em C1, a distribuição de tensões no esmalte cervical, na dentina, no LP e no osso alveolar diferiram em um modelo unitário comparado a um de três dentes, devido à presença dos contatos proximais.

The direction, type and magnitude of loads on the oclusal surface and also the characteristics of the support structures determines the stress distribution. The aim of this study was to analyze, by the finite element method, the stress distribution on the first superior premolar, in a tridimensional (3D) model subjected to various types of loadings considering the enamel anisotropic or isotropic. The geometric modeling was performed based on a computed tomography (CT) scan. The mechanical properties as well as the loading conditions determined by the Abaqus® finite element program. Axial and oblique loads were applied on the occlusal surface of the first superior premolar in the following conditions: I) 30N axial load applied simultaneously on the occlusal contacts A and B and in the mesial marginal ridge, totaling 90N; II) 90N axial load in the mesial longitudinal edge of the lingual cusp, simulating eccentric contact; III) 45N oblique load with a 45o inclination on theocclusal contact A; IV) 45N oblique load with a 45o inclination on the occlusal contact B. To estimate the possibility of failure in the simulated structures, the maximum principal stress were analyzed and compared to known tensile strength values of the tissues studied. The results showed compression stress on the side in which the load was applied and tensile stress on the opposite side. Tensile stress concentrates mainly in the cervical region of the tooth and in the alveolar insertion bone. Anisotropic models revealed areas of tensile stress concentration smaller than the isotropic models. It was concluded that the isotropic 3D models were suitable for analyzing the stress distribution in teeth, because they are less complex models to build and produced similar results compared to the anisotropic models. The cervical enamel seems to be more susceptible to fracture because of the largest stress concentration on this area, associated with its composition and anatomical characteristics

Biomecânica da união dente-implante com plataforma restauradora reduzida, sistema de retenção tipo cone morse e roscas quadradas: uma análise por elementos finitos / Biomechanics of tooth-implant union with restorative platform reduced, restraint system morse cone type and square threads: a finite element analysis

Objetivou-se, a partir do Método dos Elementos Finitos, avaliar a biomecânica da união dente-implante e implante-implante, além de estabelecer uma análise qualitativa com achados fotoelásticos prévios. Foram planejados quatro modelos tridimensionais: dois Modelos Teste (dentes unidos a implantes) e dois Modelos Controle (a mesma condição, porém implanto suportada). Os implantes (ANKYLOS® - Dentsply) apresentaram conexão cônica, roscas quadradas e pilares Switching. Suas dimensões, ângulos externos e pilares protéticos foram obtidos a partir de um projetor de perfil. Já, dentes e próteses, a partir da visão direta, tiveram suas formas externas construídas em plataforma CAD (SOLIDSWORKS). O suporte alveolar foi configurado como um retângulo (68/30/15 mm). Todos os pilares foram posicionados no suporte alveolar, conforme os modelos físicos pré-existentes, gerando modelos sólidos. O ligamento periodontal consistiu de uma camada de 0,25 mm de espessura em poliéter (Impregum Soft, 3M Espe). Os modelos de dentes foram produzidos em dentina, pilares e implantes em titânio puro, próteses em liga Níquel-Cromo (Ni-Cr), e o suporte alveolar em resina fotoelástica (Araldite® - Produtos Químicos Ciba S/A do Brasil). As propriedades da resina foram obtidas por meio de ensaio de tração. Carga pontual, vertical e estática, de 150 N, foi aplicada. Os resultados destes ensaios evidenciaram menor concentração de tensão no aspecto cervical de implantes do grupo teste. Ao se confrontar tais achados com os fotoelásticos anteriormente obtidos, foi possível estabelecer uma relação direta entre as áreas mais solicitadas para os modelos de prótese fixa (PF) de três elementos. Concluiu-se que, para as condições estudadas ¿ conexão cônica, roscas quadradas e restauração com Plataforma Switching ¿, unir dentes a implantes parece ser uma terapia clínica viável, sugerindo, inclusive, ser mais favorável que a união de implantes entre si. Além disso, a partir da afinidade positiva entre os achados das duas técnicas, pôde-se considerar validados os modelos matemáticos de prótese fixa de três elementos

The goal of this study was to evaluate, from the Finite Element Method, the biomechanics of implant-tooth union and implant-implant and to establish a qualitative analysis with previous photoelastic findings. Four three-dimensional models were planned: two Test Models (teeth attached to implants) and two Control Models (the same condition, however implant supported). The implants (ANKYLOS® - Dentsply) showed conical connection, square threads and Switching pillars. Their dimensions, external angles and abutments were obtained from a profile projector. Already, teeth and dentures, from direct view, had their external forms built in CAD platform (SOLIDSWORKS). Alveolar support wasconfigured as a rectangle (68/30/15 mm). All the pillars were placed in the alveolar support, as the pre-existing physical models, generating solid models. The periodontal ligament consists of a layer of 0.25 mm thick in polyether (Impregum Soft, 3M Espe). The models of teeth trumped up of dentin, abutments and implants of pure titanium, prosthetics of Nickel-Chrome (Ni-Cr) alloy and alveolar support in photoelastic resin (Araldite® - Chemicals Ciba S/A of Brazil). The resin properties were obtained by traction tests. Punctual and vertical static load of 150 N was applied. The results of these tests showed lower concentration of tension in the cervical aspect of the test group implants. When comparing these findings with the photoelastic previously found, it was possible to establish a direct relation between the areas most requested for fixed prosthesis (FP) models of three elements. It was concluded that, for the studied conditions tapered connection, square threads and Platform Switching restoration , joining teeth implants seems to be a viable clinical therapy, suggesting, inclusive, to be more favorable than to join implants each other. Moreover, from the positive affinity between the findings of the two techniques, it was possible to consider validated the mathematical models of fixed prosthesis of three elements

Numerical analysis of tooth movement in different plans of transparent tooth correction therapies.

BACKGROUND: The objective of this study was to investigate how treatment strategies in the same treatment affected the canine's initial displacement and the stress in periodontal ligament using three-dimensional finite element analysis. And to find out the way to design an effective treatment plan. METHODS: Based on computed tomography images of the teeth and their supporting tissues, solid models were used to build finite element models. Three treatment plans of three different transparent tooth correction therapies finite element-analyses were operated. RESULTS: The canine's initial displacement and stresses' distribution in periodontal ligament were obtained. CONCLUSIONS: For rotation movement, the canine should rotate along tooth long axis, and not combine with other kinds of tooth movement as possible. For translation movement, the combination of translation and inclination movement is helpful for the treatment.