Effect of different palatal expanders with miniscrews in surgically assisted rapid palatal expansion: A non-linear finite element analysis

ABSTRACT Introduction: Surgically assisted rapid palatal expansion (SARPE) has been the treatment of choice in subjects presenting skeletally mature sutures. Objective: The purpose of this study was to analyze stress distribution and displacement of the craniofacial and dentoalveolar structures resulting from three types of palatal expanders with surgical assistance using a non-linear finite element analysis. Material and Methods: Three different palatal expanders were designed: Model-I (tooth-bone-borne type containing four miniscrews), Model-II (tooth-bone-borne type containing two miniscrews), and Model-III (bone-borne type containing four miniscrews). A Le Fort I osteotomy was performed, and a total of 5.0 mm palatal expansion was simulated. Nonlinear analysis (three theory) method (geometric nonlinear theory, nonlinear contact theory, and nonlinear material methods) was used to evaluate stress and displacement of several craniofacial and dentoalveolar structures. Results: Regardless of the maxillary expander device type, surgically assisted rapid palatal expansion produces greater anterior maxillary expansion than posterior (ANS ranged from 2.675 mm to 3.444 mm, and PNS ranged from 0.522 mm to 1.721 mm); Model-I showed more parallel midpalatal suture opening pattern - PNS/ANS equal to 54%. In regards to ANS, Model-II (1.159 mm) and Model-III (1.000 mm) presented larger downward displacement than Model-I (0.343 mm). PNS displaced anteriorly more than ANS for all devices; Model-III presented the largest amount of forward displacement for PNS (1.147 mm) and ANS (1.064 mm). All three type of expanders showed similar dental displacement, and minimal craniofacial sutures separation. As expected, different maxillary expander designs produce different primary areas and levels of stresses (the bone-borne expander presented minimal stress at the teeth and the tooth-bone-borne expander with two miniscrews presented the highest). Conclusions: Based on this finite element method/finite element analysis, the results showed that different maxillary expander designs produce different primary areas and levels of stresses, minimal displacement of the craniofacial sutures, and different skeletal V-shape expansion.

RESUMO Introdução: A expansão rápida da maxila assistida cirurgicamente (ERMAC) tem sido o tratamento de escolha em indivíduos que apresentam suturas esqueleticamente maduras. Objetivo: O objetivo deste estudo foi avaliar, utilizando uma análise não linear com elementos finitos, a distribuição de tensões e os deslocamentos das estruturas craniofaciais e dentoalveolares gerados por três tipos de expansores palatinos usados na ERMAC. Material e Métodos: Três tipos de expansores palatinos foram projetados: Modelo I (dento-osseossuportado com quatro mini-implantes), Modelo II (dento-osseossuportado com dois mini-implantes) e Modelo III (osseossuportado com quatro mini-implantes). Uma osteotomia Le Fort I foi realizada e foi simulada uma expansão palatina total de 5,0 mm. Um método de análise não linear (três teorias - teoria da não-linearidade geométrica, teoria do contato não linear e métodos para materiais não lineares) foi utilizado para avaliar a tensão e o deslocamento de diversas estruturas craniofaciais e dentoalveolares. Resultados: Independentemente do tipo de aparelho expansor palatino, a ERMAC produziu maior expansão anterior da maxila do que posterior (ENA variou de 2,675 mm a 3,444 mm e ENP variou de 0,522 mm a 1,721 mm); o Modelo I apresentou padrão de abertura mais paralela da sutura palatina mediana, com ENP/ENA igual a 54%. Com relação à ENA, o Modelo II (1,159 mm) e o Modelo III (1,000 mm) apresentaram maior deslocamento para baixo do que o Modelo I (0,343 mm). A ENP deslocou-se mais para anterior do que a ENA com todos os aparelhos; o Modelo III apresentou o maior deslocamento para anterior da ENP (1,147 mm) e da ENA (1,064 mm). Os três tipos de expansores apresentaram deslocamento dentário semelhante e separação mínima das suturas craniofaciais. Como esperado, diferentes designs de expansores palatinos produzem diferentes áreas primárias e níveis de tensões (o expansor osseossuportado apresentou tensão mínima nos dentes, e o expansor dento-osseossuportado com dois mini-implantes apresentou o maior). Conclusões: Com base nesse estudo de elementos finitos, os resultados mostraram que diferentes designs de expansores palatinos produzem diferentes áreas primárias e níveis de tensão, com deslocamento mínimo das suturas craniofaciais e diferentes expansões esqueléticas em forma de V.

Sobrevivência em fadiga de coroas bioinspiradas bilaminadas: estudo in vitro / Fatigue survival rate of bioinspired bilaminar crowns: in vitro study

O objetivo deste estudo foi avaliar o comportamento biomecânico através da resistência à fadiga e análise por elementos finitos de coroas bioinspiradas bilaminadas com infraestruturas modificadas na superfície vestibular (Estudo A) e utilizando diferentes materiais cerâmicos com módulos elásticos distintos (Estudo B). Para isso, foram confeccionados 90 preparos para coroa total em resina epóxi G10, sobre os quais foram preparadas coroas bioinspiradas de acordo com os seguintes grupos: Estudo A - IC (infraestrutura convencional), IME (infraestrutura modificada estratificada) e IMC (infraestrutura modificada cimentada), todas confeccionadas em dissilicato de lítio (infraestrutura) + porcelana (recobrimento); Estudo B ­ DL+LEU (dissilicato de lítio + leucita), LEU+DL (leucita + dissilicato de lítio), CH+DL (cerâmica híbrida + dissilicato de lítio) e CH+LEU (cerâmica híbrida + leucita). Para o Estudo A, todas as infraestruturas foram usinadas; os recobrimentos dos grupos IC e IME foram confeccionados através da estratificação, e os recobrimentos do grupo IMC foram usinados. Já para o Estudo B, todas as peças foram usinadas, de acordo com o material cerâmico de cada grupo. Em seguida, foi realizada a cimentação adesiva dos recobrimentos sobre as infraestruturas (a depender do grupo) e das coroas sobre os preparos utilizando cimento resinoso fotopolimerizável (Variolink Esthetic LC). Após a cimentação, os espécimes foram submetidos ao teste de fadiga cíclica (10.000 ciclos, 20Hz), e como desfecho foram considerados dois eventos, em que o primeiro foi a ocorrência de trinca e/ou lascamento (evento 1) e o segundo foi a falha catastrófica do conjunto (evento 2). Os valores de carga e número de ciclos para falha em que foram observados os eventos 1 e 2 foram utilizados para realizar a análise de sobrevivência de acordo com Kaplan-Meier e Log-Rank (Mantel-Cox; 95%). As marcas de fratura e o modo de falha das coroas foram avaliados e classificados por estereomicroscópio óptico e microscópio eletrônico de varredura. Por fim, foi realizada análise por elementos finitos (FEA) para ambos os estudos, a fim de avaliar a distribuição de tensões sobre as coroas e interface adesiva. Para o Estudo A, os resultados do teste de fadiga mostraram que, considerando o evento 1 (trinca/lascamento), os grupos IC e IMC apresentaram médias de carga fadiga estatisticamente significantes entre si (733,33 N e 913,33 N, respectivamente), enquanto o grupo IME apresentou média superior (1.020 N). O mesmo foi observado para o número de ciclos em fadiga para todos os grupos. Ao considerar o evento 2 (falha catastrófica), os três grupos apresentaram médias estatisticamente semelhantes entre si (~1.028 N). Os resultados de FEA mostraram que o grupo IC concentrou maior tensão de tração do que os grupos IME e IMC. Para o Estudo B, no teste de fadiga, o grupo DL+LEU apresentou a maior média de resistência à fadiga (evento 1: 913,33 N e evento 2: 1033,33 N), enquanto todas as outras combinações de materiais cerâmicos analisadas foram estatisticamente semelhantes entre si, considerando carga e número de ciclos. Com relação ao FEA, os grupos com cerâmica híbrida (CH+DL e CH+LEU) apresentaram menores picos de concentração de tensão na infraestrutura do que os grupos com cerâmicas vítreas (DL+LEU e LEU+DL), porém, em contrapartida, concentraram maior tensão na interface adesiva. Com isso, conclui-se que a utilização da infraestrutura modificada é uma alternativa viável e promissora para tratamentos reabilitadores, apresentando sobrevivência em fadiga e distribuição de tensões satisfatórias. Além disso, a combinação entre uma infraestrutura de dissilicato de lítio e recobrimento de cerâmica a base de leucita corresponde a melhor abordagem considerando a infraestrutura modificada.(AU)

The objective of this study was to evaluate the biomechanical behavior through fatigue resistance and finite element analysis of bilaminar bioinspired crowns with modified infrastructures on the buccal surface (Study A) and using different ceramic materials with different elastic moduli (Study B). For this, 90 preparations were made for a full crown in G10 epoxy resin, on which bioinspired crowns were prepared according to the following groups: Study A - CI (conventional infrastructure), SMI (stratified modified infrastructure) and CMI (cemented modified infrastructure ), all made of lithium disilicate (infrastructure) + porcelain (veneer); Study B ­ LD+LEU (lithium disilicate + leucite), LEU+LD (leucite + lithium disilicate), HC+LD (hybrid ceramic + lithium disilicate) and HC+LEU (hybrid ceramic + leucite). For Study A, all infrastructures were machined; the coverings of the CI and SMI groups were made through stratification technique, and the veneers of the SMI group were machined. For Study B, all pieces were machined, according to the ceramic material of each group. Then, the veneers were cemented into their infrastructures (depending on the group) and crowns were cemented into preparations using light-cured resin cement (Variolink Esthetic LC). After cementing, the specimens were subjected to the cyclic fatigue test (10,000 cycles, 20Hz), and as an outcome two events were considered: the occurrence of cracking and/or chipping (event 1) and catastrophic failure (event 2). The load (N) and number of cycles to failure in which events 1 and 2 were observed were used to perform the survival analysis according to Kaplan-Meier and Log-Rank (Mantel- Cox; 95%). The fracture marks and failure mode of the crowns were evaluated and classified by optical stereomicroscope and scanning electron microscope. Finally, finite element analysis (FEA) was performed for both studies in order to evaluate the stress distribution over the crowns and adhesive interface. For Study A, the results of the fatigue test showed that, considering event 1 (cracking/chipping), the CI and CMI groups presented average to failure that were statistically significant compared to each other (733.33 N and 913.33 N, respectively), while the SMI group showed higher averages (1,020 N). Same pattern was observed for the number of cycles under fatigue for both groups. When considering event 2 (catastrophic failure), the three groups presented statistically similar means (~1,028 N). The FEA results showed that the CI group concentrated greater tensile stress than the CMI and SMI groups. For Study B, in the fatigue test, the LC+LEU group presented the highest average fatigue resistance (event 1: 913.33 N and event 2: 1033.33 N), while all other combinations of ceramic materials analyzed were statistically similar to each other, considering load and number of cycles. Regarding FEA, the groups with hybrid ceramics (HC+LC and HC+LEU) showed lower stress concentration peaks in the infrastructure than the groups with glass ceramics (LC+LEU and LEU+LC), however, on the other hand, concentrated greater tension at the adhesive interface. With this, it is concluded that the use of modified infrastructure is a viable and promising alternative for oral rehabilitation treatments, presenting satisfactory fatigue survival and adequate stress distribution. Furthermore, the combination of a lithium disilicate infrastructure and a leucite-based ceramic coating corresponds to the best approach considering the modified infrastructure.(AU)

Stress distribution in peri-implant bone, implants, and prostheses: 3D-FEA of marginal bone loss and prosthetic design / Distribuição de estresse no osso peri-implantar, implantes e próteses: análise 3D-FEA de perda óssea marginal e design protético

Objective: In response to the demand for dental implants, extensive research has been conducted on methods for transferring load to the surrounding bone. This study aimed to evaluate the stresses on the peripheral bone, implants, and prostheses under scenarios involving of the following variables: prosthesis designs, vertical bone heights, load angles, and restorative materials. Material and Methods: Three implants were inserted in the premolar and molar regions (5-6-7) of the two mandibular models. Model 1 represented 0 mm marginal bone loss and Model 2 simulated 3 mm bone loss. CAD/CAM-supported materials, hybrid ceramic (HC), resin-nano ceramic (RNC), lithium disilicate (LiSi), zirconia (Zr), and two prosthesis designs (splinted and non-splinted) were used for the implant-supported crowns. Forces were applied vertically (90°) to the central fossa and buccal cusps and obliquely (30°) to the buccal cusps only. The stresses were evaluated using a three-dimensional Finite Element Analysis. Results: Oblique loading resulted in the highest stress values. Of the four materials, RNC showed the low stress in the restoration, particularly in the marginal area. The use of different restorative materials did not affect stress distribution in the surrounding bone. The splinted prostheses generated lower stress magnitude on the bone, and while more stress on the implants were observed. Conclusion: In terms of the stress distribution on the peri-implant bone and implants, the use of different restorative materials is not important. Oblique loading resulted in higher stress values, and the splinted prosthesis design resulted in lower stress (AU)

Objetivo: Em resposta à demanda por implantes dentários, extensa pesquisa foi realizada sobre métodos para transferir carga ao osso circundante. Este estudo buscou avaliar os estresses no osso periférico, implantes e próteses em cenários que envolvem as seguintes variáveis: designs de próteses, alturas ósseas verticais, ângulos de carga e materiais restauradores. Material e Métodos: Três implantes foram inseridos nas regiões dos pré-molares e molares (5-6-7) de dois modelos de mandíbula. O Modelo 1 representou perda óssea marginal de 0 mm e o Modelo 2 simulou perda óssea de 3 mm. Materiais suportados por CAD/CAM, cerâmica híbrida (HC), cerâmica nano-resina (RNC), dissilicato de lítio (LiSi), zircônia (Zr) e dois designs de próteses (sintetizadas e não-sintetizadas) foram utilizados para as coroas suportadas por implantes. Forças foram aplicadas verticalmente (90°) à fossa central e cúspides bucais e obliquamente (30°) apenas às cúspides bucais. Os estresses foram avaliados usando Análise de Elementos Finitos tridimensional. Resultados: Cargas oblíquas resultaram nos valores mais altos de estresse. Entre os quatro materiais, RNC mostrou baixo estresse na restauração, especialmente na área marginal. O uso de diferentes materiais restauradores não afetou a distribuição de estresse no osso circundante. Próteses sintetizadas geraram menor magnitude de estresse no osso, enquanto mais estresse nos implantes foi observado. Conclusão: Em termos de distribuição de estresse no osso peri-implantar e implantes, o uso de diferentes materiais restauradores não é crucial. Cargas oblíquas resultaram em valores mais altos de estresse, e o design de prótese sintetizada resultou em menor estresse. (AU)

Effect of miniscrew placement height on the distribution of biological forces produced by clear aligner for mandibular molar distalization / 口腔疾病防治

Objective@#To explore the effect of different miniscrew placement heights on the distribution of biological forces produced by clear aligner combined with intramaxillary traction for mandibular molar distalization, to identify the miniscrew location that is conducive to the protection of lower anterior tooth anchorage and to provide a reference that can be used when designing clinical treatments.@*Methods@#Mimics, GeomagicStudio 2017, SolidWorks 2016, and Ansys workbench were used to establish finite element analysis models and perform mechanical analysis under the following six working conditions: working condition 1 was the control group without miniscrews; working conditions 2 to 5 had miniscrew in the buccal bone cortex between the first and second molars of the lower jaw 10 mm, 7 mm, 4 mm, and 1 mm from the top of the alveolar crest, respectively; working condition 6 had the miniscrew in the center of the buccal tongue at the anterior edge of the ascending branch of the lower jaw 5 mm above the occlusal plane.@*Results@#On the sagittal axis, miniscrew anchorage caused distal displacement of all teeth. Compared to the control group, in the miniscrew group, the displacement of the anterior molars exceeded that of the second molars. On the vertical axis, the result in the control group was similar to backward bending; the results in the miniscrew groups resembled the effect of a lever, lowering the lateral incisors and canines and raising the central incisors and first premolars. On the coronal axis, the second premolars and the first molars showed lingual displacement in the control group, and only the premolars and first molars showed lingual displacementin the miniscrew groups. The canines were the teeth that were most strongly affected by the change in miniscrew placement height.@*Conclusion@#The higher the miniscrew position is, the stronger the protective effect on the anterior anchorage. According to the miniscrew placement height, the mandibular arch should be properly narrowed, the central incisors and first premolars should be lowered, and the lateral incisors and canines should be raised when designing clinical treatments.

Avaliação da fixação dos avanços maxilares pela técnica de osteotomia Le Fort I / Evaluación de la fijación de avances maxilar mediante la técnica de osteotomía Le Fort I / Evaluation of the fixation of maxillary advancements by the Le Fort I osteotomy technique

Introdução: A osteotomia Le Fort I possibilita a correção de deformidades dentofaciais que envolvem o terço médio da face. Para sua fixação, convencionou-se o emprego de quatro mini-placas nos pilares zigomático-maxilar e nasomaxilar. Propôs-se então, a dispensa da fixação do segmento posterior, surgindo questionamentos relacionados à capacidade biomecânica do sistema. Objetivos: Comparar o estresse biomecânico gerado em três meios distintos de fixação da osteotomia Le Fort I frente ao movimento de avanço sagital linear maxilar de 7mm. Metodologia: Trata-se de uma pesquisa experimental laboratorial, utilizando-se da análise de elementos finitos como ferramenta analítica, a fim de constatar qual das técnicas sofrerá maior estresse biomecânico. Resultados: Constatou-se que o estresse biomecânico gerado é maior quando aplicado em 4 pontos do que quando aplicado em apenas 2 pontos. Conclusão: Os resultados obtidos fornecem informações aos cirurgiões sobre a real necessidade do uso de fixação adicional de acordo com o método de fixação planejado. No entanto, deve ser interpretado de forma cautelosa, considerando-se as limitações deste estudo. Sendo assim, uma análise incipiente, que tem como intuito o fornecimento de evidência científica de grande significância.

Introducción: La osteotomía Le Fort I permite la corrección de deformidades dentofaciales que involucran el tercio medio de la cara. Para su fijación se acordó utilizar cuatro miniplacas en los pilares cigomaticomaxilar y nasomaxilar. Entonces se propuso prescindir de la fijación del segmento posterior, planteando interrogantes relacionados con la capacidad biomecánica del sistema. Objetivos: Comparar el estrés biomecánico generado en tres medios diferentes de fijación de la osteotomía Le Fort I frente a un movimiento de avance sagital lineal maxilar de 7mm. Metodología: Se trata de una investigación experimental de laboratorio, utilizando como herramienta analítica el análisis de elementos finitos, con el fin de comprobar cuál de las técnicas sufrirá un mayor estrés biomecánico. Resultados: Se encontró que el estrés biomecánico generado es mayor cuando se aplica en 4 puntos que cuando se aplica solo en 2 puntos. Conclusión: Los resultados obtenidos brindan información a los cirujanos sobre la necesidad real de utilizar fijación adicional de acuerdo al método de fijación planificado. Sin embargo, debe interpretarse con cautela, considerando las limitaciones de este estudio. Por tanto, un análisis incipiente, que pretende aportar evidencias científicas de gran trascendencia.

Introduction: The Le Fort I osteotomy allows the correction of dentofacial deformities involving the middle third of the face. For its fixation, it was agreed to use four mini plates on the zygomaticomaxillary and nasomaxillary pillars. It was then proposed to dispense with the fixation of the posterior segment, raising questions related to the biomechanical capacity of the system. Objectives: To compare the biomechanical stress generated in three different means of fixation of the Le Fort I osteotomy against a 7mm maxillary linear sagittal advancement movement. Methodology: This is an experimental laboratory research, using finite element analysis as an analytical tool, in order to verify which of the techniques will suffer greater biomechanical stress. Results: It was found that the biomechanical stress generated is greater when applied to 4 points than when applied to only 2 points. Conclusion: The results obtained provide information to surgeons about the real need to use additional fixation according to the planned fixation method. However, it should be interpreted with caution, considering the limitations of this study. Therefore, an incipient analysis, which aims to provide scientific evidence of great significance.

Biomechanical Behavior Evaluation of a Mandibular Full-Arch Implant-Supported Prosthesis on ZrO2 and TiO2 Monotype Dental Implants / Evaluación del Comportamiento Biomecánico de una Prótesis Implante Soportada de Arcada Completa Mandibular sobre Implantes Dentales Monotipos de ZrO 2 y TiO

This in silico study aimed to evaluate the biomechanical behavior of a full-arch implant-supported prosthesis on titanium and zirconia monotype implants. A 3D mandible containing 1.0 mm thick cortical and cancellous bone was modeled. Four dental implants (3.3 x 10 mm) were inserted into the jaw model in each model. The implants consisted of Titanium (Ti-S group) and Zirconia Monotype/one-piece (Zr-S group). Fixed full-arch implant-supported prostheses were cemented onto the implant. The models were exported to the analysis software and divided into meshes composed of nodes and tetrahedral elements. All materials were considered isotropic, elastic, and homogeneous. Therefore, all contacts were considered bonded, the mandible model was fixed in all directions, applying a static structural axial load of 300 N on the bottom of the fossa of the left mola r teeth. Microstrain and von-Mises stress (MPa) were adopted as failure criteria. Comparable stress and strain values were shown in the peri-implant bone for both groups. However, the Ti-S group presented a lower stress value (1,155.8 MPa) than the Zr-S group (1,334.2 MPa). Regarding bone tissues, the Ti-S group presented 612 µε and the Zr-S group presented 254 µε. The highest strain peak was observed in bone tissues around the implant closer to the load for both groups. Evaluating monotype zirconia and titanium implants, it is suggested that the greater the rigidity of the implant, the greater the concentration of internal stre sses and the less dissipation to the surrounding tissues. Therefore, monotype ceramic implants composed of yttrium-stabilized tetragonal polycrystalline zirconia may be a viable alternative to titanium implants for full-arch prostheses.

El objetivo de este estudio in silico fue evaluar el comportamiento biomecánico de una prótesis implanto soportada de arcada completa sobre implantes monotipo de titanio y zirconia. Se modeló una mandíbula en 3D que contenía tejido óseo cortical y esponjoso de 1,0 mm de espesor. En cada modelo, se insertaron cuatro implantes dentales (3,3 x 10 mm) en el modelo de mandíbula. Los implantes consistieron en Monotipo de Titanio y Zirconia. Sobre el implante se cementaron prótesis implanto soportadas de arcada completa fija. Los modelos se exportaron al software de análisis y se dividieron en mallas compuestas por nodos y elementos tetraédricos. Todos los materiales se consideraron isotrópicos, elásticos y homogéneos. Por lo tanto, todos los contactos se consideraron cementados, el modelo mandibular se fijó en todas las direcciones, aplicando una carga vertical estructural estática de 300 N en el fondo de la fosa de los dientes molares izquierdos. Se seleccionaron la microesfuerzo y la tensión de Von-Mises (MPa) como criterios de falla. Se mostraron valores de tensión y deformación comparables en el hueso periimplantario para ambos grupos. Sin embargo, el grupo Ti-S presentó un valor de estrés menor (1.155,8 MPa) que el grupo Zr-S (1.334,2 MPa). En cuanto a los tejidos óseos, el grupo Ti-S presentó 612 µε y el grupo Zr-S presentó 254 µε. La mayor concentración de deformación en el tejido óseo se observó en los tejidos alrededor del implante más cerca de la carga para ambos grupos. Al evaluar los implantes monotípicos de zirconia y titanio, se sugiere que cuanto mayor sea la rigidez del implante, mayor será la concentración de tensiones internas y menor la disipación a los tejidos circundantes. Por lo tanto, los implantes cerámicos monotipo compuestos de zirconia policristalina tetragonal estabilizada con itrio pueden ser una alternativa viable a los implantes de titanio para prótesis de arcada completa.

Finite Element Simulation of Double-Stent Parallel Thrombectomy at Y-Shaped Bifurcation of Internal Carotid Artery / 医用生物力学

Objective To study the process of single stent and double-stent thrombectomy at the Y-shaped bifurcation of the ideal internal carotid artery by finite element simulation, analyze the stent-thrombus-vessel interaction during the thrombectomy process based on the simulation results, and provide guidance for improving the effect of stent thrombectomy at the bifurcation. Methods The CAD software was used to build the model and the finite element analysis software was used to simulate the process of single stent and double-stent thrombectomy. Results Thrombectomy was unsuccessful in single stent model and successful in double-stent model, and the maximum stress of thrombus during embolus retrieval was twice that of single stent, the maximum strain was 1.12 times that of single stent, and the maximum contact pressure on the surface of vessel was approximately twice that of single stent. Conclusions Double Solitaire stents can effectively prevent thrombus displacement at the bifurcation and successfully retrieve the thrombus, but there is a risk of fracture due to the high stress level in the middle section of the thrombus. The contact pressure of the vessel on the anterior artery side is higher during thrombectomy, and the risk of vessel damage is greater. Therefore, it is necessary to optimize the design of the stent-retriever to improve its flexibility.

Analysis on Biomechanical Relationship Between Calcaneal Cyst Lesion Size and Pathological Fracture / 医用生物力学

Objective To investigate the relationship between lesion size of solitary bone cyst ( SBC) and pathological fracture of calcaneus, so as to provide references for the treatment of SBC. Methods The three dimensional (3D) finite element model of foot and ankle was established based on CT images. Four models with gradient spherical bone defects were constructed in the focal area to simulate different SBC lesion sizes, and the biomechanical characteristics of calcaneus in different gait phases were analyzed. Results With the increasement of SBC size, the kinematics of calcaneus did not change significantly, but the peak stress of calcaneus increased gradually. When the SBC size exceeded 75% of the calcaneal width, the stress in calcaneal sulcus and cortical bone below SBC increased by 1. 48 times and 7. 74 times, respectively. Conclusions The risk of pathological fracture increases when the SBC diameter exceeds 75% of the calcaneal width, and early surgical intervention should be recommended. The calcaneal sulcus and the cortex bone below SBC are stress concentration regions and can be used as important areas to evaluate pathological fractures.

Effects of PEEK Anisotropy Formed by 3D Printing on Mechanical Properties of Femoral Substitutes / 医用生物力学

Objective Aiming at the problem of significant anisotropy in the three-dimensional ( 3D) printed polyether-ether-ketone ( PEEK) bone substitutes manufactured by material extrusion technology, taking the femur, the main load-bearing long bone of the lower limb, as an example, the biomechanical properties of the femoral model under different direction in the build chamber were evaluated by the combination of finite element analysis and in-vitro mechanical experiment. Methods A left femoral model was obtained by reconstruction from CT data. The stress and displacement of the 3D printed PEEK femur with different directions in the build chamber under five physiological postures in the human gait cycle were simulated by varying the orthogonal anisotropy mechanical properties. An in-vitro mechanical experiment was conducted to investigate the safety and stability of the femur through a 3D printed PEEK femur. Results When the long axis of the femur model was perpendicular to the building platform of the 3D printer, a better mechanical property was obtained, and the maximum von Mises stress was 46. 56 MPa, which was lower than the yield stress of PEEK, while the maximum displacement was larger than that of the natural femur under same loading condition. Therefore, the 3D printed PEEK femur met the strength requirement, but the stability needs to be improved. Conclusions The long axis is recommended to be perpendicular to the building platform when the material extrusion technology was used for the substitute of the load-bearing long bone, and the effect of its anisotropy on service performance of the substitute should be carefully considered when the 3D printing technology is used for load-bearing bone substitute.

The Wear on a Novel Motion Mode Hinged Knee Prosthesis: A Finite Element Analysis / 医用生物力学

Objective To perform finite element analysis on a novel motion mode hinged knee prosthesis, and investigate the method of wear simulation on hinged prosthesis and the influence of motion mode on wear of the prosthesis. Methods Based on the finite element model of contact stress on spherical axis prosthesis, the finite element model of wear was established according to Archard wear theory. The kinematics data during different motions were input as loading condition to simulate mechanical environment of the knee arthroplasty in physiological activities. The wear results of spherical axis prosthesis were studied. Results For tibial insert, the average and maximum contact stresses during upstairs and downstairs climbing were higher than those during walking, and the cumulative wear volume during upstairs climbing was larger than that during downstairs climbing and walking. The wear mainly occurred on lower surface of tibial insert during all 3 motions. For rotating bushing, there was only a short period of contact and wear during walking, and the cumulative wear was 0. 19 mm3. Conclusions The spherical axis motion of hinged knee prosthesis can improve the mechanical environment of knee, reduce the wear of rotating bushing, and prolong the prosthesis survival. The finite element simulation can predict the wear of hinged prosthesis effectively, and provide the theoretical basis for design and improvement of the prosthesis.

Biomechanical Evaluation of Oblique Lateral Interbody Fusion Combined with Different Internal Fixation Methods for Treating Degenerative Lumbar Scoliosis:A Finite Element Analysis / 医用生物力学

Objective To verify the biomechanical stability of oblique lateral interbody fusion ( OLIF) combinedwith different fixation methods for treating degenerative lumbar scoliosis (DLS) by three-dimensional (3D) finite element analysis. Methods The L1-S1 3D finite element DLS model ( Model 1) was established, and then the OLIF (L2-5) at 3 contiguous levels of fusion and its combination with different internal fixation methods were simulated, namely, stand-alone OLIF model ( Model 2), vertebral screw fixation model ( Model 3), unilateral pedicle screw fixation model (Model 4) and bilateral pedicle screw fixation model (Model 5) were established,respectively. Under upright, flexion, extension, lateral bending and axial rotation states, range of motion (ROM) of fusion segments, as well as cage stress, internal fixation stress, and stress distribution were recorded and analyzed. Results Under six motion states, the overall ROM of fusion segments in Models 2-5 was smaller than that of Model 1. Compared with Model 1, the overall ROM reduction of Model 3 and Model 4 was larger than that of Model 2 and smaller than that of Model 5. Under flexion and extension, the overall ROM reduction of Model 4 and Model 5 was basically equal. Under left and right lateral bending, the overall ROM reduction of Model 3 and Model 5 was basically equal. Under all motion states, the peak stress of Model 3 and Model 4 fusion cage was larger than that of Model 5 and smaller than that of Model 2. The peak stresses of L2-3, L3-4 and L4-5 fusion cages in Model 3 increased by 5. 52% , 10. 96% and 7. 99% respectively compared with Model 5 under left lateral bending, and the peak stresses of L2-3, L3-4 and L4-5 fusion cages in Model 4 increased by 8. 70% , 7. 00% and 6. 99% respectively under flexion. Under all motion states, the peak stress of screw rod in Model 5 was smaller than that of Model 3 and Model 4, and the peak stresses of screw rod in Models 3-5 were the smallest in upright state. Conclusions The OLIF with unilateral pedicle screw fixation or vertebral screw fixation can provide favorable biomechanical stability of the fusion segment. The results provide some references for clinical application of OLIF technology in the treatment of DLS.

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.

3D finite element analysis of the influence of upper lip pressure on the maxilla for patients with unilateral alveolar cleft / 口腔疾病防治

Objective @#To investigate the biomechanical effects of upper lip pressure on the maxilla in patients with a unilateral alveolar cleft and provide evidence for clinical diagnosis and treatment. @*Methods @#A 3D finite element maxillary model was generated based on cone beam CT (CBCT) data from an 11-year-old female patient with a unilateral alveolar cleft. Two different kinds of upper lip pressure, postsurgery pressure and normal pressure, were applied to the model. The displacement and stress of each reference node were compared and analyzed. @*Results @# By loading upper lip pressure, the maxillary alveolar crest rotated toward the defect and was displaced downward and backward. The displacement of the noncleft side was greater than that of the cleft side and it decreased gradually from the anterior to the posterior. The stress was concentrated on the anterior portion of the alveolar crest. The stress on the noncleft side was greater than that on the cleft side and it decreased gradually from the anterior to the posterior. The maximum stress was concentrated on the palate around the defect. The displacement and stress in the postsurgery group were greater than those of the normal group (P<0.05). @*Conclusion @#By loading upper lip pressure, the maxilla demonstrated asymmetry three-dimensionally. The adverse effects on the maxilla could be mitigated by reducing the upper lip pressure.

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.

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.