Los Músculos Isquiosurales y su Capacidad Profiláctica sobre la Translación Tibial Anterior en Lesión de Ligamento Cruzado Anterior: Una Revisión Sistemática / The Hamstrings Muscles and their Prophylactic Capacity on Anterior Tibial Translation in Anterior Cruciate Ligament Injury: A Systematic Review

La ruptura de ligamento cruzado anterior (LCA) es la lesión de rodilla más común que se trata de una reconstruc- ción quirúrgica. El objetivo principal de esta revisión fue analizar la importancia de la función de los músculos isquiosurales como factor de riesgo de posibles lesiones de LCA. Se llevó a cabo siguiendo las normas Preferred Reported Item for Systematic Reviews and Meta- analyses (PRISMA). La fuente de la recopilación de datos fue la consulta directa de las bases de datos Pubmed, Sportdiscus, Web of Science y Scopus. Para la recuperación documental, se utilizaron varias palabras clave y se evaluó la calidad de los estudios que fueron seleccionados mediante la escala PEDro. Los déficits de la función muscular en los músculos isquiosurales se han relacionado con una mayor translación tibial anterior y, como consecuencia, un incremento del estrés tensional sobre el LCA entre los 10° y 45° de flexión de rodilla. Una co-activación de los músculos isquiosurales con el músculo cuádriceps femoral puede ser de gran ayuda para reducir los factores de riesgo de la lesión LCA.

SUMMARY: Anterior cruciate ligament (ACL) rupture is the most common knee injury to undergo surgery in the sports setting. The main objective of this review was to analyze the importance of hamstring function as a risk factor for potential ACL injury. It was conducted following the Preferred Reported Item for Systematic Reviews and Meta-analyses (PRISMA) guidelines. The source of data collection was direct consultation of the Pubmed, Sportdiscus, Web of Science and Scopus databases. For documentary retrieval, several key words were used and the quality of the studies that were selected was assessed using the PEDro scale. Muscle function deficits in the hamstrings have been related to increased anterior tibial translation and, as a consequence, increased tensional stress on the ACL between 10° and 45° of knee flexion. A co-activation of the hamstrings with the quadriceps may be helpful in reducing the risk factors for ACL injury.

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.

Expression profile of microRNA secreted by rat condylar chondrocytes under tensile stress / 中华口腔医学杂志

Objective: To preliminarily explore the mechanism of tensile stress regulating endochondral osteogenesis of condyle by analyzing the expression profiles of significantly different microRNAs (miRNAs) in exosomes of rat mandibular condylar chondrocytes (MCC) under quiescent and cyclic tensile strain (CTS) conditions. Methods: Rat condylar chondrocytes were cultured under static and CTS conditions respectively (10 SD rats, male, 2 weeks old), and exosomes were extracted. The two groups of exosomes were named as control group and CTS group respectively. The differential expression miRNAs were screened by high-throughput sequencing. Bioinformatics analysis and prediction of target genes related to osteogenesis were performed by TargetScan and miRanda website. Results: The exosomes of rat condylar chondrocytes cultured under tensile stress showed a "double concave disc" monolayer membrane structure, the expression of CD9 and CD81 were positive, and the particle size distribution accorded with the characteristics of exosomes, which was consistent with that of static cultured rat condylar chondrocytes. A total of 85 miRNAs with significantly different expression were detected by high-throughput sequencing (P<0.05). The main biological processes and molecular functions of differential miRNAs were biological processes and protein binding, respectively. Kyoto Encyclopedia of Genes and Genomes (KEGG) database pathway enrichment analysis showed that there was significant enrichment in mammalian target of rapamycin (mTOR) signal pathway. The candidate target genes of miR-199a-5p include bone morphogenetic protein 3 (BMP3), endothelin converting enzyme 1, and miR-186-5p may target Smad8 and BMP3 to exert osteogenesis-related functions. Conclusions: Compared with static state, tensile stress stimulation can change the expression of miRNAs such as miR-199a-5p, miR-186-5p in the exocrine body of rat condylar chondrocytes, which can be considered as a mean to regulate the application potential of the exosomes.

Finite element analysis of artificial ankle elastic improved inserts / 中国修复重建外科杂志

OBJECTIVE@#To discuss the influence of artificial ankle elastic improved inserts (hereinafter referred to as "improved inserts") in reducing prosthesis micromotion and improving joint surface contact mechanics by finite element analysis.@*METHODS@#Based on the original insert of INBONE Ⅱ implant system (model A), four kinds of improved inserts were constructed by adding arc or platform type flexible layer with thickness of 1.3 or 2.6 mm, respectively. They were Flying goose type_1.3 elastic improved insert (model B), Flying goose type_2.6 elastic improved insert (model C), Platform type_1.3 elastic improved insert (model D), Platform type_2.6 elastic improved insert (model E). Then, the CT data of right ankle at neutral position of a healthy adult male volunteer was collected, and finite element models of total ankle replacement (TAR) was constructed based on model A-E prostheses by software of Mimics 19.0, Geomagic wrap 2017, Creo 6.0, Hypermesh 14.0, and Abaqus 6.14. Finally, the differences of bone-metal prosthesis interface micromotion and articular surface contact behavior between different models were investigated under ISO gait load.@*RESULTS@#The tibia/talus-metal prosthesis interfaces micromotion of the five TAR models gradually increased during the support phase, then gradually fell back after entering the swing phase. The improved models (models B-E) showed lower bone-metal prosthesis interface micromotion when compared with the original model (model A), but there was no significant difference among models A-E ( P>0.05). The maximum micromotion of tibia appeared at the dome of the tibial bone groove, and the ​​micromotion area was the largest in model A and the smallest in model E. The maximum micromotion of talus appeared at the posterior surface of the central bone groove, and there was no difference in the micromotion area among models A-E. The contact area of the articular surface of the insert/talus prosthesis in each group increased in the support phase and decreased in the swing phase during the gait cycle. Compared with model A, the articular surface contact area of models B-E increased, but there was no significant difference among models A-E ( P>0.05). The change trend of the maximum stress on the articular surface of the inserts/talus prosthesis was similar to that of the contact area. Only the maximum contact stress of the insert joint surface of models D and E was lower than that of model A, while the maximum contact stress of the talar prosthesis joint surface of models B-E was lower than that of model A, but there was no significant difference among models A-E ( P>0.05). The high stress area of the lateral articular surface of the improved inserts significantly reduced, and the articular surface stress distribution of the talus prosthesis was more uniform.@*CONCLUSION@#Adding a flexible layer in the insert can improve the elasticity of the overall component, which is beneficial to absorb the impact force of the artificial ankle joint, thereby reducing interface micromotion and improving contact behavior. The mechanical properties of the inserts designed with the platform type and thicker flexible layer are better.

Finite element analysis for predicting osteonecrosis of the femoral head collapse based on the preserved angles / 中国修复重建外科杂志

OBJECTIVE@#To establish finite element models of different preserved angles of osteonecrosis of the femoral head (ONFH) for the biomechanical analysis, and to provide mechanical evidence for predicting the risk of ONFH collapse with anterior preserved angle (APA) and lateral preserved angle (LPA).@*METHODS@#A healthy adult was selected as the study object, and the CT data of the left femoral head was acquired and imported into Mimics 21.0 software to reconstruct a complete proximal femur model and construct 3 models of necrotic area with equal volume and different morphology, all models were imported into Solidworks 2022 software to construct 21 finite element models of ONFH with LPA of 45°, 50°, 55°, 60°, 65°, 70°, and 75° when APA was 45°, respectively, and 21 finite element models of ONFH with APA of 45°, 50°, 55°, 60°, 65°, 70°, 75° when LPA was 45°, respectively. According to the physiological load condition of the femoral head, the distal femur was completely fixed, and a force with an angle of 25°, downward direction, and a magnitude of 3.5 times the subject's body mass was applied to the weight-bearing area of the femoral head surface. The maximum Von Mises stress of the surface of the femoral head and the necrotic area and the maximum displacement of the weight-bearing area of the femoral head were calculated and observed by Abaqus 2021 software.@*RESULTS@#The finite element models of ONFH were basically consistent with biomechanics of ONFH. Under the same loading condition, there was stress concentration around the necrotic area in the 42 ONFH models with different preserved angles composed of 3 necrotic areas with equal volume and different morphology. When APA was 60°, the maximum Von Mises stress of the surface of the femoral head and the necrotic area and the maximum displacement of the weight-bearing area of the femoral head of the ONFH models with LPA<60° were significantly higher than those of the models with LPA≥60° ( P<0.05); there was no significant difference in each index among the ONFH models with LPA≥60° ( P>0.05). When LPA was 60°, each index of the ONFH models with APA<60° were significantly higher than those of the models with APA≥60° ( P<0.05); there was no significant difference in each index among the ONFH models with APA≥60° ( P>0.05).@*CONCLUSION@#From the perspective of biomechanics, when a preserved angle of ONFH is less than its critical value, the stress concentration phenomenon in the femoral head is more pronounced, suggesting that the necrotic femoral head may have a higher risk of collapse in this state.

RANKL+ senescent cells under mechanical stress: a therapeutic target for orthodontic root resorption using senolytics / 国际口腔科学杂志·英文版

In dentistry, orthodontic root resorption is a long-lasting issue with no effective treatment strategy, and its mechanisms, especially those related to senescent cells, remain largely unknown. Here, we used an orthodontic intrusion tooth movement model with an L-loop in rats to demonstrate that mechanical stress-induced senescent cells aggravate apical root resorption, which was prevented by administering senolytics (a dasatinib and quercetin cocktail). Our results indicated that cementoblasts and periodontal ligament cells underwent cellular senescence (p21+ or p16+) and strongly expressed receptor activator of nuclear factor-kappa B (RANKL) from day three, subsequently inducing tartrate-resistant acid phosphatase (TRAP)-positive odontoclasts and provoking apical root resorption. More p21+ senescent cells expressed RANKL than p16+ senescent cells. We observed only minor changes in the number of RANKL+ non-senescent cells, whereas RANKL+ senescent cells markedly increased from day seven. Intriguingly, we also found cathepsin K+p21+p16+ cells in the root resorption fossa, suggesting senescent odontoclasts. Oral administration of dasatinib and quercetin markedly reduced these senescent cells and TRAP+ cells, eventually alleviating root resorption. Altogether, these results unveil those aberrant stimuli in orthodontic intrusive tooth movement induced RANKL+ early senescent cells, which have a pivotal role in odontoclastogenesis and subsequent root resorption. These findings offer a new therapeutic target to prevent root resorption during orthodontic tooth movement.

Biomechanical analysis of narrow dental implants for maxillary anterior rehabilitation / Análise biomecânica de implantes de diâmetro reduzido para reabilitação da região anterior da maxila

Introdução: O conhecimento da biomecânica de implantes de diâmetro reduzido indica dimensões seguras para uso clínico. Objetivo: O objetivo do presente estudo foi comparar biomecanicamente implantes de diâmetro regular e reduzido para suporte de próteses implantossuportadas unitárias na região anterior da maxila por meio de análise de elementos finitos 3D (3D-FEA). Material e método: Quatro modelos 3D-FEA foram desenvolvidos a partir de recomposição de tomografia computadorizada e dados da literatura: um bloco ósseo na região incisiva lateral superior direita com implante e coroa. M1: 3,75 x 13 mm, M2: 3,75 x 8,5 mm, M3: 2,9 x 13 mm e M4: 2,9 x 8,5 mm. Foi aplicada carga de 178 N nos ângulos 0, 30 e 60 graus em relação ao longo eixo do implante. Foram avaliados mapas de tensão de Von Mises, tensão principal máxima e microdeformação. Resultado: M3 e M4 apresentaram maiores valores de tensão e microdeformação que M1 e M2, principalmente quando foram aplicadas forças inclinadas. Porém, M3 apresentou comportamento biomecânico melhor do que M4. Conclusão: Pode-se concluir que reduzir o diâmetro dos implantes pode prejudicar a biomecânica durante a aplicação de forças, mas a distribuição e intensidade das tensões, bem como os valores de microdeformação podem ser melhorados se o comprimento do implante for aumentado

Introduction: Narrow diameter implants biomechanics knowledge indicates safe dimensions for clinical use. Objective: Purpose of the present study was biomechanically to compare regular and narrow diameter implants to support single implant-supported prosthesis in the anterior region of the maxilla by 3D finite element analysis (3D-FEA). Material and method: Four 3D-FEA models were developed form CT scan recompositing and literature data: a bone block in the right upper lateral incisive region with implant and crown. M1: 3.75 x 13 mm, M2: 3.75 x 8.5 mm, M3: 2.9 x 13 mm and M4: 2.9 x 8.5 mm. It was applied load was of 178 N at 0, 30 and 60 degrees in relation to implant long axis. Von Mises stress, maximum principal stress and microdeformation maps were evaluated. Result: M3 and M4 did show higher tension and higher microdeformation values than M1 and M2, especially when inclined forces were applied. However, M3 presented enhanced biomechanical behavior than M4. Conclusion: It can be concluded that reduce the diameter of the implants can disadvantage to the biomechanics during the application of forces, but the distribution and intensity of the stresses, as well as the micro deformation values can be improved if the length of the implant is increased

Study of nonlinear viscoelastic mechanical properties of degenerated intervertebral discs / Estudio de las propiedades mecánicas viscoelásticas no lineales de discos intervertebrales degenerados

SUMMARY: Biomechanical factors are important factors in inducing intervertebral disc degeneration, in this paper, the nonlinear viscoelastic mechanical properties of degenerated intervertebral discs were analyzed experimentally. Firstly, the loading and unloading curves of intervertebral discs before and after degeneration at different strain rates were compared to analyze the changes of their apparent viscoelastic mechanical properties; The internal stress/strain distribution of the disc before and after degeneration was then tested by combining digital image technology and fiber grating technology. The results show that the intervertebral disc is strain-rate- dependent whether before or after degeneration; The modulus of elasticity and peak stress of the degenerated disc are significantly reduced, with the modulus of elasticity dropping to 50 % of the normal value and the peak stress decreasing by about 55 %; Degeneration will not change the distribution of the overall internal displacement of the intervertebral disc, but has a greater impact on the superficial and middle AF; The stress in the center of the nucleus pulposus decreases, and the stress in the outer AF increases after degeneration. Degeneration has a great impact on the nonlinear viscoelastic mechanical properties of intervertebral disc, which has reference value for the mechanism, treatment and prevention of clinical degenerative diseases.

RESUMEN: Los factores biomecánicos son importantes en la inducción de la degeneración del disco intervertebral. En este estudio se analizaron experimentalmente las propiedades mecánicas viscoelásticas no lineales de los discos intervertebrales degenerados. En primer lugar se compararon las curvas de carga y descarga de los discos intervertebrales, antes y después de la degeneración, a diferentes velocidades de deformación para analizar los cambios aparentes de sus propiedades mecánicas viscoelásticas. La distribución interna de tensión/deformación del disco antes y después de la degeneración se probó luego combinando tecnología de imagen digital y tecnología de rejilla de fibra. Los resultados mostraron que el disco intervertebral depende de la velocidad de deformación antes o después de la degeneración; El módulo de elasticidad y la tensión máxima del disco degenerado se reducen significativamente, cayendo el módulo de elasticidad al 50 % del valor normal y la tensión máxima disminuyendo en aproximadamente un 55 %; La degeneración no cambiará la distribución del desplazamiento interno general del disco intervertebral, pero tiene un mayor impacto en la FA superficial y media; El estrés en el centro del núcleo pulposo disminuye y el estrés en el FA externo aumenta después de la degeneración. La degeneración tiene un gran impacto en las propiedades mecánicas viscoelásticas no lineales del disco intervertebral, que tiene valor de referencia para el mecanismo, tratamiento y prevención de enfermedades clínicas degenerativas.

Effect of straight-line minimally invasive access cavity on the mechanical properties of maxillary first premolars: a finite element analysis / 中华口腔医学杂志

Objective: To investigate the effects of straight-line minimally invasive access cavity on the mechanical properties of endodontically treated maxillary first premolars using finite element analysis. Methods: Micro-CT data of twenty maxillary first premolars were collected for three-dimensional reconstruction. Three access cavities, including the conventional access cavity (ConvAC), the truss access cavity (TrussAC) and the straight-line minimally invasive access cavity (SMIAC), as well as the root canal treatment procedure, were simulated in all the 20 reconstruction samples of three-dimensional models, respectively. The peak von Mises stress on the cervical area of each model, as well as the stress distribution under vertical and oblique loading circumstances, were subsequently determined by using finite element analysis. Results: In comparison to the stresses of ConvAC [buccal cervical (BC): (188.7±13.4) MPa, palatal cervical (PC): (200.9±25.7) MPa], the stresses of TrussAC [BC: (146.0±12.9) MPa, PC: (167.6±15.9) MPa] (t=9.01, P<0.001; t=4.59, P<0.001) and SMIAC [BC: (142.6±13.7) MPa, PC: (168.1±17.4) MPa] (t=9.64, P<0.001; t=3.76, P=0.004) significantly reduced the peak von Mises stress on the cervical area of the maxillary first premolars after root canal treatment. Under vertical loading conditions, SMIAC also reduced the central tendency of stresses on the occlusal surface, cervical area and root. In the case of oblique loading conditions, similar results were observed. Under both loading conditions, there was no significant difference in the peak von Mises stress on the cervical area of the maxillary first premolar between TrussAC and SMIAC groups. Conclusions: The design of SMIAC could preserve the mechanical properties of the maxillary first premolar following root canal treatment, which might have certain clinical feasibility.

The Effect of Torsion of Blood Vessel after Stent Implantation on Mechanical State of Stent / 中国医疗器械杂志

OBJECTIVE@#In daily life, the movement of the neck will cause certain deformation of the blood vessel and the stent. This study explores the quantitative influence of the torsion deformation of the blood vessel on the mechanical properties of the stent.@*METHODS@#In the finite element simulation software Abaqus, the numerical simulation of the crimping and releasing process of the stent, the numerical simulation of the torsion process of the blood vessel with the stent, and the numerical simulation of the pressure loading process of the outer wall of the blood vessel were carried out.@*RESULTS@#After the stent was implanted, when a load was applied to the outer surface of the blood vessel wall, when the applied load did not change, as the torsion angle increased, the smallest cross-sectional area in the blood vessel decreased.@*CONCLUSIONS@#After the stent is placed, when the external load is fixed, the radial support capacity of the stent will decrease as the torsion angle increases.

Effect of lower limb amputation level on aortic hemodynamics: a numerical study / 生物医学工程学杂志

It has been found that the incidence of cardiovascular disease in patients with lower limb amputation is significantly higher than that in normal individuals, but the relationship between lower limb amputation and the episodes of cardiovascular disease has not been studied from the perspective of hemodynamics. In this paper, numerical simulation was used to study the effects of amputation on aortic hemodynamics by changing peripheral impedance and capacitance. The final results showed that after amputation, the aortic blood pressure increased, the time averaged wall shear stress of the infrarenal abdominal aorta decreased and the oscillatory shear index of the left and right sides was asymmetrically distributed, while the time averaged wall shear stress of the iliac artery decreased and the oscillatory shear index increased. The changes above were more significant with the increase of amputation level, which will result in a higher incidence of atherosclerosis and abdominal aortic aneurysm. These findings preliminarily revealed the influence of lower limb amputation on the occurrence of cardiovascular diseases, and provided theoretical guidance for the design of rehabilitation training and the optimization of cardiovascular diseases treatment.

Influence of bionic texture coronary stent on hemodynamics after implantation / 生物医学工程学杂志

To explore the influence of bionic texture coronary stents on hemodynamics, a type of bioabsorbable polylactic acid coronary stents was designed, for which a finite element analysis method was used to carry out simulation analysis on blood flow field after the implantation of bionic texture stents with three different shapes (rectangle, triangle and trapezoid), thus revealing the influence of groove shape and size on hemodynamics, and identifying the optimal solution of bionic texture groove. The results showed that the influence of bionic texture grooves of different shapes and sizes on the lower wall shear stress region had a certain regularity. Specifically, the improvement effect of grooves above 0.06 mm on blood flow characteristics was poor, and the effect of grooves below 0.06 mm was good. Furthermore, the smaller the size is, the better the improvement effect is, and the 0.02 mm triangular groove had the best improvement effect. Based on the results of this study, it is expected that bionic texture stents have provided a new method for reducing in-stent restenosis.

Avaliação do tipo de retenção e o uso de diferentes intermediários na adaptação de próteses unitárias sobre implantes / Evaluation of the type of retention and the use of different abutments in the adaptation of single prostheses on implants

Atualmente, devido a perda do elemento dentário e a procura por um tratamento estético e principalmente funcional, a reabilitação com próteses sobre implante tem sido amplamente empregada, com elevada previsibilidade a longo prazo. Com isso, muito tem sido relatado na literatura acerca das possíveis complicações dessa modalidade de tratamento, principalmente relacionado às possibilidades de falhas mecânicas das próteses implantossuportadas. Por isso, o objetivo do presente projeto foi avaliar a influência na adaptação marginal e interna, da utilização do intermediário protético e do tipo de retenção das próteses (parafusada e cimentada) em implantes cone morse submetidos à ciclagem mecânica. Foram confeccionados 40 corpos de prova, no qual cada um tinha a presença de um implante, com as dimensões de 4mm de diâmetro e 11,5mm de comprimento cone morse (n = 40). Dessa forma, foi avaliado a influência da utilização do intermediário e dos sistemas de retenção em cada conexão de maneira específica. Metade dos corpos de prova de cada sistema de conexão foram confeccionados em UCLA (n=20, sendo 10 parafusadas e 10 cimentadas), enquanto que a outra metade foi utilizado um intermediário pré-fabricado (Pilar Universal (n=20, sendo 10 parafusadas e 10 cimentadas). Os corpos de prova foram submetidos à ciclagem mecânica submersos em água destilada simulando um tempo clínico de cinco anos. Além disso, foram avaliados quanto ao torque e destorque (N) e adaptação marginal e interna (µm) antes e após a ciclagem mecânica. Os dados provenientes das mensurações foram organizados em tabela em formato Excel (Microsoft Office Excel, Redmond, WA, Estados Unidos) e submetidos ao software SigmaPlot (SigmaPlot, San Jose, CA, EUA) versão 12.0. Todos os dados foram analisados inicialmente com a utilização da estatística descritiva. Em seguida, os dados para intrusão (valores positivos), extrusão (valores negativos), destorque inicial, destorque final, e descimentação foram analisados em relação a distribuição de normalidade (teste Shapiro-Wilk e igualdade de variância) e, posteriormente, foi adotada a Análise de Variância (ANOVA) a um fator (Grupos diferentes materiais: G1 a G4), quando houve normalidade dos dados, o pós teste de Tukey foi adotado para as comparações múltiplas, quando não foi identificado uma distribuição normal, empregou-se o teste de Kruskall-Wallis e pós-teste de Dunn's ou Tukey, semelhantemente foi realizada a análise específica das variáveis pilares (UCLA e Pilar Universal) e sistemas de retenção (Parafusado e Cimentado). Para todos os testes aplicou-se nível de significância de 5% (α=0,05). A análise gráfica foi considerada através de um gráfico de barras para os dados que apresentaram normalidade com valores de média e desvio padrão, e as demais análises que não apresentaram normalidade foi considerado a confecção de um boxplot para cada grupo comparativo. As próteses sobre implante utilizando pilares em zircônia tem ganhado cada vez mais espaço, além do estudo in vitro, foi realizada uma revisão sistemática para comparar a perda óssea marginal e as complicações próteticas de reabilitações utilizando pilares de zircônia cimentado e parafusado. Em relação as próteses cimentadas e parafusadas, devido as evidências conflitantes e a presença de muitas revisões sistemáticas sobre o tema, foi realizada uma overview de revisões sistemáticas, com o objetivo de compilar as informações disponiveis e avaliar a qualidade metodologica desses estudos a respeito das complicações presentes nas próteses sobre implante cimentadas ou parafusadas(AU)

Currently, due to the loss of the dental element and the search for an aesthetic and mainly functional treatment, rehabilitation with implant prostheses has been widely used, with high long-term predictability. Thus, much has been reported in the literature about the possible complications of this treatment modality, mainly related to the possibility of mechanical failure of implant-supported prostheses. Therefore, the objective of the present project was to evaluate the influence on the marginal and internal adaptation, the use of the prosthetic intermediate and the type of retention of the prostheses (screwed and cemented) in morse taper implants submitted to mechanical cycling. 40 specimens were made, in which each one had an implant, with dimensions of 4 mm in diameter and 11.5 mm in length (n = 40). In this way, the influence of the use of intermediaries and retention systems in each connection was evaluated in a specific way. Half of the specimens of each connection system were made in UCLA (n=20, being 10 screwed and 10 cemented), while the other half was used a prefabricated intermediate (Universal Abutment (n=20, being 10 screwed) and 10 cemented). The specimens were submitted to mechanical cycling submerged in distilled water simulating a clinical time of five years. In addition, they were evaluated for torque and detorque (N) and marginal and internal adaptation (µm) before and after mechanical cycling. Data from measurements were organized in a table in Excel format (Microsoft Office Excel, Redmond, WA, USA) and submitted to SigmaPlot software (SigmaPlot, San Jose, CA, USA) version 12.0. All data were initially analyzed using descriptive statistics. Then, data for intrusion (positive values), extrusion (negative values), initial detorque, final detorque, and debonding were analyzed in relation to dist determination of normality (Shapiro-Wilk test and equality of variance) and, later, the one-way Analysis of Variance (ANOVA) was adopted (Different material groups: G1 to G4), when there was normality of the data, the Tukey post test was adopted for multiple comparisons, when a normal distribution was not identified, the Kruskall-Wallis test and Dunn's or Tukey post-test were used, similarly the specific analysis of the pillar variables (UCLA and Universal Pillar) and systems retainer (Screwed and Cemented). For all tests, a significance level of 5% (α=0.05) was applied. The graphical analysis was considered through a bar graph for the data that presented normality with mean and standard deviation values, and the other analyzes that did not present normality was considered the creation of a boxplot for each comparative group. Implant prostheses using zirconia abutments have gained more and more space, in addition to the in vitro study, a systematic review was performed to compare marginal bone loss and prosthetic complications of rehabilitations using cemented and screwed zirconia abutments. Regarding cemented and screw-retained prostheses, due to conflicting evidence and the presence of many systematic reviews on the subject, an overview of systematic reviews was performed, with the objective of compiling the available information and evaluating the methodological quality of these studies regarding complications present in cemented or screw-retained implant prostheses(AU)

Comparison of the High Cycle Fatigue Behavior of the Orthodontic NiTi Wires: An in Vitro Study

Abstract Objective: To compare the high-cycle fatigue behavior of four commercially available NiTi orthodontic wires. Material and Methods: Twelve NiTi orthodontic wires, round, 0.016-in, three per brand, were selected and divided into four groups: G1 - Heat-activated NiTi, G2 - Superelastic NiTi, G3 - Therma-Ti, and G4 - CopperNiTi. The atomic absorption spectrometry method was used to determine the chemical composition of investigated NiTi wires. We also performed a fatigue test at three-point bending using a universal testing machine for 1000 cycles in a 35 °C water bath. For the first and thousandth cycle, the average plateau load and the plateau length were determined in the unloading area of the force versus displacement diagram. In addition, we calculated the difference between the average plateau load of the first and thousandth cycle (∆F), as well as the difference between the plateau length of both cases (∆L). Results: According to our results, there were no significant differences between the average plateau load of the first and thousandth cycles of each group (p>0.05) and in the plateau length of the first and thousandth cycles of the groups (p>0.05). Conclusion: There were no significant differences between the groups changing the superelasticity property after high-cycle fatigue.

Mecanosensores en el cambio de fenotipo de la musculatura lisa vascular / Mechanosensors and phenotype changes in vascular smooth muscle

Resumen: Introducción: Las células de la musculatura lisa vascular (CMLV) se caracterizan por mantener cierto grado de desdiferenciación, variando su fenotipo entre el contráctil y el secretor, de acuerdo con las necesidades del tejido, y el contráctil predominante en condiciones fisiológicas. Cualquier alteración del estímulo mecánico, ya sea en el flujo sanguíneo o la tensión mecánica ejercida sobre las CMLV, conducen a cambios de su fenotipo y remodelamiento de la vasculatura, lo que puede constituir el punto de inflexión de varias patologías relevantes en la salud pública como, por ejemplo, la hipertensión arterial. Objetivo: Realizar una revisión sobre los mecanosensores y las vías transduccionales conocidas e implicadas en el cambio de fenotipo de las CMLV. Metodología: Se realizó una búsqueda sistemática en las bases de datos PubMed, Scopus, Google Académico y Scielo sobre la mantención y cambio de fenotipo de las células de la musculatura lisa vascular asociado principalmente a el estrés mecánico, la participación de los mecanosensores más relevantes y las vías de señalización involucrados en este proceso. Conclusión: Los mecanosensores implicados en el cambio de fenotipo de las CMLV contemplan principalmente receptores acoplados a proteína G, moléculas de adhesión y canales iónicos activados por estiramiento. Los estudios se han concentrado en la activación o inhibición de vías como las proteínas quinasas activadas por mitógenos (MAPK), la vía AKT, mTOR y factores transcripcionales que regulan la expresión de genes de diferenciación y/o desdiferenciación, como las miocardinas. Existen además otros receptores involucrados en la respuesta al estrés mecánico, como los receptores tirosina quinasas. A pesar de la importancia que reviste el conocimiento de los mecanosensores y las vías implicadas en el cambio de fenotipo de las CMLV, así como el papel que cumplen en el establecimiento de patologías vasculares, es aún escaso el conocimiento que se tiene sobre los mismos.

Abstract: Introduction: Vascular smooth muscle cells (VS- MCs) are characterized by maintaining a certain de- gree of dedifferentiation. VSMCs may vary their phenotype between contractile and secretory according to tissue needs. Under physiological conditions, the predominant phenotype is contractile. Any alteration of the mechanical stimulus, either in the blood flow or the mechanical stress exerted on the VSMCs, leads to changes in their phenotype and remodeling of the vasculature. These changes can constitute the turning point in several hypertension and other diseases relevant in public health. Objective: To review the main mechanosensor and transduction pathways involved changes in VSMCs phenotype. Methods: A systematic search of PubMed, Scopus, Google Scholar and Scielo databases was carried out to ascertain the state of the art regarding the maintenance and change of VSMCs phenotype mainly associated with mechanical stress. Additionally, the participation of the most relevant mechanosensors and the signaling pathways involved in this process are discussed. Conclusion: The mechanosensors involved in the change in VSMCs phenotype mainly contempla- te G-protein-coupled receptors, adhesion molecules, and stretch-activated ion channels. Studies have been focused on the activation or inhibition of MAPK, AKT, mTOR, pathways and transcriptional factors that regulate the expression of differentiation and/or des differentiation genes such as Myocardins. There are also other receptors involved in the response to mechanical stress such as the tyrosine kinases receptor. Although the importance of understanding mechanosensors, the signaling pathways involved in VSMC phenotype switching and their role in the establishment of vascular pathologies, knowledge about them is limited.

Force degradation of elastomeric chains after storage time and mechanical brushing

Abstract The purpose of this in vitro study was to evaluate the force decrease of different elastomeric chains after different times: initial, 10 minutes, 1 day, 28 days and after mechanical brushing. Twenty orthodontic elastomeric chains segments were utilized for each commercial brand. Initially, the elastomeric chain of 15mm long were immediate stretched up to 20 mm in an Instron and the force was measured in gf. After all specimens were placed stretched on rectangular acrylic jigs with distance of 20 mm, immersed in deionized water at 37oC for 10 minutes and the force (gf) was measured again. Five test measurements of remaining force were made at the following time intervals: initial, 10 minutes, 1 day, 28 days and mechanical brushing. After 28 days, the acrylic plates with the specimens were adapted in the mechanical brushing machines (MSCT 3) and the elastomeric chains were submitted to mechanical brushing and the force (gf) measure again. The force (gf) was submitted to mixed-model ANOVA and Sidak post-hoc test (α=0.05). A statistically significant reduction in the force was found for all orthodontic elastomeric chain types after 1 day, 28 days and mechanical brushing (p<0.05). Morelli and 3M Unitek elastomeric chains showed significantly higher force than Abzil and GAC (p<0.05) after 1 day, 28 days and mechanical brushing. In conclusion, the force delivered by all elastomeric chains decayed rapidly over time. Morelli and 3M Unitek elastomeric chains consistently had a significantly greater force after mechanic brushing, while GAC the lowest.

Resumo O objetivo deste estudo in vitro foi avaliar a redução da força de diferentes cadeias elastoméricas após diferentes tempos: inicial, 10 minutos, 1 dia, 28 dias e após escovação mecânica. Vinte segmentos de cadeias elastoméricas ortodônticas foram utilizadas para cada marca comercial. Inicialmente, a cadeia elastomérica de 15 mm de comprimento foi esticada imediatamente até 20 mm na Instron e a força foi medida em (gf). Após, todas as amostras foram adaptadas esticadas em placas retangulares de acrílico na distância de 20 mm, imersas em água deionizada a 37o C por 10 minutos e a força (gf) foi medida novamente. Cinco medidas de força foram feitas nos seguintes intervalos de tempo: inicial, 10 minutos, 1 dia, 28 dias e após a escovação mecânica. Após 28 dias, as placas de acrílico com as amostras foram adaptadas na máquina de escovação (MSCT 3) e as cadeias elastoméricas foram submetidas a escovação mecânica e a medida de força (gf) novamente. Os dados da força (gf) foram submetidos a ANOVA modelo misto e teste post-hoc de Sidak (α = 0,05). Uma redução estatisticamente significativa na força foi encontrada para todos os tipos de cadeia elastomérica ortodôntica após 1 dia, 28 dias e escovação mecânica (p<0,05). As cadeias elastoméricas Morelli e 3M Unitek apresentaram força significativamente superior em relação a Abzil e GAC (p<0,05) após 1 dia, 28 dias e escovação mecânica. Em conclusão, a força distribuída por todas as cadeias elastoméricas decaiu rapidamente com o tempo. As cadeias elastoméricas Morelli e 3M Unitek consistentemente tiveram uma força significativamente maior após a escovação mecânica, enquanto GAC a mais baixa.

Characterization of Bulk-Fill Resin Composites in Terms of Physical, Chemical, Mechanical and Optical Properties and Clinical Behavior / Caracterización de Resina Compuesta Mono Incremental en Relación a las Propiedades Físicas, Químicas, Mecánicas y Ópticas y el Comportamiento Clínico

This study aims to evaluate the physical, chemical, mechanical and optical properties of Bulk-Fill resin, in relation to the literature and its proper clinical uses. A bibliographic search was performed in the main health databases PUBMED (www.pubmed.gov) and Scholar Google (www.scholar.google.com.br), in which articles published from 1994 to 2020 were collected. Laboratory studies, case reports, systematic reviews and literature reviews, which were developed in living individuals, were included. Therefore, articles that did not deal with the characteristics of the Bulk-Fill resin and its proper clinical uses were excluded. The use of Bulk-Fill resin has been progressively increasing over the years, presenting good properties, achieving success in clinical performance, ease of handling and thus has become the material of choice for dentists. In addition, its longevity demonstrates durability with mechanical properties and resistance to tooth structure. Bulk - Fill resins have characteristics similar to traditional composite resins, when performed according the usage protocol. With the use of this group of resins in a single increment, possible failures that occur during the restorative procedure can be minimized, such as: less chance of incorporating bubbles and a volumetric contraction with less stress on the interface.

Este estudio tuvo como objetivo evaluar las propiedades físicas, químicas, mecánicas y ópticas de la resina Bulk-Fill, en relación con la literatura y sus usos clínicos apropiados. Realizamos una búsqueda bibliográfica en las bases de datos de salud PUBMED (www.pubmed.gov) y Scholar Google (www.scholar.google.com.br), en la que se recopilaron trabajos que se publicaron entre 1994 y 2020. Fueron incluidos estudios de laboratorio, informes de casos, revisiones sistemáticas y revisiones de literatura, desarrollados en individuos vivos. Por tanto, se excluyeron los artículos que no trataban las características de la resina Bulk-Fill y sus usos clínicos adecuados. El uso de la resina Bulk-Fill ha ido aumentando progresivamente a lo largo de los años, presentando buenas propiedades, logrando éxito en el rendimiento clínico, facilidad de manejo y, por lo tanto, se ha convertido en el material elegido por los dentistas. Además, su longevidad demuestra durabilidad, con propiedades mecánicas y resistencia a la estructura dental.Las resinas Bulk-Fill tienen características similares a las resinas compuestas tradicionales, cuando se realizan siguiendo el protocolo de uso. Con el uso de este grupo de resinas mono incremental, es posible eliminar el paso de varios incrementos, disminuyendo a su vez el tiempo clínico. Además, se pueden minimizar las posibles fallas que se producen durante el procedimiento de restauración, tales como: menos posibilidades de incorporar burbujas y una contracción volumétrica con menos estrés en la interfaz.

Different treatment modalities using dental implants in the posterior maxilla: a finite element analysis

Abstract The objective of this study was to compare the biomechanical behavior of peri-implant bone tissue and prosthetic components in two modalities of treatment for posterior region of the maxilla, using short implants or standard-length implants associated with bone graft in the maxillary sinus. Four 3D models of a crown supported by an implant fixed in the posterior maxilla were constructed. The type of implant: short implant (S) or standard-length implant with the presence of sinus graft (L) and type of crown retention: cemented (C) or screwed (S) were the study factors. The models were divided into SC- cemented crown on a short implant; SS- screwed crown on the short implant; LC- cemented crown on a standard-length implant after bone graft in the maxillary sinus and LS- crown screwed on a standard-length implant after bone graft in the maxillary sinus. An axial occlusal loading of 300 N was applied, divided into five points (60N each) corresponding to occlusal contact. The following analysis criteria were observed: Shear Stress, Maximum and Minimum Main Stress for bone tissue and von Mises Stress for the implant and prosthetic components. The use of standard-length implants reduced the shear stress in the cortical bone by 35.75% and the medullary bone by 51% when compared to short implants. The length of the implant did not affect the stress concentration in the crown, and the cement layer acted by reducing the stresses in the ceramic veneer and framework by 42%. Standard-implants associated with cemented crowns showed better biomechanical behavior.

Resumo O objetivo do estudo foi avaliar o comportamento biomecânico do tecido ósseo peri-implantar e dos componentes protéticos em duas modalidades de tratamento para região posterior da maxila, utilizando implantes curtos ou implantes de comprimento padrão associados a enxerto ósseo em seio maxilar. Foram construídos quatro modelos 3D de uma coroa suportada por um implante osseointegrado na região posterior da maxila. O tipo de implante: implante curto (S) ou implante de comprimento padrão com presença de enxerto sinusal (L) e tipo de retenção da restauração: cimentada (C) ou parafusada (S) foram os fatores de estudo. Foi aplicada uma força oclusal de 300N, dividida em cinco pontos (60 N cada) correspondentes ao contato oclusal de um primeiro molar superior. Foram observados os seguintes critérios de análise: tensão de cisalhamento, tensão principal máxima e mínima para o tecido ósseo e tensão de Von Mises para o implante e componentes protéticos. O uso de implantes de comprimento padrão reduziu a tensão de cisalhamento no osso cortical em 35,75% e no osso medular em 51% quando comparado aos implantes curtos. O comprimento do implante não afetou a concentração de tensão na restauração. A camada de cimento atuou reduzindo as tensões na cerâmica de cobertura e infraestrutura de cerâmica em 42%. Os implantes de tamanho padrão associados às coroas cimentadas apresentaram o melhor comportamento biomecânico.

Influence of base materials on stress distribution in endodontically treated maxillary premolars restored with endocrowns / 北京大学学报(医学版)

OBJECTIVE@#To evaluate the influence of base materials on stress distribution in endodontically treated maxillary premolars restored with endocrowns using three-dimensional finite element analysis.@*METHODS@#A maxillary second premolar was scanned by Micro-CT and a three-dimensional finite element model of ceramic endocrown with 1 mm thickness of base was established. A model without base was also established as a negative control. Four kinds of conventional base materials with different elastic modulus were adopted: light cure glass ionomer(3M Vitrebond, 3 657 MPa), flowable composite resin(3M Filtek Z350XT Flowable Restorative, 7 300 MPa), high strength glass ionomer(GC Fuji Ⅸ, 13 130 MPa), and posterior composite resin(3M Filtek P60, 19 700 MPa). With a 200 N force loaded vertically and obliquely, the distribution and magnitude of stress in the tooth tissue and adhesive layer were investigated by three-dimensional finite element analysis.@*RESULTS@#The maximum von Mises stress values(vertical/oblique) in dentin and adhesive layer were measured as follows: (1) no base material: 19.39/70.49 MPa in dentin and 6.97/17.97 MPa in adhesive layer; (2) light cure glass ionomer: 19.00/69.75 MPa in dentin and 6.87/16.30 MPa in adhesive layer; (3) flowable composite resin: 18.78/69.33 MPa in dentin and 6.79/16.17 MPa in adhesive layer; (4) high strength glass ionomer: 18.71/69.20 MPa in dentin and 6.74/16.07 MPa in adhesive layer; (5) posterior composite resin: 18.61/69.03 MPa in dentin and 6.70/16.01 MPa in adhesive layer. Under the same loading condition, models with different elastic moduli of base materials had similar stress distribution patterns. The von Mises stress of tooth tissue was mainly concentrated in the tooth cervix. Under oblique load, the regions where von Mises stress concentrated in were similar to those under a vertical load, but the values increased. The stress concentration in the tooth cervix was alleviated in models with base materials compared with the model without base material. The maximum von Mises stress in the tooth tissue and adhesive layer decreased when the elastic modulus of base materials increased and got close to that of dentin.@*CONCLUSION@#The posterior composite resin of which the elastic moduli is high and close to that of dentin is recommended as base material for premolar endocrowns to alleviate the concentration of stress in tooth cervix and adhesive layer.

Three-dimensional finite element analysis of traumatic mechanism of mandibular symphyseal fracture combined with bilateral intracapsular condylar fractures / 北京大学学报(医学版)

OBJECTIVE@#To analyze the biomechanical mechanism of mandibular symphyseal fracture combined with bilateral intracapsular condylar fractures using finite element analysis (FEA).@*METHODS@#Maxillofacial CT scans and temporomandibular joint (TMJ) MRI were performed on a young male with normal mandible, no wisdom teeth and no history of TMJ diseases. The three-dimensional finite element model of mandible was established by Mimics and ANSYS based on the CT and MRI data. The stress distributions of mandible with different angles of traumatic loads applied on the symphyseal region were analyzed. Besides, two models with or without disc, two working conditions in occlusal or non-occlusal status were established, respectively, and the differences of stress distribution between them were compared.@*RESULTS@#A three-dimensional finite element model of mandible including TMJ was established successfully with the geometry and mechanical properties to reproduce a normal mandibular structure. Following a blow to the mandibular symphysis with different angles, stress concentration areas were mainly located at condyle, anterior border of ramus and symphyseal region under all conditions. The maximum equivalent stress always appeared on condylar articular surface. As the angle between the external force and the horizontal plane gradually increased from 0° to 60°, the stress on the mandible gradually concentrated to symphysis and bilateral condyle. However, when the angle between the external force and the horizontal plane exceeded 60°, the stress tended to disperse to other parts of the mandible. Compared with the condition without simulating the disc, the stress distribution of articular surface and condylar neck decreased significantly when the disc was present. Compared with non-occlusal status, the stress on the mandible in occlusal status mainly distributed on the occlusal surface, and no stress concentration was found in other parts of the mandible.@*CONCLUSION@#When the direction of external force is 60° from the horizontal plane, the stress distribution mainly concentrates on symphyseal region and bilateral condylar surface, which explains the occurrence of symphyseal fracture and intracapsular condylar fracture. The stress distribution of condyle (including articular surface and condylar neck) decreases significantly in the presence of arti-cular disc and in stable occlusal status when mandibular symphysis is under traumatic force.