Reabilitação protética de indivíduos maxilectomizados com prótese obturadora: análise pelo método de elementos finitos e revisão sistemática / Prosthetic rehabilitation of individuals maxillectomized with obturator prostheses: finite element analysis and systematic review

A prótese obturadora (PO) permite o restabelecimento estético e funcional de indivíduos maxilectomizados. Os objetivos deste estudo foram: 1. avaliar pelo método de elementos finitos (MEF), o comportamento biomecânico de infraestruturas metálicas de próteses parciais removíveis obturadoras (PPRO) para uma maxila com ressecção do tipo Classe II de Aramany, variando o tipo de conector maior; 2. realizar uma revisão sistemática com meta-análise em rede sobre a eficácia da PO, e outros tratamentos na qualidade de vida de seus usuários. No primeiro estudo, um modelo virtual simulando uma maxila Classe II de Aramany com ressecção óssea do lado esquerdo, e ausência dos dentes 24, 25, 26 e 27 foi construído no programa Rhinoceros® 7.0, a partir de duas tomografias. Em seguida, três infraestruturas de PPRO digitais foram confeccionadas variando o tipo de conector maior: grupo controle com conector maior tipo placa palatina com extensão reduzida (GC), conector maior tipo placa palatina com extensão total (ME), e conector maior tipo barra anteroposterior com extensão reduzida (AP). A análise de elementos finitos foi realizada no software Optistruct 2022, e os resultados analisados no HyperView 2022. Os resultados foram avaliados de forma qualitativa por meio da observação visual das imagens gráficas com variação dos gradientes de cores, de acordo com a distribuição de tensão, e quantitativa por meio da tensão de von Mises (σVM), tensão máxima principal (σmax), tensão mínima principal (σmin) e deslocamento (mm). No segundo estudo foi realizada uma revisão sistemática com meta-análise em rede (PROSPERO #CRD42023430827). Foram incluídos ensaios clínicos randomizados (ECRs) e estudos de intervenção não randomizados (EINRs) com pacientes reabilitados com prótese obturadora como um dos tratamentos de reabilitação. Sete desfechos reportados pelos pacientes foram analisados separadamente para cada desenho de estudo, de acordo com os questionários de QV: aparência, mastigação, dor, contato social, fala, deglutição e QV geral. Os dados foram convertidos para o questionário UW-QOL v4, exceto o contato social que foi convertido para o EORTC QLQ-H&N35. Foi usada meta-análise em rede Bayesiana modelo randômico para calcular as diferenças médias, e intervalos de credibilidade de 95% (Crl) para cada comparação entre tratamentos. A interpretação seguiu a certeza da evidência por meio da abordagem GRADE para meta-análise e a diferença mínima importante (DMI). A revisão incluiu 4 ECRs e 9 EINRs. Sete tratamentos foram avaliados: pré-cirúrgico (considerado sem tratamento), obturador pós-cirúrgico, obturador provisório, obturador convencional, obturador suportado por implante, obturador magnético e retalho, totalizando 120 comparações de tratamentos em todos os sete desfechos. Verificou-se pelos resultados do primeiro estudo que CG e AP apresentaram comportamentos semelhantes, já ME apresentou maiores valores de tensão para praticamente todos os componentes do sistema. Nenhum dos grupos apresentou valores de deslocamento significativos. Para a revisão sistemática, observou-se que a estimativa de efeito de alguns tratamentos alcançou a DMI, entretanto, o intervalo de credibilidade cruzou a linha de efeito nulo, com certeza da evidência muito baixa, portanto, nenhum tratamento foi mais eficaz que o outro. Para ambos os estudos, mais estudos laboratoriais e ensaios clínicos randomizados são incentivados para confirmar as evidências encontradas.

The obturator prosthesis (OP) allows the restoration of speech, aesthetics, and oral function in patients with maxilectomized individuals. The objectives of the study were: 1. to evaluate, using the finite element analysis (FEA) methodology, the biomechanical behavior of metallic infrastructures of removable partial denture obturator (RPDO) for a maxilla with Aramany Class II resection, varying the type of major connector; 2. carry out a systematic review with network meta-analysis on the effectiveness of the OP and other treatments on the quality of life of its users. In the first study, a virtual model simulating an Aramany Class II maxilla with bone resection on the maxillary left side and absence of teeth 24, 25, 26 and 27 was developed using the Rhinoceros® 7.0 program based on two tomography scans. After obtaining the virtual model, three infrastructures digital RPDOs were created varying the type of major connector: major connector with reduced coverage (RPDO1), major connector with extensive coverage (RPDO2) and major connector with anteroposterior bar (RPDO3). The FEA analysis was carried out using the Optistruct 2022 software, and the results were analyzed using the HyperView 2022 software. The results were evaluated qualitatively through visual observation of graphic images with variation of color gradients according to the stress distribution and quantitative von Mises stress (σVM), maximum principal stress (σmax), minimum principal stress (σmin) and displacement (mm). For the second study, the systematic review with network meta-analysis (PROSPERO #CRD42023430827). Randomized controlled trials (RCTs) and non-randomized studies of intervention (NRSIs) with obturator prosthesis as one of the treatments were included. Seven patient-reported outcomes were analyzed separately for each study design, according to the QOL questionnaires: appearance, chewing, pain, social contact, speech, swallowing and general QOL. Data were converted to the UW-QOL v4 questionnaire, except social contact, which was converted to the EORTC QLQ-H&N35. Network meta-analysis (NMA) Bayesian random model was used to calculate mean differences (MD) and 95% credibility intervals (Crl) for each treatment comparison. Interpretation followed the certainty of evidence through the GRADE approach for NMA and the least important difference (DMI). The review included 4 RCTs and 9 NRSIs. Seven treatments were evaluated: presurgical (considered no treatment), surgical obturator, interim obturator, obturator, implant-supported obturator, magnet obturator, and flap, totaling 120 treatment comparisons in all seven outcomes. The results of the first study indicate that RPDO1 and RPDO3 showed similar behaviors, while RPDO2 presented the highest stress values for all system components. None of the groups presented significant displacement values. In the systematic review, it was observed that the effect estimates of some treatments reached the DMI, however, for all treatment comparisons, the credibility interval crossed the null effect line with very low certainty of evidence. No treatment showed superiority compared to another for any outcome. For both studies, further laboratory studies and RCTs are encouraged to confirm the evidence.

Finite element analysis of cornea deformation and curvature change during the keratoplasty suturing process

Keratoplasty, which is cornea transplant surgery, is one of the treatment methods for patients with turbidity or keratitis. Recently, keratoplasty using a surgical robot was studied to increase precision. In this study, the effect of surgical factors on the deformation and curvature of the cornea were analyzed in order to improve the accuracy of keratoplasty and derive the optimal surgical factors using finite element method (FEM). Suturing tension and depth were selected as surgical factors. An FEM model, a constitutive equation, and boundary conditions were determined using experiments and reference data. Suturing tension significantly impacted deformation and curvature change, and suturing depth affected the position of the thread-cornea contact point. Both factors have a significant impact on a focal point in the retina and the patient's visual acuity after keratoplasty.

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

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

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

Estabilidad de los miniimplantes en Ortodoncia. "Biología ósea y Biomecánica" / Miniimplant stability in Orthodontics. "Bone Biology and Biomechanics"

El anclaje ha sido un aspecto crucial para la mayoría de los tratamientos de Ortodoncia. En las últimas dos décadas, el anclaje con miniimplantes ha aumentado el espectro de posibilidades para muchos tipos de tratamientos por presentar numerosas ventajas y pocas desventajas. Este artículo pretende hacer una revisión de literatura sobre los mecanismos de la biología ósea básica, como los aspectos mecánicos los activan y modulan; como se genera la estabilidad primaria y secundaria, como incide de manera crítica el porcentaje de éxito con el uso de los miniimplantes y como se ha estudiado esta interrelación por medio de modelos con elementos finitos.

Anchorage is crucial in most orthodontic treatments. During the last two decades, anchorage with mini-screw implants has increased the number of possibilities for many different types of orthodontic treatments. The aim of this paper is to present a literature review regarding how bone biology processes are elicited and modulated; how primary and secondary stability influence the success rate when mini-screw implants are used; and how this relation has been studied by means of the finite element method.

Modal analysis of human lumbar spine using finite element method / 医用生物力学

Objective To study dynamic characteristics of human lumbar spine using three-dimensional finite element method. Methods Finite element model of lumbar spine (L1~5) was developed and validated based on CT images, and the modal analysis was also conducted. Results A total of top 30-order modal parameters were extracted to obtain dynamic characteristics of the lumbar spine under free boundary conditions. Resonance frequencies of the model were concentrately distributed, but the amplitude of each order varied greatly. Amplitude near L5 segment was much larger, indicating L5 was easily to be injured. This lumbar modal analysis could provide a basis for its further dynamic analysis. Parameters such as natural frequency, modal shape and vibration amplitude of the lumbar spine would be helpful for both lumbar dynamic analysis and optimal design of man-machine interface mechanical equipment.

Three-dimensional Finite Element Analysis of the Mechanical Stress on Root from Orthodontic Tooth Movement by Sliding Mechanics / 华中科技大学学报（医学）（英德文版）

In order to study mechanical stress on root from orthodontic tooth movement by sliding mechanics, a 3-dimensional finite element model incorporating all layers of a human mandibular dental arch with orthodontic appliance has been developed to simulate mechanical stress on root from the orthodontic tooth movement. Simulated orthodontic force of 2 N at 0, 30 and 45 degree from the horizontal axis was applied to the crown of the teeth. The finite element analysis showed when or- thodontic forces were applied to the tooth, the stress was mainly concentrated at the neck of the tooth decreasing uniformly to the apex and crown. The highest stress on the root was 0.621 N/ram2 for cer- vical margin of the canine, and 0.114 N/mm2 for apical region of the canine. The top of canine crown showed the largest amount of displacement (2.417 μm), while the lowest amount of displacement was located at the apical region of canine (0.043 μm). In conclusion, this model might enable one to simulate orthodontic tooth movements clinically. Sliding force at 2 N is ideal to ensure the bodily or- thodontic tooth movement. The highest stress concentration in the roots was always localized at the cervical margin when orthodontic force of 2 N at 0, 30 and 45 degree from the horizontal axis, so there may be the same risk of root resorption when orthodontic force of 2 N at 0, 30 and 45 degree was used in clinic cases.

The three dimensional finite element analysis of the stress distribution in the three treatment options of implants restorations for the posterior partial edentulism

In this study, three treatment options to replace two posterior missing teeth were investigated using three dimensional finite element analysis: two wide(.5.0mm) implants(the experimental model I), two standard(.3.75mm) implants(the experimental model II), and three standard(.3.75mm) implants(the experimental model III). Two kinds of load case were applied ; 1) perpendicular on occlusal surface(axial load), parallel on occlusal surface(lateral load). 2) perpendicular on occlusal surface(3mm lateral to central point). The results obtained from this study were as follows; value of on-mises stress (equivalent stress) was smallest in the two wide implant among the three experimental models. It was reported that the diameter is the efficient factor than osseointegrated surface area.

The three dimensional finite element analysis of stress distribution in three treatment options of implant restoration for the posterior single tooth missing

Study of one-segment type mono-dowel spiral implant in 3D-FEM / 实用口腔医学杂志

?Objective: To study the stress distribution of one segment type mono dowel implant with various length and diameter in alveolar bone. Methods: The thickness of cortical bone is 1～2 mm, implant was in close contact with alveolar bone directly. Implants with root length of 10,12,13 and 14 mm, cast diameter of 3.6, 3.7, 3.8, 3.9 and 4.0 mm, corona tall 4 and 9 mm were put into a bone model with alveolar bone. 200 N force was loaded in vertical, 45? oblique and 45? oblique of non center. CT and 3D FEM were used to study the stress distribution and selected the morphology of alveolar bone from first molar of lower jaw and an incisor of maxillary. Results: There was an area of stress in the boundary of the cortical and cancellous bony tissue,horizontal hole. The main region of stress was at the cancellous. Thickness and shape of alveolar bone could affect the distribution of stress. The maximal Von Mises Stress was always in the boundary of cortical and bone that contacted with implant. Higher elastic modulus of bone around the implant had higher stress in cortical stress . Conclusion: The stress of cortical and cancellous bone can be depressed to rise elastic modulus of implant.

Dynamic analysis of the periodontal ligament / 实用口腔医学杂志

Objective:To investigate the influences of material properties and damping effect on the dynamic response analysis of human periodontal ligament. Methods: A 3-D finite element model of human teeth and periodontal tissue was built from graphic information obtained by CT scanning. Dynamic analysis was performed to investigate the influence of different damping effects on the stresses of periodontal ligament by the finite element method. Results: (a) No significant difference of stress between small and large deformation assumption was found, the variation was no more than 1.4%.(b) Dynamic response was obtained under ? varies from 0 to 1.2. After one mastication period, the residual stress at interior surface was larger than that at exterior surface, with a maximum value of ? r = 0.34 MPa at labial cervical area. Conclusion: Appropriate assumptions on material properties may reduce the cost of analysis. After one mastication period, some levels of residual stresses are in periodontal ligament and influenced by material damp.

Finite element analysis of the edentulous maxilla with unilateral maxillary defect after implant rehabilitation / 实用口腔医学杂志

Objective:To investigate the stress distribution of the edentulous maxilla with unilateral maxillary defect after implant rehabilitation under occlusal loads.Methods:Three dimensional finite element model of the edentulous maxilla with unilateral maxillary defect was build.The stress distribution of the edentulous maxilla under occlusal loads with computer simulated implant rehabilitation was investigated.Results:Regardless of load manner,the stress of the bone around 1 were high when just healthy side implanted,but the stress reduced after implantantion in health side combined with the implantation in zygoma in defect side.Conclusion:Implantation in health side combined with that in zygoma in defect side can reduce the stress of the bone around the implant.

Stress analysis of periodontal supporting tissues of mandibular complete overdenture based on post-core abutment / 实用口腔医学杂志

Objective:To study the stress distribution of periodontal supporting tissues of mandibular complete overdenture based on post-core abutment. Methods:3-D finite element method (FEM) was employed to investigate the stress distribution of periodontal supporting tissues of mandibular complete overdenture based on post-core abutment, the stress values of periodontal membrane and lamina dura were calculated and compared with those of natural abutment. Results:The values of stress in distal area of abutment were larger than that in medial area. Post-core reduced periodontal membrane stress value in distal area of abutment cervix dentin, as well as that in apical zone, increased the stress value in distal periodontal membrane of the middle part of root, raised the stress value of distal lamina dura of abutment cervix dentin, while reduced the stress value below the cervix dentin. Conclusion:Abutment tends to incline distally. Post-core can influence stress distribution of periodontal membrane and lamina dura and reduce the stress value on root-end.