António Ramos - Academia.edu (original) (raw)

Papers by António Ramos

Metals

In the last years, several materials and design have been assessed in an attempt to improve the m... more In the last years, several materials and design have been assessed in an attempt to improve the mechanical performance of temporomandibular joint total joint replacement (TMJ TJR) prostheses. However, the wear of the TMJ TJR condyle to the polymer-based fossa component during loading and sliding movements. That promotes the release of debris and risks of toxicity to the surrounding tissues. The purpose of this study was to perform a narrative literature review on the wear of TMJ TJR sliding contacts and potential toxicity of metallic debris to the patients. Previous studies reported a significant deterioration of the sliding contact surfaces of TMJ TJR prostheses. Material loss as a result of wear can cause a TMJ TJR condyle/fossa mismatch and the modification of the contact pressure and chewing loading. As a further consequence of wear, metal particles are released to the surrounding tissues with a high risk of local tissue and systemic toxicity through the bloodstream. The presenc...

$Research paper thumbnail of Comparison of CAD-CAM and traditional chairside processing of 4-unit interim prostheses with and without cantilevers: Mechanics, fracture behavior, and finite element analysis$

The Journal of Prosthetic Dentistry

The traditional chairside fabrication of interim fixed prostheses (IFPs) involves the autopolymer... more The traditional chairside fabrication of interim fixed prostheses (IFPs) involves the autopolymerization of a polymer powder and liquid monomer or of 2-part composite resin pastes that lead to defects in the material's microstructure. 1-8 Such defects provide stress concentrations that can lead to mechanical failure. Computer-aided design and computer-aided manufacturing (CAD-CAM) is widely available, and industrial polymerization under controlled conditions has been reported to improve the microstructure and performance of the prosthesis. 1,4-12 The fracture strength of polymethyl methacrylate (PMMA) prosthetic structures prepared by CAD-This work was financed by FCT (Fundação para Ciência e Tecnologia) in the subject of projects: POCI-01-0145-FEDER-031035_LaserMULTICER.

Sensors, 2019

Musculoskeletal disorders are becoming an ever-growing societal burden and, as a result, millions... more Musculoskeletal disorders are becoming an ever-growing societal burden and, as a result, millions of bone replacements surgeries are performed per year worldwide. Despite total joint replacements being recognized among the most successful surgeries of the last century, implant failure rates exceeding 10% are still reported. These numbers highlight the necessity of technologies to provide an accurate monitoring of the bone–implant interface state. This study provides a detailed review of the most relevant methodologies and technologies already proposed to monitor the loosening states of endoprosthetic implants, as well as their performance and experimental validation. A total of forty-two papers describing both intracorporeal and extracorporeal technologies for cemented or cementless fixation were thoroughly analyzed. Thirty-eight technologies were identified, which are categorized into five methodologies: vibrometric, acoustic, bioelectric impedance, magnetic induction, and strain. ...

Applied Thermal Engineering, 2018

highlights  Models for individual components of tankless gas water heaters are developed.  Expe... more highlights  Models for individual components of tankless gas water heaters are developed.  Experiments are conducted to determine calibration parameters for heat cell model.  Simulation for different configurations and scenarios are conducted.

Numerosos modelos de próteses de cotovelo tem sido utilizadas ao longo da ultima década, podendo

Journal of neurosurgery. Spine, Jan 6, 2015

OBJECT The purpose of this study was to evaluate the failure risk of cervical vertebrae after tot... more OBJECT The purpose of this study was to evaluate the failure risk of cervical vertebrae after total disc replacement with a keel-design prosthesis (ProDisc-C), taking into consideration the effects of vertebral body height, multilevel replacement, and the association with an adjacent fusion cage. Although promising clinical results have been reported for the ProDisc-C, some clinical studies have reported vertebral body-splitting fractures at single- and multilevel arthroplasty sites. This implant has central keels to provide solid initial stability, and some authors associate the potential risk of vertebral body failure with the keel design, especially in patients with small vertebral body height or when the implant is used at multiple levels. METHODS The study was performed using a specimen-specific C4-6 cervical-segment finite-element model to assess the compressive strains on the C-5 vertebral body for each cervical segment configuration, and synthetic polyurethane models to expe...

Journal of Medical Devices, 2011

The orthopedic market offers more than 200 hundred different femoral stems, some with scientific ... more The orthopedic market offers more than 200 hundred different femoral stems, some with scientific published results. The influence of stem geometry relatively to stress distribution on the cement mantle has been addressed by some authors. Stem geometry influences the fatigue mechanism process at the stem-cement interface and may cause aseptic loosening. This study presents a new cemented hip femoral concept. The study was based on finite element analysis and in vitro hip replacements. The numerical models allowed us to determine the cement mantle stresses of commercial stems that were compared with the ones of the new concept. The stem developed presents innovative collar and tip geometries and "organic" stem sections. The new cemented hip prosthesis reduces the average cement stresses around 25% relatively to the best commercial stems studied.

tulane.edu

This paper describes the preliminary investigation done to assess the effect of stem cross-sectio... more This paper describes the preliminary investigation done to assess the effect of stem cross-sectional geometries on stresses generated at the bone-cement and cement-stem interfaces. Simplified finite element numerical models of cemented hip replacements were used and materials were assumed isotropic and linearly elastic. The crosssections were symmetric about the medial-lateral axis. A layer of 2 mm thickness of cement was interposed between the stem and the femoral cortex and a complex system of forces and moments generated by the hip joint contact force was applied. Maximum and minimum principal stresses were determined for twelve different cross-sectional geometries at the medial, lateral, anterior and posterior aspects of the interfaces. The results obtained evidenced that organic type geometries provoke lower tensile and compression stresses; rigid (sharp) geometries and cross-sections of low second moment of area provoke higher interface stresses.

Journal of Biomechanical Engineering, 2006

The determination of biomechanical force systems of implanted femurs to obtain adequate strain me... more The determination of biomechanical force systems of implanted femurs to obtain adequate strain measurements has been neglected in many published studies. Due to geometric alterations induced by surgery and those inherent to the design of the prosthesis, the loading system changes because the lever arms are modified. This paper discusses the determination of adequate loading of the implanted femur based on the intact femur-loading configuration. Four reconstructions with Lubinus SPII, Charnley Roundback, Müller Straight and Stanmore prostheses were used in the study. Pseudophysiologic and nonphysiologic implanted system forces were generated and assessed with finite element analysis. Using an equilibrium system of forces composed by the Fx (medially direction) component of the hip contact force and the bending moments Mx (median plane) and My (coronal plane) allowed adequate, pseudo-physiological loading of the implanted femur. We suggest that at least the bending moment at the coron...

CIRP Annals - Manufacturing Technology, 2014

RevSALUS - Revista Científica da Rede Académica das Ciências da Saúde da Lusofonia, 2021

Sensors

The world population growth and average life expectancy rise have increased the number of people ... more The world population growth and average life expectancy rise have increased the number of people suffering from non-communicable diseases, namely osteoarthritis, a disorder that causes a significant increase in the years lived with disability. Many people who suffer from osteoarthritis undergo replacement surgery. Despite the relatively high success rate, around 10% of patients require revision surgeries, mostly because existing implant technologies lack sensing devices capable of monitoring the bone–implant interface. Among the several monitoring methodologies already proposed as substitutes for traditional imaging methods, cosurface capacitive sensing systems hold the potential to monitor the bone–implant fixation states, a mandatory capability for long-term implant survival. A multifaceted study is offered here, which covers research on the following points: (1) the ability of a cosurface capacitor network to effectively monitor bone loosening in extended peri-implant regions and...

IEEE Access, 2021

In this work, a fiber Bragg gratings (FBGs) based sensing insole, capable of simultaneously measu... more In this work, a fiber Bragg gratings (FBGs) based sensing insole, capable of simultaneously measure plantar force (PF) and shear force (SF) is proposed. The insole has four measuring points, strategically located for a full gait analysis. Each sensing point contains a sensor-cell which consists of a polylactic acid (PLA) structure, covered by an epoxy resin layer, and crossed by one optical fiber with two FBGs, FBG1 and FBG2, respectively. Due to the specific design of the system, the FBG1 is sensitive to both forces (with higher sensitivity to the PF), while the FBG2 is designed to detect only the SF. The instrumented insole was tested during static and gait exercises, and the results, obtained for the PF and SF monitoring, were according to those theoretically expected. INDEX TERMS Foot plantar sensor, gait cycle anomalies, multiplexed fiber Bragg gratings, pressure ulcers, shear force sensor.

Quantitative Imaging in Medicine and Surgery, 2021

The repositioning of bone segments during orthognathic surgeries often results in mandibular cond... more The repositioning of bone segments during orthognathic surgeries often results in mandibular condyle positional changes and can also affect jaw muscles, soft tissues and the temporomandibular joint (TMJ). Condylar displacements are considered as one of the factors of bone remodeling and further skeletal relapse. The quantitative approach is commonly used in comparative analyses and evaluations of the relationships between examined factors. The aim of this study is the overview of the current literature including quantitative analysis in the research of mandibular condyle positional changes as a consequence of orthognathic surgeries. Thirty articles were included in the overview. Most of the articles present a comparative and evaluative analysis of treatment results concerning different surgical approaches, fixation methods or types of skeletal defects. The correlation between condylar displacements and bone remodeling, skeletal relapse and TMJ dysfunctions were considered. The most frequently repeated study variables were: short-term changes, Class III malocclusion, yaw rotation, 3D cephalometry measurements. Quantitative data might be useful in the evaluation of patterns and range of condylar displacements for specific treatment conditions. Available literature concerning the analysed topic is characterized by great heterogeneity with regards to the purpose and methodologies of the studies. More systematic approaches and long-term considerations are needed in future research.

SPIE Proceedings, 2015

The purpose of the present study is to present a prototype of a fiber optic based buckle transduc... more The purpose of the present study is to present a prototype of a fiber optic based buckle transducer suitable for measuring strain caused by stretching of a tendon. The device has an E-shape and its central arm is instrumented with a fiber Bragg grating (FBG) sensor. The tendon adjusts to the E-form in a fashion that when it is stretched the central arm bends causing a shift of the Bragg's wavelength (λ B) that is proportional to the amount of strain. This prototype is presented as an alternative to conventional strain gauge (SG) buckle transducers.

"Dynamic stabilisation" systems have been developed in recent years to treat degenerati... more "Dynamic stabilisation" systems have been developed in recent years to treat degenerative disorders of the spinal column. In contrast to arthrodesis, the aim of the B Dyn implant is to preserve intervertebral mobility to maximise patient comfort. When developing innovative concepts, many mechanical tests need to be carried out in order to validate the different technological solutions. The present study focuses on the B Dyn "dynamic stabilisation" device (S14 Implants, Pessac, Fr.), the aim being to optimise the choice of polymer material used to realize one of the implant’s components. Phase one consisted of static tests on the implant, as a result of which a polycarbonate urethane (PCU) was selected, one material of the five elastomers tested. During phase two, dynamic tests were carried out. The fatigue resistance of the device was tested over five million cycles with the properties of the polymer elements being measured using dynamic mechanical analysis (DMA)...

Revista Portuguesa de Estomatologia, Medicina Dentaria e Cirurgia Maxilofacial, 2013

Bruxismo Postura Distúrbios temporomandibulares Músculos mastigatórios r e s u m o Introdução: Vá... more Bruxismo Postura Distúrbios temporomandibulares Músculos mastigatórios r e s u m o Introdução: Vários autores têm sugerido a existência de uma interdependência funcional entre os músculos cervicais e a musculatura mastigatória. Na sequência desta interdependência funcional, alteraç ões posturais, principalmente da cabeç a e pescoç o, podem influenciar determinados circuitos neuromusculares, conduzindo ao desenvolvimento e/ou agravamento de distúrbios temporomandibulares. Objetivo: Verificar a existência de alteraç ões da posiç ão postural da cabeç a e pescoço em bruxómanos. Materiais e métodos: Selecionaram-se 32 participantes, alunos da Faculdade de Medicina Dentária da Universidade do Porto, de ambos os géneros e idades compreendidas entre 22-26 anos. O grupo experimental incluiu 16 bruxómanos e o grupo de controlo 16 indivíduos assintomáticos. Efetuou-se a anamnese e o exame clínico para avaliar a presenç a de sinais e/ou sintomas de bruxismo. Na avaliaç ão da postura realizou-se um registo fotográfico numa vista de perfil direito, em posiç ão reta a olhar o horizonte e na posiç ão corporal habitual, que foi analisado informaticamente. Resultados: A análise dos resultados obtidos permitiu verificar que a média da diferença de angulação da cabeç a e pescoç o, entre a posiç ão reta e a posiç ão de repouso, em indivíduos bruxómanos, foi de 3,57% (± 2,16) e no grupo de controlo de 2,62% (± 2,09). Estas diferenças não se revelaram significativas (p = 0,224). Conclusão: Não se verificaram alteraç ões de postura resultantes de modificaç ões e disfunç ões a que o bruxismo se associa. No entanto, são necessários mais estudos em amostras maiores para clarificar esta questão.

Photonic Sensors, 2012

Fiber optic sensors have a set of properties that make them very attractive in biomechanics. Howe... more Fiber optic sensors have a set of properties that make them very attractive in biomechanics. However, they remain unknown to many who work in the field. Some possible causes are scarce information, few research groups using them in a routine basis, and even fewer companies offering turnkey and affordable solutions. Nevertheless, as optical fibers revolutionize the way of carrying data in telecommunications, a similar trend is detectable in the world of sensing. The present review aims to describe the most relevant contributions of fiber sensing in biomechanics since their introduction, from 1960s to the present, focusing on intensity-based configurations. An effort has been made to identify key researchers, research and development (R&D) groups and main applications.

Bone properties are one of the key components when constructing models that can simulate the mech... more Bone properties are one of the key components when constructing models that can simulate the mechanical behavior of a mandible. Due to the complexity of the structure, the tooth, ligaments, different bones etc., some simplifications are often considered and bone properties are one of them. The objective of this study is to understand if a simplification of the problem is possible and assess its influence on mandible behavior. A cadaveric toothless mandible was used to build three computational models from CT scan information: a full cortical bone model; a cortical and cancellous bone model, and a model where the Young's modulus was obtained as function of the pixel value in a CT scan. Twelve muscle forces were applied on the mandible. Results showed that although all the models presented the same type of global behavior and proximity in some locations, the influence of cancellous bone can be seen in strain distribution. The different Young's modulus defined by the CT scan gray scale influenced the maximum and minimum strains. For modeling general behavior, a full cortical bone model can be effective. However, when cancellous bone is included, maximum values in thin regions increase the strain distribution. Results revealed that when properties are assigned to the gray scale some peaks could occur which did not represent the real situation.