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At least 1,693 records · Page 94Linked to original sources
PubMed2002

Integrative biological modelling in silico.

In silico models of biological systems provide a powerful tool for integrative analysis of physiological function. Using the computational models of the heart as examples, we discuss three types of integration: structural integration implies integration across physical scales of biological organization from protein molecule to whole organ; functional integration of interacting physiological processes such as signalling, metabolism, excitation and contraction; and the synthesis of experimental observation with physicochemical and mathematical principles.

Animals↗
PubMed2002

The heart cell in silico: successes, failures and prospects.

The development of computer models of heart cells is used to illustrate the interaction between simulation and experimental work. At each stage, the reasons for new models are explained, as are their defects and how these were used to point the way to successor models. As much, if not more, was learnt from the way in which models failed as from their successes. The insights gained are evident in the most recent developments in this field, both experimental and theoretical. The prospects for the future are discussed.

Animals↗
PubMed1976

[The irradiation of air-filled cavities in a plexiglass phantom using 42 MiV bremsstrahlung].

For the investigation of dose distributions as they are produced by the existence of cavities within the irradiated volume, a nonhomogeneous plexiglass phantom has been exposed to a 42 MeV radiation due to retarding of particles. Depth dose curves as well as the ion dose of the interface being more distant from the focus have been measured using different dimensions and depths of the cavity. The modifications of the dose distribution are essentially due to the density difference producing the displacement of the depth dose curve and to multiple scattering effects. The displacement of the depth dose curve amounts to about two thirds of that dimension of the cavity which runs parallel to the radiation axis. An increase or a decrease of the ionization within the air-filled volume results from multiple scattering effects and in dependent on the shape of the cavity.

Air↗
PubMedDate not supplied

Bicortically stabilized implant load transfer.

PURPOSE: Questions exist as to the potential advantages of bicortical stabilization of implants in the mandible through engagement of the lingual cortical plate. The purpose of this investigation was to determine photoelastically the effect of lingual cortical plate engagement on implant load transfer. MATERIALS AND METHODS: Composite photoelastic models of an edentulous posterior segment of a mandible were fabricated using plastics of different modulus to simulate cortical and trabecular bone. One model included a 3.75 x 15-mm threaded implant that engaged the simulated lingual cortical plate, while in the other model the implant was centrally located within the simulated trabecular bone. A metal superstructure was cast using an abutment cylinder. Simulated vertical occlusal loads were applied to the superstructure over the implant and at fixed buccal cantilever lengths. Stresses that developed within the model were monitored photoelastically and recorded photographically. Peri-implant defects were then formed in the models and the loading and recording procedures were repeated. RESULTS: Lingual cortical plate engagement generated the highest stresses at the lingual cortical plate and the buccal crestal cortical layer at the implant neck. Stress intensity within the buccal plate at the implant neck was lower than that in the centrally placed implant. In the presence of a peri-implant defect, for all load conditions, more load was borne by the trabecular bone. Increasing cantilever lengths caused asymmetric load transfer with higher maximum stresses. DISCUSSION: For both implant placements, a large portion of the applied load was taken by the crestal cortical bone simulant. Engagement of the lingual cortical plate reduced maximum stress in the crestal cortical bone by approximately 25%. With peri-implant defects, the simulated trabecular bone provided the main support of the applied load. Longer buccal cantilever lengths increased maximum stresses for all placement and crestal bone conditions. CONCLUSIONS: The results of this investigation do not indicate a clear load transfer advantage to apical engagement of the lingual cortical plate in this model.

Alveolar Process↗
PubMedDate not supplied

Creation of a three-dimensional model of the mandible and the TMJ in vivo by means of the finite element method.

The aim of this study was to develop a three-dimensional finite element model of the mandible, including its TMJ. The model consisted of 7942 nodes and 41,010 elements, which were obtained from a convergence test, done to minimize the result error. It included cancellous and cortical bone, periodontal ligament, masticatory muscles (masseters, temporalis, lateral and internal pterygoids), teeth and the articular disk. All characteristics such as dental, mandibular, and muscle geometry were obtained from a computerized tomography (CT) of a living person. CT sections were scanned and digitized with a CAD software program. After images were adequately assembled, a vertical tracing was done which allowed the definition of a three-dimensional mesh. Modeling of teeth was carried out independently and the periodontal ligament was later included, limiting the alveolar area. Muscles were modeled based on flat-scale photographs and total muscle force was distributed in multiple vectors. The articular disk was generated having 2 mm of thickness with the combination of spring-type (axial stiffness) and gap-type (contact) elements. The model was then analyzed with finite element method (FEM) software where a mesh was generated and values for Poisson's ratio, elasticity, and shear modulus were assigned. These were orthotropic for cancellous and cortical bone, and isotropic for dentin, periodontal ligament, articular disk, and temporal bone. The boundary conditions were defined restricting the nodes on the periphery of the temporal bone. It was therefore possible to generate a three-dimensional finite element model based on information obtained in vivo.

Adult↗
PubMed2003

Experimental flow studies in an elastic Y-model.

To determine the causes and history of atherosclerosis it is necessary to understand the hemodynamic parameters of blood circulation. Hemodynamic parameters play an important role in the formation of atherosclerotic plaques, especially near bends and bifurcations where the flow separates from the wall. Here the flow is laminar and non-axial with eddies, secondary flow, flow separation and stagnation points. Stenoses are found predominantly in flow separation areas. Therefore, it is important to separately study the following flow parameters: steady and pulsatile flow, wall elasticity and non-Newtonian flow behavior of blood. A simplified silicon elastic y-model simulating the human carotid artery was used for the analysis of these parameters. This model can be used for numerical studies as well. Flow was visualized at steady flow using dyes and at pulsatile flow with a photoelastic apparatus and a birefringent solution. The local axial velocity at steady and pulsatile flow was determined with a one-component Laser-Doppler-Anemometer (LDA). Pulsatile flow was generated by a piston membrane pump. A glycerin-water solution was used to simulate the Newtonian flow behavior of blood. A DMSO-Separan water solution was used to simulate the non-Newtonian flow behavior. Pulsatile flow creates higher and lower shear rates so called oscillating shear rate compare to steady flow depending on the velocity amplitude. The non-Newtonian fluid showed a markedly different flow behavior than the Newtonian fluid especially in areas of flow separation. Shear gradients were calculated from these velocity measurements using a bicubic spline interpolation. Shear stresses were calculated from these velocity shear gradients and the viscosity of the non-Newtonian fluid at these shear gradients. At special areas, high shear stresses > 10 Pa were found. The elasticity of the model wall also influences the flow behavior. The measurements showed that the characteristics of pulsatile flow and the elasticity of the model wall should be observed concomitantly. This paper presents the steady and pulsatile flow with a Newtonian and non-Newtonian fluid in an elastic model.

Arteriosclerosis↗
PubMed2003

Dendritic cell-based glioma immunotherapy (review).

Despite advances in radiation and chemotherapy along with surgical resectioning, the prognosis of patients with malignant glioma is poor. Among the new treatments currently being investigated for malignant glioma, immunotherapy is theoretically very attractive, since it offers the potential for high tumor-specific cytotoxicity. There are increasing reports demonstrating that systemic immunotherapy using dendritic cells is capable of inducing an antiglioma response. Therefore, dendritic cell-based immunotherapy could be a new treatment modality for patients with glioma. In this review, we will discuss the implications of these findings for glioma therapy. A literature review of dendritic cell-based glioma immunotherapy was used to overview the dendritic cell in immunobiology, in the central nervous system and in tumor immunology, glioma-associated antigens, dendritic cell therapy in animal glioma model, dendritic cell therapy in clinical trials and future directions in dendritic cell therapy. Dendritic cell-based immunotherapy strategies appear promising as an approach to successfully induce an antitumor immune response and increase survival in patients with glioma. Dendritic cell therapy of glioma seems to be safe and without major side effects. Its efficacy should be further determined in randomized, controlled clinical trials. The development of methods for manipulating dendritic cells for the purpose of vaccination will enhance the clinical usefulness of these cells for biotherapy for malignant glioma.

Animals↗
PubMed2003

The proliferative state, graft-site and contact-time of competent chick ectoblast determine the quality and quantity of neural induction by Hensen's node.

We have assessed the type and amount of neural tissue induced in the chick gastrula ectoblast with increasing duration of contact with the Hensen node inducer. At least 4 h contact is necessary to induce the ectoblast in the area pellucida, 9 h in the area opaca and even longer at the margin of overgrowth. In the area pellucida, the inductive response shifts from archencephalic type at 4-6 h contact to deuterencephalic type after 9 h contact. The induced tissue volume and cell number increased as graft-host contact increased from 4-9 h, and then decreased with longer contact. We suggest that in addition to the period of contact and the grafting position on competent ectoblast, the rate of cell proliferation may control the axial specificity and morphological organization of the induced neural tissue.

Animals↗
PubMed1992

Visual interpretation compared with caliper and computerized measurements in experimental vessel stenosis.

To explain visual interpretation errors on angiograms, visual interpretation, caliper measurement, and computerized measurement of cine film were compared using each of 10 graphic models and 10 acrylic models with "stenotic vessels". Stenosis > 40% was overestimated and stenosis < 40% underestimated by visual interpretation. In caliper measurement, stenosis > 40% at exposure of 90 kV was greatly overestimated by a degree similar to the estimation by visual interpretation, and stenosis > 40% at exposures of 74 kV and 58 kV was slightly overestimated. In computerized measurement, the estimation was consistent with the actual degree of stenosis. Therefore, visual interpretation was not reliable for estimation, and computerized measurement was indispensable for estimation of vessel stenosis. Moreover, we consider the most common cause of error in visual interpretation to be optical illusions.

Cineangiography↗
PubMed2003

[Stereolithography as an additive technique in dentistry].

3D-CAD constructions offer the application of CAM-techniques for the fabrication of dental restorations. CNC-units are generally used for milling and grinding. However, the application of new additive working technology enables the construction of 3D-solid models. In the field of rapid prototyping (RP), the process of "three-dimensional printing" allows the fabrication of patterns for the lost-wax casting technique from materials such as wax or resin. This paper describes the use of a light-curing fluid resin in combination with a UV-light projection in means of stereolithography (SL). The presented CAM unit (Perfactory, DeltaMed, D-Friedberg) reduces processing times of large casting patterns by using CAD constructions. This concept focuses on the advancement of the common casting technique in dental technology by application of CAD/CAM technology.

Computer-Aided Design↗
PubMed2003

Clinical biomechanics of wear in total hip arthroplasty.

Complementary clinical and laboratory studies were performed to identify variables associated with polyethylene wear following total hip replacement, and to elucidate the mechanisms responsible for accelerated wear in the total hip arthroplasty construct. Observational cohort studies were performed using a prospective clinical database of more than 4000 consecutive primary total hip arthroplasties performed by a single surgeon, to identify wear-related variables. These variables included head size, acetabular/femoral component impingement, and third body debris. Novel digital edge detection techniques were developed and employed to accurately measure wear, and to determine the relationships of head size and third body debris to acceleration of wear. A novel sliding-distance-coupled finite element model was formulated and employed to examine the mechanisms responsible for wear. The long-term cohort studies demonstrated smaller head sizes to be associated with less wear. Third body debris generated from cable fretting was associated with an increase in wear, osteolysis, and acetabular loosening, especially with larger head sizes. The sliding-distance-coupled finite element model replicated the wear rates occurring in vitro and in vivo, demonstrating the importance of sliding distance on polyethylene wear following total hip arthroplasty. It also demonstrated substantial increases in wear associated with femoral head scratching from third body debris. Further extension of the finite element formulation demonstrated the potential for acetabular component rim damage from impingement wear, and the enhanced potential for third body ingress to the bearing surface with larger head sizes. Edge detection wear measurement techniques demonstrated that early wear rates were predictive of long-term wear rates. These complementary clinical and laboratory investigations have provided insight into 1) the significance of sliding distance and physiologic loci of motion as contributing factors in minimizing wear, 2) the deleterious effects of third body particulates in accelerating wear, 3) the potential for, and factors related to, impingement wear, and 4) the potential advantages and compromises related to the use of larger head sizes in the bearing surface construct.

Arthroplasty, Replacement, Hip↗
PubMed2003

Oogenesis in Drosophila melanogaster: a model system for studying cell differentiation and development.

Drosophila oogenesis is a complex developmental process involving the coordinated differentiation of germ line and somatic cells. Correct execution and timing of cell fate specification and patterning events is achieved during this process by the integration of different cell-cell signalling pathways, eventually leading to the generation of positional information inside the oocyte, that is instrumental for the establishment of embryonic polarity. The large body of data accumulated at both cellular and molecular levels in the last decade clearly demonstrated how Drosophila oogenesis is a genetically tractable system particularly suited for the investigation of key developmental biology questions. Our recent contribution to the field relies on the characterisation of three different mutants named tegamino (teg), hold hup (hup) and tulipano (tip), identifying novel gene functions required during oogenesis. Specifically, teg is implicated in the morphogenesis of the follicular epithelium surrounding the germ line cells in the egg chamber, hup is involved in the establishment of egg chamber polarity and tip in the regulation of the dynamic germ cell chromatin organisation.

Animals↗
PubMed2003

The use of a custom template for immediate loading with the definitive prosthesis: a clinical report.

A new approach to implant dentistry for the fully edentulous arch is presented. Using a conventional computer tomography scan and specialized surgical planning software, a fixed final prosthesis is fabricated before the surgical procedure so the prosthesis may be delivered immediately after the implants are placed. Initial prospective studies of 10 patients with observation times of up to 24 months have shown all patients to have a functional prostheses. Long-term studies are being performed to validate this new procedure.

Computer-Aided Design↗