FEM Analysis of Mandibular Prosthetic Overdenture Supported by Dental Implants: Evaluation of Different Retention Methods.

Prosthetic rehabilitation of total edentulous jaws patients is today a common technique that clinicians approach in their daily practice. The use of dental implants for replacing missing teeth is going to be a safe technique and the implant-prosthetic materials give the possibility of having long-term clinical success. Aim of this work is to evaluate the mechanical features of three different prosthetic retention systems. By applying engineering systems of investigations like FEM and von Mises analyses, how the dental implant material holds out against the masticatory strength during the chewing cycles has been investigated. Three common dental implant overdenture retention systems have been investigated. The ball attachment system, the locator system, and the common dental abutment have been processed by Ansys Workbench 15.0 and underwent FEM and von Mises investigations. The elastic features of the materials used in the study have been taken from recent literature data. Results revealed different response for both types of device, although locator system showed better results for all conditions of loading. The data of this virtual model show all the features of different prosthetic retention systems under the masticatory load. Clinicians should find the better prosthetic solution related to the patients clinical condition in order to obtain long-term results.

Numerical analysis of bone adaptation around an oral implant due to overload stress.

A finite element (FE) numerical model of an oral implant was implemented with the theory of bone adaptation to predict the response over time of the bone tissue to the implant and to explain a phenomenon regarding the clinical situation: the bone loss due to an overload stress. An adaptation routine, based on Beaupré theory, was developed to interface with the FE packages. The value of the mechanical stimulus, corresponding to the overload stress, was evaluated by applying the Taylor crack propagation theory. The predictions obtained by the numerical analyses demonstrated that the overload resorption is blocked only with spongy bone of 'good quality'.

Biomechanical analysis of the Cotrel-Dubousset spine internal fixator in different load conditions.

The aim of the present research is to analyse the mechanical behaviour of the Cotrel-Dubousset spine internal fixator using numerical and experimental techniques. Simple experimental and numerical models of a spine section (four vertebrae of the thoraco-lumbar region) were developed in order to evaluate the response of the system, particularly the stress-strain state in the rods, by means of strain-gauge measurements. The system was subjected to combined compressive and bending static loading and the deformations of the system were measured on models simulating physiological and pathological conditions, with and without the fixator.

Improvements in bio-mechanical adhesion of screws used in medical field: first application in spinal surgery.

Metallic screws are becoming more and more useful to join bones or for prosthesis support in orthopaedic and dental surgery. High biocompatible materials such as titanium alloys and hydroxyapatite ceramics are making possible the realization of stable fixation devices utilizable in load-bearing applications. The mechanical and biological anchorage of metallic screws to the bone depends on many factors: mechanical screws-bone thread matching, use of cements between bone and screw, chemical-physical treatments of screw surface, use of screw coverage films based on osteointegrating ceramics or active bioglasses, use of porous coverage films to induce bone ingrowth into the pore, and so on. The first step of the research, the aim of the present paper, is the comparison among screws of different shapes and geometric characteristics in order to find the best macromechanical system versus the different load conditions. Static and dynamic tests are applied to the screws mounted on segments of pig spine, in order to measure the mechanical characteristics of the system under tension (pull-out), bending on the principal planes along the axis of the screw and fatigue loads. Physical analysis, obtained using energetic charged particles, such as SEM, RBS, and AES, are used to characterize the screw surface compositions and morphology.

Comparative study of the mechanical behaviour of Castaman external fixator in different mounting configurations.

The mechanical behaviour of the Castaman external fixator was determined using different mounting configurations in a system that simulated a long bone fracture during the formation of the bone callus. The first stage of the study was the determination of the stress-strain characteristics of the system with monolateral mounting. The second stage, the object of this study, is the analysis of the system with bilateral mounting and a comparison between the two configurations of the external fixator examined. Strain gauge analysis was used to determine the strains and stresses in the various elements of the system (fiches and external unit). Numerical techniques (FEM) were also used in order to confirm the results obtained using the simulation system. The results obtained show clearly the greater stiffness of the bilateral system. Combined bending and compressive stresses are present on both the screws and the external units, and reveal a little asymmetrical behaviour due to the conicity of the screws.

FEM and Von Mises analyses of different dental implant shapes for masticatory loading distribution.

The rehabilitation of edentulous patients is today a challenge for the clinicians. The healthy of the hard and soft issue may be considered a fundamental element for having long-term results. The dental implant progresses about the predictable and safe results made this technique chosen from a large group of practitioners. However some problems related intra-operative and postoperative conditions may create discomfort on the patients and consequently to the clinician. The unfavourable results are often related to the bone tissue quality but sometime the dental implant shape and the prosthesis framework may undergo to technical difficulties. The purpose of this work is, through the use of appropriate FEM models, to analyse the effect of all these parameters in the construction of a prosthesis type "Toronto", evaluating all the surgical and prosthetic components in order to direct the choices made by the surgeon and to optimize the distribution of loads reducing the patient's discomfort and having a long term clinical success.

[Non tuberculous anti-TNF associated opportunistic infections]. / Infections opportunistes non tuberculeuses au cours des traitements par les anti-TNFalpha.

Anti-TNFalpha agents have revolutionized the treatment of patients with rheumatoid arthritis, spondylarthropathies and Crohn's disease. However, their use is associated with an increased risk of infections. Pyogenic infections (involving the lungs, skin and urinary tract) and tuberculosis are the more commonly observed infectious complications in patients receiving anti-TNFalpha agents. However, opportunistic infections have been increasingly reported in anti-TNFalpha-treated patients, and include non tuberculous mycobacteria, fungi (Pneumocystis jiroveci, Candida sp, Aspergillus, Cryptococcus, Histoplasma), opportunistic bacterial (Nocardia), parasitic (Leishmania) and viral (e.g. Cytomegalovirus, human herpes virus 8 [HHV 8]) infections. These infectious complications usually occur within the first months of therapy and are important causes of morbidity and mortality in anti-TNFalpha-treated patients. It is recommended to rule out infections, especially latent or active tuberculosis, before the initiation of anti-TNFalpha therapy. However, it is necessary to follow-up closely these patients to detect the possible occurrence of opportunistic infections.