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The mechanical properties of materials for spinal fixation can significantly affect spinal surgical outcomes. Traditional materials such as titanium exhibit high stiffness, which can lead to stress shielding and adjacent segment degeneration. This study investigates the biomechanical performance of titanium and PEEK (polyetheretherketone) in spinal fixation using finite element analysis, through the evaluation of the Shielding Strength Factor (SSF). Methods: A three-dimensional finite element analysis (FEA) model of an L4/L5 functional spinal unit was developed to simulate the mechanical behavior of three fixation systems: titanium screws and rods (model A), titanium screws with PEEK rods (model B), and PEEK screws and rods (model C). The analysis evaluated stress distribution and load transfer under physiological conditions, in comparison with the intact spine (baseline model). Results: The analysis showed that titanium fixation systems resulted in higher stress shielding effects, with a significant difference in stress distribution compared to PEEK. The maximum stress recorded in the neutral position was 24.145 MPa for PEEK, indicating better biomechanical compatibility. Conclusions: The results suggest that PEEK may be an attractive alternative to titanium for spinal fixation, promoting more healthy load transfer and minimizing the risk of stress shielding complications. [ABSTRACT FROM AUTHOR]

The aim of this finite element analysis (FEA) was to investigate the distribution of von Mises stress within dental implant components, as well as trabecular and cortical bone. The study considered various bone qualities that influence cortical thickness in contact with the implant, specifically examining cortical thicknesses of 0.5, 1.5, and 3 mm, corresponding to Bergkvist's classifications IV, III, and II, respectively. A simplified 3D model of the bone was developed for the analysis. Two short implants were inserted into the model: one with a 30° inclined abutment (IA) and another positioned at a 30° angle featuring a straight abutment (II). A vertical force (120 N) was applied to the upper surface of the abutments. FEA software was employed to assess the stresses on the peri-implant tissues and the implants. The findings indicated that a reduction in cortical bone thickness results in an increase in stress within the cortical bone. For IA, the stresses recorded 32.56, 56.12, and 96.14 MPa for cortical thicknesses of 3, 1.5, and 0.5 mm, respectively. Conversely, II exhibited increased stresses across all bone qualities (52.32, 76.15, and 126.32 MPa for the same cortical thicknesses). It is advisable to avoid II in cases of poor bone quality and thin cortical due to the heightened risk of overload-induced bone resorption; however, it may be preferable to use IA in scenarios involving good bone quality and thicker cortical. [ABSTRACT FROM AUTHOR]

This study aims to evaluate the mechanical behavior, by ways of the FEM, of three femoral stems made of a Ti-6Al-4V titanium alloy with transverse holes in the proximal zone and a stem made of a β-type titanium alloy with a stiffness varying from 65 GPa in the proximal zone to 110 GPa in the distal zone and the CFRP composite material. The purpose of the study was to evaluate the effect of stress shielding on an intact femoral bone. A three-dimensional model of the intact femur was created, and the three prostheses were inserted with perfect stem bone fit. Applying constraint conditions such as fixation in all directions of the distal part of the femur and the application of a static load simulating standing still during a gait cycle allowed the stresses of both the implants and the bone to be compared. Evaluating the stress shielding for the three proposed materials was possible by identifying the seven Gruen zones. We can see from the results obtained that the metal alloys produced observable stress shielding in all the Gruen zones. There was a difference for the β-type alloy which, as a result of its stiffness variation from the proximal to the distal zone, did not show any level of stress shielding in Gruen zones 1 and 2. The CFRP composite, in contrast, showed no stress shielding in all of the Gruen zones and is an excellent material for the fabrication of total hip replacements. Further in vitro and in vivo validation studies are needed to make the modeling more accurate and understand the biological effects of the use of the three materials. [ABSTRACT FROM AUTHOR]

Stress shielding is a problem for traditional metal bone fixation plates made of magnesium and titanium alloys. This problem can be solved by using composite materials with a low elastic modulus. This study analyzed the effect of carbon fiber reinforced PEEK (CFRP) composites on stress shielding under static loading using finite element simulations. Callus formation times relative to the healing period were gradually imposed according to the elapsed time, considering 1% and 75% as healing stages. The Inventor© 3D CAD 2024 software was used for modeling, and the ANSYS© FEA R2023 software was used for analysis. The results showed that metal fixation plates made of titanium and magnesium alloys transferred less stress to the bone than the CFRP fixation plate. In particular, the use of the CFRP fixation plate resulted in a higher peak stress and a more uniform stress field in the bone, especially in the bone-plate contact area, where the risk of stress shielding is higher in the 1% and 75% healing phases. [ABSTRACT FROM AUTHOR]

Total hip arthroplasty is one of the most common and successful orthopaedic operations. Occasionally, periprosthetic osteolysis associated with stress shielding occurs, resulting in a reduction of bone density where the femur is not properly loaded and the formation of denser bone where stresses are confined. To enhance proximal load transfer and reduce stress shielding, approaches, including decreasing the stiffness of femoral stems, such as carbon fibre-reinforced polymer composites (CFRPCs), have been explored through novel modular prostheses. The purpose of the present study was to analyse, by the finite element analysis (FEA) method, the effect that the variation of material for the distal part of the femoral stem has on stress transmission between a modulable prosthesis and the adjacent bone. Methods: Through three-dimensional modelling and the use of commercially available FEA software Ansys R2023, the mechanical behaviour of the distal part of the femoral stem made of CFRPC or Ti-6Al-4V was obtained. A load was applied to the head of the femoral stem that simulates a complete walking cycle. Results: The results showed that the use of a material with mechanical characteristics close to the bone, like CFRPC, allowed for optimisation of the transmitted loads, promoting a better distribution of stress from the proximal to the distal part of the femur. This observation was also found in some clinical studies in literature, which reported not only an improved load transfer with the use of CFRPC but also a higher cell attachment than Ti-6Al-4V. Conclusions: The use of a material that has mechanical properties that are close to bone promotes load transfer from the proximal to the distal area. In particular, the use of CFRPC allows the material to be designed based on the patient's actual bone characteristics. This provides a customised design with a lower risk of prosthesis loss due to stress shielding. [ABSTRACT FROM AUTHOR]

The purpose of this finite element analysis (FEA) was to evaluate the stress distribution within the prosthetic components and bone in relation to varying cement thicknesses (from 20 to 60 μm) utilized to attach a zirconia crown on a conometric cap. The study focused on two types of implants (Cyroth and TAC, AoN Implants, Grisignano di Zocco, Italy) featuring a Morse cone connection. Detailed three-dimensional (3D) models were developed to represent the bone structure (cortical and trabecular) and the prosthetic components, including the crown, cement, cap, abutment, and the implant. Both implants were placed 1.5 mm subcrestally and subjected to a 200 N load at a 45° inclination on the crown. The results indicated that an increase in cement thickness led to a reduction in von Mises stress on the cortical bone for both Cyroth and TAC implants, while the decrease in stress on the trabecular bone (apical zone) was relatively less pronounced. However, the TAC implant exhibited a higher stress field in the apical area compared to the Cyroth implant. In summary, this study investigated the influence of cement thickness on stress transmission across prosthetic components and peri-implant tissues through FEA analysis, emphasizing that the 60 μm cement layer demonstrated higher stress values approaching the material strength limit. [ABSTRACT FROM AUTHOR]

Different numerical and experimental methods have recently been introduced in the literature for the diagnosis of structural damage by using location-dependent changes in the modal parameters (natural frequencies, damping factors and mode shapes). The main task is to determine the presence, location and extent of the damage. This work is concerned with the possibility of introducing, along with a manufacturing process, an on-line quality control for structural components before assembly using modal parameters. The assembly process is usually realized by welding joints or bolts. The structural reliability of the entire system results, therefore, is dependent on the reliability of the single elementary components as well as on the local quality of the welding processes. As a result, a non-destructive control provided together with the relevant assembly or manufacturing process can be important for the integrity of the whole system. The modal analysis techniques [Giannoccaro NI, Messina A, Trentadue B, Masciocco G, Montuori G. Detection of Changes in Mechanical Components for Automobile Chassis Using Modal Data. ATA International Edition, 2001; Messina A, Williams EJ, Contursi T. J. Sound Vib. 1998, 216 (5), 791–808] lend themselves well to the case because they are based on the measurement of parameters (natural frequencies and mode shapes). They are sensitive to the structural modifications but have a different sensitivity for the variations in the generic investigated zones of the system. To enact the real possibility of using such a technique, the defects that are troublesome for integrating the assembled or elementary component must be established. These defects have to induce some variations in the checked parameters (modal parameters) in order to be out of experimental repeatability of the same parameters connected with healthy structural systems. In this work, natural frequencies are shown and compared to a non-contact optical technique subsequently experimentally reliable when used in diagnostic routines connected with geometrically similar components from a molding process.

Prosthetic retention relies on the perfect adaptation between the cap and the abutment of a dental implant. The conometric connection ensures retention similar to cemented systems, preventing bacterial infiltration and sustaining a high implant success rate. Furthermore, the material used for the cap plays a crucial role in distributing stress on the implant components and bone. Traditionally, caps use titanium (Ti), but ongoing research investigates polyetheretherketone (PEEK) for its bone‐like qualities and similar elasticity to Ti. In this finite‐element analysis study, stress and strain distributions are compared between crestal and subcrestal implants using Ti and PEEK conometric caps, assessing retention through cap displacement to determine the material best suited for proper retention aligned with implant insertion depth. In the findings, an improvement in stress and strain is indicated on trabecular bone, a reduction in stress on cortical bone, and thus enhanced implant stability due to higher stresses around the implant threads, particularly with PEEK coping and subcrestal placement. Consequently, PEEK emerges as a promising substitute for Ti in conometric caps as it absorbs stress more effectively, distributing it across prosthetics to counter stress shielding and prevent implant failure. [ABSTRACT FROM AUTHOR]

Arthroplasty is generally used to treat advanced osteoarthritis or other degenerative joint diseases. However, it can also be considered in younger patients with severe joint damage that seriously limits their function and quality of life. Young patients are at risk of aseptic mobilization and bone resorption due to the uneven distribution of stress on the contact surface between the prosthesis and the femur that generates the stress-shielding phenomenon. To overcome this occurrence, it is necessary to use biocompatible materials with a stiffness that is similar to bone. Composite hip prostheses, consisting of continuous fiber-reinforced polymers, play a progressively key role in the development of prosthetic devices. Composite materials can be designed more carefully than monolithic stems (single-phase materials such as metals), allowing for the development of more effective tissue substitutes. Our purpose of this review was to analyze the state of the art in the use of carbon femoral prostheses. In particular, the major mechanical properties of reinforcement (fiber) and matrix were outlined with their applications in the prosthetic field. [ABSTRACT FROM AUTHOR]

Today, dental implantology represents a reliable technique for treating both partial and total edentulism. The fixation of dentures on dental implants can be achieved using various techniques, where the choice of a specific technique depends on the patient's individual needs, the jawbone's condition, and the prosthesis design. Currently, the two most common types of prosthetic abutment connections are cemented and screwed, each with its own set of advantages and disadvantages. This study aimed to analyze a novel Morse cone connection system between the prosthesis and implant using finite element analysis (FEA). The analysis of connection retention was conducted using three different approaches: analytical, in vitro, and FEA. Three-dimensional models were created for systems comprising an abutment, healing cap, and crown under three inclination conditions: 0°, 15°, and 30°. Using Ansys finite element software (R1 2023), the impact of the tilt on the system retention was examined. The FEA showed results comparable with the in vitro studies regarding the retention strength for an abutment cap system with a 4° taper, obtaining 66.6 N compared with the 68 N calculated in our in vitro study. The inclination of the abutment affected the system retention due to the hole made in the abutment's surface, decreasing the contact area between components. The Morse cone prosthesis–implant connection system was found to be the most stable and efficient compared with threaded or cemented systems. The retention was influenced by factors such as the abutment conicity, insertion strength, and the contact surface between components. [ABSTRACT FROM AUTHOR]

Mechanical characterization of soft materials is a complicated inverse problem that includes nonlinear constitutive behavior and large deformations. A further complication is introduced by the structural inhomogeneity of tested specimens (for example, caused by thickness variations). Optical methods are very useful in mechanical characterization of soft matter, as they provide accurate full-field information on displacements, strains and stresses regardless of the magnitude and/or gradients of those quantities. In view of this, the present study describes a novel hybrid framework for mechanical characterization of soft membranes, combining (i) inflation tests and preliminary in-plane equi-biaxial tests, (ii) a one-shot projection moiré optical setup with two symmetric projectors that project cross-gratings onto the inflated membrane, (iii) a mathematical model to extract 3D displacement information from moiré measurements, and (iv) metaheuristic optimization hybridizing harmony search and JAYA algorithms. The use of cross-gratings allows us to determine the surface curvature and precisely reconstruct the shape of the deformed object. Enriching metaheuristic optimization with gradient information and elitist strategies significantly reduces the computational cost of the identification process. The feasibility of the proposed approach wassuccessfully tested on a 100 mm diameter natural rubber membrane that had some degree of anisotropy in mechanical response because of its inhomogeneous thickness distribution. Remarkably, up to 324 hyperelastic constants and thickness parameters can be precisely identified by the proposed framework, reducing computational effort from 15% to 70% with respect to other inverse methods. [ABSTRACT FROM AUTHOR]

Electronic holography moiré is applied to the measurement of interfacial deformation field between an embedded particle and its surrounding matrix in a non-homogeneous rubber material. A tensile specimen is subjected to creep loading. The loads are applied in steps and measurements are carried out at equal intervals of time. The final output is provided by the Holo-Moiré Strain Analyzer and gives the principal strains and their directions in the region of observation. A definition of adhesion as an experimental measurable quantity through the evaluation of contour integrals is introduced.