Higher Stress Values Research Articles

Biomechanical evaluation of six zygomatic implants versus four zygomatic implants combined with dental implants in the treatment of different maxillary defects

BackgroundThis study aims to compare the biomechanics of six zygomatic implants (ZIs) and dental implants (DIs) combined with four ZIs with different maxilla defects.MethodsThree-dimensional constructs of the ZIs, DIs human skulls, and maxillary prostheses were created using SolidWorks Software (Version 2015, Dassault Systems SolidWorks Corporation, Waltham, MA, USA). Eight finite element models of the skull with four different alveolar defect types (0–4) were constructed. Type 0: No defect; Type 1: Bilateral posterior defects; Type 2: Right posterior defect; Type 3: Anterior and left posterior defects; Type 4: Bilateral posterior and anterior defects. In two models with the same defect type (for defect types 0–2), six ZIs or two DIs combined with four ZIs were inserted into the maxilla. Six ZIs were inserted in the maxilla models with defect types 3 and 4. Vertical (150 N) and masseteric (300 N) loads were simulated on the prosthesis. The maximum Von Mises stress in the implants/surrounding bone and bone deformation were evaluated.ResultsThe maximum Von Mises stresses in bone/implant were found highest in the defect type 2 model with four ZIs combined with two DIs. The lowest maximum Von Mises stress for bone was detected in the model with defect type 0 and with six ZIs.ConclusionAmong the four types of defects, the posterior unilateral defect caused the highest stress value.

Dynamic analysis of a NiTi rotary file by using finite element analysis: Effect of cross-section and pitch length.

This study assessed stress distribution, maximum stress values and fatigue life of experimentally designed NiTi rotary files with different cross-sectional geometry and pitch length using finite element analysis (FEA). Four cross-sectional shapes (Convex triangle, S-shaped, Triple helix and Concave triangle) and two pitch lengths (2 mm and 3 mm) were tested in simulated root canals with curvatures of 30°, 45° and 60°. The FEA results indicated that convex triangle and triple helix geometries exhibited lower stress values compared to the S-shaped and concave triangle designs. Increasing the canal curvature angle resulted in higher stress values, with the S-shaped instrument showing the most significant increase (up to 12%). Instruments with shorter pitch lengths showed more even stress distribution enhancing fatigue life. The maximum stress was concentrated 5-8 mm from the tip, varying across cutting edges, with S-shaped sections experiencing the lowest forces but higher stress due to lower moments of inertia.

Experimental and digital twinning in ZnAlMg coatings

Twinning is a major deformation mechanism in various materials, especially when few dislocation slip systems are operative. It is the case of zinc-rich coatings in galvanised steel sheets, made of pancake grains on a substrate and where the slip systems with a non-vanishing component along the c-axis present high critical resolved shear stress values. In addition, the abrupt lattice orientation change associated to twinning, the stress relaxation during its propagation and the localised nature of its early stages make it difficult to reproduce this deformation mechanism by using classical crystal plasticity models conceived for dislocation slip. In this sense, this work proposes a hierarchy of three twinning models in combination with a dislocation slip crystal plasticity model, for the case of a ZnAlMg coating. These three models are: a relaxed-Taylor model applied to individual crystal orientations of the coating, a “pseudo-slip” model for twinning and a localised twinning model. The latter incorporates a linear softening in the material law accounting for the unstable twinning initiation and enforces twinning lattice reorientation. A microstructure portion extracted from an in-situ SEM tensile experiment on galvanised steel is used to perform 3D full-field finite element simulations within a finite strain formulation. SEM observations and EBSD acquisitions are used to compare simulation and experimental results during the different steps of the in-situ SEM test, regarding the deformation and damage modes of the zinc-rich coating. The focus is set on twinning evolution inside some individual grains, and the pros and the cons of the three models are finally discussed.

Stress-strain state of dental immediate prosthesis and associated tissue under the influence of external force

Purpose: to analyze the stress-strain state (SSS) of a removable plate immediate denture with a printed dentition made of polymethyl methacrylate (PMMA) and a polyethylene terephthalate (PET) base under multifactor loading conditions based on the principles of mathematical modeling. Materials and methods: For mathematical modeling of SSS, Comsol Multiphysics 5.6 software (Comsol Inc., USA) was used, which provided numerical data for analytical interpretation. We considered a flat 2D model consisting of a printed monolithic dentition and a PMMA bonding layer, a PET base, the mucous membrane of the prosthetic field and jaw bone tissue. Results: The fields of von Mises stresses (VM) and deformations under the influence of normal, oblique and tangential loads (up to 500 N), the localization of their maximum values and the average value inside the prosthetic structure, mucous membrane and bone tissue were determined. The maximum values of VM in the mucous membrane are compared with the pain threshold based on known literature data on algesiometry of the oral mucosa. An assessment was made of the critical length of microcracks (CLM) according to Griffiths, which lead to the formation of a main crack followed by brittle fracture of the structure base. Using the phase field method, the probability of crack formation in the considered model of an orthopedic structure under the influence of static loads of various magnitudes and directions was calculated. Conclusions: Using the method of mathematical modeling of SSS, it was shown that failures when using immediate dentures with printed teeth made of PMMA and a PET base can be caused by the effect of overloading the areas of the base and caused by the deformation process inside the prosthetic structure. The maximum stress in the prosthetic elements was 79.7 MPa and deformation – 0.47 mm. The pain threshold of the oral mucosa is higher than the highest stress value in the prosthetic bed according to Mises (0.002 MPa) for normal load of 500 N. The SSS heterogeneity coefficient of the removable plate immediate prosthesis model is 8.6. The critical length of a microcrack according to Griffiths is lcrit = 1.9...2.7 µm. Using the Comsol Multiphysics phase field method, it was established that the probability of the formation of a large crack in the base of the prosthesis was 6·10–3 %, 0.36 %,0.73 % for a normal, inclined and shear load of 500 N, which is a sufficient value for the operation of removable laminar dentures with printed teeth from PMMA and a PET base during the warranty period.

Impact of transpedicular fixation on thoracolumbar junction burst fracture stability: a biomechanical perspective

Introduction. The treatment of burst fractures at the thoracolumbar junction remains a contentious issue in vertebrology. Despite a broad array of surgical interventions available, many surgeons favor isolated posterior stabilization, which can be performed using either minimally invasive or open approaches. However, the biomechanical properties of these methods have not been thoroughly investigated. Objective: This study aims to evaluate the biomechanical stability of the thoracolumbar junction following transpedicular stabilization of a burst fracture at the Th12 vertebra, under different system configurations influenced by lateral flexion. Materials and Methods: A mathematical finite element model of the human thoracolumbar spine, featuring a burst fracture at the Th12 vertebra, was developed. The model included a transpedicular stabilization system with eight screws, simulating “long” stabilization. We examined four variants of transpedicular fixation using both mono- and bicortical screws, with and without the inclusion of two cross-links. Results: The study found that the load borne by the damaged Th12 vertebral body varied depending on the fixation system employed. Specifically, stress levels were 24.0 MPa, 27.3 MPa, 18.4 MPa, and 25.8 MPa for models with short screws without cross-links, long screws without cross-links, short screws with cross-links, and long screws with cross-links, respectively. At the screw entry points in the vertebral arch, the highest stress values were recorded at the L2 vertebra, showing 11.8 MPa, 14.0 MPa, 9.4 MPa, and 13.4 MPa for each respective model. Among the metal construct elements, the connecting rods consistently exhibited the highest stress, with values of 226.7 MPa, 313.4 MPa, 212.4 MPa, and 293.98 MPa, respectively. Conclusion: The results underscore that utilizing cross-links in the stabilization of burst fractures at the thoracolumbar junction, which is only feasible through an open installation, somewhat mitigates stress within the stabilized spinal segment. Meanwhile, the modeling of lateral flexion revealed only minimal differences in stress values between open and minimally invasive installations.

The onset of coarctation of the aorta before birth: Mechanistic insights from fetal arch anatomy and haemodynamics

Accurate prenatal diagnosis of coarctation of the aorta (CoA) is challenging due to high false positive rate burden and poorly understood aetiology. Despite associations with abnormal blood flow dynamics, fetal arch anatomy changes and alterations in tissue properties, its underlying mechanisms remain a longstanding subject of debate hindering diagnosis in utero. This study leverages computational fluid dynamics (CFD) simulations and statistical shape modelling to investigate the interplay between fetal arch anatomy and blood flow alterations in CoA. Using cardiac magnetic resonance imaging data from 188 fetuses, including normal controls and suspected CoA cases, a statistical shape model of the fetal arch anatomy was built. From this analysis, digital twin models of false and true positive CoA cases were generated. These models were then used to perform CFD simulations of the three-dimensional fetal arch haemodynamics, considering physiological variations in arch shape and blood flow conditions across the disease spectrum. This analysis revealed that independent changes in the shape of.the arch and the balance of left-to-right ventricular output led to qualitatively similar haemodynamic alterations. Transitioning from a false to a true positive phenotype increased retrograde flow through the aortic isthmus. This resulted in the appearance of an area of low wall shear stress surrounded by high wall shear stress values at the flow split apex on the aortic posterior wall opposite the ductal insertion point.Our results suggest a distinctive haemodynamic signature in CoA characterised by the appearance of retrograde flow through the aortic isthmus and altered wall shear stress at its posterior side. The consistent link between alterations in shape and blood flow in CoA suggests the need for comprehensive anatomical and functional diagnostic approaches in CoA. This study presents an application of the digital twin approach to support the understanding of CoA mechanisms in utero and its potential for improved diagnosis before birth.

Evaluation of stress distribution in restorations of maxillary central incisor with post-traumatic enamel-dentin fracture using two different techniques: A micro-computed tomography study

Aim: The aim of this study is to investigate the stress distribution created by two restorative techniques, adhesive reattachment of the fractured fragment and direct composite restoration, used in the treatment of a maxillary central incisor with enamel-dentin fracture. The analysis is conducted using the finite element stress analysis method on a three-dimensional (3D) model prepared based on micro-computed tomography data, following the application of different adhesive procedures on fractured teeth. Methodology: The avulsed left maxillary central incisor was scanned using a micro-computed tomography device. The obtained data was transferred to a computer and used for 3D modeling. In the models, a fracture line was created obliquely at a 45° angle, 3 mm away from the mesial surface towards the distoincisal corner of the tooth. Six restorations were planned on this model: three direct composite restorations and three adhesives, reattachments followed by composite application. The models for the adhesive reattachment method included: (1) internal dentin groove, (2) palatal composite laminate veneer, and (3) double palatal retentive groove. The models for the composite restoration technique included: (1) composite laminate veneer, (2) direct composite restoration following enamel beveling, and (3) composite application after double palatal groove preparation. Upon completion of the restorations, a 100-N force was applied from the palatal direction using the finite element stress analysis method. The results were analyzed to examine the amount and distribution of stress on the restorations and the tooth. Results: In all models, the highest stress values within tooth structures were observed in the enamel. The lowest stress value in the enamel layer was seen in model R-1, whereas the highest stress value was observed in model K-2. For direct composite restorations, the stresses on enamel, dentin, and restoration were relatively similar in each model, with no significant differences noted among these values. Among all applied composite restorations, the lowest stress value was observed in model R-3. When analyzing the stresses generated at the tooth-restoration and tooth-fractured fragment interface of the six models, the lowest stress in the enamel was observed in models R-1 and K-3, while the highest stress was seen in model R-3. Conclusion: According to the data obtained from the models, the shape of the restoration applied on the tooth, the technique used, and the location of the restoration affect the amount and distribution of stress accumulated in the tooth and restoration. However, the stress analysis results are not sufficient to evaluate the clinical success of restorations. There is a need for further studies utilizing different techniques to support the models used. How to cite this article: Olgaç Akgönül Ş, Çelenk S, Adıgüzel Ö. Evaluation of stress distribution in restorations of maxillary central incisor with post-traumatic enamel-dentin fracture using two different techniques: A finite element analysis based on micro-computed tomography data. Int Dent Res 2024;14(2):76-83. https://doi.org/10.5577/intdentres.535

Comparison of implant placement at crestal and subcrestal levels in aesthetic zone: A finite element analysis.

The success rate of the implant treatment, including aesthetics and long-term survival, relies heavily on preserving crestal peri-implant bone, as it determines the stability and long-term outcomes. This study aimed to demonstrate the stress differences in the crestal bone resulting from dental implant placement at various depths relative to the crestal bone level using finite element analysis. Three study models were prepared for implant placement at the crestal bone level (CL), 1 mm depth (SL-1),and 2mm depth (SL-2). Implants were placed in the maxillary central incisor region of each model, and 100 N vertical and oblique forces were applied. The von Mises, maximum principal (tensile), and minimum principal (compressive) stresses were evaluated. The CL model exhibited the highest stresses on the implant, abutment, and abutment screws under vertical and oblique forces. For maximum principal stress in the crestal bone under vertical force, the SL-2, SL-1, and CL models recorded values of 6.56, 6.26, and 5.77MPa, respectively. Under oblique forces, stress values for SL-1, SL-2, and CL were 25.3, 24.91, and 23.76MPa, respectively. The CL model consistently exhibited the lowest crestal bone stress at all loads and the highest stress values on the implant and its components. Moreover, considering the yield strengths of the materials, no mechanical or physiological complications were noted. Placing the implant at the crestal level or subcrestally beyond the cortical layer could potentially reduce stress and minimize crestal bone loss. However, further studies are warranted for confirmation.

Evaluation of stress distributions in endodontically treated anterior incisors under occlusal and trauma-induced forces following various restoration treatments: A finite element analysis.

The aim of this study was to calculate the stress distribution of fiberglass post associated with resin composite crown restoration and fiberglass posts with zirconia restorations in mature and immature endodontically treated central maxillary incisor under various loading conditions. The study created six different study models in a virtual environment: healthy mature maxillary central teeth, intact immature maxillary central teeth, mature maxillary central teeth with fiberglass post associated with resin composite crown restoration, immature maxillary central teeth with fiberglass post associated with resin composite crown restoration, mature maxillary central teeth with fiberglass posts and zirconia restoration, and immature maxillary central teeth with fiberglass posts and zirconia restoration. Loading conditions simulating mastication, trauma, and bruxism were applied to each of the models at different angles and amounts. The von Mises and the maximum and minimum principal stress values in tooth structures (dentin) and support structures (bone, PDL) and materials were observed using finite element stress analysis. The highest stress values in the tissue and the restoration structure were observed for masticating force and crowns rehabilitated with zirconia restorations. None of the compared loading conditions and restorations showed destructive stress values on periodontal ligament or bone. The mature and immature endodontically treated central maxillary incisors can be better rehabilitated using fiberglass post associated with resin composite crown restoration and may be preferred to zirconia restorations in order to reduce the stresses on the surrounding tissues and teeth. However, further clinical studies are needed to fully explore this topic.

Mechanical Characteristics Of Composite Materials Made From Polyester Resin Mixed With Cocopeat On Static Loads

Cocopeat is a binder between coconut fibers in coconut fiber. Cocopeat has high lignin and cellulose content and is resistant to bacteria and fungi. The aim of the research was to determine the mechanical characteristics of cocopeat mixtures with various dosage ratios of 20%, 40%, 60% to 80%. Mechanical characteristic testing is carried out by applying a load to specimens that have been made in accordance with ASTM D 638-03 standards. The maximum load given is 980N. The test results show that the highest stress value is found in the 40% cocopeat mixture composition, which is 8.1902 Mpa and the highest elastic modulus is found in the 20% cocopeat mixture composition, which is 13.8x10-3 Gpa, while the lowest tensile stress value is found in the 60% cocopeat mixture. and the lowest modulus of elasticity was found in a composition of 80% cocopeat mixture, namely 5.12 x 10-4 Gpa. Thus, more and more cocopeat powder is added to composite materials made from polyester resin. This causes a decrease in the value of stress and modulus of elasticity.

A Finite Element Analysis to Study the Stress Distribution on Distal Implants in All-on-Six Treatment Concepts as Affected Tilted and Short Implant.

The number of implants and their respective configurations for implant-supported treatment modalities have been studied for 4 implant-supported prostheses; however, it is not yet clear whether the use of tilting or short implants in rehabilitation would result in substantially improved bone/implant/prosthesis biomechanics in all-on-six concepts. This study compared the biomechanical behavior of tilted long implants and axially short implants to support fixed prostheses in an atrophic maxilla with all-on-six treatment concepts. Three different implant configurations were planned, and six models were obtained with posterior maxilla D3 and D4 bone densities in this study. Implants proper for the all-on-four concept were placed in all models. In models 1 and 2, the short implant was placed; in models 3 and 4, 30°, the mesial-angled implant was placed; and in models 5 and 6, 45°, the mesial-angled implant was placed to the molar region. In the models created, 200 N vertical and 150 N oblique (45° angled buccopalatal direction) forces were implemented to the bilateral tooth regions 4-5-6 on the rigid titanium-supported fixed hybrid prosthesis made on these models. When the stress values in the models were investigated, the oblique forces had higher stress values than the vertical forces did. When the stresses created by oblique forces were assessed, the highest values were observed in the models created with short implants, and the lowest stress values were observed in the models made with 30° angle to mesial. When bone densities were assessed, more stress values were noted in models with D4 bone density. It has been shown that mesial tilted long implants placed in the posterior molar region, in addition to all four implant treatment concepts, create less stress against undesirable oblique forces compared with short implants.

Statistical evaluation of measured biomechanical properties of human brain aneurysm samples.

<p>Human brain aneurysms may often prove fatal if not re&shy;cognized in time and treated accordingly. The understanding of development and rupture of aneurysms can significantly be improved by the application of numerical modelling, which in turn, requires the knowledge of mechanical properties of vessel wall. This study aims to identify assumed differences with respect to age, sex, spatial orientation, and rupture by utilizing detailed statistical analysis of uniaxial tensile measurements of human brain aneurysm samples, performed by the authors in a previous project.</p>. <p>At surgery of 42 patients, aneu&shy;rysm fundi were cut distally to the clip. In each case, depending on size, varying number of stripes (altogether 88) were prepared and uniaxial stress-strain measurements were performed. Quantities related to the capacity, energy absorption or stiffness were determined and statistically analysed.</p>. <p>The number of specimens in the aneurysm sample was sufficient to establish statistical differences with respect to sex and rupture (p&lt;0.05). No significant differences were detected in orientation, though higher values of stresses and deformations were ob&shy;tained in the circumferential direction com&shy;pared to the meridional direction.&nbsp;</p>. <p>Significant differences bet&shy;ween sexes with respect to ultimate deformations were demonstrated according to expectation, and the hypothesis on equality of energy capacity could be supported. Similarity of curves with respect to specimen orientation was also observed and ruptured aneurysm sacs tended to be smaller in size. It seems that differences and trends described in this paper are realistic and need to be applied in numerical modelling.</p>.

Correlation study of self-annealing-induced recrystallization and grain growth mechanism in copper foil

Copper foils demonstrate a tendency for self-annealing, which adversely impacts the stability of the products. The self-annealing induced recrystallization of copper foil is closely related to the grain growth mode. When copper foil grows in equiaxed grain mode, resulting in a decrease in tensile strength from 780 MPa to 330 MPa. Conversely, the columnar grain copper foil exhibits excellent room-temperature stability in mechanical properties. The mechanism of copper foil room temperature self-annealing behavior was put forward. It was found that the internal stress generated in the process of preparing copper foils is the key factor driving the recrystallization of equiaxed grains. This internal stress originates from nanocrystals and high-density dislocations, with the latter arising from the doping of organic elements. The initial high stress values and the plasticity of dislocations contributed to a noteworthy decrease in residual stress. As dislocation plasticity ensues, the anchoring of interstitial atoms gives rise to dislocation loops. The interaction between dislocation loops and coincident twin boundaries induces the formation of twin steps. The quantity of twins of equiaxed copper foil increases greatly after self-annealing. Conversely, the initial dislocation density of columnar grain copper foil is an order of magnitude lower than that of equiaxed grains.

Drying stress analysis and cracking prediction of the component of maize based on viscoelastic stress-strain model

To study the drying stress and predict cracking of the components of the maize kernel during drying, the viscoelastic stress-strain model of the maize kernel was developed considering the differences in viscoelastic properties of the components. The results showed that at the preheating and main drying stages, the stress was mainly caused by the uneven distribution of the moisture content and gradually increased with drying. At the cooling stage, the stress significantly increased in a short time due to the decrease in temperature. The stress of the hard endosperm was higher, the pericarp had the highest stress value, and the stress of the soft endosperm and germ was low. The crack volume percentage of the germ and pericarp was zero, which was consistent with the fact that there was no crack in the pericarp and germ, the cracks were mainly in the endosperm. The crack volume percentage of the endosperm gradually increased as drying progressed and significantly increased during the cooling stage, which was similar to the increasing trend in the crack degree of the endosperm at different drying stages. The viscoelastic stress-strain model combined with the von Mises stress criterion could be used to predict the stress crack formation of components at different drying stages.

Microstructure and properties of 3D-printed ZrCu–Ti6Al4V laminated composite

The microstructures, shape memory properties, and mechanical properties of 3D-printed ZrCu–Ti6Al4V laminated composites were investigated in this study. The microstructure of the laminated composite effectively combines the characteristics of two alloys. The shape memory effect and mechanical properties of the laminated composite are affected by the thickness of the layer. The results reveal that higher austenite transformation temperature than ZrCu with total recovery strain close to ZrCu, and a compression strain exceeding 21% can be achieved by 3D-printed ZrCu–Ti6Al4V laminated composite with thickness of 0.25 mm. Additionally, the composite with thickness of 0.5 mm demonstrates excellent fracture toughness values of 44.30 MPa⋅m1/2, as well as high yield strength and flow stress values reaching 1818 MPa and 2194 MPa respectively at a strain rate of 3500 s-1. This study highlights that incorporating Ti6Al4V layers into ZrCu through 3D-printing can significantly enhance mechanical properties while maintaining favorable shape memory properties, thus combining the advantages of functional and structural materials.

Hemodynamic assessment of severely stenotic carotid arteries

Internal carotid artery (CA) stenosis is a primary etiological factor for stroke and transient ischemic attack. The severity of arterial stenosis significantly impacts patient health and treatment decisions. Therefore, we conducted computational fluid dynamics analyses on five carotid arteries (CAs) of severe stenosis and compared them with five CAs in the control group. We improved the three-element Windkessel model method by pre-calculating the constant-pressure outlet simulation of the first cardiac cycle, which accelerated the stability of the model. The research results show that vortices were observed at the bifurcation of the CAs in the control group, whereas in the severe stenosis group, vortices predominantly occurred within the carotid sinus downstream of the stenotic segment. Notably, the vortex flow in the carotid aneurysm downstream of the stenotic segment arises due to the cross-sectional constriction induced by stenosis, which always flows in a clockwise direction and may contribute to the formation of aneurysms distal to the stenotic region. A high time-averaged wall shear stress value can effectively identify the stenosis site of CAs, while a high relative residence time value marks the protrusion near the stenosis segment. This study delved into the hemodynamic parameters between the CAs of the severe stenosis group and the control group and provided robust clinical evidence for carotid atherosclerotic disease.

Biomechanical behavior of all-on-4 concept and alternative designs under different occlusal load configurations for completely edentulous mandible: a 3-D finite element analysis

The aim of this study was to evaluate the effect of the All-on-4 design and 4 alternative implant-supported fixed prosthesis designs on stress distribution in implants, peri-implant bone, and prosthetic framework in the edentulous mandible under different loading conditions using three-dimensional finite element analysis (3D-FEA).Five different experimental finite element models (Model A (unsplinted 6), Model B (splinted 6), Model C (All-on-4), Model D (axial; 2 anterior, 2 posterior), and Model E (4 interforaminal)) were created. Three different loading conditions were applied (canine loading, unilateral I-loading, and unilateral II-loading). The highest minimum (Pmin) and the maximum (Pmax) principal stress values were acquired for cortical and trabecular bones; the highest von Mises (mvM) stress values were obtained for implants and metal frameworks. Model B and Model D showed the most favorable stress distribution. The All-on-4 design (Model C) also showed acceptable stress values close to those of Model B and Model D in the cortical and trabecular bones. In accordance with the stress values in the bone structure, the lowest stress values were measured in the implants and Co-Cr framework in Model B and Model D. The highest stress values in all structures were measured for unilateral loading- II, while the lowest values were found for canine loading. It was concluded that Model B and Model D experimental models showed better biomechanical performance in all structures. Furthermore, the use of a splinted framework, avoiding cantilevers, results in lower stress transmission. On the other hand, canine loading and unilateral loading-I exhibited the best loading conditions.

CT-based assessment of the stress state of dog spines

An urgent task of biomechanics is the study of the influence of external loads on the human musculoskeletal system, one of the main elements of which is the vertebral column. In this case, research involves considering the spine as a complex system consisting of vertebrae and the intervertebral discs that articulate them. At the moment, there are many works devoted to determining the causes of various abnormalities in the tissue fibers between the vertebrae, which leads to the development of discopathy. Dogs are the most susceptible to such changes due to their genetic predisposition. Thus, in this work, studies were carried out on the cervical spine of three animals: yorkshire terrier, russian toy terrier and half–breed. During the work, numerical modeling of samples was performed using computed tomography data. Computational experiments were carried out using the finite element method and made it possible to determine the stress state taking into account the distribution of the mechanical properties of the material. The tests corresponded to longitudinal compression of the samples. Based on the results obtained, the compressive stress field was determined, the reliability of the values was assessed according to the energy error, and the von Mises stress intensity and the rigidity of the resulting structure were calculated. Analysis of the results showed that the highest stress values are achieved between the vertebrae of the border sections of the cervical spine. On average, a sample of the Yorkshire Terrier breed is predisposed to experience greater stress compared to the results of other dogs in the experimental group. The highest rigidity corresponded to half–breed: twice as much as the average value for dwarf breeds. The distribution of the energy error showed that the areas with the highest values correspond to finite elements at the boundary between different phases of the medium. Thus, the results obtained in the framework of the study make it possible to establish the nature of the distribution of the stress state in the intervertebral discs, as well as to identify the strength indicators of the vertebral columns, taking into account the mechanical properties of various biological tissues.

Reversible adhesives from epoxy-based transesterification-induced vitrimers

Vitrimers are a class of materials that combine the excellent mechanical performance of thermosetting polymers with the malleability of thermoplastic polymers. One of the applications that most benefits from these features is structural adhesives. In this work, epoxy-based vitrimers from diglycidyl ether of bisphenol A, succinic anhydride, and trimethylolpropane are used as reversible adhesives. These materials show glass transition temperatures up to 80 °C as well as a homogeneous network structure. They also show high lap-shear stress values of up to 26 MPa. These adhesives are suitable for reversible adhesion thanks to their excellent vitrimeric behavior, with characteristic relaxation times that are under 10 min at 180 °C. This allows for the re-utilization of the same joint through re-adhesion after failure, the dismantling of adhesive joints with posterior re-bonding, and the application of the adhesive as a coating to make the joint in a different stage. The re-adhesion reaches values up to 96% with respect to the values of the first adhesion. Finally, chemical recycling is achieved through alcoholysis in ethyleneglycol, and this methodology is used to remove adhesive remains from adherend plates, so that they can be used for any other purpose. In summary, these vitrimer adhesives not only show high adhesion shear stress, suitable for structural applications, but also allow re-joining the bond in case of failure, the dismantling of the joint at the end of the bond lifetime, thermally activate the adhesive joint, and recover the adherends to be used for another purpose.

Comparison of 3D-printed and laboratory-fabricated Hyrax on stress distribution and displacement of the maxillary complex: a 3D finite element study

ObjectiveTo analyze and compare the effects of a traditional laboratory-fabricated Hyrax expander (T-Hyrax) and two different 3D-printed Hyrax expander models relative to tension points, force distribution, and areas of concentration in the craniofacial complex during maxillary expansion using finite element analysis.Materials and methodsThree maxillary expanders with similar designs, but various alloys were modeled: a T-Hyrax, a fully printed Hyrax (F-Hyrax), and a hybrid printed Hyrax (H-Hyrax). The stress distributions and magnitude of displacements were assessed with a 5 mm expansion in a symmetrical finite element model. The areas of interest included the teeth, alveolar processes, midpalatal suture, nasal complex, circummaxillary sutures (CS), and the expanders themselves.ResultsThe highest stress value (29.2 MPa) was found at the midpalatal suture of the F-Hyrax, while the lowest stress (0.90 MPa) was found at the temporozygomatic suture in the T-Hyrax. On average, the F-Hyrax increased stress at the CS by 24.76% compared with the T-Hyrax and H-Hyrax. The largest displacements were found at the upper incisor (U1) and anterior nasal spine (ANS). The findings indicated an average increase of 12.80% displacement at the CS using the F-Hyrax compared to the T-Hyrax.ConclusionThe F-Hyrax exerts more stress and displacement on the maxilla than both the T-Hyrax and H-Hyrax, where the weak link appears to be the solder joint.