Finite Element Study Research Articles

Biomechanical Effects of Stem Extension of Tibial Components for Medial Tibial Bone Defects in Total Knee Arthroplasty: A Finite Element Study.

The aim of this study was to investigate the biomechanical effects of stem extension with a medial tibial bone defect in primary total knee arthroplasty (TKA) on load distribution and stress in the proximal tibia using finite element (FE) analysis.FE simulations were performed on the tibia bone to evaluate the stress and strain on the tibia bone and bone cement. This was done to investigate the stress shielding effect, stability of the tibia plate, and the biomechanical effects in TKA models with various medial defects and different stem length models.The results demonstrated that in the bone defect model, the longer the stem, the lower the average von Mises stress on the cortical and trabecular bones. In particular, as the bone defect increased, the average von Mises stress on cortical and trabecular bones increased. The average increase in stress according to the size of the bone defect was smaller in the long stem than in the short stem. The maximal principal strain on the trabecular bone occurred mainly at the contact point on the distal end of the stem of the tibial implant. When a short stem was applied, the maximal principal strain on the trabecular bone was approximately 8% and 20% smaller than when a long stem was applied or when no stem was applied, respectively.The findings suggest that a short stem extension of the tibial component could help achieve excellent biomechanical results when performing TKA with a medial tibial bone defect.

Effect of Mixed Morphology (Simple Cubic, Face-Centered Cubic, and Body-Centered Cubic)-Based Electrodes on the Electric Double Layer Capacitance of Supercapacitors.

Supercapacitors store energy due to the formation of an electric double layer (EDL) at the interface of the electrodes and electrolyte. The present article deals with the finite element study of equilibrium electric double layer capacitance (EDLC) in the mixed morphology electrodes comprising all three fundamental crystal structures, simple cubic (SC), body-centered cubic (BCC), and face-centered cubic morphologies (FCC). Mesoporous-activated carbon forms the electrode in the supercapacitor with (C2H5)4NBF4/propylene carbonate organic electrolyte. Electrochemical interference is clearly demonstrated in the supercapacitors with the formation of the potential bands, as in the case of interference theory due to the increasing packing factor. The effects of electrode thickness varying from a wide range of 50 nm to 0.04 mm on specific EDLC have been discussed in detail. The interfacial geometry of the unit cell in contact with the electrolyte is the most important parameter determining the properties of the EDL. The critical thickness of the electrodes is 1.71 μm in all the morphologies. Polarization increases the interfacial potential and leads to EDL formation. The Stern layer specific capacitance is 167.6 μF cm-2 in all the morphologies. The maximum capacitance is in the decreasing order of interfacial geometry, as FCC > BCC > SC, dependent on the packing factor. The minimum transmittance in all the morphologies is 98.35%, with the constant figure of merit at higher electrode thickness having applications in the chip interconnects. The transient analysis shows that the interfacial current decreases with increasing polarization in the EDL. The capacitance also decreases with the increase of the scan rate.

Crystal plasticity finite element study on the microstructure and orientations evolution of {100} columnar grains in electrical steels

Most of the electrical steel slabs are composed of {100} columnar grains. After hot rolling, there is a texture gradient across the thickness. The surface shear textures (Goss texture{110}<100>, Brass texture{110}<112>, Copper texture{112}<111>) and certain <001>//ND fiber textures after hot rolling can be inherited into the finished sheet. The volume fraction and distribution of these textures after cold rolling significantly influence the magnetic properties. Therefore, a full-field crystal plasticity finite element method (CPFEM) was employed to simulate the evolution of microstructure and orientations of {100} columnar grains under plane strain compression and an additional displacement gradient component L13. Through qualitative and quantitative analysis of the simulated microstructure, it was found that under plane strain compression, {100}<110> grains were the most stable, followed by {100}<001> grains. Nearly {100}<021> orientation rotated towards {114}<481> orientation at the extremities of the simulation block. The additional displacement gradient component L13 enhanced the rotational effect. At the 45° shear direction and ends of the simulation block, the {110}<110> orientation originated from {100}<001> grains, the nearly {110}<112> orientation formed from {100}<021> grains, and the {112}<111> Copper orientation derived from {100}<110> grains. However, the simulation did not demonstrate the development of Goss shear orientation.

Effects of different tooth movement patterns and aligner thicknesses on maxillary arch expansion with clear aligners: a three-dimensional finite element study.

The objective of this study was to investigate the biomechanical effects of different tooth movement patterns and aligner thicknesses on teeth and periodontal tissues during maxillary arch expansion with clear aligners, to facilitate more precise and efficient clinical orthodontic treatments. Three-dimensional models including teeth, maxilla, periodontal ligament, and aligner were constructed and subjected to finite element analysis. Tooth displacement trends and periodontal ligament stresses were measured for seven tooth displacement patterns (divided into three categories including overall movement of premolars and molars with gradually increasing molar expansion in each step; distributed movement of premolars and molars; and alternating movement between premolars and molars at intervals) and two aligner thicknesses (0.5mm and 0.75mm) during maxillary arch expansion with clear aligners. When expanding the maxillary arch with clear aligners, the effective expansion of the target teeth mainly showed a tilting movement trend. Increasing the amount of molar expansion increased the buccal displacement of the first molar but decreased the buccal displacement of the premolars. The mean buccal displacement of the target teeth was greater in the posterior teeth interval alternating movement group (0.026mm) than in the premolar/molar distributed movement group (0.016mm) and the overall movement group (0.015mm). Increasing aligner thickness resulted in greater buccal displacement of the crowns and increased stress on the periodontal ligaments. Increasing the amount of molar expansion reduces the efficiency of premolar expansion. Alternating movement of premolars and molars at intervals achieves a higher arch expansion efficiency, but attention should be paid to the anchorage of adjacent teeth. Increasing the thickness of the aligner increases the expansion efficiency but may also increase the burden on the periodontal tissues.

Finite element studies on Triply Periodic Minimal Surfaces (TPMS)–based hip replacement implants

Finite element studies on Triply Periodic Minimal Surfaces (TPMS)–based hip replacement implants

On low velocity impact response of Sandwich composite with jute/epoxy facesheet and cenosphere reinforced functionally graded Core: Experimental and finite element approach

AbstractThe assessment of energy absorption behavior has a vital role in determining suitability of lightweight composites for impact protection applications. This study focuses on evaluating the energy absorption characteristics of cenosphere reinforced epoxy syntactic foam core and jute epoxy facesheet sandwich composite subjected to low velocity impact. The syntactic foam is composed of lightweight cenospheres embedded within an epoxy matrix, resulting in a high‐strength and lightweight composite material. Low velocity impact tests were conducted using a drop tower apparatus to simulate realistic impact conditions. The impact force, energy absorption and damage mitigation of the syntactic foam specimens with varied weight percentage of Cenosphere (0%, 10%, 20% and 30%) were measured and analyzed to assess the energy absorption behavior. The gradation revealed that the weight of top layer when compared to bottom layer is 50.49%, 70.23% and 95.74% less in syntactic foam core with 10, 20 and 30 wt% Cenosphere respectively, indicating gradation. The study demonstrates that the addition of Cenosphere up to 20 wt% enhances the energy absorption capacity of the sandwich composites by 59.37%–93.44% compared to sandwich without Cenosphere reinforced core. However, beyond this threshold, a decline in energy absorption is observed when subjected to low‐velocity impact (LVI). Fractography analysis demonstrates that the incorporation of Cenosphere induces a rough fracture surface with deep river‐like topography, indicative of greater energy absorption during impact loading. This substantiates the conclusion that Cenosphere‐reinforced syntactic foams exhibit enhanced impact resistance, making them promising materials for structures subjected to low‐velocity impact events.Highlights Development of functionally graded core sandwich composite for low velocity impact applications. Assessing the performance of developed composites under low velocity impact loading. Determining the optimal weight percentage of cenospshere in functionally graded core. Studying the fractography of developed sandwich composites. Corelation between experimental and finite element studies.

Biomechanical Analysis of Orthodontic Miniscrew-Assisted Rapid Palatal Expansion on Dental and Bone Tissues: A Finite-Element Study

Abstract This study aims to delineate the biomechanical responses in both soft and hard tissues, alongside the interactions within the surrounding bone of a human skull subjected to clinical loadings generated by a miniscrew-assisted rapid palatal expansion (MARPE) device. Cone-beam computed tomography (CBCT) scans of a 20-year-old female skull were segmented. The skull bones were meticulously modeled to reconstruct a comprehensive three-dimensional (3D) model for finite-element analysis (FEA). A displacement of 0.125 mm was applied on each side (0.25 mm total) of the MARPE device to simulate one complete turn of the jackscrew. The outcomes revealed that the miniscrews experienced a maximum equivalent von Mises stress of 264.91 MPa. Notably, the separation of the midpalatal suture exhibited a quasi-parallel deformation with an average displacement of 0.247 mm and a standard deviation of 0.006,67 mm. The ratio of the rotational angle to the lateral displacement of the zygomaticomaxillary complex was 0.6436 degree/mm. No fracture of miniscrews was observed during the activation of one turn per day.

Nonlinear finite element analysis of shear defective reinforced concrete beam to column connections strengthened with three practical techniques

Extensive research efforts over the last decades have focused on the rehabilitation of vulnerable reinforced concrete (RC) beam to column moment resisting connections. Shear failure in the panel zone of the beam to column connections (BCCs) under the lateral seismic loads stands out as one of the main reasons of the vulnerability of moment resisting frames (MRFs), potentially resulting in severe consequences for the entire structure. The main aim of this study is to fairly investigate the effectiveness of three practical retrofitting methods to eliminate the joint shear failure in the RC beam to column connections which suffer from this undesirable brittle failure mode. To achieve this, a comprehensive review categorizing available retrofit techniques for shear-defective joints is first provided, outlining their advantages and limitations. The study then presents findings from a nonlinear three-dimensional (3D) finite element (FE) study on the performance of (RC) connections, characterized by predominant joint shear mode of failure and retrofitted using the three practical techniques. In this context, the FE model is validated through the monotonic simulation of quasi static cyclic tests conducted on connections strengthened by the three practical retrofitting methods from the literature. The selected methods were diagonal steel haunch method, RC planar joint expansion, and pre-tensioning of the joint core. The models, encompassing their precise geometric details, are applied to a full-scale exterior connection experiencing shear deficiencies to evaluate their effectiveness in real-world scenarios Additionally, a parametric study is conducted to assess the effects of various influential design variables on the effectiveness of these selected strengthening methods. These findings provide insights into the efficiency of retrofit techniques, thereby informing more robust design practices aimed at enhancing the performance and resilience of vulnerable shear defective RC BCCs retrofitted using the aforementioned strengthening techniques. The study has identified key design parameters crucial for the effectiveness of retrofit techniques in practical applications. These included haunch dimensions (thickness and length) for the haunch retrofit technique, additionally, the size of the added RC blocks for planar joint expansion technique and finally the enlargement size and the amount of applied prestressing bolt loads for pre-tensioning of the joint core retrofit technique.

Non-contact targeted removal of remnant powder particles from additive manufacturing builds with nano-second laser pulsing

Post-production precision cleaning is one critical challenge in Additive Manufacturing (AM) production of high-value, critical parts/builds. A part shedding particle during its operational use could cause severe complications in critical applications such as medical devices and aerospace components. This study presents a non-contact precision particle removal procedure based on a novel Dry Laser Cleaning (DLC) framework. DLC utilizes the thermo-elastic wave generation/propagation and high-frequency surface acceleration fields to dislodge and remove remnant particles due to inertial forces from a well-defined (user-specified) cleaning zone in a non-contact manner, as opposed to cleaning the entire build surface, which could lead to undesirable re-deposition and re-location of particles as well as high cost. The removal of spherical Stainless Steel 316 L (SS316L) micro-particles commonly used in AM from polished, atomically flat Silicon (Si) wafer substrates with uniform high free surface energy using a nano-second laser pulse is experimentally and computationally investigated. In general, a rough surface has a lower average free surface energy; thus, its cleaning, compared to Si wafer, is less challenging. The data with the SS316-Si material pair offers a consistent baseline. In parallel to experiments, a fully-coupled thermo-mechanical finite element study is also conducted for transient surface acceleration simulations to predict the effectiveness of SS316L micro-particle removal from a Si wafer substrate with laser pulsation. It is observed that SS316L micro-particles with a diameter larger than 5.61 μm, 8.43 μm, and 12.24 μm can be removed entirely at 3 mm, 6 mm, and 9 mm distances from its epicenter, respectively. Accordingly, a work-of-adhesion of 990.8 mJ/m2 is selected between the SS316-Si material pair, consistent with the literature. The reported experiments and simulations demonstrate the potential of the proposed rapid precision particle removal procedure for cleaning critical powder-based AM builds, where the targeted removal of particles is essential for the safe and reliable operation of high-value builds and parts.

Effect of cement volume on biomechanical response of a spine segment treated with a PEEK polymer implant: a finite element comparative study with vertebroplasty.

In the current study, a 3D finite element study was performed to investigate the biomechanical response of an osteoporotic spine segment treated with a novel transpedicular implant (V-STRUT©, Hyprevention, France) made of PEEK (polyetheretherketone) material combined with either injections of 2, 3, 4, 5 and 6 cc of cement. The objective was to assess numerically the biomechanical performance of the implant in combination with different doses of the injected bone cement and to compare its performance with the gold standard vertebroplasty (VP) technique. A female (69yo) was selected and a 3D finite element model of an osteoporotic spine segment was built based on a Computed Tomography (CT) scan performed from T12 to L2 with corresponding intervertebral discs and ligaments. A heterogeneous distribution of bone material properties was assigned to the bone using grey scale levels. Bilateral ellipsoid geometries of the inserted cement were retained for the V-STRUT and VP models based on experimental observation performed on different patients treated with the V-STRUT device. The current study demonstrated an optimal dose of 4 cc of bilaterally injected cement for the V-STRUT and VP techniques to restore the treated segment and confirmed that the V-STRUT device in combination with bone cement is superior to VP alone in establishing the normal stiffness and in reducing the applied stress to the immediately adjacent vertebral levels.

Does the novel artificial cervical joint complex resolve the conflict between stability and mobility after anterior cervical surgery? a finite element study.

Our group has developed a novel artificial cervical joint complex (ACJC) as a motion preservation instrument for cervical corpectomy procedures. Through finite element analysis (FEA), this study aims to assess this prosthesis's mobility and stability in the context of physiological reconstruction of the cervical spine. A finite element (FE)model of the subaxial cervical spine (C3-C7) was established and validated. ACJC arthroplasty, anterior cervical corpectomy and fusion (ACCF), and two-level cervical disc arthroplasty (CDA) were performed at C4-C6. Range of motion (ROM), intervertebral disc pressure (IDP), facet joint stress (FJS), and maximum von Mises stress on the prosthesis and vertebrae during loading were compared. Compared to the intact model, the ROM in all three surgical groups demonstrated a decline, with the ACCF group exhibiting the most significant mobility loss, and the highest compensatory motion in adjacent segments. ACJC and artificial cervical disc prosthesis (ACDP) well-preserved cervical mobility. In the ACCF model, IDP and FJS in adjacent segments increased notably, whereas the index segments experienced the most significant FJS elevation in the CDA model. The ROM, IDP, and FJS in both index and adjacent segments of the ACJC model were intermediate between the other two. Stress distribution of ACCF instruments and ACJC prosthesis during the loading process was more dispersed, resulting in less impact on the adjacent vertebrae than in the CDA model. The biomechanical properties of the novel ACJC were comparable to the ACCF in constructing postoperative stability and equally preserved physiological mobility of the cervical spine as CDA without much impact on adjacent segments and facet joints. Thus, the novel ACJC effectively balanced postoperative stability with cervical motion preservation.

Biomechanical analysis of single and multi-level artificial disc replacement (ADR) in cervical spine using multi-scale loadings: A finite element study.

Artificial disc replacement (ADR) is a clinical procedure used to diagnose cervical degenerative disc disease, preserving range of motion (ROM) at the fixation level and preventing adjacent segment degeneration (ASD). This study analyzed the biomechanics of ADR by examining range of motion (ROM), stress levels in bone and implants, and strain in the bone-implant interface using multi-scale loadings. The study focused on single- and double-level patients across various loading scales during physiological motions within the cervical spine. Results showed increased ROM in single-level and double-level fixations during physiological loadings, while ROM decreased at the adjacent level of fixation with the intact cervical spine model. The Prodisc-Implant metal endplate experienced a maximum von Mises stress of 432 MPa during axial rotation, confirming the long durability and biomechanical performance of the bone-implant interface.

Influence of age-related bone density changes on primary stability in stemless shoulder arthroplasty: a multi-implant finite element study

BackgroundStemless implants were introduced to prevent some of the stem-related complications associated with the total shoulder arthroplasty. Although general requirements for receiving these implants include good bone quality conditions, little knowledge exists about how bone quality affects implant performance. The goal of this study was to evaluate the influence of age-induced changes in bone density, as a metric of bone quality, in the primary stability of five anatomic stemless shoulder implants using 3D finite element (FE) models. MethodsThe implant designs considered were based on the Global Icon, Sidus, Simpliciti, SMR, and Inhance stemless implants. Shoulder arthroplasties were virtually simulated in Solidworks. The density distributions of 20 subjects from two age groups, 20 to 40 and 60 to 80 years old, were retrieved from medical image data and integrated into three-dimensional FE models of a single humerus geometry, developed in Abaqus, to avoid confounding factors associated with geometric characteristics. For the designs which do not have a solid collar covering the entire bone surface, i.e., the Sidus, Simpliciti, SMR, and Inhance implants, contact and non-contact conditions between the humeral head component and bone were considered. Primary stability was evaluated through the assessment of micromotions at the bone-implant interface considering eight load cases related to rehabilitation activities and demanding tasks. Three research variables, considering 20 μm, 50 μm, and 150 μm as thresholds for osseointegration, were used for a statistical analysis of the results. ResultsThe decreased bone density registered for the 60-80 age group led to larger micromotions at the bone-implant interface when compared to the 20-40 age group. The Global Icon-based and Inhance-based designs were the least sensitive to bone density, whereas the Sidus-based design was the most sensitive to bone density. The establishment of contact between the humeral head component and bone for the implants that do not have a solid collar led to decreased micromotions. DiscussionAlthough the age-induced decline in bone density led to increased micromotions in the FE models, some stemless shoulder implants presented good overall performance regardless of the osseointegration threshold considered, suggesting that age alone may not be a contraindication to anatomic total shoulder arthroplasty. If only primary stability is considered, the results suggested superior performance for the Global Icon-based and Inhance-based designs. Moreover, the humeral head component should contact the resected bone surface when feasible. Further investigation is necessary to combine these results with the long-term performance of the implants and allow more precise recommendations.

KINEMATIC RESPONSES AND SEGMENTAL STIFFNESS OF NORMAL AND DEGENERATIVE L4/L5 MOTION SEGMENTS: FINITE ELEMENT STUDY

In this study, finite element (FE) models of an anatomical normal and a degenerated disc of L4–L5 motion segment, developed using different methodologies of volume mesh constructions, and ways of defining the spinal components’ material properties, were exercised and analyzed. The geometrics details were obtained using digitizing technique and segmentation of computed tomography (CT) scans; with material and structural properties of the spinal components defined based on the literature and greyscale values of CT images for the normal and degenerated L4–L5 motion segments, respectively. The predicted kinematic responses under five different physiological loadings in three anatomical reference planes for both models together with published data were analyzed. The predicted results correlated well within the range and in similar trends with published experimental results. The overall predicted responses showed different volume mesh constructions and the representation of spinal components’ material properties were accurate enough to predict the kinematic responses, although experimental results exhibit considerable divergence due to different experimental techniques. Both models exhibited different rotational and translation segmental stiffness in each corresponding loading configuration. The normal L4–L5 segment exhibited greatest axial torsional stiffness, and least extensional stiffness. The degenerated L4–L5 segment was least flexible (greatest stiffness) in extension and most flexible (least stiffness) in flexion. For compression, the axial stiffness of segment of normal segment was about 10% larger than that of the degenerated segment. The en-bloc efforts of all spinal components have contributed to the different nonlinear kinematic characteristics and segmental stiffness of these different L4–L5 motion segments.

Integrated Crashworthiness Analysis of Electric Vehicle Battery Shells and Chassis: A Finite Element Study with Abaqus

This paper aims to comprehend and predict the mechanical behavior of the genuine Tesla Model-S chassis and the battery module during a crash in Abaqus/Explicit. The parametric method was incorporated with varying impact velocities from 27.7, 55.5, and 100m/s and battery shell thickness from 1mm to 3mm. The asymmetry model was considered for both the chassis and battery pack. Aluminum 6061 and ASI430 SS are assigned to the chassis profile and the battery shells (cells). A Johnson-Cook (JC) plastic and damage failure model has been implemented to simulate realistic crash behavior. Displacement, energy, and force results were captured during the simulation. A battery shell thickness of 3mm showed higher resistance than a 1mm thick shell at 55.5 m/s. The numerical findings reveal the dynamic response in displacement and compression under various loading conditions for both individual profiles. Additionally, the study presents a detailed inspection of each cell module, graphically demonstrating how the individual cells respond to initial positions, crashes, and external deformation (shear) caused by collision energy. The finite element model is validated against previous experimental and numerical studies, successfully simulating crashworthiness. The present study provides significant insights that have the potential to improve the safety and efficiency of battery-operated vehicles through the design and optimization of their structures.

The C2 isthmus screw provided sufficient biomechanical stability in the setting of atlantoaxial dislocation-a finite element study

BackgroundThe emerging of the C2 isthmus screw fixation technique is gaining popularity in the setting of atlantoaxial dislocation or other conditions requiring fixation of C2. However, the biomechanical stability of this fixation is poorly understood.PurposeTo compare and elucidate the biomechanical stability of C2 pedicle screw (C2PS), C2 isthmus screw (C2IS) and C2 short isthmus screw (C2SIS) fixation techniques in atlantoaxial dislocation (AAD).MethodA three-dimensional finite element model (FEM) from occiput to C3 was established and validated from a healthy male volunteer. Three FEMs, C1 pedicle screw (PS)-C2PS, C1PS-C2IS, C1PS-C2SIS were also constructed. The range of motion (ROM) and the maximum von Mises stress under flexion, extension, lateral bending and axial rotation loading were analyzed and compared. The pullout strength of the three fixations for C2 was also evaluated.ResultC1PS-C2IS model showed the greatest decrease in ROM with flexion, extension, lateral bending and axial rotation. C1PS-C2PS model showed the least ROM reduction under all loading conditions than both C2IS and C2SIS. The C1PS-C2PS model had the largest von Mises stress on the screw under all directions followed by C1PS-C2SIS, and lastly the C1PS-C2IS. Under axial rotation and lateral bending loading, the three models showed the maximum and minimum von Mises stress on the screw respectively. The stress of the three models was mainly located in the connection of the screw and rod. Overall, the maximum screw pullout strength for C2PS, C2IS and C2SIS were 729.41N, 816.62N, 640.54N respectively.ConclusionIn patients with atlantoaxial dislocations, the C2IS fixation provided comparable stability, with no significant stress concentration. Furthermore, the C2IS had sufficient pullout strength when compared with C2PS and C2SIS. C2 isthmus screw fixation may be a biomechanically favourable option in cases with AAD. However, future clinical trials are necessary for the evaluation of the clinical outcomes of this technique.

Biomechanical Comparison of Different Surgical Strategies for Skip-level Cervical Degenerative Disc Disease: A Finite Element Study.

We constructed finite element (FE) models of the cervical spine consisting of C2-C7 and predicted the biomechanical effects of different surgical procedures and instruments on adjacent segments, internal fixation systems, and the overall cervical spine through FE analysis. To compare the biomechanical effects between the zero-profile device and cage-plate device in skip-level multistage anterior cervical discectomy and fusion (ACDF). ACDF is often considered the standard treatment for degenerative cervical spondylosis. However, the selection of surgical methods and instruments in cases of skip-level cervical degenerative disk disease is still controversial. Three FE models were constructed, which used noncontiguous 2-level Zero-P (NCZP) devices for C3/4 and C5/6, a noncontiguous 2-level cage-plate (NCCP) for C3/4 and C5/6, and a contiguous 3-level cage-plate (CCP) for C3/6. Simulate daily activities in ABAQUS. The range of motion (ROM), von Mises stress distribution of the endplate and internal fixation system, and intervertebral disk pressure (IDP) of each model were recorded and compared. Similar to the stress of the cortical bone, the maximum stress of the Zero-P device was higher than that of the CP device for most activities. The ROM increments of the superior, inferior, and intermediate segments of the NCZP model were lower than those of the NCCP and CCP models in many actions. In terms of the IDP, the increment value of stress for the NCZP model was the smallest, whereas those of the NCCP and CCP models were larger. Similarly, the increment value of stress on the endplate also shows the minimum in the NCZP model. Noncontiguous ACDF with zero profile can reduce the stress on adjacent intervertebral disks and endplates, resulting in a reduced risk of adjacent segment disease development. However, the high cortical bone stress caused by the Zero-P device may influence the risk of fractures.

Structural modification and biomechanical analysis of lumbar disc prosthesis: A finite element study

BackgroundMost ball-in-socket artificial lumbar disc implanted in the spine result in increased hypermobility of the operative level and overloading of the facet joint. MethodsA finite element model was established and validated for the lumbar spine (L1-L5). The structure of the Mobidisc prosthesis was modified, resulting in the development of two new intervertebral disc prostheses, Movcore and Mcopro. The prostheses were implanted into the L3/L4 level to simulate total disc replacement, and the biomechanical properties of the lumbar spine model were analyzed after the operation. FindingsFollowing the implantation of the prostheses, the mobility of operative level, peak stress of lumbar spine models, and peak stress of facet joint increased. The performance of mobility was found to be more similar between Movcore and Mobidisc. The mobility and facet joint peak stress of the Mcopro model decreased progressively with an increase in the Young's modulus of the artificial annulus during flexion, extension, and lateral bending. Among all the models, the Mcopro50 model had the mobility closest to the intact model. It showed a 3% decrease in flexion, equal range of motion in extension, a 9% increase in left lateral bending, a 7% increase in right lateral bending, and a 3% decrease in axial rotation. InterpretationThe feasibility of the new intervertebral disc prostheses, Movcore and Mcopro, has been established. The Mcopro prosthesis, which features an artificial annular structure, offers significant advantages in terms of reduced mobility of the operative level and peak stress of facet joint.

Effect of compressive and tensile forces on glucose concentration and cell viability within the intervertebral disc: A finite element study

Understanding the role of mechanical force on tissue nutrient transport is essential, as sustained force may affect nutrient levels within the disc and initiate disc degeneration. This study aims to evaluate the time-dependent effects of different compressive force amplitudes as well as tensile force on glucose concentration and cell viability within the disc. Based on the mechano-electrochemical mixture theory, a multiphasic finite element model of the lumbar intervertebral disc was developed. The minimum glucose concentration and minimum cell density in both normal and degenerated discs were predicted for different compressive force amplitudes, tensile force, and corresponding creep time. Under high compressive force, the minimum glucose concentration exhibited an increasing and then decreasing trend with creep time in the normal disc, whereas that of the degenerated disc increased, then decreased, and finally increased again. At steady state, a higher compressive force was accompanied by a lower glucose concentration distribution. In the degenerated disc, the minimum cell density was negatively correlated with creep time, with a greater range of affected tissue under a higher compressive force. For tensile force, the minimum glucose concentration of the degenerated disc raised over time. This study highlighted the importance of creep time, force magnitude, and force type in affecting nutrient concentration and cell viability. Sustained weight-bearing activities could deteriorate the nutrient environment of the degenerated disc, while tensile force might have a nonnegligible role in effectively improving nutrient levels within the degenerated disc.

Evaluating stress and displacement in the craniomandibular complex using Twin Block appliances at varied angles: A finite element study

ObjectivesThe objective of this investigation was to assess the stress and displacement pattern of the craniomandibular complex by employing finite element methodology to simulate diverse angulations of inclined planes that are incorporated in the Twin Block appliance. MethodsA 3D finite element representation was established by use of Cone Beam Computed Tomography (CBCT) scans. This comprehensive structure included craniofacial skeletal components, the articular disc, a posterior disc elastic layer, dental elements, periodontal ligaments, and a Twin Block appliance. This investigation is the first to incorporated inclined planes featuring three distinct angulations (45, 60, and 70°) as the study models. Mechanical impacts were evaluated within the glenoid fossa, tooth, condylar, and articular disc regions. ResultsIn all simulations, the stress generated by the Twin Block appliance was distributed across teeth and periodontal ligament, facilitating the anterior movement of mandibular teeth and the posterior displacement of maxillary teeth. Within the temporomandibular joint region, compressive forces on the superior and posterior facets of the condyle diminished, coinciding with the stress configuration that fosters condylar and mandibular growth. Stress dispersion homogenized in the condylar anterior facet and articular disc, with considerable tensile stress in the glenoid fossa's posterior aspect conforming to stress distribution that promote fossa reconfiguration. The 70° inclined plane exerts the highest force on the tissues. The condyle's maximum and minimum principal stresses are 0.36 MPa and −0.15 MPa, respectively, while those of the glenoid fossa are 0.54 MPa and −0.23 MPa. ConclusionThree angled appliances serve the purpose of advancing the mandible. A 45° inclined plane relative to the occlusal plane exerts balanced anteroposterior and vertical forces on the mandibular arch. Steeper angles yield greater horizontal forces, which may enhance forward growth and efficient repositioning.