Three-dimensional Finite Element Analysis Research Articles

A novel phase change material-based thermal management of electric machine windings enabled by additive manufacturing

While recent advances in additive manufacturing have provided immense opportunities for the development of next-generation electric machines, the machine thermal management has become one of the limiting factors to achieve high performances. Herein, a novel approach for the thermal management of electric machine windings under transient high-load conditions is proposed through the additive manufacturing of their magnetic cores with a thin-wall structure topology and filling their interstices with phase change materials (PCMs). The investigation initially focuses on reducing electromagnetic losses in the stator of an electric machine by changing its core topology from a bulk to a thin-wall structure. The effectiveness of PCM in curbing temperature rises within its winding is subsequently evaluated in scenarios where active cooling is absent or present. The analyses are performed by solving a set of coupled electromagnetic and heat transfer equations through a three-dimensional frequency-transient finite element analysis. The results demonstrate an increase of 74% in allowable duration before the safe temperature threshold is exceeded without active cooling. With active cooling, temperature rises are delayed by 104% at the early stages of operations. This offers a simple, low-cost, and efficient thermal management option for enhancing the performance of an electric machine and prolonging its working life.

Mechanical Influence of Edentulous Mandibular Morphology on Peri-implant Bone in Implant Prosthetics: Threedimensional Finite Element Analysis.

The purpose of this study was to examine the mechanical influence of edentulous mandibular morphology on peri-implant bone in implant prosthetics by finite element analysis. Computed tomographic data from 25 patients with edentulous mandibles were selected and the radius of mandibular curvature and the height of the mandible at the midline were measured in order to clarify the morphological characteristics of the mandible. From the measurement, two patients with the smallest and largest radii of the mandible were selected. Two types of three-dimensional finite element models consisting of the edentulous mandible (small and large radius), superstructure (a cantilever bridge), implants, and abutments were created. Four implants were inserted between the right and left mental foramina. The upper surface of the mandibular condyle was constrained, and a vertical load of 100 N was applied on the occlusal surface of the right first molar. Three-dimensional finite element analysis of each model was performed to examine the mechanical influence of the edentulous mandibular morphology on the peri-implant bone. Measurement of mandibular morphology in CT images indicated that the lower the mandibular height was, the larger was the radius of the anterior mandibular curvature. Finite element analysis revealed that a higher equivalent stress was generated in the peri-implant bone of the model with a larger radius of curvature than that of the model with a smaller radius of curvature. The highest equivalent stress in the mandible was generated in the distal margin of the peri-implant bone posterior to the loaded side of the large radius of curvature model. The mandibular morphology had a mechanical influence on the peri-implant bone.

Sensitivity assessment of the crack propagation behavior in welded stiffened panels

ABSTRACT Welded stiffened panels play an integral role in maintaining the strength, stability, and lightweight characteristics of marine vessels. The stiffeners also affect the service life of the structure under propagating cracks. In this context, properly quantifying the effect of various input parameters on the fatigue crack propagation behavior is crucial to accurately predict the service life. This paper quantifies the influence of relevant input parameters, covering geometric and mechanical properties, on the crack propagation and fatigue service life of welded stiffened panels. Three-dimensional finite element analysis, artificial neural networks, and an elastic-plastic crack advancement rule are integrated to predict the crack propagation. Variance-based sensitivity analysis is conducted to evaluate the effect of variability in the considered input parameters on the variance of the fatigue service life of these panels. It was found that neglecting the uncertainties associated with the geometric parameters can lead to unconservative estimates of the fatigue reliability.

Arching mechanism for large span flexible culverts with shallow soil covers

Soil-steel composite bridges (SSCBs) use the surrounding soil and the culvert’s flexible corrugated steel thin plates to support vertical loads above the culvert. Existing codes use empirical equations based on field measurements and full-scale tests for small and ordinary span SSCBs to estimate the arching process and how it distributes vertical stresses on the culvert walls. The empirical equations then compute the design straining actions. Recent developments in construction technology and urbanization have led to a significant increase in typical spans of SSCBs. This paper investigates large span SSCBs and the associated induced arching action using three-dimensional finite element analysis (FEA). The study compares the FEA findings of straining actions for large span SSCB case studies to the calculations of valid design codes. The comparison demonstrates that existing codes fail to predict the real arching mechanism and, consequently, the resulting straining actions. In addition, the FEA results illustrate how the arching mechanism varies as the span changes. Arching action is typically positive for relatively small spans but becomes negative as the span increases. Finally, results prove that current codes cannot accurately predict real arching, leading to inappropriate design straining actions. For large span SSCBs, these codes require modifications for the arching factors and the profile aspect ratio factors.

Ultimate bearing capacity analysis and structural optimization of packer slip

The packer's slips indent the inner wall of the casing, leaving a series of marks between the teeth of the slips and the inner wall of the casing. Excessive bite depth can result in damage to the inner wall of the casing, potentially leading to failure. To minimize damage to the inner wall of the casing and improve the ultimate bearing capacity of the slip, a three-dimensional finite element analysis model of the slips is developed and validated through laboratory experiments. The optimization objective is to minimize casing damage and maximize bearing capacity. This paper examines the correlation between the residual collapse strength of the casing and the maximum depth of slips penetrating the inner wall. It determines the critical depth value by calculating the extrusion force endured by the inner wall of the casing as an optimization evaluation index. At the same time, the optimal structural parameters of the slips were determined through numerical simulation and orthogonal experiments. These parameters include a 90° dental angle, a 21° inner cone angle, a 219 mm outer diameter, and a 6.5 mm tooth pitch. The research results indicate that the equivalent stress of the improved slip has decreased by 8.66 %. The equivalent stress on the inner wall of the casing has been reduced by 9.34 %, and the maximum tooth mark depth of the casing has decreased by 30.48 %. Furthermore, the ultimate bearing capacity of the slip has increased by 2.24 times. Research has shown that the improved slip not only reduces damage to the inner wall of the casing and minimizes stress concentration on the slip, but also increases the ultimate bearing capacity of the slip. The research results can serve as a reference for the study and application of packers.

Stress distribution pattern in all-on-four maxillary restorations supported by porous tantalum and solid titanium implants using three-dimensional finite element analysis.

Success/failure of dental implants depends on stress transfer and distribution at the bone-implant interface. This study aimed to assess the stress distribution pattern in all-on-four maxillary restorations supported by porous tantalum and solid titanium implants using three-dimensional (3D) finite element analysis (FEA). In this FEA, a geometric model of an edentulous maxilla, Zimmer screw-vent tantalum and solid titanium implants were modelled. Four models with the all-on-four concept were designed. The fifth model had 6 vertical implants (all-on-six). Two different implant types (porous tantalum and solid titanium) were modelled to yield a total of 10 models, and subjected to 200 N bilateral vertical load. Pattern of stress distribution and maximum von Mises stress values in cancellous and cortical bones around implants were analysed. In tantalum models, the effect of increasing the distal tilting of posterior implants was comparable to the effect of increasing the number of implants to 6 on von Mises stress values in cortical bone. However, in cancellous bone, the effect of increasing the tilting of posterior implants on stress was slightly greater than the effect of increasing the number of implants to 6. In solid titanium models, the effect of both of the abovementioned parameters was comparable on stress in cancellous bone; but in cortical bone, the effect of increasing the implant number was slightly greater on stress reduction. Despite similar pattern of stress distribution in bone around implants, higher maximum von Mises stress values around tantalum implants indicate higher stress transfer capacity of this type of implant to the adjacent bone, compared with solid titanium implants.

Biomechanical analysis of cervical spine (C2-C7) at different flexed postures.

Musculoskeletal diseases are often related with postural changes in the neck region that can be caused by prolonged cervical flexion. This is one of the contributing factors. When determining the prevalence, causes, and related risks of neck discomfort, having a solid understanding of the biomechanics of the cervical spine (C1-C7) is absolutely necessary. The objective of this study is to make predictions regarding the intervertebral disc (IVD) stress values across C2-C7 IVD, the ligament stress, and the variation at 0°, 15°, 30°, 45°, and 60° of cervical neck angle using finite element analysis (FEA). In order to evaluate the mechanical properties of the cervical spine (particularly, C2-C7), this investigation makes use of computed tomography (CT) scans to develop a three-dimensional FEA model of the cervical spine. A preload of 50 N compression force was applied at the apex of the C2 vertebra, and all degrees of freedom below the C7 level were constrained. The primary objective of this investigation is to assess the distribution of von Mises stress within the IVDs and ligaments spanning C2-C7 at various flexion angles: 0°, 15°, 30°, 45°, and 60°, utilizing FEA. The outcomes derived from this analysis were subsequently compared to previously published experimental and FEA data to validate the model's ability to replicate the physiological motion of the cervical spine across different flexion angles.

Three-dimensional finite element analysis on the effects of maxillary protraction with an individual titanium plate at multiple directions and locations.

: A three-dimensional-printed individual titanium plate was applied for maxillary protraction to eliminate side effects and obtain the maximum skeletal effect. This study aimed to explore the stress distribution characteristics of sutures during maxillary protraction using individual titanium plates in various directions and locations. : A protraction force of 500 g per side was applied at forward and downward angles between 0° and 60° with respect to the Frankfort horizontal plane, after which the titanium plate was moved 2 and 4 mm upward and downward, respectively. Changes in sutures with multiple protraction directions and various miniplate heights were quantified to analyze their impact on the maxillofacial bone. : Protraction angle of 0-30° with respect to the Frankfort horizontal plane exhibited a tendency for counterclockwise rotation in the maxilla. At a 40° protraction angle, translational motion was observed in the maxilla, whereas protraction angles of 50-60° tended to induce clockwise rotation in the maxilla. Enhanced protraction efficiency at the lower edge of the pyriform aperture was associated with increased height of individual titanium plates. : Various protraction directions are suitable for patients with different types of vertical bone surfaces. Furthermore, when the titanium plate was positioned lower, the protraction force exhibited an increase.

Enhancing the understanding of bolt loosening and wave transmission in bolted lap-joint connections: a numerical and experimental study using guided Lamb waves

Bolt loosening in bolted lap-joint connections can result in catastrophic failures in industrial settings. Therefore, it is crucial to investigate these connections thoroughly and implement preventative measures. However, examining such connections requires considering multiple influencing parameters. In this study, numerical simulations were conducted using three-dimensional finite element analysis in Abaqus software to evaluate these parameters in detail. The study employed a guided wave-based structural health monitoring approach and a precise ultrasonic-guided Lamb wave propagation method. Time signals were analyzed using phase shift and transmission coefficient (TC) factors as suitable indicators. Additionally, the S0 mode of the captured waves provided a highly informative wave packet for analysis due to its specific order. Initially, various simulations were carried out to determine the optimal length of the overlapping region that would result in the most effective transmission of waves. Increasing the bolt torque and the contact friction coefficient between the two plates in the overlapping region reduces the time for waves to reach the sensor and increases the TC of the passing waves. However, the saturation state does not cause any change in the received signals. Increasing the bolt torque is more effective in facilitating wave transmission through the connections than increasing the contact friction coefficient. Furthermore, variations in excitation voltage do not affect the arrival time or TC of the waves. The continuous wavelet transformation enabled a more detailed time-frequency analysis. The results demonstrate that changes in bolt torque do not impact the wave frequencies reaching the sensors, making the frequency insensitive to bolt loosening. Ultimately, the numerical simulation results were validated through experiments on a table-top laboratory sample. This research enhances researchers’ understanding of monitoring the health status of bolted lap-joint connections by investigating the impact of various parameters on guided Lamb wave transmission through these connections.

Influence of Implant Location, Number, and Design in Ischemic Zone for Implant Prosthesis Success Rate: A Comparative Three-Dimensional Finite Element Analysis.

The performance of an implant-supported prosthesis depends on the implant type, number, implant location, and prosthesis design which is directly associated with the distribution of the occlusal forces during mastication. Thepurpose of the present study is to analyze with three-dimensional (3D) finite element comparative analysis, the influence of implant location, number, and prosthesis design in the mandibular posterior region where multiple posterior teeth replacement is indicated, which in turn is associated with the longevity or Implant success rate. Mandibular posterior section, where 4 teeth are missing, based on the space available for implants and following the surgical guide instructions, a standard make four implants (1st and 2nd premolars {3.8 mm × 11.5 mm}, 1st and 2nd molar {5.1 mm × 11.5 mm}) were selected and with standardization for placement, 4 groups were created with different implant location, number and prosthesis design from the selected implants as model FM1, FM2, FM3, FM4. Finite element analysis was carried out usingANSYS software, version 14.5 (ANSYS Inc.,Canonsburg, PA, USA) for assessment of stress, strain, and deformation around implant and bone. Maximum von Mises stress on vertical loading was highest for FM4 (139.55MPa) model (center of prosthesis on premolar and molar pontics) and lowest for FM3 (53.65MPa) model (on 2ndpremolar pontic) with values in decreasing order as FM4 ˃ FM2 ˃ FM1 ˃ FM3. Maximum von Mises stress on oblique loading was highest at the distal of 1stmolar implant pontic for FM2 (539.81MPa) and lowest at the 2ndpremolar pontic for FM3 (352.48MPa) model with values as FM2˃FM1˃FM4˃FM3. Deformation for vertical and oblique loading was observed minimum at the buccal cusp and buccal crestal bone of 2ndpremolar, 1stmolaron FM3 model against highest deformation on buccal and lingual crestal bone, cuspal area of 2ndpremolar, 1stmolar implants. For oblique loading minimum deformation was seenfor the 2ndpremolar, 1stmolar cuspal area in FM3,and maximum at the 2ndpremolar region in FM1. Four single implants may be chosen if there is enough mesiodistal and buccolingual space to allow for a minimum inter-implant and inter-implant-tooth distance that can be maintained while putting the least amount of stress on the implants and bone. To reduce stress on the bone and implants, it is best to avoid long-span implant-supported prostheses when using fixed implant-supported prostheses.

Improving resistance to embedded delaminations by adding CNTs to epoxy in carbon/(epoxy + CNT) composites

Low-velocity impact on fiber-reinforced polymer (FRP) composites may cause subsurface interface delaminations. In the case of such multiple delaminations, neighboring delaminations may grow and coalesce into larger delamination under post-impact loading. The resistance to such growth is substantially influenced by the strength and stiffness of epoxy resins used in FRP composite laminates. Therefore, the current study attempts to determine how adding carbon nanotubes (CNTs) to epoxy might potentially enhance the resistance to such delaminations. A three-dimensional (3D) finite element analysis has been carried out for laminates having single embedded delamination as well as two neighboring embedded delaminations to determine the interlaminar stresses and strain energy release rate using virtual crack closure integral. Results from the current analysis show that while parameters like shape, size, and relative spacing of delamination influence the growth, however in all the cases, adding CNTs to epoxy significantly improves the resistance to the growth of both single and interacting delaminations. The effect is observed to be more pronounced when the delaminations are closely spaced and tend to coalesce into a large delamination.

Three-dimensional nonlinear finite element analysis of corroded reinforced concrete beams strengthened by CFRP sheets

This paper investigates how the corrosion process contributes to the reduction of the cross-section, ultimate tensile strength, and ductility of corroded steel reinforcing bars, as well as the bond loss between corroded steel and damaged concrete. Considering such parameters, the finite element models are constructed and validated based on the experimental data obtained from six reinforced concrete (RC) beams into three groups: two control beams, two corroded beams without strengthening, and two CFRP-strengthened corroded beams. The validated model is capable of reflecting the failure mechanism of CFRP debonding that dominates the load-carrying capacity of corroded beams after strengthening. Therefore, the numerical simulations offer a prediction platform for investigating the structural behavior of corroded RC beams strengthened with CFRP (Carbon Fiber Reinforced Polymer) sheets without a new set of experiments. Finally, the results from nonlinear finite element analyses (FEA) help to determine the effect of main parameters affecting the strengthening performance of corroded RC beams, such as concrete compressive strength, longitudinal steel reinforcement ratio, steel/concrete bond strength reduction, flexural strengthening scheme, CFRP length.

FINITE ELEMENT ANALYSIS OF REINFORCED AND UNREINFORCED DEEP SOIL MIXING COLUMNS INSTALLED IN COHESIVE AND NON-COHESIVE SOILS

A parametric study employing three-dimensional finite element analysis is used in this paper to examine the improvement of soft clay and silty loose sand under a road embankment using deep soil mixing (DSM) columns. Both soils are designed with three variables namely DSM column diameter (D), DSM column length (L) and centre-to-centre distance of the DSM columns (s). The settlement values under the road embankment constructed with and without DSM columns were obtained by numerical analysis. The analyses were also repeated for the DSM columns which were stiffened by adding I-profiles. The results showed that the improvement effect of the DSM columns on settlement is higher in soft clay. For constant improvement area ratio (ar), the maximum improvement is achieved for D = 80 cm (2.62 ft.) and increasing D did not affect the degree of improvement. In both soil types, settlement decreased with increasing L within the weak soil zone. Increasing L into the comparatively stronger soil did not significantly affect the settlement value. Although the settlement decreased with increasing ar in silty loose sand, it reached at maximum in soft clay at ar of thirty-five percent and was not affected thereafter with increasing ar values.

Comparison of the stress distribution in base materials and thicknesses in composite resin restorations

Resin-based composite materials are commonly used for restorations, but their dimensional changes during the polymerization could cause various clinical problems. This study evaluated the influence of a base of different materials and thicknesses on the stress magnitude and distribution in a second maxillary premolar with an MOD resin composite restoration using three-dimensional finite element analysis. A sound tooth without cavity was considered as the control group (ST), and another group was restored with composite resin without applying a base material in a MOD cavity (CR). The other three groups were restored with composite resin along with the following base materials: glass ionomer cement, low-viscosity resin, and tricalcium silicate, respectively (CR-GIC, CR-LR, and CR-TS). These three groups were further divided into two subgroups according to the thickness of the base layer: thin (0.5 mm) and thick (1.0 mm). The stress distribution was compared using the maximum principal stress after polymerization shrinkage and vertical loading with 600 N on the occlusal surface. Group ST showed the lowest stress value, and its stress propagation was confined to outer enamel surfaces only. Group CR demonstrated the highest stress distribution in the tooth-restoration interface with increased failure risk on marginal areas. The thin and thick subgroups of the three groups with a base layer had lower stress levels than Group CR. The base materials reduced the marginal stress caused by polymerization shrinkage of composite resin in MOD cavities. Different base materials and thicknesses did not affect the stress distribution.

Influence of occlusal reduction design on the fracture resistance and biomechanical behavior of endocrowns restoring maxillary premolars

PurposeTo investigate the effect of different occlusal reduction design on stress distribution and fracture resistance of different endocrown systems.Material and methodsSixty-four maxillary human premolars with endodontic treatment, prepared for endocrowns were divided into 2 groups (n = 32) according to the occlusal design: Butt joint preparation (B group) and Anatomical preparation (A group). Each group were subdivided into four groups according to ceramic systems: IPS E max CAD (EM group), monolithic zirconia (ZR group), Nacera Hyprid (NH group) and PEKKTON (PE group). After manufacturing of endocrowns and adhesive bonding the specimens were thermomechanically loaded and subsequently they were tested in a universal testing machine for evaluating the fracture resistance. The specimens failure mode was qualitatively assessed. The stress distribution in each group was assessed using three-dimensional finite element analysis (FEA). 1-way ANOVA and the Post Hoc Tukey HSD test were used to evaluate the data (a = .05).ResultsThe fracture resistance values between the groups showed statistically significant variations. The B PE and A PE groups had a higher ratio of fracture resistance values. Regarding failure mode, ceramic endocrowns recorded mainly irreparable failures. FEA showed that anatomical occlusal preparation have reduced the stress concentration under all endocrown systems.ConclusionEndocrowns could be used to restore endodontically treated maxillary premolars. PEKKTON endocrowns with anatomical preparations revealed most appropriate restoration. The tested new endocrown systems enhanced the biomechanical performance of the tooth.Clinical significanceThe innovative endocrown systems (PEKK, Nacera Hyprid) can be seen as a promising choice for restoration of severely-destructed endodontic treated premolars, with less stress transmit to the residual tooth structure. Although the traditional endocrown technology might increase the longevity of tooth bonding, it shouldn’t be used for clenching cases since the risk of failure is too great overall.

Laboratory and numerical analyses on polyurethane–scrap rubber-reinforced base layer

Previous studies have explored using scrap rubber in constructing the ballasted track and showed tremendous potential to mitigate noise and vibration. However, its application for slab tracks has not been extensively investigated. This study intends to utilise scrap rubber in the base layer of the slab track; however, the high stress below base layer of the slab track may render its use unsuitable. The addition of scrap rubber would improve the damping performance but reduce the elastic modulus and cause excessive settlement of the track. This paper utilises an experimental programme comprising static and cyclic triaxial testing and numerical analyses to assess the suitability of four mixes, e.g., mix-A (soil), mix-B (soil mixed with rubber), mix-C (polyurethane-treated soil), and mix-D (polyurethane-treated soil mixed with rubber), as a base layer in slab tracks. The laboratory investigations reveal that the best performance in terms of improved damping ratio and resilient modulus, and lowered excess pore water pressure and vertical strains are shown by mix-D. These experimental test findings were supplemented with the results from three-dimensional full-scale finite element analyses, which showed a drastic reduction in the vibration levels of the track with mix-D as a base layer instead of conventional lean-mix concrete.

Investigating the Influence of All-Ceramic Prosthetic Materials on Implants and Their Effect on the Surrounding Bone: A Finite Element Analysis

This study aims to assess and compare the impact of Monolithic Zirconia (MZ) and In-Ceram Zirconia (ZP) superstructures on stress distribution within implants and D2/D4 bone densities under 200 N vertical and oblique occlusal loads using three-dimensional finite element analysis via ANSYS WORKBENCH R2. The analysis employed maximum and minimum von Mises stress values. Modeling an implant (4.2 mm diameter, 10 mm length) and abutment (0.47 mm diameter), with an 8 mm diameter and 6 mm length single crown, the research identified lower von Mises stresses in D2 cancellous bone with the MZ model under vertical loading. Conversely, under oblique loading, the ZP model exhibited maximum von Mises stresses in D4 bone around the implant. This underscores the critical need to consider physical and mechanical properties, beyond mere aesthetics, for sustained implant success. The findings highlight the effect of material composition and stress distribution, emphasizing the necessity of durable and effective implant treatments.

Three-dimensional creep calculation model for reliability analysis of concrete-filled steel tubular (CFST) structure

For long-span concrete-filled steel tube (CFST) structure, it is essential to implement efficient and realistic prediction models for the long-term processes of core concrete creep. In order to systematically study the main influential factors in CFST structure creep effects, a probabilistic analysis can be performed. The objective of this paper is to analyse the long-term response of CFST structure by using time-dependent reliability method. To address the problem of creep calculation, a novel and comprehensive presentation was developed. By converting the integral-type creep law to a differential-type form with internal variables, based on the Kelvin chain model, an elastic structural analysis with generally orthotropic elastic moduli and eigenstrains was established. We have compiled a three-dimensional (3-D) finite-element analysis programme that considers the creep Poisson effect of core concrete to analyse the long-term performance of the CFST structure. This is achieved by developing a commercial finite element code, such as Usermat in ANSYS. As calculation examples, several time-dependent analyses of a CFST stub column and long-span CFST arch bridge were performed. The calculated results of long-term behaviour agree well with experimental and measured data. Considering the randomness of various input parameters, such as physical dimensions and materials of the CFST structure, we have analysed the uncertainty using the Latin-hypercube-sampling (LHS) stochastic finite-element method. The results of creep sensitivity analysis revealed that coefficient of creep model uncertainty, steel and concrete elastic modulus were the three most influential parameters for CFST stub columns’ creep, and load, coefficient of creep model uncertainty, relative humidity, steel and concrete elastic modulus were the five for CFST arch bridges’ long-term deflection. In addition, the use of Monte Carlo (MC) and response surface (RS) methods for structural stochastic reliability analysis demonstrates the ability of these approaches to assess the reliability index of long-span CFST arch bridges. This provides a valuable reference for the design and performance evaluation of CFST structures.

The effect of enhanced structure in the posterior segment of clear aligners during anterior retraction: a three-dimensional finite element and experimental model analysis

BackgroundMesial tipping of posterior teeth occurs frequently during space closure with clear aligners (CAs). In this study, we proposed a new modification of CA by localized thickening of the aligner to form the enhanced structure and investigate its biomechanical effect during anterior retraction.MethodsTwo methods were employed in this study. First, a finite element (FE) model was constructed, which included alveolar bone, the first premolars extracted maxillary dentition, periodontal ligaments (PDL), attachments and aligners. The second method involved an experimental model—a measuring device using multi-axis transducers and vacuum thermoforming aligners. Two groups were formed: (1) The control group used common CAs and (2) the enhanced structure group used partially thickened CAs.ResultsFE model revealed that the enhanced structure improved the biomechanics during anterior retraction. Specifically, the second premolar, which had a smaller PDL area, experienced a smaller protraction force and moment, making it less likely to tip mesially. In the same vein, the molars could resist movement due to their larger PDL area even though they were applied larger forces. The resultant force of the posterior tooth was closer to the center of resistance, reducing the tipping moment. The canine was applied a larger retraction force and moment, resulting in sufficient retraction of anterior teeth. The experimental model demonstrated a similar trend in force variation as the FE model.ConclusionsEnhanced structure allowed force distribution more in accordance with optimal principles of biomechanics during the extraction space closure while permitting less mesial tipping and anchorage loss of posterior teeth and better retraction of anterior teeth. Thus, enhanced structure alleviated the roller coaster effect associated with extraction cases and offered a new possibility for anchorage reinforcement in clear aligner therapy.

Mechanical behavior of endodontically treated teeth: A three-dimensional finite element analysis using displacement vector.

This study aimed to analyze the effects of core materials, remaining tooth structures, and interfacial bonding on stress distribution in endodontically treated teeth using finite element analysis (FEA). Three-dimensional FEA was conducted using a reverse engineering technique based on maxillary premolars scanned by micro-computed tomography. Six models were generated with or without ferrules and with one of the following three abutment systems: metal core, resin core, or resin core with fiber posts. In each model, bonding and debonding were assumed in the dentin and surrounding structures: bonded and debonded models. The maximum principal stress values were recorded, and stress distribution of the entire restored teeth and dentin was generated. Furthermore, the distribution of the displacement vector of the debonded models was generated. In comparing the bonded and debonded models, the debonded models showed larger values for tensile stresses than those in bonded models for all abutment models. The models without ferrules rotated around the center of the abutment, whereas those with ferrules did not show remarkable displacement in the analysis. FEA assuming fracture of adhesive interface proved to be an effective method to clarify the significance of ferrules. It prevents stress concentration in dentin by reducing the rotation of the abutment, even when the adhesive fails.