Finite Element Analysis of Different Carbon Fiber Reinforced Polyetheretherketone Dental Implants in Implant-supported Fixed Denture

OBJECTIVES

The purpose of this study is to determine the feasibility of polyetheretherketone-based dental implants, and analyze the stress and strain around different kinds of dental implants by finite element analysis.

METHODS

The radiographic data was disposed to models in Mimics 19.0. 3D models of implants, crowns and jawbones were established and combined in SolidWorks 2018. Appling axial and oblique loads of 100 N, cloud pictures were exported in Ansys Workbench 18.0 to calculate and analyze the stress and strain in and around different implants.

RESULTS

Oblique load tended to deliver more stress to bone tissue than axial load. The uniformity of stress distribution was the best for 30% short carbon fiber reinforced polyetheretherketone implants at axial and buccolingual directions. Stress shielding phenomenon occurred at the neck of 60% continuous carbon fiber reinforced polyetheretherketone and titanium implants. Stress concentration appeared in PEEK implants and the load of bone tissue would aggravate.

CONCLUSIONS

30% short carbon fiber reinforced polyetheretherketone implants demonstrate a more uniform stress distribution in bone-implant contact and surrounding bone than titanium. Stress shielding and stress concentration may be avoided in bone-implant interface and bone tissue. Bone disuse-atrophy may be inhibited in PEEK-based implants.

Single missing molar with wide mesiodistal length restored using a single or double implant-supported crown: A self-controlled case report and 3D finite element analysis

PURPOSE

Based on a self-controlled case, this study evaluated the finite element analysis (FEA) results of a single missing molar with wide mesiodistal length (MDL) restored by a single or double implant-supported crown.

METHODS

A case of a missing bilateral mandibular first molar with wide MDL was restored using a single or double implant-supported crown. The implant survival and peri-implant bone were compared. FEA was conducted in coordination with the case using eight models with different MDLs (12, 13, 14, and 15 mm). Von Mises stress was calculated in the FEA to evaluate the biomechanical responses of the implants under increasing vertical and lateral loading, including the stress values of the implant, abutment, screw, crown, and cortical bone.

RESULTS

The restorations on the left and right sides supported by double implants have been used for 6 and 12 years, respectively, and so far have shown excellent osseointegration radiographically.The von Mises stress calculated in the FEA showed that when the MDL was >14 mm, both the bone and prosthetic components bore more stress in the single implant-supported strategy. The strength was 188.62-201.37 MPa and 201.85-215.9 MPa when the MDL was 14 mm and 15 mm, respectively, which significantly exceeded the allowable yield stress (180 MPa).

CONCLUSIONS

Compared with the single implant-supported crown, the double implant-supported crown reduced peri-implant bone stress and produced a more appropriate stress transfer model at the implant-bone interface when the MDL of the single missing molar was ≥14 mm.

A 3D-FEA study on the impact of different preparation forms and materials on posterior occlusal veneers

OBJECTIVES

To study the stress distribution and bonding performance in posterior occlusal veneers and tooth bodies under different preparation forms and materials.

METHODS

An isolated lower right first molar was prepared with non-retention type (type A), cavity-retained type (type B), and encircling-retention type (type C) forms. MicroCT images of the tooth were obtained and digitally converted into three-dimensional solid models. Three-dimensional models of veneers for the three abutment teeth were designed, fabricated, and divided into nine models (AEM, ALU, AVE, BEM, BLU, BVE, CEM, CLU, and CVE) according to the material used (E.max CAD [EM], Lava Ultimate [LU] and Vita Enamic [VE]). Three-dimensional finite element stress analysis was performed by applying vertical and oblique forces (200 N) to simulate chewing loads using ABAQUS. Finally, an adhesive stiffness degradation diagram was obtained using the rotatory dislocation simulation method.

RESULTS

The BEM model had the largest equivalent stress extreme value (160.50 MP A) when a vertical load was applied to the veneers, while there was no significant difference when it was applied to dental tissues. The equivalent stress extreme values of each part under an oblique load were significantly greater than those under a vertical load. The AEM model had the largest values when the loads were applied to the veneers (350.60 MP A) and the dental tissues (40.13 MP A). The equivalent stress extreme values of the veneers were ranked as LU < VE < EM for different materials, and LU > VE > EM for dental tissues. Bonding performance results were C > B ≈ A and LU > VE > EM.

CONCLUSIONS

The cavity-retained type better protected the veneers and dental tissues than the non-retention and encircling-retention types under lateral forces. E.max CAD material, with a high elastic modulus, reduced the stress transmitted to the remaining dental tissues. Lava Ultimate exhibited the best bonding performance.

Experimental evaluation of corneal stress-optic coefficients using a pair of force test

BACKGROUND

Topography and tomography are valuable techniques for measuring the corneal shape, but they cannot directly assess its internal mechanical stresses. And nonuniform corneal stress plays a crucial biomechanical role in the progression of diseases and postoperative changes. Given the cornea's inherent transparency, analyzing corneal stresses using the photoelasticity method is highly advantageous. However, quantification of photoelasticity faces challenges in obtaining the stress-optic coefficient due to wrinkles caused by the non-spherical geometry during tensional experiments.

OBJECTIVE

In this study, we propose an innovative experimental setup aimed at generating a gradient field of simple shear stress and achieving surface flatness during corneal stretching experiments, enabling the acquisition of the stress-optic coefficient through comparison with numerical results.

METHODS

Our designed setup applies fluid pressure and force couples on the cornea. The internal fluid pressure maintains the corneal shape, preventing wrinkles, while the force couples create a stress field leading to isochromatic fringes.

RESULTS

We successfully measured the stress-optic coefficients of the porcine anisotropic cornea in ex-vivo as 1.87 × 10-9 (horizontal) and 1.97 × 10-9 (vertical) (m2/N). Each isochromatic fringe order represents a shear stress range of 6.05 × 104 Pa under a low tension.

CONCLUSIONS

This study establishes a significant connection between corneal photoelastic patterns and the quantification of corneal stress by enabling direct measurement through advanced photoelastic visualization technology for clinical applications.

A magnesium screw with optimized geometry exhibits improved corrosion resistance and favors bone fracture healing

Stress-induced corrosion impairs the mechanical integrity of magnesium (Mg) and its alloys as potential orthopedic implants. Although there has been extensive work reporting the effects of stress on Mg corrosion in vitro, the geometric design principles of the Mg-based orthopedic devices still remain largely unknown. In this work, a numerical simulation model mimicking fractured bone fixation and surgical animal models were applied to investigate the effects of the geometric design of Mg screws on the stress distribution and the stress-induced degradation behavior. Finite element (FE) analysis was used for calculation of stress concentrations around the Mg screws, with different thread type, thread pitch, and thread width. Afterward, the Mg screws of the pre-optimization and post-optimization groups exhibiting the highest and lowest stress concentrations, respectively, were implanted in the fractured distal femora and back subcutaneous tissue of rabbits. Encouragingly, there was a significant difference between the pre-optimization and the post-optimization groups in the degradation rate of the stressed screw parts located around the fracture line. Interestingly, there was no significant difference between the two groups in the degradation rate of the non-stressed screw parts. Consistently, the Mg screw post-optimization exhibited a significantly lower degradation rate than that pre-optimization in the back subcutaneous implantation model, which generated stress in the whole screw body. The alteration in geometric design did not affect the corrosion rate of the Mg screws in an immersion test without load applied. Importantly, an accelerated new bone formation with less fibrous encapsulation around the screws was observed in the Mg group post-optimization relative to the Mg group pre-optimization and the poly (lactic acid) group. Geometry optimization may be a promising strategy to reduce stress-induced corrosion in Mg-based orthopedic devices. STATEMENT OF SIGNIFICANCE: Stress concentrations influence corrosion characteristics of magnesium (Mg)-based implants. The geometric design parameters, including thread type, thread pitch, and thread width of the Mg screws, were optimized through finite element analysis to reduce stress concentrations in a fractured model. The Mg screws with triangular thread type, 2.25 mm pitch, and 0.3 mm thread width, exhibiting the lowest maximum von Mises stress, showed a significant decrease in the volume loss relative to the Mg screws pre-optimization. Compared with the Mg screw pre-optimization and the poly(lactic acid) screw, the Mg screw post-optimization favored new bone formation while inhibiting fibrous encapsulation. Collectively, optimization in the geometric design is a promising approach to reduce stress-induced corrosion in Mg-based implants.

Examining the optimum panel pillar dimension in longwall mining considering stress distribution

Longwall mining method is widely used for underground coal production in the world. Additional stresses occur surrounding the longwall during underground mining. Stresses occurring surrounding the longwall are investigated by many researchers for years. How these stresses affect longwall production, gob, main gate, tailgate and main haulage road has been always an important issue. In this study, the effect of the safety pillar left at the end of the panel on the main haulage road is investigated. For this purpose, 6 models with different pillar distances are created and the stresses occurring in the main haulage road, tailgate and main gate at different pillar distances are examined. It has been demonstrated with numerical models that the optimum pillar distance according to these stress conditions does not damage the main haulage road, tailgate and main gate. In addition, the pillar distance of 10 m gives maximum coal recovery efficiency, and it has been shown by numerical models that the stresses occurring in the main haulage road, main gate and tailgate are not damaging to these galleries.

Finite element study on post-screw removal stress in toy poodle radius with different plate designs and screw arrangements

Background

The study employs finite element analysis to investigate stress distribution in the radius of toy poodles after screw removal. The examination focuses on the biomechanical implications of varied screw hole configurations using 1.5 and 2.0-mm locking compression plates (LCPs) with notched head T-Plates.

Aim

To provide a noninvasive approach to analyzing the immediate consequences of screw removal from the radius bone in toy poodles. Specifically, it explores the impact of varied plate designs and screw arrangements on stress distribution within the forelimb bones.

Methods

The study constructs a three-dimensional bone model of the toy poodle's forelimb based on computed tomography (CT) images. Simulations were designed to replicate jumping and landing from a 40 cm height, comparing stress distribution in the radius post-screw removal.

Results

The analysis reveals significant variations in stress distribution patterns between the two LCPs. The radius implanted with the 2.0-mm LCP displays a uniform stress distribution, contrasting with the 1.5-mm plates. Localized stress concentration is observed around the screw holes, while trabecular bone regions near the screw holes exhibit lower stress levels.

Conclusion

The study highlights the plate designs and screw configurations that affect bone stress in toy poodle forelimbs post-screw removal. The findings provide valuable insights for veterinarians, aiding informed decisions in veterinary orthopedic practices.

Stress distribution and roof subsidence of surrounding strata considering in situ coal conversion and CO2 mineralization backfilling: Photoelastic experiments using 3D-printed models of mining faces and goafs

Coal, a reliable and economical fuel, is expected to remain the primary energy source for power generation for the foreseeable future. However, conventional mining and utilization of coal has caused environmental degradation and infrastructure damage. An in situ coal conversion method has been proposed to mitigate environmental problems and reduce CO2 emissions resulting from coal extraction and utilization. This method involves the in situ conversion and utilization of coal, backfilling of waste rock, and CO2 mineralization to backfill the goaf. In this study, the impact of mining and conversion activities on the surrounding strata was evaluated to ascertain the effectiveness and advantages of the in situ coal conversion method. Transparent stope models were created using three-dimensional printing technology. The stress distribution and deformation characteristics of the surrounding strata were examined using photoelasticity and digital image correlation methods. The results were compared with those obtained using the traditional backfill mining method. The comparison revealed that the disturbance to the surrounding strata was 14.4 times less in the in situ conversion method than in the traditional backfill mining method. Additionally, the disturbance height at the roof and the disturbance depth at the floor were 4.2 and 2.1 times lower, respectively. The roof subsidence in the in situ conversion method was 1.97 times less than that in the traditional backfill mining method. These results confirm the advantages of minimizing the disturbance to surrounding rocks and controlling the subsidence of roof strata.

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.

Comparison of stress distribution around all-on-four implants of different angulations and zygoma implants: a 7-model finite element analysis

BACKGROUND

In recent years, zygomatic implants and the all-on-four treatment concept have been increasingly preferred for rehabilitation of atrophic maxillae. However, debate continues regarding the optimal configuration and angulation of the implants. The aim of this study was to analyze the biomechanical stress in implants and peri-implant bone in an edentulous maxilla with zygomatic implants and the all-on-four concept, using multiple implant configurations.

METHODS

A total of 7 models consisting different combinations of 4-tilted dental implants and zygomatic implants were included in the study. In each model, a total of 200 N perpendicular to the posterior teeth and 50 N with 45° to the lateral tooth were applied. A finite element analysis was performed for determination of stress distribution on implants and peri-implant bone for each model.

RESULTS

Higher stress values were observed in both cortical and trabecular bone around the 45°-tilted posterior implants in all-on-four models when compared to zygomatic implants. In cortical bone, the highest stress was established in an all-on-four model including 45°-tilted posterior implant with 4,346 megapascal (MPa), while the lowest stress was determined in the model including anterior dental implant combined with zygomatic implants with 0.817 MPa. In trabecular bone, the highest stress was determined in an all-on-four model including 30°-tilted posterior implant with 0.872 MPa while the lowest stress was observed in quad-zygoma model with 0.119 MPa. Regarding von Mises values, the highest stress among anterior implants was observed in an all-on-four model including 17° buccally tilted anterior implant with 38.141 MPa, while the lowest was in the including anterior dental implant combined with zygomatic implants with 20,446 MPa. Among posterior implants, the highest von Mises value was observed in the all-on-four model including 30°-tilted posterior implant with 97.002 MPa and the lowest stress was in quad zygoma model with 35.802 MPa.

CONCLUSIONS

Within the limits of the present study, the use of zygoma implants may provide benefit in decreasing biomechanical stress around both dental and zygoma implants. Regarding the all-on-four concept, a 17° buccal angulation of anterior implants may not cause a significant stress increase while tilting the posterior implant from 30° to 45° may cause an increase in the stress around these implants.

Biomechanical insights into ankle instability: a finite element analysis of posterior malleolus fractures

BACKGROUND

Posterior malleolus fractures are known to be associated with ankle instability. The complexities involved in obtaining precise laboratory-based spatial pressure measurements of the ankle highlight the significance of exploring the biomechanical implications of these fractures.

METHODS

Finite element analysis was utilized to examine the stress distribution across the contact surface of the ankle joint, both in its natural state and under varied sagittal fracture line angles. The study aimed to identify stress concentration zones and understand the influence of sagittal angles on stress distribution.

RESULTS

Three distinct stress concentration zones were identified on the ankle's contact surface: the anterolateral tibia, the anteromedial tibia, and the fracture line. The most significant stress was observed at the fracture line when a fracture occurs. Stress at the fracture line notably spikes as the sagittal angle decreases, which can potentially compromise ankle stability. Larger sagittal angles exhibited only minor stress variations at the contact surface's three vertices. It was inferred that sagittal angles below 60° might pose risks to ankle stability.

CONCLUSIONS

The research underscores the potential implications of fractures on the stress profile of the ankle joint, emphasizing the role of the contact surface in ensuring stability. The identification of three zones of stress concentration and the influence of sagittal angles on stress distribution offers a valuable reference for therapeutic decision-making. Further, the study reinforces the importance of evaluating sagittal fracture angles, suggesting that angles below 60° may compromise ankle stability.

Influence of dental implant/mini-implant design on stress distribution in overdentures: a systematic review

PURPOSE

Critically evaluate the existing literature and answer the question, "Does the dental implant/mini-implant design influence the stress distribution in prosthetic overdentures according to finite element analysis?".

METHODS

This systematic review was registered in the Open Science Framework (osf.io/2bquj) and followed the PRISMA protocols. The custom search strategy was applied to 4 databases. In vitro experimental studies that evaluated the influence of dental implant/mini-implant design on stress distribution in overdentures by FEM, without time and language restrictions, were included. The selection process was carried out in two stages by two reviewers independently. Risk of bias analysis was performed by a checklist of important parameters.

RESULTS

Sixty articles were evaluated by their title and abstract, four were selected for full reading, three were relevant, and nine were included by additional search. The 12 studies have a low risk of bias. The meta-analysis could not be performed due to the heterogeneity of the data (implant type, design variation, load intensity, and direction).

CONCLUSION

It can be inferred from the evaluated literature that design modifications influence the stress distribution, but as the FEM presents limitations inherent to the in vitro study, clinical trials are necessary to infer the effectiveness of the modifications. It should be noted that there is no consensus on which is the best thread design and that implants with a very narrow diameter are subject to the highest stress concentration.

Stress distribution of one-piece and two-piece mini-Implant overdentures with various attachment systems and diameters: A finite element analysis

PURPOSE

We investigated and compared the stress distribution within one- and two-piece mini-implants for overdentures with three different attachments (ball, Locator, and magnet) and two different diameters using three-dimensional finite element (3D FE) analysis and a monotonic bending test. The goal was to identify the most beneficial implant attachment system design for mini-implant overdentures with a lower risk of implant fracture.

METHODS

Twelve 3D FE models simulating a mandible segment with one- and two-piece mini-implants with different attachment systems, diameters, and overdentures were created using three-dimensional computer-aided design (CAD) software. Vertical and oblique forces (45° to the longitudinal axis of the implant) of 100 N were applied to the dentures. The stress distribution was analyzed. A bending test was performed on a mini-implant (Locator, 2.4 mm) using a testing machine to quantify the load at yield stress.

RESULTS

One-piece mini-implants showed lower maximum stress compared to two-piece mini-implants. Among the three designs, the magnet attachment systems showed the maximum stress. The maximum von Mises stress occurred at the neck of the implants, which was surrounded by cortical bone in all models, and under both loading conditions.

CONCLUSIONS

Focusing on the attachments and one- and two-piece designs of mini-implant overdentures using CAD models to reduce confounding factors affecting the stress distribution, we concluded that one-piece mini-implants tended to show lower stress compared to two-piece mini-implants. Mini-implant overdentures with Locator and ball attachments demonstrated lower stress within the implants compared to those with magnet attachments under vertical and oblique loading conditions.

Comparison of Raman imaging assessment methods in phase determination and stress analysis of zirconium oxide layer

This work describes Raman imaging and its data evaluation methods by using the software's original features: built-in fitting function and K-means cluster analysis (KMC) followed by fitting in an external environment. For the first time, these methods were compared in terms of their principles, limitations, versatility, and process duration. The performed analysis showed the indispensability of Raman imaging in terms of phase distribution, phase content calculation, and stress determination. Zirconium oxide formed on different zirconium alloys under various oxidation conditions was selected as an exemplary material for this analysis. The reason for the material choice is that it is an excellent example of the application of this type of Raman analysis since both phase distribution and stress analysis in zirconium oxide are of crucial importance for the development of zirconium alloys, especially for nuclear applications. The juxtaposition of the results showed advantages and limitations of both procedures allowing a definition of the criteria for selecting the evaluation method for different applications.

Crack modes and toughening mechanism of a bioinspired helicoidal recursive composite with nonlinear recursive rotation angle-based layups

The rotation angle is an important parameter affecting the performance of helical structures, and helical structures with nonlinearly increasing rotation angles have been studied. The fracture behavior of a 3D-printed helicoidal recursive (HR) composite with nonlinear rotation angle-based layups was investigated by performing quasistatic three-point bending experiments and simulations. First, the crack propagation paths during the loading of the samples were observed, and the critical deformation displacements and fracture toughness were calculated. It was found that the crack path that propagated along the soft phase increased the critical failure displacement and toughness of the samples. Then, the deformation and interlayer stress distribution of the helical structure under static loading were obtained by finite element simulation. The results showed that the variation in the rotation angle between the layers caused different degrees of shear deformation at the interface between adjacent layers, resulting in different shear stress distributions and thus different crack modes of the HR structures. The mixed-mode I + II cracks induced crack deflection, which slowed the eventual failure of the sample and improved the fracture toughness.

Stress Trajectory Variations During Occlusal Loading in Human Skull with a Maxillofacial Defect: A Finite Element Analysis

Background and Aim

Biting forces from the teeth are distributed to the facial bones and to the skull through the stress trajectories. The presence of a bony defect in either the maxilla or mandible might lead to variations in the stress distribution. The aim of this study was to evaluate the stress distribution and variations in stress trajectories from biting forces in a human skull with maxillofacial defect using a finite element (FE) model.

Methodology

In this study, a cone beam computed tomography (CBCT) of an adult male patient with a maxillectomy defect consequent to surgical treatment of mucormycosis is evaluated for the stress distribution from the biting forces of the remaining posterior teeth. Finite element model without the mandible was constructed from the patient's CBCT data. Occlusal loading forces of 600 N were applied on each side of the maxillary teeth. Stress trajectories were visualised through the stress distribution pattern.

Results

The results showed deviations in the normal stress distribution during occlusal loading and variations in zygomatic and pterygoid stress trajectories in the maxillofacial and skull regions in our FE model due to the bony defect.

Conclusion

We conclude that a skeletal maxillofacial defect should be reconstructed to resume proper stress distribution during functional forces to maintain a healthy craniofacial skeleton.

Influence of femoral bowing on stress distribution of the proximal femur: a three-dimensional finite element analysis

BACKGROUND

Whether femoral bowing or its direction has a mechanical effect on the proximal femur is unclear. This study aimed to define the changes in stress distribution in the proximal femur associated with femoral bowing using finite element analysis.

METHODS

We created four femoral models: original, entire lateral bowing, entire anterior bowing, and the middle of both (50% anterolateral bowing) from computed tomography data of women with standard bowing. Each model's stress distribution was compared by two-layering the stress distribution under loading conditions during walking. We also evaluated displacement vectors.

RESULTS

In all directions of femoral bowing, the stress increased in the femoral neck and the femoral trochanter in the 50% anterolateral bowing. The direction of deformation of the vector for the femoral head increased anteroinferiorly in the 50% anterolateral bowing.

CONCLUSIONS

This study showed that the stress distribution at the proximal femur shifted laterally. The high-stress area increased at the femoral neck or trochanter due to increasing femoral bowing. Femoral bowing also increases the anteroinferior vector in the femoral head. This study provides valuable insights into the mechanism of proximal femoral fractures in older adults.

Variation in stress distribution modified by mandibular material property: a 3D finite element analysis

BACKGROUND

Temporomandibular joint disorder (TMD) is a common oral and maxillary facial disease. Finite element method (FEM) has been widely used in TMD studies. Material assignment significantly affects FEM results. The differences in the methods of material assignment used in previous studies have not been comprehensively assessed for further calculations.

METHODS

The mandible material modelling approaches were of four types, namely: uniform modelling with (A) cortical bone; and (B) cancellous bone; (C) semi-uniform modelling with division of cortical and cancellous bone; and (D) non-uniform modelling with Computed tomography (CT) gray value related modulus. Meanwhile, the Young's modulus of values ranging from 20 to 300 GPa were considered for the teeth. Ten modellings were used to analyze and discuss the differences in contact pressure and contact force.

RESULTS

(1) The increase in teeth elastic modulus increased the maximum contact pressure on the alveolar bone and contact force on teeth, but induced insignificant stress variation on the temporomandibular joint; (2) The location of the maximum contact pressure was steady for all four modelling approaches of the mandibular material. However, the maximum contact pressure and contact force exhibited an insignificant difference.

CONCLUSIONS

Teeth with a higher elastic modulus significantly enhanced the stress concentration in the alveolar bone; in contrast, it induced minor variations in the temporomandibular joint stress states. The extreme stress regions predicted by the four mandibular models were consistent with the actual damaged regions. However, non-uniform modellings based on CT values could better describe the mechanical properties of the human bone, which should be primarily considered.

A composite resin core with a new zirconia tube reduces the surface strain at the cervical area of a mandibular molar: A model tooth study

PURPOSE

This study aimed to evaluate the surface strain at the cervical area of endodontically treated molars with a large pulp chamber restored using a composite resin core with three different types of core build-up systems.

METHODS

Reproduction models of human mandibular molars with prepared post spaces were used in this study. Roots duplicated with a composite resin were used as the experimental teeth. Three types of core build-up systems were used: composite resin core(RC), composite resin core with fiber posts (FC), and composite resin core with a prefabricated zirconia tube (ZC). Each group comprised eight specimens. Crowns made of yttria partially stabilized zirconia were cemented with dual-cure resin cement. Four strain gauges were attached to the surfaces of each specimen: the cervical area of the root and crown, on the buccal and lingual sides. The surface strain at each cervical area was measured using a static loading test and statistically analyzed.

RESULTS

In the case of static loading to the buccal cusp inner slope, ZC showed a significantly lower strain than RC in the crown on the buccal side and in the root and FC in the root. In the central fossa, ZC showed a significantly lower strain than FC in the root on the lingual side.

CONCLUSIONS

The prefabricated zirconia tube reduced the surface strain at the cervical area of the buccal/lingual root in molars; however, the effect was small in the cervical area of the crown.

Experimental studies for the progressive assessment of stress distributions on orthodontic archwire

This paper presents experimental studies to examine effect of crowding stages on stress distributions on orthodontic archwire using loading tests and 2D photogrammetry technique. Three specimens representing crowding II, crowding I, and alignment stage were fabricated based on a 3D images of upper teeth. Engaged NiTi archwire is loaded with weights to induce deformation, and 2D photogrammetry technique was used to loaded wire and curvature change of the engaged wire from the captured images. Axial and flexural stresses were obtained, which were used to calculate von Mises stress distributions along the wire. The results show that the averaged von Mises stress of archwire was released in about 10% when the alignment of teeth changes from crowding II to I and crowding I to alignment. Comparing all three stages, it was common that flexural stresses were much larger than the axial stresses. In addition, the wire stresses were concentrated more on molar teeth area due to anchorage effect, regardless of crowding stage. This study shows not only how stresses were distributed along the wire but also how stress distributions on wire change as orthodontic treatment proceeded, which can be used to improve effectiveness of treatment and develop wire design.

Impact of different axial wall designs on the fracture strength and stress distribution of ceramic restorations in mandibular first molar

BACKGROUND

The purpose of this study was to investigate the fracture strength and stress distribution of four ceramic restorations.

METHODS

Forty human mandibular first molars were collected and randomized into four groups after establishing the distal defect: full crown group with 4 mm axial wall height (AWH) (FC4); short AWH crown group with 2 mm AWH (SC2); occlusal veneer group with 0 mm AWH (OV0); occlusal distal veneer group with only the distal surface prepared, and 4 mm AWH (OD4). The teeth were prepared according to the groups and the ceramic restorations were completed using celtra duo ceramic blocks. The ceramic thickness of the occlusal surface is about 1.5 mm and the edge is about 1 mm. The failure load values and fracture modes of each group were detected by mechanical test in vitro. According to the groups to establish three-dimensional finite element analysis (FEA) models, a 600 N loading force was applied vertically using a hemispherical indenter with a diameter of 6 mm. and compare the stress distribution under the condition of different restorations.

RESULTS

In vitro mechanical tests showed that the failure load values were SC2 (3232.80 ± 708.12 N) > OD4 (2886.90 ± 338.72 N) > VO0 (2133.20 ± 376.15 N) > FC4(1635.40 ± 413.05 N). The failure load values of the short AWH crown and occlusal distal veneer were significantly higher than that of occlusal veneer and full crown (P<0.05). The fracture modes of the full crown and occlusal veneer groups were mainly ceramic fractures and some were restorable tooth fractures. The short AWH crown and occlusal distal veneer groups presented with three fracture modes, the proportion of non-restorable tooth fracture was higher. The results of FEA show that under the spherical loading condition, the stress of ceramic was concentrated in the contact area of the loading head, the maximum von Mises stress values were FC4 (356.2 MPa) > VO0 (214.3 MPa) > OD4 (197.9 MPa) > SC2 (163.1 MPa). The stress of enamel was concentrated in the area where the remaining enamel was thinner, the maximum von Mises stress values was OD4 (246.2 MPa) ≈ FC4 (212.4 MPa) > VO0 (61.8 MPa) ≈ SC2 (45.81 MPa). The stress of dentin is concentrated in the root furcation and the upper third region of the root. However, stress concentration was observed at the tooth cervix in the full crown.

CONCLUSION

Under certain conditions, the occlusal distal veneer shows better performance than the full crown.

Stress distribution around kerogen particles as a measure of the initiation of bitumen-filled microfractures in organic-rich source rocks

In this article, we present a method used to model the initiation of bitumen-filled microfractures in immature, organic-rich source rocks. The first part presents the method used to calculate the stress distribution around the kerogen particles. The second part explains the method used to calculate the pressure change as a function of the transformation ratio and the resulting overpressure.•

The effective principal stresses acting on the kerogen boundary were calculated.

•

Kerogen geometries were determined using the measured aspect ratio of the kerogen traces obtained from the petrography observation.

•

To estimate overpressure, the increase in pressure due to the transformation of kerogen to bitumen was calculated.

A Novel Anatomical Locking Guide Plate for Treating Acetabular Transverse Posterior Wall Fracture: A Finite Element Analysis Study

Objective

To improve the treatment of the acetabular transverse posterior wall fracture (ATPWF), a novel anatomical locking guidance plate (NALGP) was designed and compared with traditional fixations using finite element analysis.

Methods

The ATPWF model was constructed using the three‐dimensional finite element model of the half pelvis via the Mimics software and three internal devices were used to fix this model: the posterior‐column locking plate with anterior‐column screws (PCLP), double‐column locking plates (DCLP), and NALGP. Next, mesh division was conducted by solid 187 tetrahedral elements in the workbench software. After defining the boundary condition and material properties, each assembly model was loaded in an increasing manner with a downward vertical force of 200, 400, and 600 N, respectively. The loading force was directed at 45 degrees upward in the coronal plane and 25 degrees backward in the sagittal plane. Finally, the stress distribution and stress peak of plates and screws were measured and evaluated, and the displacement of fracture fragments under different loading force was assessed among the three groups.

Results

For stress distribution, it was found that the stress mainly acted on the posterior‐column plate, especially concentrated at the middle and lower section of the plate in all three groups after fixation on the ATPWF. In addition, most stresses of screws appeared on the lag screws instead of the common screws. The common screws in the NALGP group experienced larger stresses under all loading force, while those in the DCLP group withstood less stresses compared to those in the PCLP group. For the displacement of fracture fragments, the NALGP group were found to have less fracture fragment displacements than the PCLP group, but had comparable results to DCLP at both the transverse fracture and the posterior wall fracture sites.

Conclusion

The newly‐designed fixation device showed superiorities on fracture stabilization over PCLP, but had comparable stability to DCLP. This suggests that the DCLP might be unnecessary for treating ATPWF in some instances because it might cause bigger surgical trauma and blood loss.

Stress on the posteromedial region of the proximal tibia increased over time after anterior cruciate ligament injury

PURPOSE

Anterior cruciate ligament (ACL) injury induces anterior and rotatory instability of the knee. However, the effect of this instability on the stress distribution in the knee joint in living participants is not clear. The aim of this study was to compare the distribution pattern of subchondral bone density across the proximal tibia in the knees with and without ACL injury, and to investigate the correlation between the distribution patterns of the subchondral bone density and the duration of ACL-deficiency.

METHODS

Radiographic and computed tomography (CT) data pertaining to 20 patients with unilateral ACL injury without combined injury (ACL-deficient group) and 19 nontraumatic subjects (control group) were collected retrospectively. Subchondral bone density of the proximal tibia was assessed using CT-osteoabsorptiometry. Both the medial and lateral compartments of the proximal tibia were divided into three subregions of equal width in the sagittal direction. The percentage of high subchondral bone density areas (HDA%) in each subregion was quantitatively analyzed.

RESULTS

HDA% of the posteromedial region was significantly higher in the ACL-deficient group (mean: 21.6%) than in the control group (14.7%) (p = 0.002). In contrast, HDA% of the anteromedial region was significantly lower in the ACL-deficient group (9.4%) than in the control group (15.3%) (p = 0.048). The logarithm of the time elapsed from ACL injury to CT examination showed a significant correlation with HDA% in the posteromedial region (p = 0.032).

CONCLUSIONS

Subchondral bone density in the posteromedial region significantly increased after ACL injury and correlated with the duration of ACL-deficiency in semi-log manner in meniscus intact knees. The increase in stress on the posteromedial region after ACL injury, which induces a change in the subchondral bone density, justifies early ACL reconstruction after ACL injury.

Finite Element Analysis of a New Type of Spinal Protection Device for the Prevention and Treatment of Osteoporotic Vertebral Compression Fractures

Objective

To study the effectiveness of a new spinal protection device for preventing and treating osteoporotic vertebral compression fractures (OVCFs) by finite element analysis (FEA).

Methods

One healthy volunteer and one patient with 1‐segment lumbar vertebral compression fractures were included in this experimental study. The DICOM files of two different lumbar spiral computed tomography (CT) scans were converted into STL files, and 3D finite element models of the lumbar spine were generated for normal and L1 vertebral fracture spines. A new type of spinal protection device was applied to reduce the stress on the anterior vertebral edge and direct the center of gravity posteriorly. The stress distribution characteristics of different finite element models of the lumbar spine were analyzed, revealing the characteristics of the stress distributed along the spine under the action of the new spinal protection device.

Results

Under normal conditions, the stress was mainly distributed in the middle and posterior columns of the spine. When the anterior border of the L1 vertebral body was fractured and collapsed, the stress distribution shifted toward the anterior column due to the center of gravity being directed forward. According to finite element analysis of the spine with the new protection device, the stress in the middle and posterior columns tended to increase, and that in the anterior column decreased. After the new type of spinal fixation device was applied, the stress at the L1 and L2 vertebral endplates decreased to a certain extent, especially that at the L1 vertebral body. The maximum stress on the L1 vertebral body decreased by 20% after the auxiliary device was applied.

Conclusions

According to the FEA results, the new spinal protection device can effectively prevent and treat osteoporotic vertebral compression fractures (OVCFs), and can alter the stress distribution in the spine and reduce the stress in the anterior column of the vertebral body, especially in vertebral compression fractures.

Fracture resistance and stress distribution of weakened teeth reinforced with a bundled glass fiber-reinforced resin post

OBJECTIVES

To make an in vitro assessment of fracture resistance of weakened and non-weakened teeth receiving intraradicular reinforcement using Rebilda bundled glass fiber-reinforced composite posts (GT), Rebilda conventional glass fiber posts (RP), or both systems combined (GT + RP).

MATERIALS AND METHODS

Eighty sound bovine incisors were prepared and divided randomly into eight groups as follows: (a) nWnR: without simulating weakness, and without intraradicular reinforcement; (b) WnR: simulating weakness, but without intraradicular reinforcement; (c) nWGT: without simulating weakness, but with GT; (d) WGT: simulating weakness, and with GT; (e) nWRP: without simulating weakness, but with RP; (f) WRP: simulating weakness, and with RP; (g) nWGTRP: without simulating weakness, but with GT + RP; (h) WGTRP: simulating weakness, and with GT + RP. The specimens were subjected to the load-to-fracture test using the DL-2000MF universal testing machine. The finite element method assessed the mechanical behavior and stress distribution in endodontically treated teeth.

RESULTS

The groups nWGTRP and WGTRP presented the best results in the load-to-fracture test, with the former being better than the latter, but with no statistically significant difference (P > 0.05). However, there was a significant difference between these and the other groups (P < 0.05), except for nWRP. Stress distribution inside the canal wall was different among the groups, with promising mechanical behavior for nWGTRP and nWRP.

CONCLUSIONS

The Rebilda conventional fiber post (RP), combined with the Rebilda bundled glass fiber-reinforced composite post (GT) improves the resistance and stress distribution of immature teeth.

CLINICAL RELEVANCE

Longitudinal fracture is less frequent in teeth restored with GT and RP posts.

Biomechanical analysis of rigid and non-rigid connection with implant abutment designs for tooth-implant supported prosthesis: A finite element analysis

BACKGROUND/PURPOSE

The design of the connectors and implant abutments could affect the stress distribution of the tooth-implant supported prosthesis (TISP) entire system after loading. Therefore, the purpose of this study was to investigate the stress distribution of the TISP in different connectors and different implant abutments after loading.

MATERIALS AND METHODS

The TISP design used in this study was divided into six models. R1, R2 and R3 represented the tooth and the one-piece, two-piece and three-piece abutment implant system connected by a rigid connector, respectively, while NR1, NR2 and NR3 were the corresponding tooth-abutment implant systems connected by a non-rigid connector. A vertical occlusal load of 50 N was applied at a right angle on the 6 occlusal points of the occlusal surface.

RESULTS

As a result, regarding the maximum average stress distribution, R1 and NR1 appeared on the implant fixture, and the other four models were on the implant abutment. On the other hand, regardless of the abutment implant system, the maximum von Mises stress generated by the rigid connector was greater than the corresponding non-rigid connector in the cortical bone around implant. In addition, the three-piece abutment implant system had lower von Mises stress than the one-piece and two-piece implant systems in the cortical bone.

CONCLUSION

It is concluded that by adding a flexible non-rigid connector and three-piece abutment device design to TISP, the occlusal load of the implant was dispersed, and the stress could be gradually introduced into the relatively strong implant abutment.

Development of an optimal relief method for the palatal plate by stress analysis

BACKGROUND

Plate dentures cannot be easily modified after fabrication; therefore, the sites and magnitude of relief must be effectively assessed at the time of fabrication. However, a considerable variation exists in the magnitude of optimal relief and relief range, and there are no guidelines that present these clearly, leading the dentists to decide subjectively. Thus, this study aims to develop an optimal relief method to improve the stress bearing capacity of the palatal mucosa.

METHODS

The objective of this study, namely, the borderline, was set in steps. A three-dimensional finite element model for the pseudopalatal plate was created and used to evaluate the changes in stress distribution in the palatal mucosa due to the selective relief of stresses above the borderline. The resulting data were used to develop the optimal relief method.

RESULTS

In the relief model with a borderline of 0.04 MPa or higher, the distribution volume at which a high stress of 0.20 MPa or higher is generated was approximately 800% of that with the no-relief model, and in the relief model with a borderline of 0.06 MPa or higher, the respective ratio was approximately 280%. On the other hand, the relief models with a borderline of 0.14 MPa or higher were approximately 60%. In the mid-palatal relief model, the distribution volume at which a stress of 0.20 MPa or higher was generated was 180% of that in the relief model.

CONCLUSIONS

The supportive strength of plates can be increased by selectively applying optimal relief rather than standard relief, allowing for easier and more effective plate-denture treatment.

Stress distribution in the bonobo (Pan paniscus) trapeziometacarpal joint during grasping

The primate thumb plays a central role in grasping and the basal trapeziometacarpal (TMC) joint is critical to its function. The TMC joint morphology varies across primates, yet little is known about form-function interaction within in the TMC joint. The purpose of this study was to investigate how stress distributions within the joint differ between five grasping types commonly employed by bonobos (Pan paniscus). Five cadaveric bonobo forearms were CT scanned in five standardized positions of the hand as a basis for the generation of parametric finite element models to compare grasps. We have developed a finite element analysis (FEA) approach to investigate stress distribution patterns in the TMC joint associated with each grasp type. We hypothesized that the simulated stress distributions for each position would correspond with the patterns expected from a saddle-shaped joint. However, we also expected differences in stress patterns arising from instraspecific variations in morphology. The models showed a high agreement between simulated and expected stress patterns for each of the five grasps (86% of successful simulations), while partially (52%) and fully (14%) diverging patterns were also encountered. We identified individual variations of key morphological features in the bonobo TMC joint that account for the diverging stress patterns and emphasized the effect of interindividual morphological variation on joint functioning. This study gives unprecedented insight in the form-function interactions in the TMC joint of the bonobo and provides an innovative FEA approach to modelling intra-articular stress distributions, a valuable tool for the study of the primate thumb biomechanics.

[Finite element analysis of the graft stresses after anterior cruciate ligament reconstruction]

OBJECTIVE

To explore the stress distribution characteristics of the graft after anterior cruciate ligament (ACL) reconstruction, so as to provide theoretical reference for the surgical plan of ACL reconstruction.

METHODS

Based on 3D MRI and CT images, finite element models of the uninjured knee joint and knee joint after ACL reconstruction were established in this study. The uninjured knee model included femur, tibia, fibula, medial collateral ligament, lateral collateral ligament, ACL and posterior cruciate ligament. The ACL reconstruction knee model included femur, tibia, fibula, medial collateral ligament, lateral collateral ligament, ACL graft and posterior cruciate ligament. Linear elastic material properties were used for both the uninjured and ACL reconstruction models. The elastic modulus of bone tissue was set as 17 GPa and Poisson' s ratio was 0.36. The material properties of ligament tissue and graft were set as elastic modulus 390 MPa and Poisson's ratio 0.4. The femur was fixed as the boundary condition, and the tibia anterior tension of 134 N was applied as the loading condition. The stress states of the ACL of the intact joint and the ACL graft after reconstruction were solved and analyzed, including tension, pressure, shear force and von Mises stress.

RESULTS

The maximum compressive stress (6.34 MPa), von Mises stress (5.9 MPa) and shear stress (1.83 MPa) of the reconstructed ACL graft were all at the anterior femoral end. It was consistent with the position of maximum compressive stress (8.77 MPa), von Mises stress (8.88 MPa) and shear stress (3.44 MPa) in the ACL of the intact knee joint. The maximum tensile stress of the graft also appeared at the femoral end, but at the posterior side, which was consistent with the position of the maximum tensile stress of ACL of the uninjured knee joint. More-over, the maximum tensile stress of the graft was only 0.88 MPa, which was less than 2.56 MPa of ACL of the uninjured knee joint.

CONCLUSION

The maximum compressive stress, von Mises stress and shear stress of the ACL graft are located in the anterior femoral end, and the maximum tensile stress is located in the posterior femoral end, which is consistent with the position of the maximum tensile stress of the ACL of the uninjured knee joint. The anterior part of ACL and the graft bore higher stresses than the posterior part, which is consistent with the biomechanical characteristics of ACL.

Titanium alloy cannulated screws and biodegradable magnesium alloy bionic cannulated screws for treatment of femoral neck fractures: a finite element analysis

Background

Cannulated screws (CS) are one of the most widely used treatments for femoral neck fracture, however, associated with high rate of complications. In this study, we designed a new type of cannulated screws called degradable magnesium alloy bionic cannulated screws (DMBCS) and our aim was to compare the biomechanical properties of DMBCS, the traditionally used titanium alloy bionic cannulated screws (TBCS) and titanium alloy cannulated screws (TTCS).

Methods

A proximal femur model was established based on CT data of a lower extremity from a voluntary healthy man. Garden type III femoral neck fracture was constructed and fixed with DMBCS, TBCS, and TTCS, respectively. Biomechanical effect which three type of CS models have on femoral neck fracture was evaluated and compared using von Mises stress distribution and displacement.

Results

In the normal model, the maximum stress value of cortical bone and cancellous bone was 76.18 and 6.82 MPa, and the maximum displacement was 5.52 mm. Under 3 different fracture healing status, the stress peak value of the cortical bone and cancellous bone in the DMBCS fixation model was lower than that in the TTCS and TBCS fixation, while the maximum displacement of DMBCS fixation model was slightly higher than that of TTCS and TBCS fixation models. As the fracture heals, stress peak value of the screws and cortical bone of intact models are decreasing, while stress peak value of cancellous bone is increasing initially and then decreasing.

Conclusions

The DMBCS exhibits the superior biomechanical performance than TTCS and TBCS, whose fixation model is closest to the normal model in stress distribution. DMBCS is expected to reduce the rates of post-operative complications with traditional internal fixation and provide practical guidance for the structural design of CS for clinical applications.

Finite element analysis of the lumbar spine in adolescent idiopathic scoliosis subjected to different loads

OBJECTIVE

To explore the biomechanical changes of the lumbar spine segment of idiopathic scoliosis under different loads by simulating six kinds of lumbar spine motions based on a three-dimensional finite element (FE) model. Methods According to the plain CT scan data of L1-L5 segment of an AIS patient, a three-dimensional FE model was established to simulate the biomechanics of lumbar scoliosis under different loads. The lumbar model was reconstructed using Mimics20.0, smoothed in Geomagic2013, assembled in Solidworks 2020, with FE analysis performed using Workbench19.0. Results The completed model had a total of 119029 C3D4 solid elements, 223805 nodes, including finely reconstructed tissue structures. In patients with AIS, the range of motion (ROM) is reduced under all loads. Under flexion loads, the vertebral concave stress distribution is greater; under extension lateral bending, and rotation load at the posterior side of the vertebral body, the stress is concentrated in the L3 vertebral arch. The buffering effect of intervertebral disc on the rotational load is the weakest. Different loads of AIS cause corresponding changes in the force and displacement of different positions of the vertebral body or intervertebral discs. Conclusions The change in physiological shape of the lumbar vertebrae limits the ROM of the lumbar vertebrae. The stress showed a trend of local concentration which located in the concave side of the scoliosis. The stress on the lumbar vertebrae comprising the greatest curvature is the most excessive. The stress in the intervertebral disc under the rotating load is greater than that under other kinds of loads, and the intervertebral disc is more likely to be injured because of the rotating load.

Establishment of optimal variable elastic modulus distribution in the design of full-crown restorations by finite element analysis

To establish optimal elastic modulus distribution throughout the entire all-ceramic crown, aiming at improvement of the mechanical properties of the restoration as well as the adhesive interface, seven 3D models of mandibular first premolars of zirconia monolithic and bilayer crowns and lithium disilicate monolithic and bilayer crowns were constructed. The elastic modulus distribution of 8-layer crown A referred to human enamel, B was calculated by a genetic algorithm (GA) to minimize the principle stresses on the crown, and C minimized the shear stresses at the cementing lines. After applying a static load of 600 N, the maximum principle stresses were calculated and analyzed by finite element analysis (FEA). Group C were found to have the lowest peak shear stress at the cementing line and moderate peak tensile stress in the crown. Introduction of the modified elastic modulus distribution from human enamel into the entire all-ceramic crown reinforces the mechanical properties of the whole restoration as well as the adhesive interface against chipping and debonding.

Functional assistance for stress distribution in cell culture membrane under periodically stretching

Dynamic cell cultures simulate the in vivo cell environment for a regular loading system with curtain strains. However, it is difficult to obtain strains that are suitable for cells without conducting multiple trials. This study develops a device that increases the strain gradient by changing the tensile section, in order to determine the effect of various cyclic strains on cultured human keratinocytes (HK) cells. This device is used to determine the effect of 3% and 5% cyclic strain and shear strain on cell proliferation and arrangement at 1 Hz. The results show that compared with static and 3% strain, a 5% cyclic strain better inhibits the proliferation of HK cells. Compared to the initial cell attachment when there is no specific directionality, the cells are aligned in the vertical stretching direction after cyclic stretching. This equipment increases the efficiency of the experiment and more intuitively maps the cell behavior and shape to the strain field and the response to the shear strain.

A multiscale model for multiple platelet aggregation in shear flow

We developed a multiscale model for simulating aggregation of multiple, free-flowing platelets in low-intermediate shear viscous flow, in which aggregation is mediated by the interaction of αIIbβ3 receptors on the platelet membrane and fibrinogen (Fg). This multiscale model uses coarse grained molecular dynamics (CGMD) for platelets at the microscales and dissipative particle dynamics (DPD) for the shear flow at the macroscales, employing our hybrid aggregation force field for modeling molecular level receptor ligand bonds. We define an aggregation tensor and use it to quantify the molecular level contact characteristics between platelets in an aggregate. We perform numerical studies under different flow conditions for platelet doublets and triplets and evaluate the contact area, detaching force and minimum distance between different pairs of platelets in an aggregate. We also present the dynamics of applied stress and velocity magnitude distributions on the platelet membrane during aggregation and quantify the increase in stress in the contact region under different flow conditions. Integrating the knowledge from our previously validated models, together with new aggregation scenarios, our model can dynamically quantify aggregation characteristics and map stress and velocity distribution on the platelet membrane which are difficult to measure in vitro, thus providing an insight into mechanotransduction bond formation response of platelets to flow-induced shear stresses. This modeling framework, together with the tensor method for quantifying inter-platelet contact, can be extended to simulate and analyze larger aggregates and their adhesive properties.

Evaluation of different fixation methods with finite element analysis in total mandibular subapical osteotomy

PURPOSE

The purpose of the study was to evaluate the stress distribution in various miniplates that were used in cases that underwent advancement with total mandibular subapical osteotomy (TMSO) using finite element analysis (FEA).

MATERIAL AND METHOD

Cone beam computed tomography (CBCT) images of a patient with appropriate bone tissues were used as a reference for the modeling of the mandible. In all mandibular models, horizontal TMSO was performed in a region 5 mm away from the apex of the teeth and vertical TMSO was performed in the retromolar region, 10 mm posterior to the second molar tooth. After TMSO, the dentoalveolar segment was advanced 3 mm and miniplates were placed symmetrically at four points for fixation. Four different miniplates with 2.0 mm thickness were used. Three different forces were applied to the models. Stress distribution on the models was evaluated using maximum von Mises stress values.

RESULTS

The maximum von Mises stress occurred in Y + I and Y + L models following the application of 300 N force from the incisal. An evaluation of posterior unilateral force indicated that the stress was remarkably high in the models with a posterior I-plate. The stress in the Y + I model was higher under unilateral force compared to the stress in other models. Under posterior bilateral force, the maximum von Mises stress values ​​occurred in the I-plates of T + I, Y + I, and L + I models (1006, 1012, and 1004 MPa, respectively).

CONCLUSION

Within the limitations of our study, we found that the ideal stress distribution was in the T + L and L + L plate combinations in the plates used for fixation after advancement with TMSO.

Cementum thickening leads to lower whole tooth mobility and reduced root stresses: An in silico study on aging effects during mastication

In the course of a lifetime the crowns of teeth wear off, cementum thickens and the pulp closes-in or may stiffen. Little is known about how these changes affect the tooth response to load. Using a series of finite element models of teeth attached to the jawbone, and by comparing these to a validated model of a 'young' pig 3-rooted tooth, the effects of these structural changes were studied. Models of altered teeth show a stiffer response to mastication even when material properties used are identical to those found in 'young' teeth. This stiffening response to occlusal loads is mostly caused by the thicker cementum found in 'old' teeth. Tensile stresses associated with bending of dentine in the roots fall into a narrower distribution range with lower peak values. It is speculated that this is a possible protective adaptation mechanism of the aging tooth to avoid fracture. The greatest reduction in lateral motion was seen in the bucco-lingual direction. We propose that greater tooth motion during mastication is typical for the young growing animal. This motion is reduced in adulthood, favoring less off-axis loading, possibly to counteract natural bone resorption and consequent compromised anchoring.

Stress distribution and deformation in six tie wings Orthodontic bracket during simulated tipping - A finite element analysis

BACKGROUND AND OBJECTIVES

Four tie wings brackets are widely used in orthodontics, while the Six Tie Wings Brackets (STWB) are recently emerging in fixed orthodontic appliances due to their claim for less friction and thus faster teeth movement. The aim of this work was to evaluate the stress distribution and deformation during simulated mesio-distal tipping forces in Stainless Steel (SS) six tie wings orthodontic bracket using Finite Element Analysis (FEA).

METHODS

A six tie wings bracket (Synergy®, RMO, USA) dimensions were measured using the Vision system and a 3D model of the bracket was constructed. A Finite Element (FE) model was developed and mesio-distal tipping forces of 1.22 N to 1.96 N (125 to 200 gm) in increments were applied on the gingival and incisal slot walls. The stress distribution and deformation were recorded at specific points in the bracket and analyzed.

RESULTS

The maximum deformation and stress distribution for the mesial and distal tipping forces of 1.96 N were recorded as 0.137 µm and 10.60 MPa respectively. The stress concentration was more at the junction of the slot wall and the slot base. For mesial tipping,the deformation was more on the disto-incisal and mesio-gingival tie wings. Similarly, for distal tipping the deformation was more on the mesio-incisal and disto-gingival tie wings. The mid-tie wings showed minimal deformation during both distal and mesial tipping.

CONCLUSIONS

Our study visualized both the mesial and distal tipping forces induced stress distribution in the bracket tie wing-slot junctions. The deformation was present maximum in the mesio-incisal and disto-incisal tie wings and minimal in the mid-tie wings. Clinicians should be aware of this behavior of STWB in making decisions to alter the tipping forces in the archwire to compensate for the tie wing deformation in refining the teeth position.

Stress distribution analysis of oral mucosa under soft denture liners using smoothed particle hydrodynamics method

This study aims to simulate the stress distributions of oral mucosa under different soft denture liners using the smoothed particle hydrodynamics (SPH) method. The Young's modulus and viscosity of denture liners composed of silicone (Sofreliner Super Soft and Sofreliner Tough Medium, Tokuyama Dental), acrylic (Vertex Soft, Vertex Dental), and a tissue conditioner (Visco-gel, Dentsply Sirona) were measured using a creep meter. A numerical simulation model that represents the stress distribution of oral mucosa under soft denture liners was also developed using the SPH method. The oral mucosa was divided into four regions: A) buccal border, B) buccal shelf, C) crest of residual ridge, and D) lingual border. For each region, the von Mises stress (hereafter, referred to as "Mises stress") of the oral mucosa was calculated. Based on a creep test, Sofreliner Super Soft and Sofreliner Tough Medium silicone liners showed an elastic behavior, whereas Vertex Soft acrylic liner and Visco-gel tissue conditioner showed a viscoelastic behavior. In addition, Sofreliner Super Soft and Visco-gel exhibited a large strain. The numerical simulation revealed that the mean Mises stress was the highest in region A and lowest in region D. Vertex Soft acrylic liners resulted in a statistically lower Mises stress on the oral mucosa compared to the other three soft denture liners. Different soft denture liner materials lead to different stress distributions on the oral mucosa. The acrylic soft denture liners cause a lower Mises stress on the oral mucosa than the silicon soft denture liners. This suggests that acrylic soft denture liners would be more effective for manufacturing painless dentures than silicone soft denture liners.

Prediction of Stress Distribution Applied to the Triangular Fibrocartilage Complex: A Finite Element Analysis

Purpose

The triangular fibrocartilage complex (TFCC) is an important tissue stabilizer for the distal radioulnar joint, but stress distribution on the TFCC is not clear. The purpose of this study was to report the stress distribution of the TFCC using finite element analysis (FEA).

Methods

Pathological specimens of the wrist joint from an 80-year-old man were imported into a finite element analysis software package, and regions of interest including bone, soft tissue, and TFCC were extracted to create a 3-dimensional model. The material properties were obtained from previous research using cadaver specimens. To allow large deformations, we used hyperelastic elements to model the TFCC and soft tissue. Bone was defined as a uniform tissue that did not break. With the carpals and radius constrained, the rotation axis was set at the center of the ulnar head and a force was applied to move the ulnar head in pronation and supination. Under these boundary conditions, the behavior of the TFCC was extracted as a moving image. The average value of the maximum principal stress for each component of the TFCC was extracted and graphed.

Results

In the supinated position, the maximum principal stress was found on the palmar side of the TFCC (eg, on the tension side). In pronation, the maximum principal stress was found on the dorsal side.

Conclusions

This study clearly showed the 3-dimensional structure of the TFCC and analyzed its stress distribution under load. In supination, mean values of the maximum principal stress were greater on the palmar fibers than the dorsal fibers. In pronation, mean maximum principal stress was greater on the dorsal fibers than the palmar fibers.

Clinical relevance

Knowing the distribution of stresses in the TFCC is an important factor in developing treatment strategies for a pathologic TFCC.

Determination of stress distribution on periodontal ligament and alveolar bone by various tooth movements - A 3D FEM study

Aim

The purpose of this study was to evaluate the stress distribution on the maxillary central incisors by various tooth movements using three-dimensional finite element modeling with varying periodontal ligament (PDL) thickness and different alveolar bone height (at the apex and alveolar crest).

Material and methods

A Finite Element Modeling model was created using surface data of the tooth using SolidWorks Software. Different types of force (intrusion, extrusion, tipping, and bodily movement) were applied on the maxillary central incisor, with two different periodontal ligament thickness (0.15 mm and 0.24 mm) and alveolar bone height (at the apex and alveolar crest). Stress generated due to force applied due to different types of tooth movement was calculated and compared.

Results

Maximum stresses generated under intrusion, extrusion, tipping, bodily movement were 9.0421 E^-003 N/mm² for 0.15 mm pdl at alveolar bone, 7.2833 E^-5 N/mm²for 0.24 mm pdl labio-lingually, 9.1792 E^-002 N/mm² at 0.15 mm pdl at alveolar bone height and 6.2208 E^-6 N/mm² for 0.24 mm pdl at alveolar crest respectively.

Conclusion

The stress pattern seen was nearly the same in all the cases in both PDL thickness. The maximum stress pattern was found to be at the apex of the central incisor, reducing from apex to the cervical region. Intrusion, extrusion, and tipping movement showed the greatest amount of relative stress at the apex of the maxillary central incisor. The bodily movement produced forces at root apex and distributed it all over.

Stress influence on orthodontic system components under simulated treatment loadings

BACKGROUND AND OBJECTIVE

Mini-implants have been developed and effectively used by clinicians as anchorage for orthodontic tooth movement. The objective of this study was to elucidate the stress response of orthodontic forces on the periodontal system, bone tissues, mini-implant and the bracket-enamel interface.

METHODS

Computer tomography images of a commercially available mini-implant, an orthodontic bracket bonded to a central incisor, and jawbone section models were used to reconstruct three dimensional computer models. These models were exported and meshed in an ABAQUS^Ⓡ finite-element package. Material properties, multi-segment interactions, boundary and loading conditions were then applied to each component. Finite-element analyses were conducted to elucidate the effect of orthodontic force on the equivalent von Mises stress response within the simulated orthodontic system.

RESULTS

The highest stress values in the orthodontic system were predicted at the mini-implant neck, at the interface of the cortical bone, and gradually decreased in the internal apical direction of the miniscrew. On the alveolar bone, the maximum stress values were located in the alveolar cortical bone near the cervical areas of the mini-implant, which is in line with clinical findings of area where bone loss was found post orthodontic tooth treatment. Another peak of von Mises stress response was found in the enamel bracket junction with a maximum up to 186.05 MPa. To ensure good bonding between the enamel and bracket, it is vital to select carefully the type and amount of bonding materials used in the bracket-enamel interface to assure an appropriate load distribution between the teeth and alveolar bone. The results also revealed the significance of the periodontal ligaments, acting as an intermediate cushion element, in the load transfer mechanism.

CONCLUSIONS

This study is sought to identify the stress response in a simulated orthodontic system to minimize the failure rate of mini-implants and bracket loss during orthodontic treatment.

Finite Element Analysis of Stress Distribution in Flat and Elevated-Rim Polyethylene Acetabular Liners

Backgroud

No study has compared flat and elevated-rim polyethylene liners in terms of stress distribution on the bearing surface. The purpose of this study was to investigate the difference in stress distribution between flat and elevated-rim polyethylene liners.

Methods

A stress analysis was performed by using the 3-dimensional finite element method. The cup was placed at an open angle of 20°, the flat liner and the liner with a 10° elevation was placed at inclination angles of 80°, 70°, and 60°.

Results

Compared with the 60° flat liner, the 80° and 70° flat liners showed higher stress at the liner edge. In the elevated-rim liner, the stress was high at the liner edge along the cup edge. When the von Mises equivalent stress was applied to each element of the liner, the high stress area (volume) was the largest for the 80° flat liner, second largest for the 80° elevated-rim liner, and third largest for the 70° flat liner. The average contact pressure also followed the same order.

Conclusions

Elevated-rim liners affect the stress distribution by increasing the area of contact. However, since elevated-rim liners exhibit high stress at the cup edge, they are likely to result in new problems including liner failure. These findings could aid surgeons in the selection of liners and determination of revision methods such as isolated liner exchange vs. acetabular cup revision for a well-fixed metal cup with a higher inclination angle in revision total hip arthroplasty.

Ideal placement of an implant considering the positional relationship to an opposing tooth in the first molar region: a three-dimensional finite element analysis

Background

Excessive loading from the occlusion is known as a major pathological factor in implant failure. The force applied to the implant varies depending on the positional relationship to an opposing tooth in clinical cases. However, no studies have clarified the relationship between the discrepancy and mechanical complications.

Materials and methods

The study enrolled patients whose mandibular first molar was missing and was opposed by a natural maxillary first molar. The horizontal and vertical distance between the residual ridge and the occlusal surface of the maxillary first molar were measured from computerized tomograms. Subsequently, four finite element models were constructed in combinations of horizontal and vertical discrepancies. Additionally, the effect of inclined implantation and angled abutments were examined in a large clearance model. Maximum von Mises stress values generated in abutments under 90° or 60° loading vectors were compared with a three-dimensional finite element method.

Results

Data from 123 subjects (39 males and 84 females, average age 55.2 ± 11.4 (SD) years) were collected for the analyses. Under all conditions, the stress on the load side (the buccal side) was concentrated on the platform, and the stress on the opposite side (the lingual side) was concentrated on the top of the abutment tube inserted into the implant. In comparison to 90° loading vectors, the maximum von Mises stresses of each model were 1.20 to 2.67 times under 60° loading vectors. For inclined implantation, the maximum stress was 8.4% less at a 90° load and 9.7% less at a 60° load compared with vertical implantation. With angled abutments, the maximum stress was 15.7% less at a 90° load and 30.0% less at a 60° load compared with vertical implantation.

Conclusion

In cases of progressive alveolar resorption with a large clearance between the implant and the opposing teeth, a higher stress concentration was observed at the joint between the implant and the abutment. Our findings also showed that stress concentration around this area can be reduced by the use of inclined implantation and angled abutments under the condition of a horizontal offset between the implant and opposing teeth.

Numerical Three-dimensional Finite Element Modeling of Cavity Shape and Optimal Material Selection by Analysis of Stress Distribution on Class V Cavities of Mandibular Premolars

Aim:

Adhesive restoration does not depend primarily on the configuration of the shape of the cavity. Under varying loading conditions, it is essential to know the stress concentration and load transfer mechanism for distinct cavity shapes. The aim of this study was to evaluate and compare the biomechanical characteristics of various cavity shapes, namely oval, elliptical, trapezoidal, and rectangular shapes of class V cavities on mandibular premolars restored with amalgam, glass ionomer cement, and Cention N using three-dimensional (3D) finite element analysis.

Materials and Methods:

A 3D prototype of a mandibular premolar was generated by Digital Imaging and Communications in Medicine (DICOM) images obtained from the cone beam computed tomography and imported to 3D modeling software tool, SpaceClaim. The four distinct load magnitudes of 100, 150, 200, and 250N were applied as a pressure load perpendicular to the lingual plane of the lingual cusp of the occlusal surface (normal load) and at 45° to same (oblique load). The stress distribution patterns and the maximum von Mises stresses were analyzed and compared.

Results:

The occlusal stresses were distributed from the force loading point in an approximate actinomorphic pattern, and when the force load was close to the margin, the stress was much greater.

Conclusion:

Ovoid cavity showed lesser stress concentration and deformation for each of the tested restorative material.

Finite element analysis and experimental evaluation on stress distribution and sensitivity of dental implants to assess optimum length and thread pitch

BACKGROUND AND OBJECTIVE

The dental implant is one of the long term proper remedies to recover a missed tooth as a different prosthetic rehabilitation way. The finite element (FE) method and photoelasticity test are employed to achieve stress distribution and sensitivity in dental implants in order to obtain optimum length and thread pitch.

METHODS

The finite element method and experimental test are developed to evaluate stress distribution and sensitivity around dental implants. Three dimensional FE models of implant-abutment, cortical bone and cancellous bone are created by considering a variation of 0.6 to -1 mm on threads pitch while the implant lengths range from 8.5 mm to 13 mm. Then, axial and oblique forces are applied to the models to obtain the resultant stress contours.

RESULTS

The results indicate that the resultant von Mises stresses in the implant-abutment, cortical bones, and cancellous bones are different. The optimized setting for length and pitch is suggested according to maximum von Mises stress and sensitivity analysis.

CONCLUSIONS

It is concluded that the present FE model accurately predicts stress distribution pattern in dental implants. The results indicate that sensitivity of length play a more significant role in comparison with thread pitch. The accuracy of FEM results in comparison with those of the photoelasticity test recommends applying computation methods in medical practice as great potential in terms of future studies.

Traditional and bionic dynamic hip screw fixation for the treatment of intertrochanteric fracture: a finite element analysis

PURPOSE

The dynamic hip screw (DHS) is widely used for fixing intertrochanteric femur fractures. A porous bionic DHS was developed recently to avoid the stress concentration and risk of post-operative complications associated with titanium alloy DHSs. The purpose of this study was to compare the effects of traditional titanium alloy, bionic titanium alloy, and bionic magnesium alloy DHS fixation for treatment of intertrochanteric fractures using finite element analysis.

METHODS

A three-dimensional model of the proximal femur was established by human computed tomography images. An intertrochanteric fracture was created on the model, which was fixed using traditional and porous bionic DHS, respectively. The von Mises stress, maximum principal stress, and minimum principal stress were calculated to evaluate the effect of bone ingrowth on stress distribution of the proximal femur after fixation.

RESULTS

Stress concentration of the bionic DHS model was lower compared with traditional DHS fixation models. The von Mises stress, maximum principal stress, and minimum principal stress distributions of bionic magnesium alloy DHS models improved, along with simulation of the bone healing process and magnesium alloy degeneration, assumed to biodegrade completely 12 months post-operatively. The distribution of maximum principal stress in the secondary tension zone of the bionic DHS model was close to the intact bone. In the minimum principal stress, the region of minimum stress value less than - 10 MPa was significantly improved compared with traditional DHS models.

CONCLUSION

The bionic magnesium alloy DHS implant can improve the stress distribution of fractured bone close to that of intact bone while reducing the risk of post-operative complications associated with traditional internal fixations.

Effect of central retainer shape and abduction angle during preparation of teeth on dentin and cement layer stress distributions in endocrown-restored mandibular molars

To study the effect of central retainer shape and abduction angle during tooth preparation on stress distribution in endocrown-restored molars via finite element (FE) analysis, we constructed five FE models with different central retainer shapes and abduction angles. Under an oblique load, the distributions of maximum tensile stress in cervical dentin around the endocrown and on the cement layer, as well as maximum shear stress on the cement layer, were more balanced in the FE model in which the central retainer shape was generated based on the anatomical form of the pulp chamber. Moreover, there were no differences in stress distributions among FE models with different abduction angles. Therefore, the shape of the central retainer should be designed on the basis of the anatomical form of the pulp chamber; abduction angle during tooth preparation does not influence the repair effect of endocrown-restored mandibular molars.

Influence of Configuration on Stress Distribution of Pulmonary Monocusp Leaflet

PURPOSE

For the relief of right ventricular outflow tract obstruction in operative treatment of tetralogy of Fallot and other complex congenital heart diseases, transannular monocusp patch operations are often necessary to prevent right ventricular pressure overload and reduce pulmonary regurgitation. However, long-term durability of a monocusp leaflet is unsatisfactory, its failure is believed to be related to mechanical stress, whose distribution is primarily affected by geometric configurations. Therefore, the influence of several geometrical parameters on stress distribution of leaflet is investigated.

METHODS

Five parameters affecting leaflet configuration were established: angle between free edge of the leaflet and vessel wall, angle formed by the two end points of free edge, length of the free edge of the leaflet, height of the leaflet, and shape of elliptic conical surface constituting the leaflet surface. The first four parameters were fixed, and two factors were defined to describe the last parameter. Seven models with different values of these factors were analyzed using finite element method at the pressure of the pulmonary artery loaded on the leaflet.

RESULTS

The peak stresses of all models occurred at end points of the free edge of the leaflet (tear high-risk regions). The middle of leaflet had the greatest stress gradient and produced tissue wrinkling; this area could be the risk region of calcification. Both factors were noted to influence the stress distribution, and one of the factors could also relieve the wrinkling.

CONCLUSIONS

The leaflet of model (1.2_min) had the most even stress distribution and lowest peak principal stress, which was the optimal choice among all the models.

Effect of the restorative technique on load-bearing capacity, cusp deflection, and stress distribution of endodontically-treated premolars with MOD restoration

Objectives

To evaluate the influence of the restorative technique on the mechanical response of endodontically-treated upper premolars with mesio-occluso-distal (MOD) cavity.

Materials and Methods

Forty-eight premolars received MOD preparation (4 groups, n = 12) with different restorative techniques: glass ionomer cement + composite resin (the GIC group), a metallic post + composite resin (the MP group), a fiberglass post + composite resin (the FGP group), or no endodontic treatment + restoration with composite resin (the CR group). Cusp strain and load-bearing capacity were evaluated. One-way analysis of variance and the Tukey test were used with α = 5%. Finite element analysis (FEA) was used to calculate displacement and tensile stress for the teeth and restorations.

Results

MP showed the highest cusp (p = 0.027) deflection (24.28 ± 5.09 µm/µm), followed by FGP (20.61 ± 5.05 µm/µm), CR (17.72 ± 6.32 µm/µm), and GIC (17.62 ± 7.00 µm/µm). For load-bearing, CR (38.89 ± 3.24 N) showed the highest, followed by GIC (37.51 ± 6.69 N), FGP (29.80 ± 10.03 N), and MP (18.41 ± 4.15 N) (p = 0.001) value. FEA showed similar behavior in the restorations in all groups, while MP showed the highest stress concentration in the tooth and post.

Conclusions

There is no mechanical advantage in using intraradicular posts for endodontically-treated premolars requiring MOD restoration. Filling the pulp chamber with GIC and restoring the tooth with only CR showed the most promising results for cusp deflection, failure load, and stress distribution.