Potential dynamic corneal response parameters for myopia: relationships between axial length with whole eye movement at the first and second applanations and the highest concavity.

PURPOSE: To investigate the correlation between whole eye movement (WEM) parameters measured using Corvis ST and axial length (AL) to explore whether AL affects WEMs. METHODS: This single-center, cross-sectional study included data from healthy subjects and patients preparing for refractive surgery at the Qingdao Eye Hospital of Shandong First Medical University. Data were collected from July 2021 to April 2022. We first determined the correlations of WEMs at the time of corneal first applanation (A1_WEM), highest concavity (HC_WEM), and second applanation (A2_WEM), as well as the maximum value of WEM (WEM_Max) with AL. Subsequently, we established a series of regression models to analyze the relationships between different WEM values and AL. RESULTS: AL was negatively correlated with HC_WEM, A2_WEM, and WEM_Max (r = - 0.28, - 0.23, and - 0.22, respectively; P < 0.001). The correlation between AL and A1_WEM was not significant (P = 0.77). According to the adjusted regression models, AL was negatively associated with HC_WEM (Model 2: ß = -7.39, P < 0.001) and WEM_Max (Model 4: ß = -3.52, P = 0.02), while the associations of AL with A1_WEM (Model 1: P = 0.61) and A2_WEM (Model 3: P = 0.23) were not significant. CONCLUSIONS: AL is an independent negative influencing factor for HC_WEM. WEM is a potentially useful parameter that reflects the biomechanical properties of the eye behind the cornea in myopia.

Chemical Activation of Piezo1 Alters Biomechanical Behaviors toward Relaxation of Cultured Airway Smooth Muscle Cells.

Inspired by the well-known phenomenon of stretch-induced airway dilation in normal lungs and the emerging stretch-responsive Piezo1 channels that can be chemically activated by specific agonists such as Yoda1, we attempted to investigate whether chemical activation of Piezo1 by Yoda1 can modulate the biomechanical behaviors of airway smooth muscle cells (ASMCs) so that it may be exploited as a novel approach for bronchodilation. Thus, we treated in vitro cultured rat ASMCs with Yoda1, and examined the cells for calcium signaling, cell stiffness, traction force, cell migration, and the mRNA expression and distribution of molecules relevant to cell biomechanics. The data show that ASMCs expressed abundant mRNA of Piezo1. ASMCs exposed to 1 µM Yoda1 exhibited a potent but transient Ca2+ signaling, and treatment with 1 µM Yoda1 for 24 h led to decreased cell stiffness and traction force, all of which were partially reversed by Piezo1 inhibitor GsMTx4 and Piezo1 knockdown, respectively. In addition, ASMCs treated with 1 µM Yoda1 for 24 h exhibited impaired horizontal but enhanced vertical cell migration, as well as significant changes in key components of cells' contractile machinery including the structure and distribution of stress fibers and alpha-smooth muscle actin (α-SMA) fibrils, the mRNA expression of molecules associated with cell biomechanics. These results provide the first evidence that chemical activation of Piezo1 by Yoda1 resulted in marked pro-relaxation alterations of biomechanical behaviors and contractile machinery of the ASMCs. These findings suggest that Piezo1-specific agonists may indeed have great potential as alternative drug agents for relaxing ASMCs.

The role of the extracellular matrix in the development of heart valve disease: Underestimation or undercomprehension?

The function of metalloproteinases of the extracellular matrix and their inhibitors has emerged with a crucial role in valve diseases. Both the expression of matrix metalloproteinases and their inhibitors are susceptible to modification in patients with severe mitral insufficiency. This process is due to substantial changes in the collagen structure during mechanical stress on the mitral valve leaflets. Several studies have measured the level of deformation of the mitral leaflets with the use of the finite element analysis method by establishing the stiffness of the cellular and extracellular elements of the mitral valve leaflets. Evidence suggested the possible underestimation of the stiffness of the leaflets. This implies greater stress on the components of the extracellular matrix in the circumferential and radial strains that involve the mitral leaflets during chronic regurgitation. The remodeling process during mechanical stress phenomena involves both the cellular compartment and the extracellular matrix and can be adaptive or maladaptive as showed in patients who receive a pulmonary autograft to replace the diseased aortic valve. However, adaptive remodeling can be driven using resorbable polymers that interfere with the extracellular matrix. Further investigation is required for the understanding of the mechanisms that determine the structural changes of the extracellular matrix and to prevent them.

A Systematic Study of Restorative Crown-Materials Combinations for Dental Implants: Characterization of Mechanical Properties under Dynamic Loads.

This study aimed to find the optimum mechanical characteristics of the restorative materials for the manufacture of implant crowns subjected to impact loading when different combinations of materials are used for the inner and outer crown. Several combinations of external-internal crown restorative materials were analyzed. The dynamic stresses at eight different zones of a dental implant subjected to an impact load and the influence of several mechanical properties, such as the Young's modulus, Poisson's ratio, density, and initial velocity, were analyzed and compared. A detailed 3D model was created, including the crown, the retention screw, the implant, and a mandible section. The model was then built by importing the 3D geometries from CAD software. The whole 3D model was carefully created in order to guarantee a finite element mesh that produced results adjusted to physical reality. Then, we conducted a numerical simulation using the finite element method (FEM). The results of the FEM analysis allowed for evaluating the effect that different combinations of restorative materials and mechanical properties had on the stress distribution in various regions of the implant. The choice of restorative material is a factor to be considered in order to preserve the integrity of osseointegration. Restorative materials transfer more or less stress to the dental implant and surrounding bone, depending on their stiffness. Therefore, an inadequate Young's modulus of the rehabilitation material can affect the survival of the implant over time. Eight interactive graphics were provided on a web-based surface platform to help clinical dentists, researchers, and manufacturers to select the best restorative materials combination for the crown.

Assessment of Biomechanical Behavior of Endodontically Treated Premolar Teeth Restored with Novel Endocrown System.

OBJECTIVE: Despite the increased popularity of endocrowns, there is no clear consensus considering their effectiveness to restore severely-destructed endodontically treated premolars. This study aimed to assess the biomechanical behavior of endodontically treated maxillary first premolars restored with a novel endocrown system compared to the conventional one. MATERIALS AND METHODS: Twenty sound human maxillary first premolars were collected. After endodontic treatment, they were divided into 2 groups (n=10) according to the system used for endocrown fabrication. Group C (Control): conventional monolithic IPS e.max CAD endocrowns. Group P: novel bi-layered endocrowns (Pekkton ivory coping veneered with cemented IPS e.max CAD). All specimens were subjected to 10000 thermal cycles followed by 240000 dynamic load cycles. Surviving specimens were subjected to fracture resistance test followed by qualitative analysis using Stereomicroscopy and Scanning Electron Microscopy. RESULTS: A significantly higher load was observed for Group P (1831.37 ± 240.69 N) than Group C (1433.47 ± 174.39 N) (p ⟨ 0.001). A statistically significant difference was observed considering the failure mode (p = 0.036), with more favorable fractures detected with Group P. CONCLUSIONS: The tested novel endocrown system improved the biomechanical behavior of the tooth/ restoration complex in the restored endodontically treated maxillary first premolars. CLINICAL SIGNIFICANCE: The tested novel endocrown system with a PEKK coping veneered with cemented IPS e.max CAD can be considered a promising option for restoration of severely-destructed endodontically treated premolar teeth. It can be considered as a conservative alternative option to the conventional treatment modalities.

Biomechanical Assessment of Restored Mandibular Molar by Endocrown in Comparison to a Glass Fiber Post-Retained Conventional Crown: 3D Finite Element Analysis.

PURPOSE: To compare equivalent and contact stresses in a mandibular molar restored by all-ceramic crowns through two methods: ceramic endocrowns and ceramic crowns supported by fiber-reinforced composite (FRC) posts and core, by using 3D finite element analysis during normal masticatory load. MATERIALS AND METHODS: Three 3D models of a mandibular first molar were made and labeled as such: intact molar with no restoration (A); ceramic endocrown-restored molar (B); ceramic crown supported by FRC posts and core restored molar (C). By using 3D FE analysis with contact components, normal masticatory load was simulated. The mvM stresses in all models were calculated. Maximal mvM stresses in the ceramic of restorations, dentin, and luting cement were contrasted among models and to values of materials' strength. Contact shear and tensile stresses in the restoration/tooth interface around restorations were also calculated. RESULTS: The highest mvM stress levels in the enamel and dentin for the tooth restored by ceramic endocrown were lower in the crown ceramic than in tooth restored with FRC posts and all-ceramic crowns; however, in the resin adhesive cement interface it was lower for ceramic crown supported by FRC posts than the in ceramic endocrown restoration. The maximum contact shear and tensile stress values along the restoration/tooth interface of ceramic endocrowns were lower than those with ceramic crowns supported by FRC posts. CONCLUSIONS: Ceramic endocrown restorations presented a lower mvM stress level in dentin than the conventional ceramic crowns supported by FRC posts and core. Ceramic endocrown restorations in molars are less susceptible to damage than those with conventional ceramic crowns retained by FRC posts. Ceramic endocrowns properly cemented in molars must not be fractured or loosen during normal masticatory load. Therefore, ceramic endocrowns are advised as practicable, minimally invasive, and esthetic restorations for root canal treated mandibular molars.

Evaluation of the relationship of corneal biomechanical metrics with physical intraocular pressure and central corneal thickness in ex vivo rabbit eye globes.

The relationship of corneal biomechanical metrics provided by the Ocular Response Analyzer (ORA) and Corvis ST (CVS) with physical intraocular pressure (IOPp) and central corneal thickness (CCT) was evaluated. Thirty fresh enucleated eyes of 30 rabbits were used in ex vivo whole globe inflation experiments. IOPp was measured with a pressure transducer and increased from 7.5 to 37.5 mmHg in steps of 7.5 mmHg while biomechanical data was acquired using the ORA and CVS. At least 3 examinations were performed at each pressure level, where CCT and twelve biomechanical metrics were recorded and analyzed as a function of IOPp. The biomechanical metrics included corneal hysteresis (CH) and corneal resistance factor (CRF), obtained by the ORA. They also included the applanation times (A1T, A2T), lengths (A1L, A2L) and velocities (A1V, A2V), in addition to the highest concavity time (HCT), peak distance (PD), radius (HR) and deformation amplitude (DA), obtained by the CVS. The variation of CCT and the twelve biomechanical metrics for the 30 rabbit eyes tested across the 5 pressure stages considered (inter-pressure differences) were statistically significant (P = 0.00). IOPp was highly to moderately correlated with most biomechanical metrics, especially CRF, A1T, A1V, A2V, PD and DA, while the relationships with CH, A2T, A1L and HCT were poor. IOP has important influences on most corneal biomechanical metrics provided by CVS and ORA. Two biomechanical metrics A1V and HR were influenced by CCT after correcting for the effect of IOP in most pressure stages, while the correlation with others were weak. Comparisons of research groups based on ORA and CVS with different IOPs and CCTs may lead to possible misinterpretations if both or one of which are not considered in the analysis.

Biomechanical characterization of the central fibrous region of the forearm interosseous Membrane: Implications for finite element modeling.

The interosseous membrane (IOM) of the forearm plays a crucial role in facilitating forearm function and mechanical load transmission between the radius and ulna. Accurate characterization of its biomechanical properties is essential for developing realistic finite element models of the forearm. This study aimed to investigate the mechanical behavior and material properties of the central fibrous regions of the IOM using fresh frozen cadavers. Ten forearms from five cadavers were dissected, preserving the IOM and identifying the distal accessory band (DAB), central band (CB), and proximal accessory band (PAB). Bone-ligament-bone specimens were prepared and subjected to uniaxial tensile testing, with the loading direction aligned with the fiber orientation. Force-displacement curves were obtained and converted to force-strain and stress-strain curves using premeasured fiber lengths and cross-sectional areas. The results demonstrated distinct mechanical responses among the IOM regions, with the PAB exhibiting significantly lower force-strain behavior compared to the DAB and CB. The derived force-strain and stress-strain relationships provide valuable insights into the regional variations in stiffness and strength of the IOM, highlighting the importance of considering these differences when modeling the IOM in finite element analysis. In conclusion, this study establishes a foundation for the development of advanced finite element models of the forearm that accurately capture the biomechanical behavior of the IOM.

Investigation of the effects of graded models on the biomechanical behavior of a bone-dental implant system under osteoporotic conditions.

OBJECTIVE: To investigate the effects of graded models on the biomechanical behavior of a bone-implant system under osteoporotic conditions. Methodology : A finite element model (FEM) of the jawbone segments with a titanium implant is used. Two types of models (a graded model and a non-graded model) are established. The graded model is established based on the graded variation of the elastic modulus of the cortical bone and the non-graded model is defined by homogeneous cortical bone. The vertical and oblique loads are adopted. The max von Mises stresses and the max displacements of the cortical bone are evaluated. RESULTS: Comparing the two types of models, the difference in the maximum von Mises stresses of the cortical bone is more than 20%. The values of the maximum displacements in the graded models are considerably less than in the non-graded models. CONCLUSIONS: These results indicate the significance of taking into account the actual graded properties of the cortical bone so that the biomechanical behavior of the bone-implant system can be analyzed accurately.

Optimization of stress distribution of bone-implant interface (BII).

Many studies have found that the threshold of occlusal force tolerated by titanium-based implants is significantly lower than that of natural teeth due to differences in biomechanical mechanisms. Therefore, implants are considered to be susceptible to occlusal trauma. In clinical practice, many implants have shown satisfactory biocompatibility, but the balance between biomechanics and biofunction remains a huge clinical challenge. This paper comprehensively analyzes and summarizes various stress distribution optimization methods to explore strategies for improving the resistance of the implants to adverse stress. Improving stress resistance reduces occlusal trauma and shortens the gap between implants and natural teeth in occlusal function. The study found that: 1) specific implant-abutment connection design can change the force transfer efficiency and force conduction direction of the load at the BII; 2) reasonable implant surface structure and morphological character design can promote osseointegration, maintain alveolar bone height, and reduce the maximum effective stress at the BII; and 3) the elastic modulus of implants matched to surrounding bone tissue can reduce the stress shielding, resulting in a more uniform stress distribution at the BII. This study concluded that the core BII stress distribution optimization lies in increasing the stress distribution area and reducing the local stress peak value at the BII. This improves the biomechanical adaptability of the implants, increasing their long-term survival rate.

Influence of plate size and screw distribution on the biomechanical behaviour of osteosynthesis by means of lateral plates in femoral fractures.

Distal femoral fractures are fractures associated with high rates of morbidity and mortality, affecting to three different groups of individuals: younger people suffering high-energy trauma, elderly people with fragile bones and people with periprosthetic fractures around previous total knee arthroplasty. They have been classically treated with conventional plates and intramedullary nails and more recently with locked plates that have increased their indications to more types of fractures. The main objective of the present work is the biomechanical study, by means of finite element simulation, of the stability achieved in the osteosynthesis of femoral fractures in zones 4 and 5 of Wiss, by using locked plates with different plate lengths and different screw configurations, and analysing the effect of screw proximity to the fracture site. A three dimensional (3D) finite element model of the femur from 55-year-old male donor was developed, and then a stability analysis was performed for the fixation provided by Osteosynthesis System LOQTEC® Lateral Distal Femur Plate in two different fracture zones corresponding to the zones 4 and 5 according to the Wiss fracture classification. The study was focused on the immediately post-operative stage, without any biological healing process. The obtained results show that more stable osteosyntheses were obtained by using shorter plates. In the cases of longer plates, it results more convenient disposing screws in a way that the upper ones are closer to fracture site. The obtained results can support surgeons to understand the biomechanics of fracture stability, and then to guide them towards the more appropriate osteosynthesis depending on the fracture type and location.

Biomechanical behavior of the three-dimensionally printed surgical plates for mandibular defect reconstruction: a finite element analysis.

The aim of the study was to investigate the biomechanical behavior of three-dimensionally (3D)-printed surgical plates used for mandibular defect reconstruction, compare them with conventional surgical plates, and provide experimental evidence for their clinical application. Three-dimensional models were created for the normal mandible and for mandibular body defects reconstructed using free fibula and deep circumflex iliac artery flaps. Three-dimensional finite element models of reconstructed mandibles fixed using 3D-printed and conventional surgical plates were established. Vertical occlusal forces were applied to the remaining teeth and the displacement and Von Mises stress distributions were studied using finite element analysis. The normal and reconstructed mandibles had similar biomechanical behaviors. The displacement distributions for the surgical plates were similar, and the maximum total deformation occurred at the screw hole of the anterior segment of the surgical plates. However, there were differences in the Von Mises stress distributions for the surgical plates. In reconstructed mandibles fixed using 3D-printed surgical plates, the maximum equivalent Von Mises stress occurred at the screw hole of the posterior segment, while in those fixed using conventional surgical plates, the maximum equivalent Von Mises stress was at the screw hole of the anterior segment. In the mandible models reconstructed with the same free flap but fixed with different surgical plates, the plates had similar biomechanical behaviors. The biomechanical behavior of 3D-printed surgical plates was similar to conventional surgical plates, suggesting that 3D-printed surgical plates used to reconstruct mandibular body defects with vascularized autogenous bone grafts could lead to secure and stable fixation.

A Computer Method for Pronation-Supination Assessment in Parkinson's Disease Based on Latent Space Representations of Biomechanical Indicators.

One problem in the quantitative assessment of biomechanical impairments in Parkinson's disease patients is the need for scalable and adaptable computing systems. This work presents a computational method that can be used for motor evaluations of pronation-supination hand movements, as described in item 3.6 of the Unified Parkinson's Disease Rating Scale (MDS-UPDRS). The presented method can quickly adapt to new expert knowledge and includes new features that use a self-supervised training approach. The work uses wearable sensors for biomechanical measurements. We tested a machine-learning model on a dataset of 228 records with 20 indicators from 57 PD patients and eight healthy control subjects. The test dataset's experimental results show that the method's precision rates for the pronation and supination classification task achieved up to 89% accuracy, and the F1-scores were higher than 88% in most categories. The scores present a root mean squared error of 0.28 when compared to expert clinician scores. The paper provides detailed results for pronation-supination hand movement evaluations using a new analysis method when compared to the other methods mentioned in the literature. Furthermore, the proposal consists of a scalable and adaptable model that includes expert knowledge and affectations not covered in the MDS-UPDRS for a more in-depth evaluation.

The influence of the combined impairments and apical mesh surgery on the biomechanical behavior of the pelvic floor system.

Objective: The prolapse mechanism of multifactorial impairment of the female pelvic floor system and the mechanics of the pelvic floor after apical suspension surgery are not yet understood, so we developed biomechanical models of the pelvic floor for the normal physiological state (0°) and 90° pathological state. Methods: Under different types and levels of the impairments and uterosacral suspensions, the possible changes in the morphometric characteristics and the mechanical characteristics of suspension and support functions were simulated based on the biomechanical models of the pelvic floor. Results: After the combined impairments, the descending displacement of the pelvic floor cervix and the stress and displacement of the perineal body reached maximum values. After surgical mesh implantation, the stresses of the normal pelvic floor were concentrated on the uterine fundus, cervix, and top of the bladder and the stresses of the 90° pathological state pelvic floor were concentrated on the uterine fundus, uterine body, cervix, middle of the posterior vaginal wall, and bottom of the perineal body. Conclusion: After the combined impairments, the biomechanical support of the bladder and sacrococcyx in the anterior (0°) and 90° pathological state pelvic floor system is diminished, the anterior vaginal wall dislodges from the external vaginal opening, and the posterior vaginal wall forms "kneeling" profiles. The pelvic floor system may evolve with a tendency toward the cervical prolapse with anterior and posterior vaginal wall prolapse and eventually prolapse. After surgical mesh implantation, the cervical position can be better restored; however, the load of combined impairment of the pelvic floor is mainly borne by the surgical mesh suspension, the biomechanical support function of pelvic floor organs and sacrococcyx was not repaired by the physiological structure, and the results of uterosacral suspension alone may be poor.

Mechanical behavior of infrapatellar fat pad of patients affected by osteoarthritis.

The infrapatellar fat pad (IFP) is an adipose tissue present in the knee that lies between the patella, femur, meniscus and tibia, filling the space between these structures. IFP facilitates the distribution of the synovial fluid and may act to absorb impulsive actions generated through the joint. IFP in osteoarthritis (OA) pathology undergoes structural changes characterized by inflammation, hypertrophy and fibrosis. The aim of the present study is to analyze the mechanical behavior of the IFP in patients affected by end-stage OA. A specific test fixture was designed and indentation tests were performed on IFP specimens harvested from OA patients who underwent total knee arthroplasty. Experiments allowed to assess the typical features of mechanical response, such as non-linear stress-strain behavior and time-dependent effects. Results from mechanical experimentations were implemented within the framework of a visco-hyperelastic constitutive theory, with the aim to provide data for computational modelling of OA IFP role in knee mechanics. Initial and final indentation stiffness were calculated for all subjects and statistical results reveled that OA IFP mechanics was not significantly influenced by gender, BMI and sample preparation. OA IFP mechanical behavior was also compared to that of other adipose tissues. OA IFP appeared to be a stiffer adipose tissue compared to subcutaneous, visceral adipose tissues and heel fat pads. It is reasonable that fibrosis induces a modification of the tissue destabilizing the normal distribution of forces in the joint during movement, causing a worsening of the disease.

Effect of Different Protection on Lateral Ankle during Landing: An Instantaneous Impact Analysis.

Ankle sprain is the most common injury during parachute landing. The biomechanical behavior of the tissues can help us understand the injury mechanism of ankle inversion. To accurately describe the injury mechanism of tissues and assess the effect of ankle protection, a stable time of landing was obtained through the dynamic stability test. It was used for the boundary condition of the foot finite element (FE). The FE model was provided a static load equal to half of the bodyweight applied at the distal tibia and fibula; a foot-boot-brace FE model was established to simulate the landing of subjects on an inversion inclined platform of 0-20°, including non-, external, and elastic ankle braces. Compared with the non-ankle brace, both the external and elastic ankle braces decreased the peak strains of the cal-fibular, anterior Ta-fibular, and posterior Ta-fibular ligaments (15.2-33.0%), and of the peak stress of the fibula (15.2-24.5%). For the strain decrement of the aforementioned ligaments, the elastic brace performed better than the external ankle brace under the inversion of the 10° condition. The peak stress of the fibula (15.6 MPa) decreased up to 24.5% with an elastic brace and 5.6-10.3% with an external brace. The findings suggested that the behaviors of lateral ankle ligaments and fibula were meaningful for the functional ability of the ankle. This provides some suggestions regarding the optimal design of ankle protection.

The biomechanical effect of root amputation and degree of furcation involvement on intracoronally splinted upper molar teeth - An in vitro study.

OBJECTIVES: The aim of this study was to evaluate the effect of the amount of periodontal support and the presence or absence of root amputation on the fracture resistance of intracoronally splinted maxillary molar teeth. MATERIALS AND METHODS: 48 extracted human upper first molars and 48 s premolars were included in the study. All teeth underwent standard mesio-occluso-distal (MOD) (molars) and standard occluso-distal (OD) (premolars) cavity preparation. After the preparation, all molars were root canal treated, and 48 molar-premolar units were created by intracoronal splinting. The units were randomly divided into 4 groups (Groups A-D, 12 units per group): in Groups C and D, the disto-buccal (DB) roots of the molars were amputated, while in Groups A and B, no root amputation was performed. All units were embedded in methacrylate resin at different levels: in Groups A and C, at 4 mm apically from the cemento-enamel junction (CEJ), while in Groups B and D, at 6 mm apically from the CEJ, mimicking the different stages of furcation involvement. All units were submitted first to dynamic and then to static, load-to-fracture mechanical testing. Fracture resistance values were recorded fracture mode was analysed. RESULTS: During the load-to-facture test, Groups A and B (without root amputation) were characterized by significantly higher fracture resistance values compared to Groups C and D (with root amputation) (p < 0.05). Regarding fracture mode, irreparable fracture was more frequent in Group D (with root amputation and advanced furcation involvement) than in any other group (n = 8). CONCLUSIONS: Root amputation has a negative effect on the fracture resistance of intracoronally splinted upper first molar-second premolar units with modeled furcation involvement.

Biomechanical Behavior and Life Span of Maxillary Molar According to the Access Preparation and Pericervical Dentin Preservation: Finite Element Analysis.

INTRODUCTION: This study investigated the significance of pericervical dentin after coronal canal flaring on the biomechanical behavior and life span of a maxillary molar using finite element analysis (FEA). METHODS: In addition to the intact tooth (IT) model, 4 experimental FE models were designed: conservative access cavity model (CON), and 3 models with different radicular preparations for the coronal 4 mL considering 3 instruments: ProTaper SX model (SX), OneFlare model (OF), and Gates-Glidden model (GG). Cyclic loading of 50 N was applied on the occlusal surface and number of cycles until failure (NCF) was compared with the IT model. Mathematical analysis was done to evaluate the stress distribution patterns and calculated maximum von Mises (VM) and maximum principal stresses. RESULTS: Access cavity preparation (CON) decreased NCF significantly when compared with the IT model (93.99%). The coronal preparation of the root canal did not have a significant effect even when the preparation was taken to the extreme (GG: 92.02%). VM analysis confirmed apical dispersion of stresses, with maximum value registered on the occlusal surface in the GG model (7.88 MPa), and minimum on the IT model (7.01 MPa). The furcation area showed higher maximum principal stresses, yet stress values remained minimal and distributed over larger surfaces with the progressive enlargement among models. CONCLUSIONS: Within the limitations of this study, coronal canal flaring affects tooth integrity minimally, and when loading conditions lie within normal functional ranges, tooth structure has the capacity to disperse increasing stresses over a wider surface area.

Mechanical characterization and material modeling of ascending aortic aneurysm with different bicuspid aortic cusp fusion morphologies.

Bicuspid aortic valve (BAV) is frequently associated with ascending thoracic aortic aneurysm (ATAA). Impact of cusp fusion patterns on biomechanics and microstructure of the ATAA remains unknown. This study aims to investigate biaxial mechanical properties of the ATAAs with right-left (RL) and right-noncoronary (RN) cusp fusion patterns. Fresh ATAA samples (n = 26) were obtained from patients who underwent surgical aneurysm repair. Biaxial extension tests were performed to characterize mechanical behaviors of the RL and RN BAV-ATAAs. A material model was fitted to biaxial experimental data to obtain model parameters. Histological and mass fraction analyses were employed to investigate the underlying microstructure and dry weight percentages of elastin and collagen in the ATAA tissue. The RL and RN BAV-ATAAs exhibited nonlinear and anisotropic mechanical responses to biaxial loading. Tissue stiffness of the RN BAV-ATAAs was significantly higher than that of the RL BAV-ATAAs in the circumferential (2679 ± 755 vs 1942 ± 578 kPa, mean ± SD, p = 0.04) and longitudinal (2535 ± 630 vs 1709 ± 512 kPa, mean ± SD, p = 0.02) directions under the equibiaxial stresses. Laminar structure of elastic fibers was disrupted in both RL and RN BAV-ATAAs. Notably, interstitial fibrosis and thinner elastic fibers were identified in the RN BAV-ATAAs. Mass fraction of collagen was significantly higher for the RN BAV-ATAAs than that of the RL BAV-ATAAs. The tissue stiffness in the circumferential direction was significantly increased and strongly correlated with the mass fractions of collagen for both RL and RN BAV-ATAAs. Our results suggest that elastic properties of the RN BAV-ATAAs are more deteriorated than those of the RL BAV-ATAAs. Changes in biomechanical properties may have great impact on ascending aortic dilation.

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.