STATEMENT OF PROBLEM: Accurate implant placement is essential for the success of dental implants. This placement influences osseointegration and occlusal forces. The freehand technique, despite its cost-effectiveness and time efficiency, may result in significant angular deviations compared with guided implantation, but the effect of angular deviations on the stress-strain state of peri-implant bone is unclear. PURPOSE: The purpose of this finite element analysis (FEA) study was to examine the effects of angular deviations on stress-strain states in peri-implant bone. MATERIAL AND METHODS: Computational modeling was used to investigate 4 different configurations of dental implant positions, each with 3 angles of insertion. The model was developed using computed tomography images, and typical mastication forces were considered. Strains were analyzed using the mechanostat hypothesis. RESULTS: The location of the implant had a significant impact on bone strain intensity. An angular deviation of ±5 degrees from the planned inclination did not significantly affect cancellous bone strains, which primarily support the implant. However, it had a substantial effect on strains in the cortical bone near the implant. Such deviations also significantly influenced implant stresses, especially when the support from the cortical bone was uneven or poorly localized. CONCLUSIONS: In extreme situations, angular deviations can lead to overstraining the cortical bone, risking implant failure from unfavorable interaction with the implant. Accurate implant placement is essential to mitigate these risks.

• MeSH
• Finite Element Analysis MeSH
• Dental Stress Analysis methods   MeSH
• Biomechanical Phenomena MeSH
• Mandible diagnostic imaging   MeSH
• Stress, Mechanical MeSH
• Dental Implants * MeSH
• Publication type
• Journal Article MeSH

This study investigates the risk of head injuries, specifically concussions, from falling objects in workplace accidents. A case study focuses on a construction worker who sustained a head injury despite wearing a protective helmet. Utilizing finite element (FE) analysis, the helmet-head system was modeled to assess impact forces and head accelerations. The helmet, made of High-Density Polyethylene with a 6-point suspension system, was tested against falling objects of 332 g and 665 g. Simulations, conducted from heights of 5 to 25 m, revealed that objects weighing as little as 332 g could cause severe concussions from a 10-meter fall. These findings demonstrate that helmets, while mitigating some impact, absorb significantly less energy than the kinetic energy of falling objects. The analyses carried out confirmed the worker's statement that his injury was caused by a foreign object falling on his head, which was protected by a helmet.

• MeSH
• Finite Element Analysis MeSH
• Biomechanical Phenomena MeSH
• Brain Concussion * prevention & control   MeSH
• Humans MeSH
• Accidents, Occupational * prevention & control   MeSH
• Head Protective Devices * MeSH
• Accidental Falls * prevention & control   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Case Reports MeSH

BACKGROUND: Total knee arthroplasty (TKA) with all-polyethylene tibial (APT) components has shown comparable survivorship and clinical outcomes to that with metal-backed tibial (MBT). Although MBT is more frequently implanted, APT equivalents are considered a low-cost variant for elderly patients. A biomechanical analysis was assumed to be suitable to compare the response of the periprosthetic tibia after implantation of TKA NexGen APT and MBT equivalent. METHODS: A standardised load model was used representing the highest load achieved during level walking. The geometry and material models were created using computed tomography data. In the analysis, a material model was created that represents a patient with osteopenia. RESULTS: The equivalent strain distribution in the models of cancellous bone with an APT component showed values above 1000 με in the area below the medial tibial section, with MBT component were primarily localised in the stem tip area. For APT variants, the microstrain values in more than 80% of the volume were in the range from 300 to 1500 με, MBT only in less than 64% of the volume. CONCLUSION: The effect of APT implantation on the periprosthetic tibia was shown as equal or even superior to that of MBT despite maximum strain values occurring in different locations. On the basis of the strain distribution, the state of the bone tissue was analysed to determine whether bone tissue remodelling or remodelling would occur. Following clinical validation, outcomes could eventually modify the implant selection criteria and lead to more frequent implantation of APT components.

• MeSH
• Finite Element Analysis MeSH
• Metals MeSH
• Humans MeSH
• Polyethylene MeSH
• Prosthesis Design MeSH
• Knee Prosthesis * MeSH
• Aged MeSH
• Tibia diagnostic imaging   surgery   MeSH
• Arthroplasty, Replacement, Knee * MeSH
• Check Tag
• Humans MeSH
• Aged MeSH
• Publication type
• Journal Article MeSH

We present comprehensive biomechanical analyses of abdominal aortic aneurysms (AAA) for 43 patients. We compare stress magnitudes and stress distributions within arterial walls of abdominal aortic aneurysms (AAA) obtained using two simulation and modelling methods: (a) Fully automated and computationally very efficient linear method embedded in the software platform Biomechanics based Prediction of Aneurysm Rupture Risk (BioPARR), freely available from https://bioparr.mech.uwa.edu.au/; (b) More complex and much more computationally demanding Non-Linear Iterative Stress Analysis (Non-LISA) that uses a non-linear inverse iterative approach and strongly non-linear material model. Both methods predicted localised high stress zones with over 90% of AAA model volume fraction subjected to stress below 20% of the 99th percentile maximum principal stress. However, for the non-linear iterative method, the peak maximum principal stress (and 99th percentile maximum principal stress) was higher and the stress magnitude in the low stress area lower than for the automated linear method embedded in BioPARR. Differences between the stress distributions obtained using the two methods tended to be particularly pronounced in the areas where the AAA curvature was large. Performance of the selected characteristic features of the stress fields (we used 99th percentile maximum principal stress) obtained using BioPARR and Non-LISA in distinguishing between the AAAs that would rupture and remain intact was for practical purposes the same for both methods.

• MeSH
• Finite Element Analysis MeSH
• Aortic Aneurysm, Abdominal * MeSH
• Aorta, Abdominal MeSH
• Biomechanical Phenomena MeSH
• Humans MeSH
• Stress, Mechanical MeSH
• Models, Cardiovascular MeSH
• Aortic Rupture * MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH

Biomechanical performance plays an important role in the long-term service of dental implants. Loosening and fatigue damage of the central screw are the most common problems. This research investigated the effect of the central screw taper angle on the loosening performance and fatigue characteristics of dental implants. Central screws with four taper angles, 30°, 60°, 90° and 180°, were processed and tested. The loosening performance of the screws under initial and postload conditions was compared. Then, the fatigue characteristics of dental implants was measured. Finally, the wear and fracture modes of the screws were observed. The damage locations were verified by finite element analysis (FEA). The results showed that the central screws with 30° taper had substantially better anti-loosening performance and less fretting wear. The central screws with 180° taper had a higher preload, resulting in a longer fatigue life. Furthermore, the fatigue fracture of the central screw occurred at the level of the first thread position, consistent with the FEA results. In the future clinical applications, central screws with a 30° taper angle may improve anti-loosening performance and prolong fatigue life by increasing the tightening torque.

• MeSH
• Finite Element Analysis MeSH
• Dental Stress Analysis MeSH
• Bone Screws MeSH
• Torque MeSH
• Dental Implants * MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH

The vertex has been used as a suitable control stimulation site in repetitive transcranial magnetic stimulation studies. The objectives of this study are (1) to assess cognitive performance (CP) after theta burst stimulation (TBS); (2) to evaluate whether clinically relevant cortical areas might be reached by vertex stimulation and how that might influence CP. Twenty young healthy subjects performed a cognitive task prior to and immediately after intermittent TBS (iTBS) and continuous TBS (cTBS) of two active cortical stimulation sites and the vertex. We used the Wilcoxon signed-rank test to compare the pre- and post-stimulation reaction times (RTs) and a mixed ANOVA analysis to evaluate the effect of the stimulation on changes in RTs. A three-dimensional finite-element model (FEM) was used to calculate the vertex TBS-induced electrical field (E-field) in the adjacent regions of interest (ROIs). Correlation analyses were performed between E-fields in the ROIs and cognitive outcomes. We found a significant effect only of the stimulation time factor (F (1,12) = 65.37, p < 0.001) on RT shortening, with no superiority of the active site stimulation compared to the vertex stimulation. In 73.5% of vertex TBS sessions, a significant E-field was induced in at least one ROI. We found a negative association between the magnitude of the iTBS-induced E-fields and RT changes (R = - 0.54, p = 0.04). TBS protocols may lead to changes in CP when applied over the craniometrically targeted vertex. We therefore suggest not using a conventional approach as a vertex targeting method.

• MeSH
• Head * MeSH
• Humans MeSH
• Reaction Time MeSH
• Theta Rhythm MeSH
• Transcranial Magnetic Stimulation * methods   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH

BACKGROUND AND OBJECTIVE: Estimating patient specific annual risk of rupture of abdominal aortic aneurysm (AAA) is currently based only on population. More accurate knowledge based on patient specific data would allow surgical treatment of only those AAAs with significant risk of rupture. This would be beneficial for both patients and health care system. METHODS: A methodology for estimating annual risk of rupture (EARR) of abdominal aortic aneurysms (AAA) that utilizes Bayesian statistics, mechanics and patient-specific blood pressure monitoring data is proposed. EARR estimation takes into consideration, peak wall stress in AAA computed by patient-specific finite element modeling, the probability distributions of wall thickness, wall strength, systolic blood pressure and the period of time that the patient is known to have already survived with the intact AAA. Initial testing of proposed approach was performed on fifteen patients with intact AAA (mean maximal diameter 51mm±8mm). They were equipped with a pressure holter and their blood pressure was recorded over 24 hours. Then, we calculated EARR values for four possible scenarios - without considering any days of survival prior identification of AAA at computed tomography scans (EARR_0), considering past survival of 30 (EARR_30), 90 (EARR_90) and 180 days (EARR_180). Finally, effect of patient-specific blood pressure variability was analyzed. RESULTS: Consideration of past survival does indeed significantly improve predictions of future risk: EARR_30 (1.04%± 0.87%), EARR_90 (0.67%± 0.56%) and EARR_180 (0.47%± 0.39%) which are unrealistically high otherwise (EARR_0 5.02%± 5.24%). Finally, EARR values were observed to vary by an order as a consequence of blood pressure variability and by factor of two as a consequence of neglected growth. CONCLUSIONS: Methodology for computing annual risk of rupture of AAA was developed for the first time. Sensitivity analyses showed respecting patient specific blood pressure is important factor and should be included in the AAA rupture risk assessment. Obtained EARR values were generally low and in good agreement with confirmed survival time of investigated patients so proposed method should be further clinically validated.

• MeSH
• Aortic Aneurysm, Abdominal * diagnostic imaging   MeSH
• Bayes Theorem MeSH
• Risk Assessment MeSH
• Humans MeSH
• Stress, Mechanical MeSH
• Models, Cardiovascular MeSH
• Tomography, X-Ray Computed MeSH
• Patient-Specific Modeling MeSH
• Risk Factors MeSH
• Aortic Rupture * diagnostic imaging   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH

Cíl: Při narození existuje komunikace mezi pravou a levou komorou, tato komunikace však po narození zmizí. V některých případech komunikace přetrvává a komory nemohou fungovat nezávisle na sobě. Tato abnormalita působí problémy, například hypertenzi, a komplikuje práci srdečních chlopní. Cílem této studie bylo analyzovat změny v napětí a deformaci stěny způsobené umístěním záplaty na junkci a zajištění optimalizované geometrie záplaty. Metody: Pro tento účel byly metodou konečných prvků (finite element, FE) vypracovány modely dvou typů kruhových a eliptických záplat se shodnými materiálovými vlastnostmi, následně byly vypočítány a srovnány výsledky těchto dvou různých geometrií. Výsledky: Při stejných hraničních a zátěžových podmínkách výsledky ukázaly, že eliptická záplata je spojena s menším napětím stěny a je bezpečná pro použití v komorách ve srovnání s kruhovou záplatou. Závěr: Výsledky této studie mají význam nejen pro stanovení míry napětí a deformace stěny po našití záplaty, ale i pro zajištění optimalizované geometrie spojené s nižší incidencí komplikací.

Purpose: At birth, there is a communication between the right and left ventricles, but this communication disappears after the birth. In some cases, the communication has been continued and ventricles cannot operate independently on each other. This abnormal communication causes problems, such as hypertension and heart valves complications. The purpose of this study was to analyse alterations in stress and strain caused by placement of a patch on junction and offering optimized geometry for it. Methods: For this purpose, finite element (FE) models of two types of circular and elliptical patches with the same material properties were established and the results of these two different geometries were calculated and compared. Results: Considering the same boundary and loading conditions, the results revealed that the elliptical patch triggers less stresses and is safe to use in ventricle compared to the circular one. Conclusion: The results of the concurrent study have implications not only for understanding of the magnitudes of the stress and strain because of a patch but also for providing an optimized geometry which brings about less complications.

OBJECTIVES: The technique of meshed skin grafting is known since 1960s. It was shown that there is a difference between the declared and real expansion ratio of the skin meshed graft. We hypothesize that the orientation of the Langer's lines in a split thickness skin graft is a key parameter in the resulting expansion ratio. METHODS: The skin graft meshing process was analyzed in two steps. In the first step, ex vivo uniaxial tests of human skin were performed. This served as an input for the constitutive model used for numerical simulations. In the second step, finite element analyses were performed so that stress distributions and expansion ratios could be determined. RESULTS: It was shown that peaks of true stress tended to be concentrated around the vertex of the mesh pattern region for all cases. The declared expansion was impossible to obtain for all expansion ratios having the meshing incision perpendicular to the Langer's lines. The highest difference between declared and real expansion ratio reaches 37%. CONCLUSIONS: With regard to literature dealing with expansion of skin grafts by meshing, a high scatter amongst data results is observed. This finding was also explained by our research, demonstrating the significance of Langer's lines and their relative orientation to the direction of meshing.

• MeSH
• Finite Element Analysis MeSH
• Biomechanical Phenomena MeSH
• Dermatologic Surgical Procedures * MeSH
• Tissue Expansion MeSH
• Skin Physiological Phenomena * MeSH
• Skin * MeSH
• Humans MeSH
• Stress, Mechanical MeSH
• Tensile Strength MeSH
• Skin Transplantation methods   MeSH
• Transplants physiology   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH