This study investigated the effect of implant thickness and material on deformation and stress distribution within different components of cranial implant assemblies. Using the finite element method, two cranial implants, differing in size and shape, and thicknesses (1, 2, 3 and 4 mm, respectively), were simulated under three loading scenarios. The implant assembly model included the detailed geometries of the mini-plates and micro-screws and was simulated using a sub-modeling approach. Statistical assessments based on the Design of Experiment methodology and on multiple regression analysis revealed that peak stresses in the components are influenced primarily by implant thickness, while the effect of implant material is secondary. On the contrary, the implant deflection is influenced predominantly by implant material followed by implant thickness. The highest values of deformation under a 50 N load were observed in the thinnest (1 mm) Polymethyl Methacrylate implant (Small defect: 0.296 mm; Large defect: 0.390 mm). The thinnest Polymethyl Methacrylate and Polyether Ether Ketone implants also generated stresses in the implants that can potentially breach the materials' yield limit. In terms of stress distribution, the change of implant thickness had a more significant impact on the implant performance than the change of Young's modulus of the implant material. The results indicated that the stresses are concentrated in the locations of fixation; therefore, the detailed models of mini-plates and micro-screws implemented in the finite element simulation provided a better insight into the mechanical performance of the implant-skull system.
- MeSH
- Finite Element Analysis * MeSH
- Implants, Experimental * MeSH
- Skull * MeSH
- Humans MeSH
- Stress, Mechanical * MeSH
- Computer Simulation * MeSH
- Check Tag
- Humans MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
Úvod a cíl práce: Mechanický přenos zatížení na kost ovlivňuje kromě materiálových vlastností implantátu (mikrodesign), zejména typ použitého závitu a jeho parametry (makrodesign). Rozeznáváme čtyři základní tvary závitů: a) metrický, b) plochý, c) pilovitý, d) obrácený pilovitý a dva modifikované tvary podle ISO TC 150 normy: e) ISO Shallow HA kortikální a f) ISO Deep HB spongiózní. Mechanický přenos charakterizuje míru přenosu mechanického napětí ze závitu do kosti a je menší než jedna. V ideálním případě je roven jedné, ale vlivem odlišné pevnosti a pružnosti kosti a materiálu závitu je obtížné této hodnoty dosáhnout. Byly stanoveny dva cíle studie. Prvním bylo zjistit rozložení napjatosti (tj. tlakového, tahového a smykového napětí) nejčastěji používaných typů závitů zubních implantátů na rozhraní implantát – kost. Druhým cílem byl popis mechanické kompatibility (čili mechanického přenosu zatížení z implantátu na okolní kost) u stejných typů závitů. Metody: Pro modelování vlivu tvaru závitu implantátu na rozložení napětí v místě rozhraní implantát – kost jsme použili metodu konečných prvků v programu MSC Marc (MSC Software s.r.o., ČR) a metodiku podle Gefena, při které jsme analýze podrobili celou délku kontaktu implantátu s kostí. Definování okrajových podmínek. Velikost zatěžující síly byla F = 100 N, směr síly byl totožný s dlouhou osou implantátu a působiště síly bylo v jeho krčkové části.Charakterizování materiálového modelu. K popisu materiálových vlastností kosti jsme použili izotropní model, který definují dvě konstanty: Youngův modul pružnosti (E) a Poissonovo číslo (μ).Definování typu úlohy. Model byl simulován jako prostorová osově symetrická úloha. Výsledky: Z hlediska tahového napětí se ukazuje jako nejlepší závit ISO Shallow HA, v případě tlakového a smykového napětí se jeví nejvhodnějším plochý závit. Výsledky spočítané metodou konečných prvků u všech typů simulovaných závitů potvrzují, že v závitovém spojení je největší podíl napětí soustředěn v prvních cervikálních závitech. Diskuse a závěr: Z provedených simulací plyne, že profil závitu hraje významnou roli v ovlivnění velikosti a rozložení napětí v okolní kosti a mechanické kompatibility. Naše matematická studie neprokazuje, že existuje jeden ideální závit pro dentální implantát.
Introduction, Aim: Mechanical transfer of load onto the bone affects, besides implant material properties (microdesign), especially the type of thread used and its parameters (macrodesign). There are four basic types of thread: a) metric, b) flat, c) saw-tooth, d) inverted saw-tooth and two modified shapes as specified in standard ISO TC 150: e) ISO Shallow HA cortical, and f) ISO Deep HB cancellous. Mechanical transfer is a characteristic of the rate of mechanical stress transfer from thread to bone, which is less than one. The value of one constitutes an ideal situation but due to different strengths and elasticities in the bone and in the thread material, respectively, this value is difficult to achieve. Two objectives were set for the study. The one was to establish stress (tensile, compressive, and shear) distribution with the most used types of dental implant threads at the implant bone contact. The other objective was to characterize mechanical compatibility (or mechanical transfer of load from implant onto adjacent bone) with the same types of thread. Methods: The Finite Element Method using MSC Marc (MSC Software s.r.o.) program and methodology by Amit Gefen were utilized while the entire implant bone contact length was analysed. The model generation process consists of three stages. Definition of boundary conditions. The load force was F = 100N, direction of force was identical with the implant longitudinal axis while the origin of force was at its cervical area.Establishing material model characteristics. Isotropic model, specified with two constants, was used to establish characteristics of material properties: Young’s modulus of elasticity (E) and Poisson’s ratio (μ)Task specifications. The model was simulated as a 3D axisymmetric task. Results: The ISO Shallow HA thread comes out as the best one from the tensile stress’s point of view whereas the flat thread appears to be the most convenient when considering compressive or shear stress. The results computed using the Finite Element Method with all types of threads simulated confirm that the largest part of stress in threaded connection is found in the foremost cervical turns of thread. Discussion and Conclusion: The simulations carried out implicate that the thread cross section shape plays an important role in affecting stress amplitude and distribution adjacent to the bone as well as mechanical compatibility. Our mathematical study does not prove that there is one single ideal type of thread for dental implants.
- Keywords
- dentální implantát, analýza konečných prvků, mechanická kompatibilita, napětí, závit,
- MeSH
- Finite Element Analysis * statistics & numerical data MeSH
- Bone Screws MeSH
- Stress, Mechanical * MeSH
- Denture Design MeSH
- Tensile Strength MeSH
- Shear Strength MeSH
- Computer Simulation MeSH
- Dental Implants * classification standards MeSH
- Publication type
- Evaluation Study MeSH
This study aimed to introduce a procedure for determining the bilinear elastic moduli (E1 and E2) of the periodontal ligament for a mathematical tooth model to analyse stress in the mandible. The bone and tooth morphology were scanned from a dry skull and an extracted intact tooth, respectively, and reconstructed in a three-dimensional finite element model. The model showed good agreement with previously reported in vivo premolar movement when an E1 for the first phase tooth movement of 0.05 MPa and an E2 for the second phase of 8.0 MPa with ε(12) of 0.075 were adopted. The mandible model analysis indicated that a remarkably high maximum compressive stress in the cervical cortical bone and the tensile stress in areas of masticatory muscle attachment were found. Future stress analyses using a jaw model may follow the process of determination of bilinear moduli to enhance accurate simulation with less calculation time.
- MeSH
- Finite Element Analysis MeSH
- Models, Biological MeSH
- Biomechanical Phenomena MeSH
- Tooth Apex anatomy & histology MeSH
- Humans MeSH
- Mandible anatomy & histology physiology MeSH
- Stress, Mechanical MeSH
- Elastic Modulus MeSH
- Masseter Muscle anatomy & histology physiology MeSH
- Pterygoid Muscles anatomy & histology physiology MeSH
- Temporal Muscle anatomy & histology physiology MeSH
- Odontometry MeSH
- Periodontal Ligament physiology MeSH
- Computer Simulation MeSH
- Image Processing, Computer-Assisted methods MeSH
- Movement MeSH
- Bicuspid anatomy & histology physiology MeSH
- Alveolar Process anatomy & histology physiology MeSH
- Bite Force MeSH
- Imaging, Three-Dimensional methods MeSH
- Tooth Root anatomy & histology MeSH
- Tooth Crown anatomy & histology MeSH
- Tooth Socket anatomy & histology physiology MeSH
- Check Tag
- Humans MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
A three-dimensional finite element model of a vascular smooth muscle cell is based on models published recently; it comprehends elements representing cell membrane, cytoplasm and nucleus, and a complex tensegrity structure representing the cytoskeleton. In contrast to previous models of eucaryotic cells, this tensegrity structure consists of several parts. Its external and internal parts number 30 struts, 60 cables each, and their nodes are interconnected by 30 radial members; these parts represent cortical, nuclear and deep cytoskeletons, respectively. This arrangement enables us to simulate load transmission from the extracellular space to the nucleus or centrosome via membrane receptors (focal adhesions); the ability of the model was tested by simulation of some mechanical tests with isolated vascular smooth muscle cells. Although material properties of components defined on the basis of the mechanical tests are ambiguous, modelling of different types of tests has shown the ability of the model to simulate substantial global features of cell behaviour, e.g. "action at a distance effect" or the global load-deformation response of the cell under various types of loading. Based on computational simulations, the authors offer a hypothesis explaining the scatter of experimental results of indentation tests.
- MeSH
- Finite Element Analysis MeSH
- Models, Biological MeSH
- Mechanotransduction, Cellular physiology MeSH
- Cytoskeleton MeSH
- Humans MeSH
- Stress, Mechanical MeSH
- Myocytes, Smooth Muscle chemistry cytology physiology MeSH
- Computer Simulation MeSH
- Muscle, Smooth, Vascular chemistry cytology physiology MeSH
- Check Tag
- Humans MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
BACKGROUND: The aim of this paper was to design a finite element model for a hinged PROSPON oncological knee endoprosthesis and to verify the model by comparison with ankle flexion angle using knee-bending experimental data obtained previously. METHOD: Visible Human Project CT scans were used to create a general lower extremity bones model and to compose a 3D CAD knee joint model to which muscles and ligaments were added. Into the assembly the designed finite element PROSPON prosthesis model was integrated and an analysis focused on the PEEK-OPTIMA hinge pin bushing stress state was carried out. To confirm the stress state analysis results, contact pressure was investigated. The analysis was performed in the knee-bending position within 15.4-69.4° hip joint flexion range. RESULTS: The results showed that the maximum stress achieved during the analysis (46.6 MPa) did not exceed the yield strength of the material (90 MPa); the condition of plastic stability was therefore met. The stress state analysis results were confirmed by the distribution of contact pressure during knee-bending. CONCLUSION: The applicability of our designed finite element model for the real implant behaviour prediction was proven on the basis of good correlation of the analytical and experimental ankle flexion angle data.
- MeSH
- Algorithms MeSH
- Finite Element Analysis MeSH
- Equipment Failure Analysis MeSH
- Models, Biological * MeSH
- Computer-Aided Design MeSH
- Knee Joint physiopathology MeSH
- Muscle, Skeletal physiopathology MeSH
- Humans MeSH
- Stress, Mechanical MeSH
- Elastic Modulus MeSH
- Bone Neoplasms physiopathology surgery MeSH
- Tensile Strength MeSH
- Compressive Strength MeSH
- Computer Simulation MeSH
- Prosthesis Fitting methods MeSH
- Prosthesis Design MeSH
- Knee Prosthesis * MeSH
- Tendons physiopathology MeSH
- Software MeSH
- Muscle Contraction MeSH
- Check Tag
- Humans MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
- Validation Study MeSH
- MeSH
- Finite Element Analysis * utilization MeSH
- Anisotropy MeSH
- Bone Density MeSH
- Humans MeSH
- Musculoskeletal Physiological Phenomena MeSH
- Neural Networks, Computer * MeSH
- Computer Simulation utilization MeSH
- Bone Remodeling * physiology MeSH
- Statistics as Topic MeSH
- Models, Theoretical MeSH
- Imaging, Three-Dimensional utilization MeSH
- Check Tag
- Humans MeSH
- MeSH
- Finite Element Analysis * utilization MeSH
- Models, Anatomic MeSH
- Arteries * anatomy & histology physiology MeSH
- Biomechanical Phenomena MeSH
- Blood Pressure MeSH
- Humans MeSH
- Mechanical Phenomena MeSH
- Computer Simulation MeSH
- Elasticity physiology MeSH
- Statistics as Topic MeSH
- Models, Theoretical MeSH
- Materials Testing * methods instrumentation MeSH
- Check Tag
- Humans MeSH
- Publication type
- Research Support, Non-U.S. Gov't MeSH
INTRODUCTION AND HYPOTHESIS: Objective of this study was to develop an MRI-based finite element model and simulate a childbirth considering the fetal head position in a persistent occiput posterior position. METHODS: The model involves the pelvis, fetal head and soft tissues including the levator ani and obturator muscles simulated by the hyperelastic nonlinear Ogden material model. The uniaxial test was measured using pig samples of the levator to determine the material constants. Vaginal deliveries considering two positions of the fetal head were simulated: persistent occiput posterior position and uncomplicated occiput anterior position. The von Mises stress distribution was analyzed. RESULTS: The material constants of the hyperelastic Ogden model were measured for the samples of pig levator ani. The mean values of Ogden parameters were calculated as: μ1 = 8.2 ± 8.9 GPa; μ2 = 21.6 ± 17.3 GPa; α1 = 0.1803 ± 0.1299; α2 = 15.112 ± 3.1704. The results show the significant increase of the von Mises stress in the levator muscle for the case of a persistent occiput posterior position. For the optimal head position, the maximum stress was found in the anteromedial levator portion at station +8 (mean: 44.53 MPa). For the persistent occiput posterior position, the maximum was detected in the distal posteromedial levator portion at station +6 (mean: 120.28 MPa). CONCLUSIONS: The fetal head position during vaginal delivery significantly affects the stress distribution in the levator muscle. Considering the persistent occiput posterior position, the stress increases evenly 3.6 times compared with the optimal head position.
- MeSH
- Finite Element Analysis MeSH
- Labor Presentation * MeSH
- Pelvic Floor diagnostic imaging MeSH
- Fetus * MeSH
- Swine MeSH
- Pregnancy MeSH
- Delivery, Obstetric MeSH
- Animals MeSH
- Check Tag
- Pregnancy MeSH
- Female MeSH
- Animals MeSH
- Publication type
- Journal Article MeSH
Patient-specific approach is gaining a wide popularity in computational simulations of biomechanical systems. Simulations (most often based on the finite element method) are to date routinely created using data from imaging devices such as computed tomography which makes the models seemingly very complex and sophisticated. However, using a computed tomography in finite element calculations does not necessarily enhance the quality or even credibility of the models as these depend on the quality of the input images. Low-resolution (medical-)CT datasets do not always offer detailed representation of trabecular bone in FE models and thus might lead to incorrect calculation of mechanical response to external loading. The effect of image resolution on mechanical simulations of bone-implant interaction has not been thoroughly studied yet. In this study, the effect of image resolution on the modeling procedure and resulting mechanical strains in bone was analyzed on the example of cranial implant. For this purpose, several finite element models of bone interacting with fixation-screws were generated using seven computed tomography datasets of a bone specimen but with different image resolutions (ranging from micro-CT resolution of 25 μm to medical-CT resolution of 1250 μm). The comparative analysis revealed that FE models created from images of low resolution (obtained from medical computed tomography) can produce biased results. There are two main reasons: 1. Medical computed tomography images do not allow generating models with complex trabecular architecture which leads to substituting of the intertrabecular pores with a fictitious mass; 2. Image gray value distribution can be distorted resulting in incorrect mechanical properties of the bone and thus in unrealistic or even completely fictitious mechanical strains. The biased results of calculated mechanical strains can lead to incorrect conclusion, especially when bone-implant interaction is investigated. The image resolution was observed not to significantly affect stresses in the fixation screw itself; however, selection of bone material representation might result in significantly different stresses in the screw.
Dental implant failure is mainly the consequence of bone loss at peri-implant area. It usually begins in crestal bone. Due to this gradual loss, implants cannot withstand functional force without bone overload, which promotes complementary loss. As a result, implant lifetime is significantly decreased. To estimate implant success prognosis, taking into account 0.2 mm annual bone loss for successful implantation, ultimate occlusal forces for the range of commercial cylindrical implants were determined and changes of the force value for each implant due to gradual bone loss were studied. For this purpose, finite element method was applied and von Mises stresses in implant-bone interface under 118.2 N functional occlusal load were calculated. Geometrical models of mandible segment, which corresponded to Type II bone (Lekholm & Zarb classification), were generated from computed tomography images. The models were analyzed both for completely and partially osseointegrated implants (bone loss simulation). The ultimate value of occlusal load, which generated 100 MPa von Mises stresses in the critical point of adjacent bone, was calculated for each implant. To estimate longevity of implants, ultimate occlusal loads were correlated with an experimentally measured 275 N occlusal load (Mericske-Stern & Zarb). These findings generally provide prediction of dental implants success.
- MeSH
- Finite Element Analysis * MeSH
- Dental Stress Analysis MeSH
- Time Factors MeSH
- Humans MeSH
- Mandible pathology MeSH
- Stress, Mechanical MeSH
- Osseointegration MeSH
- Bite Force MeSH
- Weight-Bearing MeSH
- Imaging, Three-Dimensional MeSH
- Dental Implants * MeSH
- Dental Prosthesis Design MeSH
- Check Tag
- Humans MeSH
- Publication type
- Journal Article MeSH
