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PubMed2003

Finite element method analysis of the tooth movement induced by orthodontic forces.

The finite element method is a useful technique for measuring structural stress and for movement analyses. The objective of this investigation was to get a more accurate estimation of tooth movement depending on application point when a tipping orthodontic force is applied. The three-dimensional model of un upper canine, consisting of 4,000 hexahedron elements with 2,367 nodes was obtained. Horizontal, orally directed 1N tipping orthodontic force was applied to the model on five different levels of the tooth crown. The three-dimensional mathematical finite element model is useful in analyzing the tooth movement in response to orthodontic forces. The tipping tooth movement is greater if the force is applied closer to its neck, or more gingivally.

Cuspid↗

PubMed2002

Assessment of the ultrasonic dental scaler insert.

The ultrasonic dental scaler is an invaluable tool in the fight against dental calculus and periodontal disease. The purpose of this study was to assess the natural frequency of the straight internal ultrasonic scaler insert 30K FSI-SLI-10S (Dentsply International, York, USA) and to measure the displacement observed at the tip when operated under different generator settings. Two approaches were used: finite element analysis and scanning laser vibrometry. The Finite Element Analysis method was employed to calculate the expected modes of vibration of the insert. Scanning laser vibrometry was used to measure displacements of the tip during operation. It was found the insert had two modes of vibration around the operating frequency of 30 kHz; these modes were first order bending in two orthogonal planes.

Dental Scaling↗

PubMed1995

Three-dimensional finite element stress analysis of the polypropylene, ankle-foot orthosis: static analysis.

An asymmetric 3-dimensional finite element model (FEM) of the ankle-foot orthosis (AFO) together with the ankle-foot complex was developed using the computer aided design (CAD) program PATRAN. Static analysis of normal and pathological motions of the ankle-foot complex such as the "drop-foot" problem were conducted using the FEM program ADINA. A total of 313 three dimensional solid elements and 10 truss elements were used. Heel strike and toe-off condition were simulated. Results revealed that the peak compressive stress (1.6 MPa) in the AFO model occurred in the heel regions of the AFO and the maximum tensile stress (0.8 MPa) occurred in the neck region of the AFO during toe-off. Parametric analyses revealed that the model was sensitive to the elastic moduli of the AFO and of the soft tissue, but was relatively insensitive to the ligament stiffness. The results confirmed the hypothesis that peak stresses in the orthosis occur in the heal and neck regions of the orthosis.

Ankle Joint↗

PubMed2002

Mechanical behavior of coronary stents investigated through the finite element method.

Intravascular stents are small tube-like structures expanded into stenotic arteries to restore blood flow perfusion to the downstream tissues. The stent is mounted on a balloon catheter and delivered to the site of blockage. When the balloon is inflated, the stent expands and is pressed against the inner wall of the coronary artery. After the balloon is deflated and removed, the stent remains in place, keeping the artery open. Hence, the stent expansion defines the effectiveness of the surgical procedure: it depends on the stent geometry, it includes large displacements and deformations and material non-linearity. In this paper, the finite element method is applied (i) to understand the effects of different geometrical parameters (thickness, metal-to-artery surface ratio, longitudinal and radial cut lengths) of a typical diamond-shaped coronary stent on the device mechanical performance, (ii) to compare the response of different actual stent models when loaded by internal pressure and (iii) to collect suggestions for optimizing the device shape and performance. The stent expansion and partial recoil under balloon inflation and deflation were simulated. Results showed the influence of the geometry on the stent behavior: a stent with a low metal-to-artery surface ratio has a higher radial and longitudinal recoil, but a lower dogboning. The thickness influences the stent performance in terms of foreshortening, longitudinal recoil and dogboning. In conclusion, a finite element analysis similar to the one herewith proposed could help in designing new stents or analyzing actual stents to ensure ideal expansion and structural integrity, substituting in vitro experiments often difficult and unpractical.

Computer Simulation↗

PubMed2004

Cranial mechanics and feeding in Tyrannosaurus rex.

It has been suggested that the large theropod dinosaur Tyrannosaurus rex was capable of producing extremely powerful bite forces and resisting multi-directional loading generated during feeding. Contrary to this suggestion is the observation that the cranium is composed of often loosely articulated facial bones, although these bones may have performed a shock-absorption role. The structural analysis technique finite element analysis (FEA) is employed here to investigate the functional morphology and cranial mechanics of the T. rex skull. In particular, I test whether the skull is optimized for the resistance of large bi-directional feeding loads, whether mobile joints are adapted for the localized resistance of feeding-induced stress and strain, and whether mobile joints act to weaken or strengthen the skull overall. The results demonstrate that the cranium is equally adapted to resist biting or tearing forces and therefore the 'puncture-pull' feeding hypothesis is well supported. Finite-element-generated stress-strain patterns are consistent with T. rex cranial morphology: the maxilla-jugal suture provides a tensile shock-absorbing function that reduces localized tension yet 'weakens' the skull overall. Furthermore, peak compressive and shear stresses localize in the nasals rather than the fronto-parietal region as seen in Allosaurus, offering a reason why robusticity is commonplace in tyrannosaurid nasals.

Animals↗

PubMed2002

The impact of material characteristics on the mechanical properties of a poly(L-lactide) coronary stent.

Biodegradable polymer stents as an alternative to metallic vascular stents have long been under discussion. However, for various reasons no such stent concept has been made available for commercial use until today. One reason may be, that still little is known about the mechanical properties of polymer stents and their dependency on the material characteristics. In this study, finite element analysis is used to investigate the mechanical properties of a balloon expandable PLLA stent under various load conditions. It is shown, how material parameters, such as elastic modulus, yield level and material hardening, influence stent recoil and collapse behavior.

Angioplasty, Balloon, Coronary↗

PubMed2007

Margin failures in brittle dome structures: relevance to failure of dental crowns.

Margin cracks in loaded brittle dome structures are investigated. Dome structures consisting of glass shells filled with polymer resin, simulating the essential features of brittle crowns on tooth dentin, provide model test specimens. Disk indenters of diminishing elastic modulus are used to apply axisymmetric loading to the apex of the domes. Previous studies using hard indenters have focused on fractures initiating in the near-contact region of such specimens, including radial cracks at the glass undersurface directly below the contact axis. Here, we focus on fractures initiating at the remote support margins. Margin cracks can become dominant when loading forces are distributed over broad contact areas, as in biting on soft matter, here simulated by balsa wood disks. Cracks preinitiated at the dome edges during the specimen preparation propagate under load around the dome side into segmented, semilunar configurations reminiscent of some all-ceramic crown failures. Finite element analysis is used to determine the basic stress states within the dome structures, and to confirm a shift in maximum tensile stress from the near-contact area to the dome sides with more compliant indenters.

Crowns↗

PubMed2002

Residual stresses at the stem-cement interface of an idealized cemented hip stem.

During the operation of total hip arthroplasty, when the cement polymerizes between the stem implant and the bone, residual stresses are generated in the cement. The purpose of this study was to determine whether including residual stresses at the stem-cement interface of cemented hip implants affected the cement stress distributions due to externally applied loads. An idealized cemented hip implant subjected to bending was numerically investigated for an early post-operative situation. The finite element analysis was three-dimensional and used non-linear contact elements to represent the debonded stem-cement interface. The results showed that the inclusion of the residual stresses at the interface had up to a 4-fold increase in the von Mises cement stresses compared to the case without residual stresses.

Bone Cements↗

PubMed2000

[Mechanics of palatal expansion in the occlusal plane].

The mechanics of a transpalatal arch in the occlusal plane (symmetrical V-bends, asymmetrical V-bends and step-bends) is studied through four methods: simulation of the teeth movements with a typodont, measure of the forces and the moments with a mechanical system composed of pulleys and dead load devices, photo-elastic stress analysis, finite element stress analysis. Typodont experimentations display the dental movements: the easiest one is rotation; it is more difficult to observe distalization and mesialisation that occur with a version of the tooth. An experimental apparatus, composed of pulleys and dead load devices, allows to measure forces and moments released by a transpalatal arch, depending on the level of the activations. The authors notice that the distalization force for an asymmetrical V-bend activation is low, about 0.2 Newton for 5 degrees of activation. Photo-elastic stress analysis affords a visualization of the shear stresses induced by a transpalatal arch within the supporting structures of a root, thanks to the observation of colored fringes in a model constituted with two molars included in a birefringent resin. Meanwhile, the manipulation of the photo-elastic resin is not easy and the interpretation of the results remains difficult. The finite element method is a numerical analysis and consists in the fragmentation of the studied structure in a certain number of elements, where forces and moments can be applied: the three dimensional program analyses the stress and strains in these elements. Thus, we can: 1.--visualize strains and stresses of a transpalatal arch, when it is inserted in the lingual molar sheaths; 2.--observe the dental movements due to the activations of the transpalatal arch (rotation, version, mesialisation, distalization); 3.--study the stress induced in the periodontal tissue. The results of these studies are complementary and in agreement. Particularly, the second method (measure of forces and moments) and the finite element method provide a mathematical and visual model that could explain clinical results: thus, the main purpose of this research is to understand the orthodontic mechanics used in the edgewise or segmented technique.

Adult↗

PubMed2005

Design and fabrication of broadband graded ultrasonic transducers with rectangular kerfs.

Broadband ultrasound imaging is capable of achieving superior resolution in clinical applications. An effective and easy way of manufacturing broadband transducers is desired for these applications. In this work, a graded material in which the piezoelectric plate is mechanically graded with rectangular grooves is introduced. Finite element analysis (FEA) demonstrated that the graded piezoelectric material could achieve a broadband, time-domain response resulting from multiple resonant modes. Experimental tests were carried out to validate these theoretical results. Based upon the FEA designs, several single-element transducers were fabricated using either a nondiced ceramic or a diced, graded ceramics. A superior bandwidth of 92% was achieved by the graded transducer when compared to a bandwidth of 56% produced by the nondiced ceramic transducer at the expense of a reduced sensitivity.

Ceramics↗

PubMed2005

Laser bonded microjoints between titanium and polyimide for applications in medical implants.

Bioencapsulation of medical implant devices, and neural implant devices in particular, requires development of reliable hermetic joints between packaging materials that are often dissimilar. Titanium-polyimide is one of the biocompatible material systems, which are of interest to our research groups at Wayne State University and Fraunhofer USA. We have found processing conditions for successful joining of titanium with polyimide using near-infrared diode lasers or fiber lasers along transmission bonding lines with widths ranging from 200 to 300 microm. Laser powers of 2.2 and 3.8 W were used to create these joints. Laser-joined samples were tested in a microtester under tensile loading to determine joint strengths. In addition, finite element analysis (FEA) was conducted to understand the stress distribution within the bond area under tensile loading. The FEA model provides a full-field stress distribution in and around the joint that cause eventual failure. Results from the investigation provide an initial approach to characterize laser-fabricated microjoints between dissimilar materials that can be potentially used in optimization of bio-encapsulation design.

Equipment Failure Analysis↗

PubMed2005

A numerical approach to evaluate the fatigue life of monolimb.

Monolimb refers to a transtibial prosthesis with the prosthetic socket and the shank being molded into one piece of thermoplastic material. Shank flexibility of a monolimb can improve gait and comfort. However, fatigue failure of monolimbs under cyclic walking load is an important concern. This study is to evaluate the fatigue life of a monolimb designed for a transtibial amputee, based on finite element analysis, the statistical Miner's rule and reliability analysis. Stress uncertainty due to modeling error and the scatter in fatigue test data were considered. Results indicated that the accuracy of fatigue life evaluation of monolimb depends significantly on the precision of stress estimation. In addition, relationship between fatigue failure probability and the number of walking steps was suggested providing a reference for clinicians to determine the interval of the inspection for the monolimb.

Amputees↗

PubMed2005

Design of a front-end integrated circuit for 3D acoustic imaging using 2D CMUT arrays.

Integration of front-end electronics with 2D capacitive micromachined ultrasonic transducer (CMUT) arrays has been a challenging issue due to the small element size and large channel count. We present design and verification of a front-end drive-readout integrated circuit for 3D ultrasonic imaging using 2D CMUT arrays. The circuit cell dedicated to a single CMUT array element consists of a high-voltage pulser and a low-noise readout amplifier. To analyze the circuit cell together with the CMUT element, we developed an electrical CMUT model with parameters derived through finite element analysis, and performed both the pre- and postlayout verification. An experimental chip consisting of 4 X 4 array of the designed circuit cells, each cell occupying a 200 X 200 microm2 area, was formed for the initial test studies and scheduled for fabrication in 0.8 microm, 50 V CMOS technology. The designed circuit is suitable for integration with CMUT arrays through flip-chip bonding and the CMUT-on-CMOS process.

Computer Simulation↗

PubMed1999

Implant design considerations for the posterior regions of the mouth.

The posterior regions of the mouth sustain greater forces, yet often present poorer bone density. A biomechanical approach, often presented to decrease risk factors in such regions, is to increase implant surface area. Most manufacturers provide implants in various lengths. The longest implants are typically inserted into the anterior regions of the mouth, where forces of less magnitude and superior bone quality are present. A finite element analysis supports the hypothesis that implant length is a secondary parameter for stress distribution. A common approach is to enhance implant surface area in the posterior regions primarily by focusing on diameter. However, this increases surface area by only 30% for conventional thread designs despite the fact that forces increase by > 300% in the posterior regions. A change in implant diameter and thread design may increase surface area by > 300%. Such increases in surface area may decrease stresses to the crestal bone regions and reduce both crestal bone loss and early loading implant failure.

Alveolar Process↗

PubMed2006

[Influence of bicortical anchorage on the natural frequencies of dental implant].

OBJECTIVE: To investigate the influences of bicortical anchorage on values of natural frequencies of dental implants utilizing the 3-dimensional finite element analysis. METHODS: Using the commercial code of Solidworks, 3-D models of a screw-shaped dental implant and a mandibular bone segment were generated. After the 3-D implant-bone complex was meshed by ABAQUS software, effects of bicortical anchorage on the buccolingual and axial first-order natural frequencies of the implant were computed. RESULTS: Bicortical anchorage increased both the buccolingual and axial natural frequencies remarkably. As the bicortical anchorage got deeper, the frequencies correspondingly got higher. CONCLUSION: Bicortical anchorage can increase the buccolingual and axial primary stability of dental implants.

Dental Implantation, Endosseous↗

PubMed2006

The effect of occlusal contact localization on the stress distribution in complete maxillary denture.

The fracture of acrylic resin dentures is an unresolved problem in removable prosthodontics despite many efforts to determine its cause. Unfavourable occlusion could be playing an important role in the fracture of the denture. The aim of this study was to investigate the effect of occlusal contact localization on the stress distribution in complete maxillary denture bases utilizing two-dimensional finite element analysis. The results of this study have shown that maximum compressive stresses in a complete maxillary denture under functional masticatory forces concentrates always on the artificial tooth/denture base junction irrespective to the occlusal contact localization. Tensile stresses were observed in areas toward the midline, although the midline itself usually had lower stresses. Shifting the occlusal contacts to a more buccal localization resulted in an increase of the calculated stresses. As a conclusion, it can be speculated that the buccal placement of the occlusal contacts may play a role in the fatigue fracture of the complete maxillary denture.

Acrylic Resins↗

PubMed2005

A comparison of the effects of two canal preparation techniques on root fracture susceptibility and fracture pattern.

The purpose of the study was to determine whether rotary nickel-titanium (NiTi) canal preparation strengthens roots, and whether the fracture pattern can be predicted by finite element analysis (FEA) models. From a fracture mechanics viewpoint, structural defects, cracks or canal irregularities are likely to play a major role in fracture susceptibility of the roots, because stresses can be exponentially amplified at these sites. By incorporating defects into a smooth round canal using rotary NiTi, theoretically the roots could be strengthened. 25 teeth were prepared using hand files and another 25 using rotary NiTi. After obturation, all teeth were subject to loading until fracture; load and patterns were recorded. Four FEA models were created from fractured roots. No significant difference of fracture load between the two techniques was found. Mesio-distal fracture occurred more often in the rotary NiTi group. Stress patterns in three of the four FEA models correlated well with the observed fracture patterns.

Analysis of Variance↗

PubMedDate not supplied

Stresses at the cervical lesion of maxillary premolar--a finite element investigation.

OBJECTIVES: The objective of this study was to use a three-dimensional (3-D) finite element model to investigate normal stress distribution to substantiate the tooth flexure mechanism. The study also compared the changes in the stresses by different occlusal loading sites and directions. METHODS: The 3-D finite element analysis was used. A maxillary premolar was selected to construct the simulation model. The model was constructed step-by-step for convergence and validity. Seven load conditions for various load sites and different directions were simulated to the model. RESULTS: The maximal principal stress and minimal principal stress distributions developed within the structures of seven load conditions were output and their stress distributions on z-plane at the vertical midline were shown. The peak tensile stress of the cervical area for various load conditions were compared and listed. CONCLUSIONS: This study has shown that the presence of tensile stresses in the cervical region of a maxillary premolar by various loading sites and different directions. The results coincided with the stress-induced theory, hence sustaining it. The relationship of the affected factors of leverage to the development of cervical abfraction lesions, was explored.

Bicuspid↗