Three-dimensional large displacement analysis of orthodontic appliances

An incremental technique for predicting the nonlinear load-displacement characteristics of orthodontic appliances is developed. The analysis is based upon a three-dimensional finite-difference formulation which permits the treatment of appliances that have arbitrary configurations and non-uniform material and cross-sectional properties. The effects of intermediate loading and attached springs may also be studied.

The results show the activated configurations and the associated force-couple systems for three appliances that are activated to the yield point. The incremental analysis results are compared to those of the linear solution for each case.     

固定矫治对儿童口腔微生态环境的影响

固定矫治的放置,增加细菌粘附能力,从而改变口腔微生态环境。本文就固定矫治对儿童口腔内微生态环境变化如：菌斑生物膜的变化、致龋菌数量的改变、牙周致病菌的变化、唾液的性质和牙齿形态及结构等方面改变的研究进展作一综述。     

Large deformation analysis of some basic problems in biophysics

This study is concerned with the application of a possible form of a strain-energy function suitable for soft biological tissues. Two problems considered here are related to simultaneous extension and inflation of cylindrical arteries, and inflation of the left ventricle under a given internal pressure. The values of the material constants are obtained via comparison of theoretical results with experimental findings. Some details concerning the wall stresses and the elastic stiffness are also given in the paper. For each case, it is seen that experiment and theory are in good agreement.     

Microbiological and clinical periodontal effects of fixed orthodontic appliances in pediatric patients

The aim of this study was to evaluate changes of microbiota in ten patients undergoing orthodontic treatment. For each patient clinical examination of gingival index (GI) and plaque index (PI) were performed at the first molars at: baseline (T1), 2 (T2), 4 (T3) and 12 weeks (T4). At the same time subgingival plaque and tongue samples were taken for the microbiological study. Clinical results showed that at T4, the mean PI score was significantly lower than T1 and the GI was markedly reduced. Microbiological results showed that at T1 and T4 facultative aerobic bacteria were prevalent, whereas anaerobic bacteria were more common at T2 and T3.     

Large deformation of isotropic biological tissue

The requirements for the development of a general potential function describing the behavior of homogeneous, isotropic biological tissue are discussed and such a function is proposed. It is shown that this function yields both tensile and torsional results compatible with existing data.     

Large deformation shear properties of liver tissue

Characterization of the mechanical properties of soft biological tissues is important for establishing the mechanical tolerances of the tissues, and for input to computational models. In this work, the viscoelastic properties of bovine liver tissue in shear loading have been measured using relaxation and constant shear rate loading. The tissue is nonlinearly viscoelastic for strains greater than 0.2%, has a yield strain of approximately 10, and shows moderate strain-rate sensitivity. The response can be modelled using a nonlinear viscoelastic differential model previously developed for brain tissue.     

Large deformation mechanics of the enucleated eyeball

Large deformation of enucleated pig eyeballs under rigid cylindrical indenters was studied analytically and experimentally. The analytic model for the eyeball consists of a fluid-filled spherical membrane composed of an incompressible, elastic material with an exponential strain energy function. The Rayleigh-Ritz technique provided an approximate solution via a potential energy formulation. Comparison with results from tests on eyeballs and a water-filled rubber (Mooney-Rivlin) shell shows good agreement at large deflection, where membrane action dominates. Due to the highly nonlinear stress-strain relations for the sclera, the load remains relatively small until the indenter displacement approaches 40-60 percent of the eyeball radius, and then the load increases rapidly. Depending on the indenter size, either a perforation or a rupture type of failure occurs.     

Metallic ion content and damage to the DNA in oral mucosa cells of children with fixed orthodontic appliances

Although the metal devices used in orthodontic treatments are manufactured highly resistance to corrosion, they may still suffer some localized corrosion resulting from the oral cavity conditions. The corrosion causes the release of metals from the alloys used for their manufacture. In this report, we evaluated the in vivo metal ions release of three alloys (stainless steel, titanium and nickel-free) usually used in the orthodontics treatments and its genotoxicity. We applied to 15 patients, between 12 and 16 years, 4 tubes and 20 brackets. Samples from oral mucosa were taken before the treatment and 30 days later. The concentration of the titanium, chromium, manganese, cobalt, nickel, molybdenum and iron were detected using inductively coupled plasma mass spectrometry (ICP-MS). The genotoxicity was measured with a comet assay (Olive moment). The oral mucosa cells in contact with the stainless steel alloy displayed the greatest titanium and manganese concentrations and those in contact with the nickel-free alloy presented the greatest concentration of chromium and iron. Both alloys, stainless steel and nickel-free, induced a higher DNA damage in the oral mucosa cells than the titanium alloy, in which the Olive moment was similar to controls. Based on the results of our study, we can conclude that titanium brackets and tubes are the most biocompatible of the three alloys.     

Passive deformation analysis of human leukocytes

The following analysis presents an experimental and theoretical study of the passive viscoelastic behavior of human leukocytes. Individual neutrophils in EDTA were observed both during their partial aspiration into a small micropipette and after expulsion from a large micropipette where the cell had been totally aspirated and deformed into a sausage shape. To analyze the data, a passive model of leukocyte rheology has been developed consisting of a cortical shell containing a Maxwell fluid which describes the average properties of the cell cytoplasm. The cortical shell represents a crosslinked actin layer near the surface of the cell and is assumed to be under pre-stressed tension. This model can reproduce the results of experiments using micropipette for both short-time small deformation and slow recovery data after large deformation. In addition, a finite element scheme has been established for the same model which shows close agreement with the analytical solution.     

Stereomicroscope analysis of enamel surface after orthodontic bracket debonding

After orthodontic brackets debonding, the remaining resin has to be removed. The purpose of this study was to determine the most efficient method as well as to introduce a new method of composite removal. The study was carried out on a sample of 30 premolars, extracted for orthodontic purposes. Brackets had been bonded using the Ortho One Bisco composite resin. After the removal of brackets, samples were randomly divided into three groups of ten. Composite remnants in the first group were removed using the Band Driver (KaVo). For the second group, the tungsten carbide bur (Komet) was applied. In the third group, composite remnants were removed manually, using adhesive removing pliers (ORMCO). The samples were analysed using a light-stereomicroscope (Olympus). Photomicrographs were examined and the ARI (Adhesive Remnant Index) was calculated. Post Hoc tests (Scheffe, Tukey) indicated a statistically significant difference between groups 1 and 2 as well as between groups 1 and 3. The tungsten carbide bur was found to be the most efficient instrument for composite remnant removal.     

Numerical analysis of orthodontic treatment elements of pseudo-elastic NiTi alloys]

In orthodontic treatment malpositions of teeth are often corrected by fixed appliances, consisting, in part, of loops made by the orthodontist. The most important alloys in use are steel, cobalt-chromium, or titanium-molybdenium alloys. The static force systems of fixed appliances made of these materials are well known from experimental and numerical studies, but as they may change during tooth movement, we are often confronted with problems in therapy. The introduction of pseudoelastic nickel titanium alloys (NiTi) into orthodontic treatment, offers the chance of improving the effectiveness and reliability of orthodontic devices. In the present paper a plane finite element (FE) for the analysis of orthodontic loops is presented. It enables the determination of the nonlinear behaviour of pseudoelastic NiTi-alloys and is capable of simulating large structural displacements and rotations accompanied by moderate strains. A comparative numerical and experimental study shows the efficiency of this element. The associated results reflect pseudoelastic effects on certain loop designs, and reveal the benefits for the orthodontist and his patients.     

Computational analysis of lung deformation after murine pneumonectomy

In many mammalian species, the removal of one lung (pneumonectomy) is associated with the compensatory growth of the remaining lung. To investigate the hypothesis that parenchymal deformation may trigger lung regeneration, we used microCT scanning to create 3D finite element geometric models of the murine lung pre- and post-pneumonectomy (24 h). The structural correspondence between models was established using anatomic landmarks and an iterative computational algorithm. When compared with the pre-pneumonectomy lung, the post-pneumonectomy models demonstrated significant translation and rotation of the cardiac lobe into the post-pneumonectomy pleural space. 2D maps of lung deformation demonstrated significant heterogeneity; the areas of greatest deformation were present in the subpleural regions of the lobe. Consistent with the previously identified growth patterns, subpleural regions of enhanced deformation are compatible with a mechanical signal – likely involving parenchymal stretch – triggering lung growth.     

Optical aspect of deformation analysis in the bone-denture complex

The aim of this study was to register and measure any deformation of mandible models under load. The method for full field measurement of strain is done by using the ARAMIS three-dimensional image correlation system. The system uses two digital cameras that provide a synchronized stereo view of the specimen and the results show the complete strain field during the tests. The biggest deformation values were just under the working force of the biggest intensity 500 N, and for the region of the lower second premolar the deformation is 625 microm. The following study is presented that highlight the use of stereometric measuring system for modern research. It is shown that this measuring methodology can capture the trends of the experiments.     

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.     

Large scale gene expression analysis of cholesterol-loaded macrophages

We conducted large scale gene expression analysis of the response of macrophages to exposure to oxidized low density lipoprotein (Ox-LDL). Much of the vessel wall lesion of atherosclerosis is composed of macrophages that have become engorged with cholesterol. These resulting "foam cells" contribute to the progression of vascular disease through several pathways. As a potential model of foam cell formation, we treated THP-1 cells with 12-O-tetradecanoylphorbol 13-acetate to differentiate them into a macrophage-like phenotype and subsequently treated them with oxidized low density lipoprotein for various time periods. RNA from Ox-LDL treated and time-matched control untreated cells was hybridized to microarrays containing 9808 human genes. 268 genes were found to be at least 2-fold regulated at one or more time points. These regulation patterns were classified into seven clusters of expression profiles. The data is discussed in terms of the overall pattern of gene expression, the thematic classification of the responding genes, and the clustering of functional groups in distinct expression patterns. The magnitude and the temporal patterns of gene expression identified known and novel molecular components of the cellular response that are implicated in the growth, survival, migratory, inflammatory, and matrix remodeling activity of vessel wall macrophages. In particular, the role of nuclear receptors in mediating the gene expression modulation by Ox-LDL is highlighted.