The most appropriate position and number for absolute anchorages for orthodontic tooth movements

Absolute anchorages proved to be very effective for orthodontic tooth movements. We used a 3D digitizer to record each tooth on pre-treatment diagnostic and post-treatment predictive setup models and then 3D coordinate system conversion was performed to make the coordinate values comparable. An arithmetic calculation of vector and moment based on the orthodontic forces and the tooth displacement under preliminary premises undertaken to decide the most favorable position and number for absolute anchorages. Position--For two-dimensional and three-dimensional calculations, the most appropriate positions for absolute anchorages should theoretically be on the line of resultant force (2D) and the plane (3D) where the total moment effect tends to be zero. Number--As for the number of the absolute anchorages needed, it depends on the number of target teeth. Different combinations of target teeth provide different sets of results.     

Three-dimensional analysis of orthodontic tooth movement

A three-dimensional finite element model was used to investigate the biomechanical response of an upper canine tooth. The physical model was developed from ceramic replicas and X-rays, and consisted of cancellous and cortical bone, the periodontal ligament, dentine and pulp chamber. Horizontal forces were applied at the tip of the crown and at the cervical margin and a rotational force was applied at the cervical margin of the tooth crown. The resulting displacements and stress field for each load case are presented with particular emphasis being placed on the response of the periodontal ligament. The investigation shows that quantitative information on initial tooth movement can be accurately predicted and used to evaluate the response of orthodontic treatment.     

A visco-elastic model for the prediction of orthodontic tooth movement

This study presents a biomechanical model of orthodontic tooth movement. Although such models have already been presented in the literature, most of them incorporate computationally expensive finite elements (FE) methods to determine the strain distribution in the periodontal ligament (PDL). In contrast, the biomechanical model presented in this work avoids the use of FE methods. The elastic deformation of the PDL is modelled using an analytical approach, which does not require setting up a 3D model of the tooth. The duration of the lag phase is estimated using the calculated hydrostatic stresses, and bone remodelling is predicted by modelling the alveolar bone as a viscous material. To evaluate the model, some typically used motion patterns were simulated and a sensitivity analysis was carried out on the parameters. Results show that despite some shortcomings, the model is able to describe commonly used motion patterns in orthodontic tooth movement, in both single- and multi-rooted teeth.     

A mechanobiological model of orthodontic tooth movement

Orthodontic tooth movement is achieved by the process of repeated alveolar bone resorption on the pressure side and new bone formation on the tension side. In order to optimize orthodontic treatment, it is important to identify and study the biological processes involved. This article presents a mechanobiological model using partial differential equations to describe cell densities, growth factor concentrations, and matrix densities occurring during orthodontic tooth movement. We hypothesize that such a model can predict tooth movement based on the mechanobiological activity of cells in the PDL. The developed model consists of nine coupled non-linear partial differential equations, and two distinct signaling pathways were modeled: the RANKL–RANK–OPG pathway regulating the communication between osteoblasts and osteoclasts and the TGF-β pathway mediating the differentiation of mesenchymal stem cells into osteoblasts. The predicted concentrations and densities were qualitatively validated by comparing the results to experiments reported in the literature. In the current form, the model supports our hypothesis, as it is capable of conceptually simulating important features of the biological interactions in the alveolar bone—PDL complex during orthodontic tooth movement.     

A periodontal ligament driven remodeling algorithm for orthodontic tooth movement

While orthodontic tooth movement (OTM) gains considerable popularity and clinical success, the roles played by relevant tissues involved, particularly periodontal ligament (PDL), remain an open question in biomechanics. This paper develops a soft-tissue induced external (surface) remodeling procedure in a form of power law formulation by correlating time-dependent simulation in silico with clinical data in vivo (p<0.05), thereby providing a systematic approach for further understanding and prediction of OTM. The biomechanical stimuli, namely hydrostatic stress and displacement vectors experienced in PDL, are proposed to drive tooth movement through an iterative hyperelastic finite element analysis (FEA) procedure. This algorithm was found rather indicative and effective to simulate OTM under different loading conditions, which is of considerable potential to predict therapeutical outcomes and develop a surgical plan for sophisticated orthodontic treatment.     

Quantitative approach for the prediction of tooth movement during orthodontic treatment

The orthodontic treatment is aimed to displace and/or rotate the teeth to obtain the functionally correct occlusion and the best aesthetics and consists in applying forces and/or couples to tooth crowns. The applied loads are generated by the elastic recovery of metallic wires linked to the tooth crowns by brackets. These loads generate a stress state into the periodontal ligament and hence, in the alveolar bone, causing the bone remodeling responsible for the tooth movement. The orthodontic appliance is usually designed on the basis of the clinical experience of the orthodontist. In this work, a quantitative approach for the prediction of the tooth movement is presented that has been developed as a first step to build up a computer tool to aid the orthodontist in designing the orthodontic appliance. The model calculates the tooth movement through time with respect to a fixed Cartesian frame located in the middle of the dental arch. The user interface panel has been designed to allow the orthodontist to manage the standard geometrical references and parameters usually adopted to design the treatment. Simulations of specific cases are reported for which the parameters of the model are selected in order to reproduce forecasts of tooth movement matching data published in experimental works.     

Docking of hydrophobic ligands with interaction-based matching algorithms

MOTIVATION: Matching of chemical interacting groups is a common concept for docking and fragment placement algorithms in computer-aided drug design. These algorithms have been proven to be reliable and fast if at least a certain number of hydrogen bonds or salt bridges occur. However, the algorithms typically run into problems if hydrophobic fragments or ligands should be placed. In order to dock hydrophobic fragments without significant loss of computational efficiency, we have extended the interaction model and placement algorithms in our docking tool FlexX. The concept of multi-level interactions is introduced into the algorithms for automatic selection and placement of base fragments. RESULTS: With the multi-level interaction model and the corresponding algorithmic extensions, we were able to improve the overall performance of FlexX significantly. We tested the approach with a set of 200 protein-ligand complexes taken from the Brookhaven Protein Data Bank (PDB). The number of test cases which can be docked within 1.5 A RMSD from the crystal structure can be increased from 58 to 64%. The performance gain is paid for by an increase in computation time from 73 to 91 s on average per protein-ligand complex. AVAILABILITY: The FlexX molecular docking software is available for UNIX platforms IRIX, Solaris and Linux. See http://cartan.gmd.de/FlexX for additional information.     

Finite element-based force/moment-driven simulation of orthodontic tooth movement

The objectives of this study were to develop a numerically controlled experimental set-up to predict the movement caused by the force systems of orthodontic devices and to experimentally verify this system. The presented experimental set-up incorporated an artificial tooth fixed via a 3D force/moment sensor to a parallel kinematics robot. An algorithm determining the initial movement of the tooth in its elastic embedding controlled the set-up. The initial tooth movement was described by constant compliances. The constants were obtained prior to the experiment in a parameterised finite element (FE) study on the basis of a validated FE model of a human molar. The long-term tooth movement was assembled by adding up a multiple of incremental steps of initial tooth movements. A pure translational movement of the tooth of about 8 mm resulted for a moment to force ratio of ? 8.85 mm, corresponding to the distance between the bracket and the centre of resistance. The correct behaviour of this linear elastic model in its symmetry plane allows for simulating single tooth movement induced by orthodontic devices.     

Biological aspects of orthodontic tooth movement: A review of literature

This review of literature describes the cellular and molecular biology of orthodontic tooth movement, including various theories and effect of chemical mediators on tooth movement. The better understanding of the tooth movement mechanism will inspire the clinicians to design and implement effective appliances that will result in maximum benefits and minimum tissue damage to the patients. This paper also emphasizes the applied aspect of different medication and hormones, during orthodontic treatment, on the signaling molecules which produce bone remodeling.     

Fast index based algorithms and software for matching position specific scoring matrices

Background  

In biological sequence analysis, position specific scoring matrices (PSSMs) are widely used to represent sequence motifs in nucleotide as well as amino acid sequences. Searching with PSSMs in complete genomes or large sequence databases is a common, but computationally expensive task.     

Study of bone remodeling in corticotomy-assisted orthodontic tooth movement in rats

The goal of this study was to determine the structure change of the alveolar bone and the expression of a group of bone remodeling-related factors. Sixty healthy male Wistar rats were randomly divided into three groups. Selective alveolar decortication (SAD), tooth movement (TM), and “combined therapy” (SAD+TM) was performed in group I, II, and III, respectively. On days 0, 7, 14, 21, and 42, a Micro-CT scan was performed on the maxillary alveolar bone and tooth. In addition, on days 0, 7, 14, 21, 28, and 42, some of the rats were killed by cervical dislocation and tissues were harvested. Analysis of scan data revealed a significant decrease in bone density of the alveolar bone at 14 days post-surgery, and increased at 42 days post-surgery to a level higher than that before the surgery. Microarray and bioinformatics analysis were performed to explore gene expression profile in three groups (SAD, TM, and SAD+TM), and a large number of differentially expressed genes were identified. In addition, real-time polymerase chain reaction was performed to determine the expression of bone remodeling-related factors. The expression of osteoblast-related cytokines, including osteopontin, bone sialoprotein, and osteocalcin, and osteoclast regulators macrophage-colony stimulating factor (M-CSF) and RANKL (activator of nuclear factor KB receptor ligand) were increased in group III, suggesting that there was increased bone synthesis and activation of bone absorption. Moreover, group III had a unique alveolar bone remodeling pattern: RANKL and osteoprotegerin-promoted alveolar remodeling. In conclusion, during the early stage of orthodontic tooth movement, corticotomy can accelerate the movement of teeth, modulate the state of bone metabolism, and activate osteogenesis and osteoclast, which support the theory of regional acceleratory phenomenon.     

Tensile bond strength of orthodontic resins on the human tooth surface

Composite resin has been used in the field of orthodontics for more than twenty years. Although there have been many studies and discussions regarding the bond strength of orthodontic brackets to the human tooth surface, a definitive conclusion has not yet been established. In this study, sixty bicuspids extracted from teenagers were employed for testing, in conjunction with 6 different brands of orthodontic resins: Concise, Unitek, Ormco, American, Mono-lok and Right-on. On the buccal surface of the crown, the tensile bond strength for the various resins were tested and recorded. The bond strength was 0.69 kg/mm2 for Concise, 0.64 kg/mm2 for Unitek, 0.58 Kg/mm2 for Ormco, 0.55 kg/mm2 for American, 0.54 kg/mm2 for Mono-log and 0.45 kg/mm2 for Right-on, respectively. The broken surfaces were examined by scanning electron microscopy, as well as energy dispersive x-ray spectrometry. The broken surfaces were either at interface between the resin and bracket base, at the resin itself, interface between tooth surface and resin or in a combination of them. On the broken surface of the bracket base, components of broken tooth fragments were also detected. The percentage for the frequency of samples of each type of orthodontic resin of broken tooth fragments found was 30% for Concise, 10% for Unitek, 50% for Ormco, 40% for American, 50% for Mono-lok and 80% for Right-on.(ABSTRACT TRUNCATED AT 250 WORDS)     

正畸力引起的牙周组织内白细胞介素-1 mRNA含量变化的研究

目的 研究在正畸牙移动中牙周组织炎症反应的情况和白细胞介素-1(interleukin-1,IL-1) mRNA表达水平是否发生一定的变化.方法 选取中国医科大学实验动物部Wistar大鼠36只,分别采用石蜡切片HE染色和实时定量 RT-PCR 的方法检测施加正畸力后1、3、7和14 d牙周组织内炎症反应和IL-1α及IL-1β mRNA的含量变化.结果 机械力使牙周组织内炎症反应明显,同时IL-1α和IL-1β mRNA的含量增加,对于IL-1α,其mRNA含量在3 d后明显增加,7 d后达到高峰,之后下降;而IL-1β mRNA的含量在加力1 d后即开始增加,3 d后达到峰值,随后下降.结论 在正畸牙移动中,牙周组织内炎症反应明显;IL-1α和IL-1β mRNA的含量增加,并有一定的时相特异性.     

Tissue changes in the rabbit periodontal ligament during orthodontic tooth movement

In this (semi) quantitative animal study the reaction of the periodontal ligament (PDL) to experimental tooth movement is described. To this end, rabbit first incisors were moved sideways with helical torsion springs for periods varying from 3-24 hours. The initial force of the springs was 50 gf. The histomorphology of the PDL was studied in 5 microns thick plastic sections. Comparison with control animals and animals wearing passive springs showed that tooth movement leads to an increased trauma in the PDL within only a few hours. This trauma is characterized by hyalinization, tears and ruptures in the fibres and blood vessels, and by the presence of extravascular erythrocytes and pyknosis. Tissue damage significantly increased with time. After 24 hours of tooth movement, the PDL fibers are compressed or stretched in 68% of the sections and the blood vessels in the PDL are compressed or stretched in 62% of the sections. Even in the controls, more than 15% of the sections displayed slightly stretched or compressed fibers, and about 10% showed slightly compressed or stretched blood vessels. This indicates that some damage is regularly present in a normally functioning PDL. Increases in the percentage of sections with blood vessel compression are found in all groups wearing passive springs, especially after 6 hours. A high concordancy in compression and tension patterns of blood vessels and fibers is present in 83% of the sections. Pyknotic cells are practically confined to areas with compressed PDL fibers in rabbits wearing active springs. Extravascular erythrocytes were found in sections with all types of fiber patterns. A significant majority of extravascular erythrocytes, however, was found in areas with compressed fibers.     

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.     

Expression pattern of YAP and TAZ during orthodontic tooth movement in rats

Orthodontic tooth movement (OTM) is a periodontal tissue remodeling and regeneration process that is caused by bio-mechanical stimulation. This mechanical–chemical transduction process involves a variety of biological factors and signaling pathways. It has been shown that the Hippo-YAP/TAZ signaling pathway plays a pivotal role in the mechanical–chemical signal transduction process. Moreover, YAP and TAZ proteins interact with RUNX family proteins via different mechanisms. To explore the regulation of the Hippo signaling pathway during periodontal tissue remodeling, we examined the upper first molar OTM model in rats. We examined YAP, TAZ and RUNX2 expression at 12 hours, 24 hours, 2 days (2d), 4 days, 7 days (7d) and 14 days (14d) after force application. Haemotoxylin and eosin staining, immunohistochemical staining and western blot analysis were used to examine the expression level and localization of these proteins. We found that YAP, TAZ and RUNX2 expression started increasing at 2d, YAP and TAZ expression was proportional to the orthodontic force applied until peaking at 7d, and at 14d the expression started to decrease. YAP and TAZ were observed in osteocytes, bone matrix and periodontal ligament cells during OTM. Furthermore, using double labeling immunofluorescence staining, we found that the increase in TAZ expression was associated with RUNX2 expression, however, YAP and RUNX2 showed different expression patterns. These results suggest that the Hippo-YAP/TAZ signaling pathway participates in periodontal tissue remodeling through various mechanisms; TAZ may adjust bone tissue remodeling through RUNX2 during OTM, while YAP may regulate periodontal cell proliferation and differentiation.     

Time-related PDL: viscoelastic response during initial orthodontic tooth movement of a tooth with functioning interproximal contact-a mathematical model

Most anteroposterior orthodontic movements of posterior teeth have to overcome the "resistance" of adjacent teeth with functioning interproximal contacts. The aim of this study was to develop a mathematical model describing initial posterior tooth movement associated with functioning interproximal contacts in relation to the viscoelastic mechanical behavior of the human periodontal ligament (PDL). A linear viscoelastic 2D mathematical model was modified to depict tipping movement around the center of rotation (C(rot)) of a premolar where tipping is restrained by adjacent teeth. Equilibrium equations were applied taking into account the sagittal moment developed around the C(rot). The constants of the model were analyzed and applied to a numerical model that can simulate short-term tooth creep movement caused by a tipping force. Changes in force magnitude (0.5-3N) and crown length (6-10mm) were analyzed until no movement was observed (steady state). Premolar displacement in contact with adjacent teeth showed a non-linear progression over time with an initial sharp tipping movement followed by a transient period of 2.6-7.1min. As tipping force increased the transient period increased. A similar but smaller effect was observed with an increase in crown length. The premolar initial displacement within the arch (3.2-19.5microm) is about seven-fold smaller than retraction/protraction movement of an incisor. These suggest reduction in tooth displacement when functioning interproximal contact is present and clinically recommend establishing a space in the direction of tooth displacement before tooth movement.     

Expression of genes for gelatinases and tissue inhibitors of metalloproteinases in periodontal tissues during orthodontic tooth movement

Orthodontic tooth movement progresses by a combination of periodontal ligament (PDL) tissue and alveolar bone remodeling processes. Besides the remodeling of alveolar bone around the moving teeth, the major extracellular matrix (ECM) components of PDLs, collagens, are degenerated, degraded, and restructured. Matrix metalloproteinases (MMPs) and their specific inhibitors, tissue inhibitors of metalloproteinases (TIMPs), act in a co-ordinated fashion to regulate the remodeling of periodontal tissues. We hypothesized that the expression levels of the genes for MMP-2, MMP-9, and TIMPs 1–3 are increased transiently in the periodontal tissue during orthodontic tooth movement. To test this hypothesis, we employed an animal model of tooth movement using rats, as well as in situ hybridization to analyze the expression levels of Mmp-2, Mmp-9, and Timps 1-3. The expression levels of these genes increased transiently in cells of periodontal tissues, which include cementoblasts, fibroblasts, osteoblasts, and osteoclasts, at the compression side of the moving teeth. The transient increases in gene expression at the tension side were mainly limited to osteoblasts and cementoblasts. In conclusion, the expression levels of Mmp-2, Mmp-9, and Timps 1-3 increase transiently during orthodontic tooth movement at both the tension and compression sides. The expression of these genes is regulated differentially in the periodontal tissue of the tension side and compression side. This altered pattern of gene expression may determine the rate and extent of remodeling of the collagenous ECM in periodontal tissues during orthodontic tooth movement.