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.     

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.     

Investigation of effective intrusion and extrusion force for maxillary canine using finite element analysis

Abstract

Orthodontic tooth movement is mainly regulated by the biomechanical responses of loaded periodontal ligament (PDL). We investigated the effective intervals of orthodontic force in pure maxillary canine intrusion and extrusion referring to PDL hydrostatic stress and logarithmic strain. Finite element analysis (FEA) models, including a maxillary canine, PDL and alveolar bone, were constructed based on computed tomography (CT) images of a patient. The material properties of alveolar bone were non-uniformly defined using HU values of CT images; PDL was assumed to be a hyperelastic–viscoelastic material. The compressive stress and tensile stress ranging from 0.47 to 12.8?kPa and 18.8 to 51.2?kPa, respectively, were identified as effective for tooth movement; a strain 0.24% was identified as the lower limit of effective strain. The stress/strain distributions within PDL were acquired in canine intrusion and extrusion using FEA; root apex was the main force-bearing area in intrusion–extrusion movements and was more prone to resorption. Owing to the distinction of PDL biomechanical responses to compression and tension, the effective interval of orthodontic force was substantially lower in canine intrusion (80–90?g) than in canine extrusion (230–260?g). A larger magnitude of force remained applicable in canine extrusion. This study revised and complemented orthodontic biomechanical behaviours of tooth movement with intrusive–extrusive force and could further help optimize orthodontic treatment.     

Parametric Finite Element Analysis and Closed-formSolutions in Orthodontics

The goal and clinical relevance of this work was the development of closed formulas that are correct and simple enough for a fast decision making by the orthodontist in the daily praxis. This paper performs a parametric three-dimensional finite element linear analysis on a maxillary central incisor with a root of paraboloidal shape, which is subjected to typical orthodontic force-systems. Parameters of most importance, such as the tooth mobility in translation and in pure moment rotation including orthodontic centers, as well as the stresses inside the periodontal ligament are calculated for a large variety of over four hundred different couples of root lengths and root diameters around a nominal value. Regression analysis is afterwards performed and establishes closed-form solutions, which are also explained in terms of analytical strain energy and hydrostatic stress considerations within the periodontal ligament characterised by a small compressibility. The obtained expressions include both the root length as well as the root diameter.     

Alveolar bone response distal to applied orthodontic forces in ovariectomized rats

Objectives:The aim of this study was to investigate the effect of the application of orthodontic tooth forces on the alveolar bone distal to the loaded teeth, in ovariectomized female rats.Methods:Twenty-four eight-month-old Wistar rats were divided into one group ovariectomized at the age of six months and one control. An orthodontic appliance delivering a mesial traction force of 60 gr* was placed on the right maxillary 1^st molar of all animals for 14 days. Histology of the alveolar bone, of the adjacent and distal teeth to the loaded molar and the contralateral side, was performed following euthanasia.Results:In the non-ovariectomized rats, extensive resorption was noticed in the direction of the orthodontic movement in the 2^nd and 3^rd molar interdental space, whereas the respective contralateral interdental space did not show any remodeling activity. Ovariectomized rats displayed reduced osseous tissue in the interdental space of both sides. The alveolar bone in the interradicular area of the 2^nd loaded molar revealed frontal resorption, whereas, the alveolar interradicular bone of the contralateral 2^nd molar showed internal resorption.Conclusions:In conclusion, orthodontic forces applied to the dentoalveolar complex of ovariectomized rats affect bone remodeling, even in areas distal to the site of force application. This finding should be taken into account during orthodontic treatment of women during menopause.     

Applications of Surface–Surface Matching Algorithms for Determination of Orthodontic Tooth Movements

Orthodontic tooth movements are described as the differences between initial and final tooth positions. A computer based method for determination of tooth movements for different treatment methods was developed. A total of 20 casts of the upper jaw of patients treated with tooth positioners or fixed appliances were used as a basis for this study. Tooth movement was analysed on casts before (C ⁱ) and after treatment (C ^f). The casts were digitized either with a COMT or 3D laser scanning systems. After digitization, the models were superimposed in the palate by using a surface–surface matching algorithm. Tooth surfaces of the orthodontically moved teeth were segmented and determination of tooth movement was accomplished by matching the moved teeth from C ⁱ to C ^f. The resulting transformations delivered three dimensional information on translations and rotations. An accuracy of 0.2?mm in translations and 1 degree in rotations could be demonstrated, showing the different efficiency of treatment schemes.     

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.     

A novel method for the three-dimensional (3-D) analysis of orthodontic tooth movement-calculation of rotation about and translation along the finite helical axis.

The purpose of this study was to establish a novel method for evaluating orthodontic tooth movement in three-dimensional (3-D) space. The present system consisted of the following procedures at a given treatment period: (1) 3-D tooth positions were measured with a 3-D surface-scanning system using a slit laser beam; (2) the 3-D shape data were registered automatically at the maxillary first molars, and the coordinate systems were normalized; (3) the rotation matrix and translation vector were calculated from the automatic registration of the two position data for a given tooth; (4) the finite helical axes of teeth were calculated as the locus of zero rotational displacement; and (5) tooth movement was presented as rotation about and translation along the finite helical axis. To test this system, a male patient (age 22 yr 2 months) with Angle Class III malocclusion and moderate crowding of the anterior teeth, who had been treated using a standard multi-bracket appliance, was used as a model case in this study. Impressions for a dental cast model were taken at five phases; immediately before and after application of the appliance, and 10 days, 1 month and 2 months after beginning treatment. The results demonstrated that the present analytical method can more simply describe the movement of a given tooth by rotation about and translation along the finite helical axis, and provides quantitative visual 3-D information on complicated tooth movement during orthodontic treatment.     

Comparison of methods to determine the centre of resistance of teeth

In orthodontic treatment, the locations of the centre of resistance (CR) of individual teeth and the applied load system are the major determinants for the type of tooth movement achieved. Currently, CR locations have only been specified for a relatively small number of tooth specimen for research purposes. Analysing cone beam computed tomography data samples from three upper central incisors, this study explores whether the effort to establish accurate CR estimates can be reduced by (i) morphing a pre-existing simplified finite element (FE) mesh to fit to the segmented 3D tooth-bone model, and (ii) individualizing a mean CR location according to a small parameter set characterising the morphology of the tooth and its embedding. The FE morphing approach and the semi-analytical approach led to CR estimates that differ in average only 0.04 and 0.12 mm respectively from those determined by very time-consuming individual FE modelling (standard method). Both approaches may help to estimate the movement of individual teeth during orthodontic treatment and, thus, increase the therapeutic efficacy.     

Micro-CT监测尼古丁对大鼠正畸牙移动过程中牙周改建的影响

目的:探讨不同摄取量的尼古丁对大鼠正畸过程牙周改建的影响。方法:选择120只雄性Wistar大鼠并将其随机分为四组:A组-空白对照,B组-正畸模型,C组-正畸并0.01 mg/m L尼古丁给药,D组-正畸并1 mg/m L尼古丁给药。分别于实验开始后第1、3、7、14、21天通过Micro-CT和HE染色观察模型牙齿移动距离和牙周组织改变并通过ELISA实验检测IL-17的表达。结果:Micro-CT扫描显示:正畸建模组相对于空白对照组在牙移动距离、骨体积分数、骨密度等指标均有明显变化,变化最大幅度发生在D组,B、C两组之间的差异没有统计学意义(P0.05)。21天,D组移动距离达到0.80±0.06 mm,明显高于B、C组(P0.05)。相较于空白对照组(A组),B、C、D三组Micro-CT测量的骨体积分数、骨密度、骨小梁厚度均降低,D组骨密度值降至1108.36±8.86mg/cm3。HE染色结果显示:D组在21天时破骨细胞增多并出现牙根吸收陷窝伴牙周膜纤维排列混乱;ELISA检测显示B、C组IL-17的含量在第7天时达到峰值,D组则在14天含量最高。结论:高浓度的尼古丁可加速正畸牙齿的移动速度及牙槽骨吸收,增加牙周组织中的破骨细胞及IL-17表达水平。     

Tooth growth and replacement in Ctenolucius hujeta, a neotropical characoid fish

The predaceous neotropical characoid fish Ctenolucius has an essentially homodont dentition, the number of teeth increasing linearly with age. The basic manner of tooth replacement suggests that Ctenolucius is a primitive characoid. Tooth replacement continues throughout life and is similar to that of tetrapods, involving replacement waves which pass from the back to the front of the jaws. The waves containing the greatest number of teeth are found just anterior to the middle of the jaws. In the upper jaw the increase in the number of teeth is restricted to the anterior portion (premaxillary) whereas the number on the posterior part (maxillary) remains constant. In specimens measuring from 68–230 mm in standard length the posterior portion of the upper jaw doubles in length whereas the anterior portion triples. It is suggested that the area immediately anterior to the middle of the jaw, where replacement waves are longest, is where most of the increase in tooth numbers occurs. During growth of the teeth the absolute height is always greater than the absolute width as the shape changes. The final shape of the recurved conical teeth is determined only in the last stages of tooth formation when the main axis of growth abruptly changes.     

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.     

微种植体支抗压低上颌磨牙的研究进展

在口腔科诊疗工作中经常会见到因下颌磨牙长期缺失导致对颌磨牙伸长的情况,这将直接导致对颌磨牙修复空间不足。这种病例需要通过压低伸长的上颌磨牙来获取足够的空间,以利于下颌磨牙的修复。另外,高角和开牙合病例要想获得良好的治疗效果也需要通过压低磨牙来进行垂直向控制,因此压低上颌磨牙成为临床工作的重要内容。压低上颌磨牙的方法除了牙合垫、高位牵引头帽、手术等之外,还有微种植体支抗,它又称为"绝对支抗"由钛或合金制成,分为自攻型和助攻型。由于创伤小,植入部位灵活,手术简单,压低磨牙效果显著,所以自临床应用以来得到大力推广。因此本文就微种植体支抗压低上颌磨牙的临床应用、压低效果评价、副作用及防治措施和生物力学研究等方面作一综述。     

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.     

Concept for development of new individual treatment devices in orthodontics using 3-dimensional numerical simulation of bone remodeling]

The present study is part of a research project that includes different components for the simulation of orthodontic tooth movement and comparing experimental results. This concept includes the development of a bone remodelling algorithm, as well as experimental studies on tooth movement. After the acquisition and evaluation of specific experimental data of the patient's situation, the individual components have to be integrated to verify and forecast tooth movement. The aim is to design individual treatment devices as well as to shorten treatment while making it more effective. The geometry of the teeth and that of the surrounding alveolar bone both influence the orthodontic tooth movement. For this reason, an exact morphological tooth model for the valid simulation of the tooth movement is needed, and can be constructed from computed tomography data. Simulation of tooth movement can then be compared with "in vivo" measurements of the orthodontic tooth movement. In this study, a specially developed hybrid retraction spring is employed. This spring enables the application of a defined, almost constant force system. The "in vivo" determined tooth movement is simulated with the aid of special positioning and measuring devices. Meanwhile, the active force system can be determined by 6-component force/moment sensors. The experimentally measured force system, "in vivo" measurements of tooth movement and the CT model are now available for numerical simulation for the first time.     

口腔正畸治疗牙周病致前牙移位的临床疗效观察

目的:探究口腔正畸治疗牙周病致前牙移位的临床疗效,为牙周病治疗提供依据。方法:选择2011年8月~2013年8月间我院28例因牙周病致前牙移位患者(464颗)。所有患者均进行牙周病治疗,再行口腔正畸治疗,观察患者治疗前后的各项指标变化。结果:经治疗,有效率为67.24%(312/464);与治疗前相比,患者治疗后牙齿松动度、探诊出血率、前牙覆牙合值、前牙覆盖值及牙周袋深度明显减轻或降低,治疗前后比较差异均有统计学差异(均P0.05);牙槽骨高度改变无统计学意义(P0.05)。结论:通过口腔正畸治疗牙周病致前牙移位,不仅可有效减轻病患牙齿的松动度,改善病患的出血情况,还能有效纠正病患覆牙合覆盖关系以及降低病患的牙周袋深度。安全性好,值得临床推广。     

Distribution of 3H-proline within transseptal fibers of the rat following release of orthodontic forces

Maxillary right first molar teeth of rats were tipped mesially with an orthodontic appliance for 2 weeks (experimental group), 3H-proline was injected, and orthodontic forces were removed 6 hr later (time 0). The contralateral molar teeth of treated (internal control group) and age- and weight-matched untreated animals (external control group) were also studied. Diastemata were created between the molar teeth by the orthodontic appliance, and transseptal fibers between first and second (P less than 0.001) and second and third molars (P less than 0.005) were significantly lengthened as compared to external and internal controls at time 0. Diastemata between molar teeth were closed 5 days after removal of orthodontic force. Transseptal fibers adjacent to the source of the orthodontic force (mesial region) had the highest mean number of 3H-proline-labeled proteins at time 0 and at all times following removal of the force (P less than 0.001), and had the highest rate of labeled protein removal (P less than 0.001). Half-lives for removal of 3H-proline-labeled transseptal fiber proteins were significantly greater in mesial and distal regions and significantly less in middle regions of experimentals than in corresponding regions of external controls (P less than 0.001). These data suggest the following: 1) transseptal fibers adjust their length by rapid remodeling in regions experiencing a tensile force; 2) collagenous protein turnover within the middle third of the transseptal fibers is more rapid subsequent to release of orthodontic force than during normal physiologic drift, suggesting that this region adapts rapidly to changes in adjacent tooth position and that these fibers do not play a significant role in relapse of orthodontically relocated teeth; and 3) significant differences in turnover rates of 3H-proline-labeled transseptal ligament proteins of external and internal control quadrants suggest that tooth movement produces both local and systemic effects on collagenous protein metabolism.     

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.     

双线排龈法在烤瓷冠修复牙体缺损中的临床应用

目的:探讨双线排龈法在烤瓷冠修复牙体缺损中的临床应用效果,为临床提供参考。方法:选择2014年3月至2016年3月来我院拟行烤瓷冠修复的96例患者,按照患者入院顺序交替分为观察组和对照组,每组48例。观察组48例(56颗牙)采用双线排龈法,对照组48例(52颗牙)采用单线排龈法,观察和比较两组的排龈效果及随访24周的基牙与游离龈是否完全排开,龈沟宽度是否合适,牙体预备后肩台的边缘是否清晰、连续,印模肩台是否清晰、连续,有无气泡,模型是否清晰、光滑,牙龈有无渗血等。结果:观察组基牙与游离龈排开不全、印模肩台不清晰不连续或有气泡、模型不清晰不光滑、牙龈渗血的发生率均显著低于对照组(P0.05)。修复后24周,两组的修复体边缘隐蔽性比较差异无统计学意义(P0.05),观察组0级牙数为52颗(92.9%),对照组0级牙数为41(80.8%),观察组的牙周组织情况明显优于对照组(P0.05)。结论:在前牙烤瓷冠修复中应用双线排龈法的排龈效果较单线排龈法更好。