舌侧正畸上颌第一磨牙牙根及牙周组织的应力分析

目的采用有限元的方法研究舌侧矫治过程中上颌第一磨牙牙根、牙周膜、牙槽骨应力分布的特点。方法应用三维激光扫描的方法建立上颌第一磨牙、牙周膜、牙槽骨及矫治器的有限元模型,进行不同方式的加载并观察牙根、牙周膜、牙槽骨及其各个截面的应力分布。结果舌侧矫治上颌第一磨牙的最大Vonmises应力、最大拉应力、最大压应力基本都是牙根>牙周膜>牙槽骨,当牙齿趋于整体移动时,牙根、牙周膜、牙槽骨都处于均匀的低应力分布,各项应力都要小于倾斜移动,旋转移动。牙根、牙周膜、牙槽骨的各项应力基本都是牙颈部平面或根分叉平面>根上1/3平面>根中1/3平面>根下1/3平面。结论舌侧矫治过程中上颌第一磨牙及牙周组织在牙颈部平面或根分叉平面应力最大,临床上应注意观察这些部位的变化。整体移动更有利于牙齿及牙周组织的健康。     

牙槽骨降低对牙周膜内应力的影响

为了解牙齿的牙槽骨降低对牙周膜内应力的大小和分布的影响规律,本文建立了一包括第二双尖牙和第二磨牙的下颌骨段的三维有限元模型,模拟牙齿在咀嚼时的受力状况进行加载,计算分析了牙槽骨为五种不同的高度水平时牙周膜内的应力值。计算结果表明:牙周膜内的应力随牙槽骨降低而逐渐增大,但在牙周膜的不同部位应力增加的幅度不同。牙周膜内应力的增加与牙槽骨降低之间的关系不是线性的,牙槽骨吸收在根长的20％以内时应力的增长较平缓,牙槽骨吸收超过根长的20％以后应力的增加幅度明显加大。     

支抗力作用下上颌第一磨牙牙周膜应力的三维有限元分析

目的研究上颌第一磨牙在支抗力作用下牙周膜的应力分布情况。方法应用薄层CT技术以及ANSYS10.0有限元分析软件建立上颌第一磨牙及其牙周膜、牙槽骨的有限元模型。模拟3种不同大小的支抗力对模型中的上颌第一磨牙进行加载,应用三维有限元法分析上颌第一磨牙在支抗力作用下牙周膜的应力分布情况。结果当上颌第一磨牙颊侧中心受到近中水平向支抗力时,近颊根的颊侧近中颈部、近中颈部和腭侧根的近中颈部主要受压应力,远颊根的远中颊侧颈部主要受拉应力,牙周膜表面的最大应力值出现在近颊根的近中颈部。牙周膜有向近中腭侧转动的趋势。随着加载力的增加,牙周膜表面的应力值也随之增大。结论在临床正畸治疗时,应考虑第一磨牙颊侧是否能提供足够的支抗。     

不同牙槽骨高度条件下上颌牙列牙周组织应力分布的三维有限元分析

目的研究不同牙槽骨高度条件下上颌牙列牙周组织的应力分布规律,为牙周丧失患者的正畸治疗提供参考。方法利用所建上颌牙列、牙周膜、牙槽骨、MBT直丝弓矫治器的三维实体模型,通过ANSYS workbench软件转化为三维有限元模型,模拟滑动法关闭拔牙间隙,对不同牙周丧失条件下的牙周组织应力和位移情况分别进行模拟分析。结果随着牙槽骨高度的丧失,前牙的牙周膜应力和牙齿位移先减小后增大,后牙的牙周膜应力和牙齿位移持续增大,当牙槽骨水平吸收达4 mm时,第一磨牙的牙周膜应力值明显增加。结论对于牙周丧失的患者,在使用MBT直丝弓矫治技术以滑动法关闭间隙的治疗过程中,应增加磨牙支抗,矫治力值也应相应减小。     

舌侧与颊侧正畸上颌第一磨牙应力的有限元分析

舌侧与颊侧正畸在整体内收前牙时,上颌第一磨牙都受到近中向的矫治力,但矫治力的作用点及作用方向是不同的.本实验通过有限元的方法,研究上颌第一磨牙分别受到舌侧与颊侧近中向矫治力时,牙根及牙周膜、牙槽骨的应力分布特点,为舌侧正畸提供生物力学依据.     

3种不同施力方式远移上颌第一磨牙牙周膜应力的三维有限元分析

目的:用有限元方法分析3种不同施力方式远移上颌第一磨牙时牙周膜应力分布。方法:应用薄层CT技术及ANSYS8.0有限元软件建立上颌第一磨牙、牙周膜、牙槽骨的有限元模型。全部采用8节点的六面体单元,包括15 747个节点,67 401个单元。在ANSYA8.0有限元软件中分别对其进行3种不同方式的加载和计算。结果:不同的加载方式所产生的牙周膜应力分布不同。当牙冠颊侧施加200 g远中向力时,牙周膜远中颈部及腭侧根出现压力集中区。牙周膜的最小应力为0.031359 Pa,远中颈部最大应力为0.9854 Pa。当牙冠腭侧施加200 g远中向水平力时,牙周膜远中颈部及颊侧出现压应力集中区。牙周膜的最小应力为0.033099 Pa,远中颈部最大应力为1.144 Pa。当牙冠颊侧、腭侧同时各施加100 g远中向水平力时,牙周膜远中颈部中部出现压力集中区。牙周膜的最小应力为0.031367 Pa,远中颈部最大应力为0.783538 Pa。结论:远移磨牙时,单侧给予单纯水平力时,会出现牙齿的旋转和远中倾斜,当颊舌向同时加载水平向力时,可以克服牙齿的旋转趋势。     

正畸力内收前牙对牙槽骨吸收程度不同后牙的影响

目的 通过有限元法模拟不同程度的后牙牙槽骨吸收状态,分析骨吸收情况下的牙周应力分布和总位移趋势,以便为临床施加合适的矫治力提供指导。方法 在建立正常牙槽骨高度（1号模型）的基础上,通过删减单元格获得后牙牙槽骨高度水平均衡降低2、4、6 mm的2、3、4号模型;在各模型上进行模拟加载,加载力1.47 N,分析在施加矫治力的情况下,各模型后牙组牙的牙周膜初应力及牙齿初始总位移的分布情况。结果 随着牙槽骨高度的降低,后牙组牙总位移增加,牙周膜Von Mises应力逐渐增大,当牙槽骨吸收达4 mm时,应力值和牙齿初始总位移值明显增加。结论 对于伴有牙槽骨丧失的患者,应当避免受力或显著减小受力,避免造成牙周组织不可逆的损伤和牙根、牙槽骨的持续吸收。     

正畸力内收前牙对牙槽骨吸收程度不同后牙的影响

目的 通过有限元法模拟不同程度的后牙牙槽骨吸收状态,分析骨吸收情况下的牙周应力分布和总位移趋势,以便为临床施加合适的矫治力提供指导。方法 在建立正常牙槽骨高度（1号模型）的基础上,通过删减单元格获得后牙牙槽骨高度水平均衡降低2、4、6 mm的2、3、4号模型;在各模型上进行模拟加载,加载力1.47 N,分析在施加矫治力的情况下,各模型后牙组牙的牙周膜初应力及牙齿初始总位移的分布情况。结果 随着牙槽骨高度的降低,后牙组牙总位移增加,牙周膜Von Mises应力逐渐增大,当牙槽骨吸收达4 mm时,应力值和牙齿初始总位移值明显增加。结论 对于伴有牙槽骨丧失的患者,应当避免受力或显著减小受力,避免造成牙周组织不可逆的损伤和牙根、牙槽骨的持续吸收。     

Tomas微种植体矫治力系统竖直倾斜磨牙的三维有限元研究

目的 探讨微种植体复合矫治力系统竖直倾斜磨牙的影响.方法 对上颌第二恒磨牙向近中、颊侧倾斜的干燥头颅骨进行多层螺旋CT扫描,利用有限元软件建立上颌第二恒磨牙及其牙周支持组织的三维有限元模型,并观察计算机模拟微种植体位于不同位置、施加不同的远中向力和根颊向力偶矩时磨牙牙周膜的位移.结果 当微种植体位于第二恒磨牙近中颊侧牙槽骨,进行力学加载时,磨牙产生向远中倾斜、腭侧旋转的趋势;位于近中(牙合)面和近中腭侧牙槽骨,进行力学加载时,磨牙均产生向远中倾斜、颊侧旋转的趋势.结论 合理运用复合矫治力系统可以更有效地竖直倾斜磨牙.     

上颌第一磨牙远中移动时牙周膜应力分布的非线性三维有限元分析

目的:对上颌第一磨牙远中移动时牙周膜的应力分布进行非线性有限元分析,并与线性分析结果比较,为临床提供生物力学依据。方法:采用Mimics、Geomagic、ProE、Ansys Workbench等软件相结合的方法,建立包含上颌第一磨牙、牙周膜、牙槽骨、骨松质、骨皮质、颊面管的三维有限元模型,分别将牙周膜材料设定为非线性材料和线弹性材料,模拟临床远移上颌第一磨牙的操作,使用不同组合的负荷方式进行加载。结果:非线性模型中,牙周膜Von Mises等效应力峰值分布和压应力峰值分布均存在低应力通道：当符合条件M_t/F- M_r/F≈2时,等效应力峰值处于较低水平;当符合条件M_t/F≈M_r/F时,压应力峰值处于较低水平。线性模型中,牙周膜相关应力值均较高且变化剧烈,无低应力通道。结论:牙周膜应力分布存在低应力通道,远中移动上颌第一磨牙时,应尽量使施加的力偶矩与力比值满足低应力条件。     

A finite element model of apical force distribution from orthodontic tooth movement

This study was undertaken to determine the types of orthodontic forces that cause high stress at the root apex. A 3-dimensional finite element model of a maxillary central incisor, its periodontal ligament (PDL), and alveolar bone was constructed on the basis of average anatomic morphology. The maxillary central incisor was chosen for study because it is one of the teeth at greatest risk for apical root resorption. The material properties of enamel, dentin, PDL, and bone and 5 different load systems (tipping, intrusion, extrusion, bodily movement, and rotational force) were tested. The finite element analysis showed that purely intrusive, extrusive, and rotational forces had stresses concentrated at the apex of the root. The principal stress from a tipping force was located at the alveolar crest. For bodily movement, stress was distributed throughout the PDL; however, it was concentrated more at the alveolar crest. We conclude that intrusive, extrusive, and rotational forces produce more stress at the apex. Bodily movement and tipping forces concentrate forces at the alveolar crest, not at the apex.     

Effect of loaded orthodontic miniscrew implant on compressive stresses in adjacent periodontal ligament

Objectives:To describe the relationship between the proximity of miniscrew implants (MSIs) to the periodontal ligament (PDL) and stress in the PDL under different load magnitudes and different bone properties.Materials and Methods:Sixteen subject-specific finite element models of the region of the maxillary first molar and second premolar were developed using computed tomography images of four patients. For each patient, an MSI surface model derived from micro-computed tomography was placed at four different distances from the premolar PDL. Finite element analysis was conducted with mesial load on the MSI, increasing from 1 N to 4 N. Peak absolute compression stress (CS) was calculated at each 1 N step. Stepwise multiple regression modeling was conducted to explain compressive stress by proximity, load magnitude, and bone properties.Results:The multiple regression model explained 83.47% of the variation of CS and included all three factors: proximity, load magnitude, and bone properties. The model expected significant interaction between the bone properties and load magnitude, implying that strong bone properties could be associated with significant increases in CS at small increases in load.Conclusions:To ensure the safety of adjacent roots, MSIs should be placed at least 1 mm from the roots. Assessment of alveolar bone properties is recommended when the use of MSI is intended, as some patients may present with strong bone properties and thereby a high risk of MSI-induced root resorption.     

Mechanical stress generated by orthodontic forces on apical root cementum: a finite element model

OBJECTIVES: 1) To determine the mechanical stress generated at the root apex during different types of tooth movement using a finite element model of an ideal, human maxillary central incisor. 2) To determine the relationship of thickness of cementum and the magnitude of mechanical stress at the root apex. DESIGN: Computer simulation. SETTING AND SAMPLE POPULATION: Not applicable, computer simulation. EXPERIMENTAL VARIABLES: Tooth and investing tissue layers (enamel, dentin, cementum, pulp, periodontal ligament, and alveolar bone). OUTCOME MEASURE: Von Mises and maximum principal stresses. RESULTS: Increasing the apical thickness of cementum increases the amount of mechanical stress. CONCLUSION: A finite element model incorporating all layers of a human maxillary central incisor has been developed. This model was used to determine the location and magnitude of mechanical stress generated for all regions of the tooth, PDL, and enclosed alveolar bone, when orthodontic forces are applied to the tooth. Mechanical stresses were found to increase at the root apex with increasing thickness of apical cementum.     

Analysis of stress in the periodontium of the maxillary first molar with a three-dimensional finite element model.

The aim of this study was to simulate the stress response in the periodontium of the maxillary first molar to different moment to force ratios, and to determine the moment to force ratio for translational movement of the tooth by means of the finite element method. The three-dimensional finite element model of the maxillary first molar consisted of 3097 nodes and 2521 isoparametric eight-node solid elements. The model was designed to dissect the periodontal ligament, root, and alveolar bone separately. The results demonstrate the sensitivity of the periodontium to load changes. The stress pattern in the periodontal ligament for a distalizing force without counterbalancing moments showed high concentration at the cervical level of the distobuccal root due to tipping and rotation of the tooth. After various counterrotation as well as countertipping moments were applied, an even distribution of low compression on the distal side of the periodontal ligament was obtained at a countertipping moment to force ratio of 9:1 and a counterrotation moment to force ratio of 5:1. This lower and uniform stress in the periodontal ligament implies that a translational tooth movement may be achieved. Furthermore, high stress concentration was observed on the root surface at the furcation level in contrast with anterior teeth reported to display high concentration at the apex. This result may suggest that the root morphology of the maxillary first molar makes it less susceptible to apical root resorption relative to anterior teeth during tooth movement. The stress patterns in the periodontal ligament corresponded with the load types; those on the root appeared to be highly affected by bending and the high stiffness of the root.     

骨皮质切开术对比格犬前磨牙压入移动影响的三维形态学研究

目的 评估骨皮质切开术辅助前磨牙压低的加速效应和牙根、牙槽骨改建情况。方法 8只比格犬的下颌骨两侧随机分为实验侧、对照侧,实验侧用骨皮质切开术和微种植体支抗（MIA）压低第三前磨牙（P3）和第四前磨牙（P4）,对照侧用MIA压低P3和P4。在术前和加力后2、4、8、12周分别拍摄锥形束CT,分析P3、P4的压低量、根分叉和根尖区的牙根吸收量以及周围牙槽骨高度降低量。结果 实验侧牙齿的压低量明显大于对照侧（P<0.05）;实验侧和对照侧牙齿根分叉、根尖区的牙根均出现吸收,加力后12周实验侧根尖区牙根吸收小于对照侧（P<0.05）;牙槽骨高度随着加力时间的延长而降低,加力后8、12周时,对照侧牙槽骨高度降低量明显小于实验侧（P<0.05）。结论 骨皮质切开术能加速磨牙的压低,同时能减少压低过程中的牙根吸收。     

Three-dimensional finite element analysis of stress in the periodontal ligament of the maxillary first molar with simulated bone loss.

The purpose of the study was to use the finite element method to simulate the effect of alveolar bone loss on orthodontically induced stress in the periodontal ligament of the maxillary first molar. A 3-dimensional finite element model of a tooth with different levels of bone height was constructed to estimate the reduction in force and the increase in moment to force (M/F) ratio necessary to obtain evenly distributed stress in the periodontal ligament of a tooth with horizontal bone loss. The 3-dimensional finite model comprised a maxillary first molar, the periodontal ligament, and alveolar bone and consisted of 3097 nodes and 2521 elements. An anterior force of 300 g was applied at the center of the buccal crown surfaces of teeth with normal bone height and with bone loss that ranged from 2.0 to 6.0 mm. The results showed that force magnitude required lowering from 80% (2-mm bone loss) and gradually to 37% (6-mm bone loss) of the initial load applied to the tooth without bone loss. The countertipping moment (gram-millimeters) to force (gram) ratio should increase from 9 (no bone loss) to nearly 13 (6-mm bone loss) to maintain the same range of stress in the periodontal ligament as was obtained without bone loss. A linear relationship was observed between the amount of bone loss, the desired reduction in force magnitude, and the increase in M/F ratio. The results of this study indicate that a combination of force reduction and increased M/F ratio is required to achieve uniform stress in the periodontal ligament of a tooth with bone loss.     

Three-dimensional finite element analysis for stress in the periodontal tissue by orthodontic forces

This study was designed to investigate the stress levels induced in the periodontal tissue by orthodontic forces using the three-dimensional finite element method. The three-dimensional finite element model of the lower first premolar was constructed on the basis of average anatomic morphology and consisted of 240 isoparametric elements. Principal stresses were determined at the root, alveolar bone, and periodontal ligament (PDL). In all loading cases for the buccolingually directed forces, three principal stresses in the PDL were very similar. At the surface of the root and the alveolar bone, large bending stresses acting almost in parallel to the root were generally observed. During tipping movement, stresses nonuniformly varied with a large difference from the cervix to the apex of the root. On the other hand, in case of movement approaching translation, the stresses induced were either tensile or compressive at all occlusogingival levels with some difference of the stress from the cervix to the apex. The pattern and magnitude of stresses in the periodontium from a given magnitude of force were markedly different, depending on the center of rotation of the tooth.     

Stress distribution in maxillary alveolar ridge according to finite element analysis using micro-CT

The purpose of the present study was to evaluate stress distribution by finite element analysis in an accurate model simulating trabecular bone using micro-CT. Dentulous and edentulous maxillary jaws of Japanese adult cadavers were used (5 sides each; total, 10 sides). Imaging was performed using a micro-CT, followed by reconstruction with 3-D images. Finite element analysis models were developed using the maxilla with average bone morphometry. A load corresponding to occlusal force was applied in different loading conditions, followed by evaluation of stress distribution. In dentulous maxillas, a load was applied in the dental axis direction to the first molar crown (LD). In edentulous maxillas, a load was applied directly to a circular area 4mm in diameter (LER0) to a cylinder 4mm in diameter and 10mm in height (LER10) corresponding to the first molar area. Stress was concentrated in cortical bone around the first molar, trabecular bone and cortical bone at the maxillary sinus base in LD, cortical bone of the alveolar ridge in LER0, and trabecular bone around the cylinder and cortical bone at the maxillary sinus base in LER10. LER0 showed a stress distribution markedly different from that in LD. Compared with LER0, LER10 showed a stress distribution close to that in LD. A model simulating trabecular bone allows a more accurate evaluation of stress distribution.