Stress distribution pattern in a root of maxillary central incisor having various root morphologies

Abstract Objective: To investigate stress distribution in the roots of maxillary central incisors bearing various types of root morphologies with regard to application of different types of orthodontic forces using the finite element model (FEM). Materials and Methods: FEMs of maxillary central incisors with different root morphologies (normal, short, blunt, dilacerated, and pipette) were constructed, and orthodontic forces in various directions (intrusion, extrusion, tipping, and rotational) were applied to the tooth axis at the bracket level. Result: On application of various forces, significantly increased stress was seen at the apex of the root with dilacerated morphology and at the cervical one-third region of the tooth with the short root. Increased stress was observed at the middle one-third region in the tooth with the pipette-shaped root during intrusion and extrusion. Conclusions: In the present study, the stress distribution pattern indicates that the maxillary central incisors with deviated root morphology are at higher risk of root resorption.     

Stress distribution pattern in a root of maxillary central incisor having various root morphologies: A finite element study

Objective:To investigate stress distribution in the roots of maxillary central incisors bearing various types of root morphologies with regard to application of different types of orthodontic forces using the finite element model (FEM).Materials and Methods:FEMs of maxillary central incisors with different root morphologies (normal, short, blunt, dilacerated, and pipette) were constructed, and orthodontic forces in various directions (intrusion, extrusion, tipping, and rotational) were applied to the tooth axis at the bracket level.Result:On application of various forces, significantly increased stress was seen at the apex of the root with dilacerated morphology and at the cervical one-third region of the tooth with the short root. Increased stress was observed at the middle one-third region in the tooth with the pipette-shaped root during intrusion and extrusion.Conclusions:In the present study, the stress distribution pattern indicates that the maxillary central incisors with deviated root morphology are at higher risk of root resorption.     

Relationship between dental anomalies and orthodontic root resorption of upper incisors

The aim of this study was to examine the potential relationship between the occurrence of orthodontic root resorption and presence of dental anomalies such as tooth agenesis and pipette-shaped roots. Dental anomalies and root resorption were assessed on dental panoramic tomographs (DPT) of 88 subjects, 27 males and 61 females, mean age 28.4 (SD = 11.3 years), selected from orthodontic patients on the basis of the following exclusion criteria: previous fixed appliance treatment, bad quality of the DPTs and no visibility of the periodontal ligament of every tooth, and younger than 15 years of age at the onset of treatment with fixed edgewise appliance lasting at least 18 months. A pipette-shaped root was identified as defined by a drawing. Tooth agenesis was assessed on DPTs and from subjects' dental history. Root resorption was calculated as the difference between the root length before and after treatment, with and without a correction factor (crown length post-treatment/crown length pre-treatment). If one of the four upper incisors showed root resorption of ≥2.3 mm with both formulas, the patient was scored as having root resorption. Chi-square tests indicated that there was no relationship between orthodontic root resorption and agenesis (P = 0.885) nor between orthodontic root resorption and pipette-shaped roots (P = 0.800). There was no relationship between having one of the anomalies and root resorption either (P = 0.750). In the present study, it was not possible to confirm on DPTs a relationship between orthodontic root resorption and dental anomalies, such as agenesis and pipette-shaped roots.     

Anomalous dental morphology and root resorption during orthodontic treatment: a pilot study

The present study investigated the relation between anomalous dental morphology and root resorption during orthodontic treatment. One hundred and eleven sets of orthodontic records (a total of 1,630 teeth) were examined. Root resorption was determined from post-treatment panoramic radiographs using a five-grade quantitative measurement. It was found that patients with short or blunt roots before treatment underwent significant root shortening during orthodontic treatment. Patients with any one dental anomaly had a significantly higher degree of root resorption compared with patients with no dental anomaly. Invaginated teeth, teeth with thin or pipette-shaped roots and teeth with short or blunt roots were likely to be more susceptible to root resorption than those without such anomalies. Possible linkages between the aetiological factors of dental anomalies and the susceptibility to root resorption were discussed. The presence of anomalous dental morphology should be taken into account in orthodontic treatment planning.     

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.     

不同牙槽骨高度的磨牙压低时牙周膜应力分析

目的：通过建立具有不同牙槽骨高度的上颌第一磨牙三维有限元模型,在压力载荷下,计算分析其牙周膜应力的大小和分布,为正畸治疗提供力学参考。方法：采用CT对上颌第一磨牙进行扫描,建立牙槽骨发生不均衡水平吸收的上颌第一磨牙的三维有限元数字模型,计算加载垂直向的压低力时,牙周膜应力的大小和分布。结果：当牙槽骨从正常高度降低3.5 mm时,加载产生的牙周膜应力增加平缓,高应力集中部位在根分叉处;而牙槽骨降低超过6.0 mm,根分叉部分暴露时,牙周膜应力明显增加,应力集中的部位转移至根尖及根1/3处。结论：当牙槽骨高度降低未超过6 mm时(牙槽骨吸收未超过根长的48%),应根据牙槽骨的丧失程度来减小矫治力值;当牙槽骨高度降低6 mm以上时(牙槽骨吸收超过根长48%),磨牙的根分叉完全暴露,则应显著减小矫治力值。     

大鼠正畸性牙根吸收及牙齿移动差异的研究

目的建立大鼠正畸性牙根吸收模型,比较一个加力周期内不同加力时间及不同加力力值时大鼠牙齿的移动差异及牙根吸收情况。了解时间、力值与牙齿移动及牙根吸收的关系。方法选择月龄相同,体质量相近的SD雄性成年大鼠建立正畸牙移动模型,按不同加力时间分为1、3、5、7、10、14d组,按加力大小分为40g、60g、80g力组。测量不同组别正畸牙移动量,采用连续切片观察牙根吸收情况。结果各组牙齿移动距离不同;牙根吸收主要表达在根中1/3区域;吸收程度与加力时间及力值有关。结论1、成功建立大鼠正畸性牙根吸收模型。2、不同加力时间及不同力值各组牙齿移动距离存在显著差异。3、不同加力时间及不同力值组牙根吸收存在规律性。     

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.     

Biomechanical effects of cervical lesions and restoration on periodontally compromised teeth.

OBJECTIVE: The purpose of this study was to photoelastically evaluate the effects of cervical root lesions and their restoration on stress distribution in periodontally compromised teeth. METHOD AND MATERIALS: Three-dimensional composite photoelastic models of a maxillary first premolar with buccal cervical root lesions were fabricated. Two different lesion configurations, wedge- and shallow saucer-shaped, at 20% alveolar bone height reduction were tested. A 35% reduction model was given a wedge-shaped lesion. The lesions were restored with microfine resin composite. Vertical loads of 7.5 lbs were applied to the unrestored and restored models at the tip of the buccal cusp and the tip of the lingual cusp. The resulting stresses within the tooth models were monitored and recorded photographically in the field of a circular polariscope arrangement. RESULTS: For buccal cusp loading of the unrestored models, stress concentrated at the apex of the lesion regardless of the lesion shape or periodontal support conditions. The highest stress concentration was observed around the apex of the wedge-shaped lesion on the 35% reduction model. Restoring the lesions changed stress distribution. Restoration of the lesions resulted in a marked stress reduction at the lesion apex. Stress along the gingival restoration-model interface was characteristic for the restored situation. The interfacial stress followed the contour of the restoration most closely for the wedge-shaped lesion on the 20% support reduction model. CONCLUSION: The shape and dimension of the lesion as well as periodontal support status has considerable influence on stress distribution, especially around the lesion, restored or not restored.     

Biomechanics of cervical tooth structure lesions and their restoration.

OBJECTIVE: The purpose of this study was to evaluate photoelastically the effects of a cervical tooth structure lesion and its restoration on stress distribution within a tooth. METHOD AND MATERIALS: Three-dimensional composite models of a maxillary first premolar with a buccal cervical lesion were fabricated. Two types of cervical lesion were tested: one was wedge shaped and had a sharp line angle at the apex of the lesion, and the other was more rounded and saucer shaped. Vertical loads of 10 lb were applied to the unrestored and restored models at the tip of the buccal cusp, the tip of the lingual cusp, and the center of the occlusal surface. The resulting stresses within the tooth model were monitored and recorded photographically in the field of a circular polariscope arrangement. RESULTS: In the unrestored situation, stress concentrated at the apex of the lesion, regardless of the lesion configuration. However, the sharper, wedge-shaped lesion demonstrated a more severe stress concentration. In the restored situation, stress around the lesion apex and the lingual cervical lesion decreased, while stresses at the gingival and occlusal margins of the lesion increased, compared with the unrestored situation. These tendencies were most obvious when the buccal cusp was loaded. CONCLUSION: The presence of a cervical lesion changed occlusal load-induced stress distribution and concentrated stress at the apex of the lesion. The shape and dimension of the lesion governed the severity of stress concentration. Restoration of the cervical lesion relieved concentrated stress at the apex of the lesion.     

Stress Distribution on Trephine-Resected Root-end in Targeted Endodontic Microsurgery: A Finite Element Analysis

IntroductionThis study aimed to determine if stress distribution from occlusal loads after targeted endodontic microsurgery (TEMS) differed for trephine-resected flat and curved root-ends, with and without bone graft.MethodsFinite element analysis models were constructed from cone-beam computed tomography data of a TEMS-treated maxillary central incisor. Models included flat and curved resected root-ends, with and without apical bone graft, and normal or root canal filled controls. In centric occlusion, axial force was directed on mesial and distal lingual marginal ridges at 120° angle. For lateral excursion, additional mesiodistal forces were applied from centric occlusion. For edge biting, axial force was directed on the incisal edge. Under occlusal loads, stress distribution patterns on tooth and root-end circumference were analyzed.ResultsIn normal and root filled controls, occlusal stress was distributed on labial and palatal root surfaces, concentrated in the labial cervical area, and maximized at the apex. For resected root-ends, occlusal loads concentrated stress on the labial cervical area. With bone graft, maximum stress concentration shifted to the apex, which implied stress relief and dispersion from the cervical root area. Stress patterns on the root-end were more widely spread in models with apical bone graft, whereas curved root-end showed stress concentrating arc especially when without apical bone support. The mean stress values on root-end circumference were significantly higher in curved than flat root-end (P < .05), especially with apical bone support (P < .05).ConclusionsOcclusal stress patterns on a maxillary central incisor were markedly affected by root-end resection configuration and apical bone support. Trephine-resected curved root-end had stress pattern concentrated on its circumference. Curved and flat root-ends had labial cervical stress that was relieved by bone graft. TEMS resected root-ends should be flattened and bone grafted to disperse stress from occlusal loads.     

低强度脉冲超声促进大鼠正畸性牙根吸收的修复

目的 研究低强度脉冲超声(low-intensity pulsed ultrasound,LIPUS)对大鼠正畸性牙根吸收的作用.方法 158只Wistar大鼠建立正畸牙移动根吸收的动物模型,100 g初始力值加载于大鼠右侧上颌两中切牙与第一磨牙之间14 d,随机分为空白对照组、加力组、100 MW/cm2超声治疗组和...     

根管治疗牙正畸加力后根吸收的相关因素研究

目的研究固定正畸治疗对根管治疗牙牙根吸收的影响和相关因素分析。方法选择正畸治疗前口腔内已完善根管治疗牙45例,利用治疗前后的全口曲面断层片,以改良根吸收分级法评估患者治疗前后牙根形态变化,分析正畸治疗对根管治疗后牙根吸收的影响。结果①正畸治疗后根管治疗牙牙根吸收有所增加,差异具有统计学意义（P〈0．001）;②性别是影响正畸治疗后根管治疗牙牙根吸收方程最为显著的因素（P〈0．05）,提示女性发生根吸收的风险大于男性;③正畸治疗后根管治疗牙与对侧活髓牙比较牙根吸收程度的改变差异没有统计学意义（P〉0．05）;④在所观察的样本中,无论根管治疗牙齿与活髓牙均未见3级根吸收。结论根管治疗牙在固定正畸治疗后可能发生一定程度的根吸收改变,但并不比活髓牙的风险更高。     

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.     

应用前倾弯弓丝治疗开（牙合）畸形的生物力学研究

目的　探讨应用前倾弯弓丝矫治开畸形的效果。方法　建立包括牙周膜、牙槽骨、　1及　6的三维有限元模型 ,分析矫治力作用下牙体与牙周组织的应力分布以及牙体的位移情况 ,明确牙齿移动的机理。结果　①　6牙根表面、牙周膜、牙槽骨所受的最大拉应力均位于远中侧牙颈部 ,二种工况分别是 :0 .1830MPa ,0 .14 5 1MPa ;0 .0 2 0 2MPa,0 .0 16 0MPa ;0 .0 4 0 7MPa ,0 .0 32 3MPa ;最大压应力位于近中侧的牙颈部 ,分别是 :- 0 .0 2 2 7MPa,- 0 .0 180MPa;- 0 .0 186MPa,- 0 .0 14 7MPa ;- 0 .0 117MPa,- 0 .0 0 92MPa。②　1牙根表面、牙周膜、牙槽骨所受的最大拉应力均位于根尖区 ,二种工况分别是 :0 .4 36 2MPa ,0 .830 3MPa ;0 .0 0 5 5MPa ,0 .0 0 4 4MPa;0 .0 0 4 8MPa ,0 .0 0 38MPa ;最大压应力均位于舌侧牙颈部 ,分别为 :- 0 .0 0 2 2MPa ,- 0 .0 0 18MPa ;- 0 .0 0 06MPa ,- 0 .0 0 0 5MPa;- 0 .0 0 38MPa ,- 0 .0 0 0 3MPa;③运动趋势 :前牙产生向及舌向运动 ;支抗磨牙会产生近中龈向、远中向及牙冠向颊侧倾斜的复杂运动。结论　利用前倾弯弓丝治疗开畸形 ,支抗磨牙的移动趋势不利于患者后牙的直立及平面改建 ,不利于矫治效果的稳定。应用该方法矫治开畸形时 ,必须在支抗磨牙区增加相     

微型种植体下颌骨三维有限元模型的建立

目的探索一种可行的建立包含微型种植体不同植入方向及角度的下颌骨三维有限元模型的方法,为支抗种植体相关研究提供模型支持。方法本文基于CT数据,采用CAD（Pro/E）及ANSYS软件,用轮廓延伸法建立简化下颌骨模型,模拟临床实际常用植入部位,建立微型种植体不同植入方向及角度的下颌骨三维有限元模型。结果建立了5个真实螺纹形态的微型种植体植入的下颌骨有限元模型。结论本实验建立的有限元模型的几何相似性、生物力学相似性及临床适应性均达到实验要求,为支抗种植体三维有限元分析提供了一种准确、灵活、快速的平台。     

Effect of continuous versus intermittent orthodontic forces on root resorption: A microcomputed tomography study

Objectives:To compare the extent of root resorption and the amount of tooth movement between continuous orthodontic force and intermittent orthodontic force that was activated in a similar way to a 4-week orthodontic adjustment period.Materials and Methods:Twenty-five patients who required the extraction of upper first premolars were recruited in this study. A buccally directed continuous force of 150 g was applied to the upper first premolar on one side for 15 weeks. A buccally directed intermittent force (28 days on, 7 days off) of the same magnitude was applied to the contralateral first premolar. The teeth were extracted at the end of the experimental period and processed for volumetric evaluations of resorption craters. The degree of tooth movement and rotation were measured on the study models.Results:Continuous force application displayed significantly higher root resorption volume than the intermittent force application (P < .05), particularly on the buccal and lingual surfaces (P < .05) and the middle third of the root (P < .01). There was more tipping and rotational movement in the continuous force group.Conclusions:In a 4-week orthodontic adjustment period, intermittent force significantly reduced the amount of root resorption compared with continuous force. Although there was less degree of tooth movement with intermittent force, unwanted rotational movement was avoided. This is crucial in patients who are predisposed to orthodontically induced inflammatory root resorption, and the use of this intermittent regimen should be considered.     

Biological markers for evaluation of root resorption

BACKGROUND: External apical root resorption is a pathologic consequence of orthodontic tooth movement. Cementum and dentin are removed from the root surface while active force is present. OBJECTIVE: The aim of this study was to identify and quantify extracellular matrix proteins, dentin matrix protein 1 (DMP1), dentin phosphophoryn (PP), and dentin sialoprotein (DSP) in the gingival crevicular fluid (GCF) of subjects undergoing orthodontic treatment. METHODS: Subjects with mild (less than 2mm) and severe (more than 2mm) root resorption during orthodontic treatment were identified by radiographs. A control group of subjects with neither signs of root loss nor undergoing orthodontic treatment was also identified. GCF was collected from the upper incisors by using filter paper strips (Periopaper). The absorbed GCF was eluted and the proteins were separated by SDS-PAGE analysis and stained. Western blot and ELISA were also performed. One-way ANOVA and Scheffé test were used for statistical analysis. RESULTS: SDS-PAGE analysis identified proteins at 77, 66, 55, 50 and 26kDa. Immunoblotting did not show any differential expression pattern between control and study groups. ELISA results revealed a significant difference in the concentrations of DMP1, PP and DSP between control and root resorption groups. Concentration of PP and DSP in severe root resorption group was also statistically higher than in mild root resorption group. CONCLUSION: DSP and PP could be suitable biological markers for monitoring root resorption during orthodontic treatment, since a significant difference in the level of these dentin specific proteins is detected in all groups.     

正畸治疗中牙根发育对牙根吸收影响的临床研究

目的探讨正畸治疗对正畸治疗前不同的牙根发育状况与正畸治疗中出现的牙根吸收的影响。方法120例经固定矫治青少年,检测其前磨牙、尖牙区的744颗牙齿正畸治疗前牙根发育状况及正畸治疗后牙根的等级。按正畸治疗前牙根是否发育完成分为发育完成组和发育未完成组两组。分析正畸治疗后牙根吸收情况。结果正畸治疗前牙根发育未完成的牙齿在正畸治疗中牙齿继续发育完成,牙根根管形态发育正常,无牙根吸收情况。正畸治疗前牙根发育完成的牙齿在正畸治疗后牙根出现不同比例的牙根吸收情况。两组之间有显著的组间差异(P<0.01)。结论 正畸治疗前牙根是否发育完成对正畸治疗中牙根是否出现吸收有显著的影响。     

Finite element analysis of rapid canine retraction through reducing resistance and distraction

Objective

The aims of this study were to compare different surgical approaches to rapid canine retraction by designing and selecting the most effective method of reducing resistance by a three-dimensional finite element analysis.

Material and Methods

Three-dimensional finite element models of different approaches to rapid canine retraction by reducing resistance and distraction were established, including maxillary teeth, periodontal ligament, and alveolar. The models were designed to dissect the periodontal ligament, root, and alveolar separately. A 1.5 N force vector was loaded bilaterally to the center of the crown between first molar and canine, to retract the canine distally. The value of total deformation was used to assess the initial displacement of the canine and molar at the beginning of force loading. Stress intensity and force distribution were analyzed and evaluated by Ansys 13.0 through comparison of equivalent (von Mises) stress and maximum shear stress.

Results

The maximum value of total deformation with the three kinds of models occurred in the distal part of the canine crown and gradually reduced from the crown to the apex of the canine; compared with the canines in model 3 and model 1, the canine in model 2 had the maximum value of displacement, up to 1.9812 mm. The lowest equivalent (von Mises) stress and the lowest maximum shear stress were concentrated mainly on the distal side of the canine root in model 2. The distribution of equivalent (von Mises) stress and maximum shear stress on the PDL of the canine in the three models was highly concentrated on the distal edge of the canine cervix.

Conclusions

Removal of the bone in the pathway of canine retraction results in low stress intensity for canine movement. Periodontal distraction aided by surgical undermining of the interseptal bone would reduce resistance and effectively accelerate the speed of canine retraction.