三维有限元分析在牙周夹板研究中的应用

牙周炎是口腔常见病、多发病,是牙齿松动的主要原因之一.牙周夹板一直以来是松牙固定的有效手段,它可以将多个牙连成一个整体,形成一个“多根巨牙”,共同承担咬合力,有效地分散牙周膜及牙槽骨的应力,为牙周组织的愈合创造有利条件.三维有限元分析法是研究复杂模型应力分布的生物力学方法,近年来广泛应用于牙周夹板的研究中,该方法可以逼...     

Stresses at the dentinoenamel junction of human teeth--a finite element investigation.

A three-dimensional, linear, elastic finite element model of a maxillary first premolar from longitudinal ground sections was developed to investigate stress variation in the enamel and dentin adjacent to the dentinoenamel junction (DEJ). The effect of regional variation in the contour of the DEJ on the stress patterns for enamel and dentin was also analyzed. The normal (compressive or tensile) and shear stresses in the dentin and enamel surfaces of the DEJ were computed for a vertical load of 170 N acting on the entire occlusal surface of the model. The normal stresses in dentin and enamel were maximum on the occlusal surface of the model and diminished along the buccal and lingual surfaces of the DEJ. However, the magnitude of the normal stresses increased at the cervical enamel, which also showed increased values for shear stress distribution. The normal and shear stresses were markedly affected by the contour of the DEJ and the thickness of enamel in the occlusal third on the buccal and lingual surfaces. The results suggested that because the mechanical interlocking between enamel and dentin in the cervical region is weaker than in other regions of the DEJ, enamel in this region may be susceptible to belated cracking that could eventually contribute to the development of cervical caries.     

Initial effect of multiloop edgewise archwire on the mandibular dentition in Class III malocclusion subjects. A three-dimensional finite element study

The purpose of this study was to compare the effect of a multiloop edgewise archwire (MEAW) with a plain ideal archwire (IA) on distal en masse movement of the mandibular dentition. A three-dimensional finite element model (3D FEM) of the mandibular dentition, without third permanent molars, was constructed to include the periodontal membrane (PDM), alveolar bone, standard edgewise bracket (0.018 x 0.025 inch), stainless steel IA (0.016 x 0.022 inch), and MEAW (0.016 x 0.022 inch). Stress distribution and displacement of the mandibular dentition were analyzed when Class III intermaxillary elastics (300 g/side) and 5 degree tip-back bends from the first premolar to the second molar were applied to the IA and the MEAW for distal en masse movement of the mandibular dentition. Compared with the IA, the discrepancy in the amount of tooth displacement was less and individual tooth movement with the MEAW was more uniform and balanced. There was minimal vertical displacement or rotation of the teeth with the MEAW when compared with the IA. The MEAW seems to have advantages for distal en masse movement of the mandibular dentition.     

MEAW弓丝“L”形曲的力学分析

目的初步研究多曲方丝弓矫治技术力学系统的力学特性.方法采用3D梁单元建立不同托槽间距下"L"形曲的三维有限元模型,对模型进行网格划分,并输入材料性能参数,用ANSYS软件进行模拟,计算产生的应力.结果多曲方丝弓矫治系统中各牙段之间的刚度各不相同,前牙段明显高于后牙段,解释了MEAW技术在一根弓丝上同时实现前牙稳定和后牙移动的矫治机理.结论MEAW技术在同一根弓丝上可以同时实现稳定前牙和移动后牙的矫治机理是因为前后牙段弓丝刚度之间存在显著差异.     

Effects of cervical headgear and edgewise appliances on growing patients.

Maxillary basal bone, dentoalveolar, and dental changes in Class II Division 1 patients treated to normal occlusion by using cervical headgear and edgewise appliances were retrospectively evaluated. A sample of 45 treated patients was compared with a group of 30 untreated patients. Subjects were drawn from the Department of Orthodontics, Araraquara School of Dentistry, Brazil, and ranged in age from 7.5 to 13.5 years. The groups were matched based on age, gender, and malocclusion. Roughly 87% of the treated group had a mesocephalic or brachicephalic pattern, and 13% had a dolicocephalic pattern. Cervical headgear was used until a Class I dental relationship was achieved. Our results demonstrated that the malocclusions were probably corrected by maintaining the maxillary first molars in position during maxillary growth. Maxillary basal bone changes (excluding dentoalveolar changes) did not differ significantly between the treated and the untreated groups. Molar extrusion after the use of cervical headgear was not supported by our data, and this must be considered in the treatment plan of patients who present similar facial types.     

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.     

Stresses in the periodontal ligament

Measurements have been made of the root areas of forty five extracted teeth. These have been used to calculate the theoretical pressures that may occur in the region of the alveolar crest and their increase with progressive loss of alveolar bone when a lateral force is applied to the crown of the tooth. Pressures generated in the periodontal ligament as a result of axial loadings have also been calculated and compared with those due to lateral loadings. The results suggest that a very rapid increase in pressures in the periodontal ligament would occur with bone losses in excess of 55 per cent in the case of lateral loadings and over 80 per cent in the case of axial loading. The implications for clinical practice are discussed.     

方丝弓矫治器三维有限元力学模型的建立

目的:以有限元方法建立方丝弓矫治器的力学分析数字模型。方法:采用powerSHAPE3040造型软件,在已有的下颌三维数字模型基础上,划出托槽槽沟中心平面(H)、颊面牙体长轴和托槽中心,以其为基准,构建下颌左侧牙列槽沟为0.018in(1in=2.54cm)的托槽模型。这些托槽在各牙位的槽底厚度相同,托槽槽沟在同一H平面。然后据此托槽和H平面构建出0.016in×0.022in的平直方丝模型。再用ANSYS分析系统将这些三维模型转化为三维有限元模型。牙、牙周膜、牙槽骨和托槽以4点四面体单元划分,弓丝以10点四面体单元划分。结果:获得下颌牙列及其托槽和平直方丝的三维有限元模型。该托槽槽底带有转矩,所建平直方丝在H平面上与托槽槽沟均匀接触,因此初始状态彼此无作用力。结论:该模型初步建立了用三维有限元法对固定矫治技术进行全牙列分析的平台。     

多曲方丝对下颌中切牙牙周膜应力分布有限元分析

目的:对多曲方丝弓技术中打开咬合所产生的力学系统进行有限元分析,了解多曲方丝弓打开咬合时下颌中切牙牙周膜应力分布情况。方法:建立下颌牙列各牙齿、牙槽骨及切牙牙周膜的有限元模型。然后进一步模拟临床在中切牙处加载75g垂直向下的力,按照考虑或不考虑牙周膜的两种情况,求得牙周膜的应力分布。结果:两种情况下牙周膜部位最大值变化很大。在不考虑牙周膜时,牙根颈部应力最大值达21.6×105g/mm2;考虑牙周膜的缓冲作用时牙根及牙周膜上的应力分布相对均匀,且绝对值变小,但牙槽嵴顶部应力峰值明显变大。结论:①本研究建立的下颌牙列的三维有限元模型,比较符合实际情况,可以适用于多曲方丝弓矫治技术的研究。②多曲方丝弓作用下下颌中切牙牙周膜应力从颈缘到根尖逐渐减小,但在牙槽嵴顶部应力峰值明显增大,易出现牙周膜透明性变。     

Stresses at the cervical lesion of maxillary premolar--a finite element investigation

Objectives. The objective of this study was to use a three-dimensional (3-D) finite element model to investigate normal stress distribution to substantiate the tooth flexure mechanism. The study also compared the changes in the stresses by different occlusal loading sites and directions.

Methods. The 3-D finite element analysis was used. A maxillary premolar was selected to construct the simulation model. The model was constructed step-by-step for convergence and validity. Seven load conditions for various load sites and different directions were simulated to the model.

Results. The maximal principal stress and minimal principal stress distributions developed within the structures of seven load conditions were output and their stress distributions on z-plane at the vertical midline were shown. The peak tensile stress of the cervical area for various load conditions were compared and listed.

Conclusions. This study has shown that the presence of tensile stresses in the cervical region of a maxillary premolar by various loading sites and different directions. The results coincided with the stress-induced theory, hence sustaining it. The relationship of the affected factors of leverage to the development of cervical abfraction lesions, was explored.     

Mechanical behavior of tooth, periodontal membrane, and mandibular bone by the finite element method.

Simulation of the human tooth, periodontal membrane, and mandibular bone was attempted basing on the anatomical form and dimension, and the experimental data of each component were examined by the two-dimensional finite element method. Following problems were investigated: (1) Which of two factors, elastic modulus or Poisson's rate, in periodontal membrane played an important role for supporting the tooth, and (2) Characteristics of tooth and alveolar bone displacement, and stress distribution in periodontal membrane and mandibular bone were investigated under a definite condition. It is clarified that Poisson's ratio plays a much important role than the elastic modulus and this method is more suitable for simulating the model equivalent to human body and for examining the internal stress and it's displacement than the strain gauge and photoelastic method.     

可摘式螺旋扩弓装置配合方丝弓矫正器的临床研究

探讨一种简单,可靠,稳定的扩弓方法,方法选择１６例生长发育各期需扩弓矫治的患者,在常规戴入方丝弓矫治器的同时使用摘式螺旋扩弓装置扩大牙弓。扩弓装置平均截入时间６个月,方丝弓矫澡器戴入１－２年。结论该方法可提高扩弓效率,减少复诊次数,是一种行之有效的扩弓,适用于生长发育各期的患者。     

Three-dimensional finite element analysis in distal en masse movement of the maxillary dentition with the multiloop edgewise archwire

The purpose of this study was to compare the effects of a multiloop edgewise archwire (MEAW) on distal en masse movement with a continuous plain ideal archwire (IA). Three-dimensional finite element models (FEM) of the maxillary dentition in which the second permanent molars had been extracted were constructed to include the periodontal membrane, alveolar bone, standard edgewise bracket (0.018 x 0.025 inch), stainless steel IA (0.016 x 0.022 inch), and MEAW (0.016 x 0.022 inch). The stress distribution and displacement of the maxillary dentition were analysed when Class II intermaxillary elastics (300 g/side) and 5 degree tip-back bends were applied to the IA and MEAW for distal en masse movement of the maxillary dentition. Compared with the IA, the MEAW showed that the discrepancy in the amount of tooth displacement was lower and individual tooth movement was more uniform and balanced. There was minimal vertical displacement or rotation of the teeth using the MEAW when compared with the IA. The MEAW seems to have advantages for distal en masse movement of the maxillary dentition.     

Dynamic study of miniplates by finite element method

Three-dimensional analysis by means of the finite element method was made of displacement and principal stress at various parts of plates and bone fragments. The plates were 4 Champy, AO, Luhr, Steinh?user 4-hole, short miniplates (Plates 1,2,3, and 4) and Plate 5, which was the same as the others except that it was made of titanium. To all of these plates loads were applied in the directions of the Y and Z axes on the free(right)ends. The plates were fixed in place by means of screw holes 1 and 2 in the left ends. In addition, various kind of osteosynthesis were performed on 2 bone fragments with Plate 1. The left ends of these fragments were fixed in place, and loads were applied to the free(right)ends in the Y and Z axes. 1) When load was applied in the direction of the Y axis, displacements along the Y and X axes were greatest in the case of Plate 5 and next greatest in Plate 1. Displacement along the Z axis was greatest in Plate 3 and next greatest in Plate 5. Displacement along the X axis was least in Plate 3 and displacement along Y and Z axes were least in Plate 4. 2) When load was applied in the direction of the Z axis, displacements along the all axes were greatest in Plate 5, next greatest in Plate 1, and least in Plate 4. 3) In all plates, when load was applied in the direction of the Y axis, maximum principal stresses occured above the region between screw holes 2 and 3. Minimum principal stress, however, concentrated below the area between screw holes 2 and 3 in all models. 4) In all plate models, when loads was applied in the direction of the Z axis, maximum principal stresses concentrated in the outer central part of each plate in the region between the vicinity of the right edge of screw hole 2 and the vicinity of the left edge of screw hole 3. Minimum principal stress, on the outer hand, concentrated in the inner middle region of the plate in a zone corresponding to that in which maximum principal stress concentrated.(ABSTRACT TRUNCATED AT 400 WORDS)     

上颌牙列及方丝弓矫治器三维有限元模型的建立及验证

目的快速建立高精度的上颌方丝弓矫治器的三维有限元分析模型并进行验证。方法通过多层螺旋CT扫描,获得上、下颌骨及牙列的数据,采用Mimics、Catia及ABAQUS软件相结合的方法,建立包括上颌牙列、牙周膜、牙槽骨、方丝弓矫治器的三维有限元模型,并观察计算机模拟矫治力作用下上颌中切牙应力分布。采用激光散斑剪切实验力学的方法进行验证。结果建立了包含方丝弓矫治器的上颌牙列的三维有限元模型,计算机模拟作用下的应力分布情况与激光散斑剪切试验结果相近,模型的精确性得到了初步有效的验证。结论所建立的三维有限元模型仿真性好,方法便捷有效,为采用有限元法进行正畸生物力学分析的深入研究打下基础。同时可为临床矫治提供一定的指导意义。     

打开咬合时下颌中切牙及牙周膜应力分布的有限元研究

目的对下颌中切牙及其牙周膜在打开咬合时所产生的力学系统进行有限元分析,了解打开咬合时下颌中切牙及牙周膜应力分布的情况。方法建立下颌牙列各牙齿、牙槽骨及切牙牙周膜的三维有限元模型。然后,进一步模拟临床,在中切牙处加载15 g 垂直向下的力,求得牙齿以及牙周膜的应力分布情况。结果牙根表面最大应力值分布复杂,在根尖处可见应力集中区,应力集中区集中在颈缘处,向根方应力值逐渐变小,表现为典型的弯曲变形应力分布特征。舌侧、近中面主应力值相对较小,最大应力值在远唇轴角处。牙槽嵴顶部的应力值最大值达20.5×10~5g/mm~2。结论 1)本研究建立的下颌牙列的三维有限元模型,可以适用于临床上打开咬合等矫治技术的研究。2)矫治力作用下下颌中切牙牙周膜上应力从颈缘到根尖逐渐减小,但在牙槽嵴顶部应力峰值明显增大。     

Biomechanical investigation into the role of the periodontal ligament in optimising orthodontic force: a finite element case study

ObjectivesThis paper aimed to precisely locate centres of resistance (CRe) of maxillary teeth and investigate optimal orthodontic force by identifying the effective zones of orthodontic tooth movement (OTM) from hydrostatic stress thresholds in the periodontal ligament (PDL).MethodsWe applied distally-directed tipping and bodily forces ranging from 0.075 N to 3 N (7.5 g to 300 g) onto human maxillary teeth. The hydrostatic stress was quantified from nonlinear finite element analysis (FEA) and compared with normal capillary and systolic blood pressure for driving the tissue remodelling. Two biomechanical stimuli featuring localised and volume-averaged hydrostatic stresses were introduced to describe OTM. Locations of CRe were determined through iterative FEA simulation.ResultsAccurate locations of CRes of teeth and ranges of optimal orthodontic forces were obtained. By comparing with clinical results in literature, the volume average of hydrostatic stress in PDL was proved to describe the process of OTM more indicatively. The optimal orthodontic forces obtained from the in-silico modelling study echoed with the clinical results in vivo.ConclusionsA universal moment to force (M/F) ratio is not recommended due to the variation in patients and loading points. Accurate computational determination of CRe location can be applied in practice to facilitate orthodontic treatment. Global measurement of hydrostatic pressure in the PDL better characterised OTM, implying that OTM occurs only when the majority of PDL volume is critically stressed. The FEA results provide new insights into relevant orthodontic biomechanics and help establish optimal orthodontic force for a specific patient.