Impact of Canal Taper and Access Cavity Design on the Life Span of an Endodontically Treated Mandibular Molar: A Finite Element Analysis

IntroductionThis study investigated the impact of different canal tapers and access cavity designs on the life span of endodontically treated mandibular first molars using the finite element method.MethodsFinite element analysis was performed on simulated models with 3 access cavity designs (traditional, conservative, and truss). The mesial canals were prepared to either constant tapers of 25/.04 and 25/.06 or a variable taper corresponding to the cumulative canal preparation shapes of TruNatomy Prime (Dentsply Sirona, Charlotte, NC) and ProTaper Gold F2 (Dentsply Sirona). The distal canals in all models had a 40/.04 preparation. Using occlusal fingerprint analysis, all models were subjected to cyclic occlusal loading until model failure. The number of cycles until failure, the location of failure, stress distribution patterns, and the maximum von Mises stresses were assessed.ResultsThe traditional access models showed a lower life span than the conservative and truss models regardless of the canal taper, whereas there was not a notable difference in the conservative and truss models. The stresses migrated apically along the root surface and remarkably on the mesial aspect of the mesial root and the furcation area’s outer surface. After root canal preparation with different tapers, there were no evident changes in the pattern and magnitude of the stresses distributed along the root surface.ConclusionsThe life span of the tooth is affected more significantly by the access cavity design than the root canal preparation taper. Because stress patterns migrate apically rather than concentrate in the pericervical area, crack initiation and propagation might occur anywhere on the root surface.     

The Effect of Access Cavity Designs and Sizes of Root Canal Preparations on the Biomechanical Behavior of an Endodontically Treated Mandibular First Molar: A Finite Element Analysis

IntroductionThis study aimed to compare the biomechanical properties of a mandibular first molar with different endodontic cavity designs and increasing sizes of root canal preparations using finite element analysis (FEA).MethodsThe experimental finite element models were designed with 3 different endodontic access cavities and 2 sizes of canal preparations: traditional access cavity, conservative access cavity, and truss access cavity and #30/.04 and #40/.04 of root canal preparations. Vertical and oblique loads were applied with a 250-N static force to simulate masticatory forces. Mathematical analysis was performed to evaluate the stress distribution patterns. Maximum von Mises (VM) stresses were assessed at the occlusal surface; cervical line; and 1 , 3, 5, and 7 mm from the root apices.ResultsDecreasing the size of the access cavity was associated with a higher magnitude of cervical stresses. The magnitude of VM stresses was maximum at the 7-mm level and was minimum at the 1-mm level from the root apex. Increasing the size of the access cavity was associated with the transmission of stresses to a further apical direction regardless of the extent of root canal enlargement. The root canal enlargement from #30 to #40 increased radicular VM stresses within all models.ConclusionsWithin the limitations of this study, conservative and truss access designs preserved a significant volume of tooth structure. The extent of root canal enlargement should be as small as practical without jeopardizing the biologic objectives of root canal treatment.     

A Comparison of Volume of Tissue Removed and Biomechanical Analysis of Different Access Cavity Designs in 2-rooted Mandibular First Molars: A Multisample 3-dimensional Finite Element Analysis

IntroductionThe aim of this study was to compare the biomechanical properties and the amount of coronal tissue removed among the different access cavities with a multisample 3-dimensional finite element analysis in the mandibular first molar. The correlation between the amount of tissue removed and the fracture resistance of the teeth was also analyzed.MethodsMicro-computed tomography data from 20 2-rooted mandibular first molars were included in this study as 3-dimensional modeling prototypes. Models of untreated molars and molars treated with the traditional access cavity (TradAC), the conservative access cavity (ConsAC), and the straight-line minimally invasive endodontic access cavities (SMIAC) were created. Each model was loaded in 3 ways to simulate the functional conditions of occlusion. The amount of tissue removed and the maximum stress in the cervical region were recorded and analyzed, and the correlation between them was also analyzed.ResultsThe amount of coronal tissue and pericervical dentin (PCD) removed in SMIAC and ConsAC was less than that of TradAC. The mean maximum stress in the cervical region was significantly smaller in SMIAC and ConsAC than in TradAC. The amount of hard tissue and PCD loss was positively correlated with the maximum stress in the cervical region of the tooth.ConclusionsIn mandibular first molars, it could be beneficial to improve the fracture resistance of the tooth after endodontic treatment by the minimally invasive access cavity to reduce the loss of coronal tooth tissue and PCD. The SMIAC may be an option balancing biomechanical properties and clinical convenience.     

上颌第一磨牙分体桩核冠的三维有限元分析

目的：应用三维有限元分析不同直径和长度的分体桩核冠修复磨牙后牙根及核桩的应力分布规律,比较分体桩的直径和长度对修复磨牙的影响。方法：应用螺旋CT扫描及医学影像传输与转录技术,建立不同直径和长度的分体桩核冠的上颌第一磨牙三维有限元模型,比较不同载荷下各桩核冠修复磨牙后牙根及核桩的应力分布规律。结果：减少核桩的长度,可以降低牙根及核桩的应力峰值;牙根的应力随着核桩直径的增加而增加,而核桩的应力随其直径的增加而减少。结论：适当减少核桩的长度和直径有利于提高修复体的成功率。     

Biomechanical Properties of First Maxillary Molars with Different Endodontic Cavities: A Finite Element Analysis

Introduction

The aim of this study was to compare the biomechanical properties of first maxillary molars with different endodontic cavities using the finite element method.

Effect of Different Endodontic Access Cavity Designs in Combination with WaveOne Gold and TruNatomy on the Fracture Resistance of Mandibular First Molars: A Nonlinear Finite Element Analysis

IntroductionThis study evaluated the effect of traditional and conservative endodontic access cavity designs in combination with WaveOne Gold and TruNatomy instrumentation systems on the fracture resistance of mandibular first molars by means of nonlinear finite element analysis (FEA).MethodsMicro-CT images of 4 human mandibular first molars were used to generate representative FEA models. The mandibular first molars samples were scanned before and after endodontic access cavity preparation and instrumentation of all 3 canals. Five nonlinear static loads were applied vertically and horizontally to specific contact points on the occlusal surface of the teeth. Maximum von Mises stress before failure and distribution of von Mises strains were recorded and compared between groups.ResultsMolars with conservative endodontic access cavities required similar levels of loads to reach failure compared with their control samples, whereas molars with traditional endodontic access cavities required significantly reduced loads in order to fail. According to the numerical investigation, the type of instrumentation system was found to have an insignificant effect on the fracture resistance of the teeth under study. Von Mises stress was concentrated around the cervical region and in the larger distal roots for all numerical models.ConclusionsThe fracture resistance of mandibular first molars is influenced significantly by a reduction in dental hard tissue, which was found to control the level of the ultimate failure load for each tooth.     

上颌中切牙斜形折裂修复设计的有限元分析

目的:通过三维有限元方法分析研究上颌中切牙斜形折裂采用不同方式修复后的应力分布。方法:利用CBCT及三维有限元软件,建立上颌中切牙斜形折裂的有限元模型,并对缺损牙按照3种修复方法建模,分析各组模型在侧向力下的Von Mises等效应力和最大主应力分布与峰值。结果:(1)同种折断模式下,剩余牙体组织等效应力值:纤维桩核冠组最大,5 mm髓腔固位冠组最小;修复体等效应力值:铸造桩核冠组最大,纤维桩核冠组最小;纤维桩核冠组粘结层的等效应力峰值最高。(2)随着肩领高度增加,剩余牙体组织等效应力均减小,纤维桩核冠组和铸造桩核冠组比髓腔固位冠组递减率更大;且舌侧肩领高度增加比唇侧肩领高度增加所造成的剩余牙体组织等效应力递减率更大。结论:完整且高度足够的牙本质肩领是上前牙大面积缺损时采用纤维桩核冠和铸造桩核冠修复的必要条件,当牙本质肩领不完整时,舌侧肩领比唇侧肩领更有利于提高残根的抗折性。当上颌中切牙斜形折裂,肩领不完整时,采用髓腔固位冠修复的应力分布优于桩核冠,其中固位体深度为5 mm的髓腔固位冠可能是最佳修复方式;若采用桩核冠修复,铸造桩核冠比纤维桩核冠更有利于剩余牙体组织应力均匀分布。     

The Effect of Endodontic Access Cavities on Fracture Resistance of First Maxillary Molar Using the Extended Finite Element Method

Introduction

The purpose of this study was to predict the fracture resistance of an endodontically treated first maxillary molar with diverse access cavities using the extended finite element model (XFEM).

Effects of Conservative Access and Apical Enlargement on Shaping and Dentin Preservation with Traditional and Modern Instruments: A Micro-computed Tomographic Study

IntroductionThis ex vivo study aimed to evaluate the shaping abilities and preservation of dentin with traditional and modern instruments after using sizes 25 and 40 in oval canals of mandibular incisors with conservative access.MethodThirty mandibular incisors with single straight oval canals were selected and assigned into 2 groups (n = 15) according to the instrument system used during preparation, Slim Shaper (SS) plus Apical Shaper (AS) and Protaper Gold (PG). The samples were subjected to micro-computed tomography before and after preparation with sizes 25 and 40. The shaping parameters evaluated included canal volume and surface area, amount of unprepared root canal walls, and reduction in pericervical dentin.ResultsCanal volume and surface area were significantly increased after enlargement with each instrument size (P < .01). The percentage of unprepared areas showed a significant intragroup decrease after using PG F2 and F4 or SS 3 and AS (P < .05). Intergroup comparison showed no significant differences. Pericervical dentin was reduced in all groups. The intragroup comparison only revealed a significant reduction (P < .01) between PG F2 and F4. In addition, a significant decrease in pericervical dentin (P < .05) was observed between PG F4 40/.06 and AS 40/.03. No significant differences were observed between PG F2 25/.08 and SS 3 25/.04.ConclusionIncreasing the instrumentation size from 25 to 40 significantly reduces the percentage of unprepared areas regardless of the system used. In addition, using a modern system with a regressive taper allows the maintenance of pericervical dentin without compromising shaping efficacy in the apical third of the mandibular incisors with oval canals and conservative access.     

Evaluating the Effect of Oblique Ridge Conservation on Stress Distribution in an Endodontically Treated Maxillary First Molar: A Finite Element Study

IntroductionAlthough the maxillary first molar (MFM) has been frequently subjected to stress analysis in endodontic investigations, the available data about the effect of its oblique ridge are quite sparse. The aim of this study includes evaluating the effect of the residual oblique ridge on the stress distribution after preparing conservative access cavities.MethodsBased on the cone-beam computed tomographic data, the model of an intact MFM and 5 cavity designs were prepared for endodontic treatment, which were consequently filled with gutta-percha and dental resin composite (6 total models). All models were subjected to 4 types of occlusal loading; finite element analysis via ABAQUS CAE software (Dassault Systemes, Vélizy-Villacoublay, France) was accomplished, whereas other software programs such as (Mimics Research Materialise, Leuven, Belgium) and 3-Matic Research (Materialise) were also incorporated in different stages for detecting stress distribution.ResultsThe stress distribution on the MFM is not only dependent on the remaining width of the oblique ridge but also on the type of loading. The most stress on the cervical region was concentrated on the palatal root in some type of loading, whereas the least stress on the occlusal surface was recorded when the whole oblique ridge was replaced by the composite resin.ConclusionsWhen the occlusal contacts are occurring only on the palatal cusp, the stress distribution on the oblique ridge is noticeably affected by the cavity design.     

上颌第一磨牙远中移动时牙周应力分布的三维有限元分析

目的　研究上颌第一磨牙远中移动时其牙周组织应力分布情况,探讨上颌第一磨牙远中移动的最佳荷载方式,为临床应用提供生物力学基础。方法　采用正常的头颅骨,通过螺旋CT扫描的方法建立上颌第一磨牙的三维有限元模型。使用4种不同负荷方式对模型进行加载,计算上颌第一磨牙远中移动的最佳荷载方式。结果　上颌第一磨牙远中移动时,不同的加载所产生的牙周的应力分布不同。在上颌第一磨牙颊面中心附近施加远中力并结合抗衡力矩(Mt/F=10, Mr/F=6)可以在牙周膜的远中面获得平均分布的低压应力,它能使牙齿倾向于整体移动。结论　正确的荷载方式可消除旋转和倾斜,使上颌第一磨牙整体远中移动。     

上颌前磨牙隧道洞型应力分析

目的: 分析边缘嵴高度和修复材料对上颌前磨牙隧道洞型的应力影响。方法: 建立边缘嵴高度分别为1.5 mm、2.5 mm、3.5 mm的上颌前磨牙隧道洞型的三维有限元模型。修复材料设定为复合树脂(CR)和树脂加强型玻璃离子(GIC)。在正常咬合接触区加载垂直于牙面的100 N的力,计算牙釉质、牙本质和修复材料的应力分布,评估其失效风险。结果: 对于不同边缘嵴高度,摩尔库伦失效值在边缘嵴高度为2.5 mm时最低;对于不同修复材料,复合树脂修复的隧道洞型摩尔库伦失效值较低。结论: 边缘嵴高度为2.5 mm,复合树脂修复的隧道洞型具有更好的力学性能。     

下颌第一磨牙全瓷冠疲劳寿命预测的三维有限元分析

目的:对EmpressⅠ、EmpressⅡ、In-Ceram Alumina以及In-Ceram Zirconia4种不同材料的下颌第一磨牙全瓷冠进行疲劳寿命预测。方法:模拟1、5、10年间,相当于最大咬合力的循环疲劳载荷,加载于全瓷冠模型。通过有限元疲劳分析软件MSC.Fatigue预测各种材料全瓷冠的失效概率。结果:基于本有限元疲劳分析,EmpressⅠ、EmpressⅡ、In-Ceram Alumina以及In-Ceram Zirconia这4种均可应用于后牙全瓷冠。其中采用EmpressⅠ制作的全瓷冠较其他3种材料具有较高的失效概率(3.15%~7.486%)。结论:有限元疲劳分析有助于全瓷修复材料临床应用前的耐疲劳强度的判断。     

倾斜角度对种植体骨界面生物力学影响的三维有限元分析

目的 :分析不同倾斜种植对种植体界面应力、应变及位移分布状况的影响。方法 :在第一磨牙区分别垂直及向舌侧倾斜10°、20°、30°植入种植体 ,建立下颌骨三维有限元模型。模拟咀嚼肌力加载 ,分析在正中咬合情况下种植体骨界面应力、应变及位移分布情况。结果 :随着倾斜角度的增大 ,种植体骨界面应力、应变及位移均增加。倾斜30°种植时 ,种植体骨界面应力显著性增大(P<0.01)。结论 :种植体倾斜角度应小于30°。     

Comparison of the Mechanical Behavior between Controlled Memory and Superelastic Nickel-Titanium Files via Finite Element Analysis

IntroductionThe aim of this study was to evaluate the flexibility and torsional stiffness of a controlled memory (CM) nickel-titanium (NiTi) file and compare its mechanical responses with those of a superelastic NiTi file with the same geometry using finite element simulation.MethodsA commercially available instrument with a tip size of 30 and a 0.06 taper was selected for this study. The geometric model for finite element analysis was generated by micro–computed tomographic scanning, and the data for the constitutive model of controlled memory NiTi were obtained from the literature. The numeric analysis was performed in ABAQUS (SIMULIA, Providence, RI) with boundary conditions that were based on the ISO 3630-1 specification.ResultsThe CM NiTi file exhibited the least bending moment and maximum stress value (523 MPa) under 45° bending simulation. However, the least torsional stiffness was calculated for this same instrument.ConclusionsThe higher flexibility and potential fatigue resistance of the CM NiTi files were confirmed, indicating that this new technology represents an improvement in the mechanical behavior of the rotary NiTi files.     

Study of Deflections in Maxillary Major Connectors: A Finite Element Analysis

The Major connector is the major component of the cast partial denture to which all other parts are directly or indirectly attached. It also provides cross arch stability to help resist displacement by functional stresses. The major connector should be rigid. A flexible major connector causes an unequal distribution of forces with changes in their intensity and may cause damage to the supporting structures. Thus rigidity is of paramount to resist flexing and torquing forces. The commonly used major connectors for the maxillary arch are Anteroposterior strap, palatal strap and complete palatal plate. Application of load on the prosthesis will result in deflection. The magnitude and direction of the deflection that the prosthesis undergoes depends on the rigidity of the major connector. (1) To determine the deflection seen in maxillary removable partial denture frameworks under simulated occlusal load. (2) To compare the rigidity and deflection characteristics of different maxillary major connectors used in maxillary Kennedy’s class I, class II, class III and class IV situations. A CT scan of human edentulous maxilla was taken and each section from the incisive foramen to the hamular notch was projected on the graph paper and three dimensional volumes were created from the connected successive profiles to define the final solid geometry of bone. Six framework models with different Maxillary major connectors such as Anteroposterior straps and complete palatal plate for Kennedy’s class I, class II, class III and class IV situations were created. Three Dimensional Finite Element Models corresponding to the geometric model were created using ANSYS 9.0 version. The model was assigned the material properties. A vertical biting force of 20 N was applied. The results showed maximum displacements were observed at the posterior edge of the saddle for all the frameworks. Anteroposterior palatal strap in class III and class IV situation showed the least deflection when compared to class I and class II (distal extension situation) Anteroposterior palatal strap is more rigid connector than the full palatal plate, single palatal strap, and U-shaped palatal strap and can be used in all situations.     

Influence of Progressive Versus Minimal Canal Preparations on the Fracture Resistance of Mandibular Molars: A 3-Dimensional Finite Element Analysis

IntroductionThis study compared the residual tooth strength and stress distribution of a mandibular molar prepared with different variable tapered file systems using finite element analysis (FEA).MethodsTwo preaccessed mandibular molar TruTeeth (Endo 3DP; Acadental, Lenexa, KS) were subjected to simulated endodontic treatment in this study. One tooth was instrumented with ProTaper Gold (Dentsply Tulsa Dental Specialties, Tulsa, OK), and the other was instrumented with V-Taper 2H (SS White Dental, Lakewood, NJ). The 2 teeth were scanned using micro–computed tomographic imaging, and stereolithographic surface meshes were developed for FEA. Each model was subjected to a 200-N multipoint load-simulating mastication. The results of the FEA provided quantitative and qualitative measurements for von Mises stress distribution and total deformation.ResultsThe maximum von Mises stress was greater in the ProTaper Gold–prepared model than the V-Taper 2H prepared model. In both models, total deformation values were highest in the clinical crown on the buccal aspect of the tooth. The highest stress values were found in the pericervical dentin, and stress decreased apically through the root.ConclusionsWithin the limitations of this study, it can be concluded that the maximum stress values within the tooth prepared by ProTaper Gold were higher than those in the tooth prepared by V-Taper 2H. Canal preparation with the V-Taper 2H system preserves more pericervical dentin, which may increase the resistance to fracture.     

上颌窦底提升不同高度对种植义齿受力影响的三维有限元分析

目的:研究上颌窦底提升后种植义齿修复时,不同提升高度对种植体-骨界面应力状况的影响,为其临床应用提供生物力学参考依据。方法:采用健康志愿者的CT扫描数据,通过Mimics 11.0软件,建立上颌第一磨牙缺失、含上颌窦的上颌骨三维有限元模型,并模拟植入10 mm长标准种植体1枚。模拟上颌骨骨量不足,建立上颌窦底分别提升2、4、6 mm的种植义齿模型,并以无需窦底提升的种植义齿模型为对照。分别从垂直、颊向30°和舌向30°三个方向,对种植义齿上部结构牙冠咬合面中心点施加100 N的集中载荷,用三维有限元分析方法对不同模型的种植体-骨界面进行应力分析。结果:各模型在同一加载条件下,皮质骨的应力最大,松质骨和人工骨的应力值接近。随着窦底提升高度的增高,种植体颈部周围骨组织的应力总体呈先降后升的趋势,在提升高度为4 mm时最小。颊舌向加载时产生的应力远大于垂直载荷下产生的应力。结论:上颌骨后部骨量不足时,上颌窦底提升植骨可以大大改善种植体-骨界面内应力,植骨高度为4 mm时,种植体-骨界面应力总体最小;垂直载荷更有利于种植体-骨界面的应力分布状况,在临床设计种植义齿上部结构时应尽量减小或避免斜向载荷。     

桩影响前牙烤瓷冠修复后牙本质应力分布的三维有限元分析

采用三维有限元法分析桩对上颌中切牙金属烤瓷冠修复后牙本质应力分布的影响。选择一标准的上颌中切牙，经包埋、螺旋ＣＴ扫描、图形数字化，采用ＳｕｐｅｒＳＡＰ有限元分析软件在微机上建立三维有限元模型，模拟了牙槽骨、牙周膜、牙本质、桩、金属烤瓷冠的金属帽状冠及烤瓷层等结构，与临床实际结构类似。分别分析ＳＤＡ－Ⅱ型中熔合金桩修复前后，牙本质应力分布情况。结果表明：金属桩可改变牙本质原有的应力分布模式，使桩与牙本质交界区应力值增大；但与此同时又降低了牙本质应力峰值，Ｖｏｎｍｉｓｅｓ应力降低１３．９８％，最大主应力降低７．０５％。即从力学角度提示：合理桩修复可防止牙体断裂。     

弧形牵张成骨重建人体下颌骨颏部节段性缺损的三维有限元研究

目的:建立下颌骨颏部节段性缺损弧形牵张成骨的三维有限元模型,研究弧形牵张成骨重建下颌骨颏部节断性缺损过程中,不断变化方向的牵张力对新骨组织形成的影响。方法:建立颏部节段性缺损的三维有限元模型,并把简化后的弧形牵张器有限元模型置入截断后的下颌骨,模拟弧形牵张成骨,并测量在弧形牵张成骨过程中下颌骨整体位移及其von Mises应力分布。结果:在未考虑唇颊侧软组织作用的前提下,弧形牵张成骨形成的新骨向舌侧生长,重建的下颌骨弧度较原下颌骨弧度变小。von Mises应力主要集中于牵张器在下颌骨的固位处。结论:在弧形牵张成骨重建下颌骨缺损过程中,牵张力本身就促使新骨组织向舌侧生长,从而使重建的下颌骨弧度较正常时小。此项研究为临床上如何克服弧形牵张成骨所形成的下颌骨弧度较小的不足,提供了一定的理论依据。