Evaluation of Design Parameters of Dental Implant Shape, Diameter and Length on Stress Distribution: A Finite Element Analysis

The aim was to evaluate the design parameters of dental implants shape, diameter and length on stress distribution by finite element analysis (FEA).The objectives of the study was to compare the influence of stress distribution in the implants of screw-vent tapered and parallel design by varying the implant diameter with a standard implant length. Six dental implant models have been simulated three-dimensionally. The influence of diameter and length on stress distribution was evaluated by Group I: for screw-vent tapered design (Zimmer Dental Implant Carlsbad, CA, USA) (1) Dental implant model with diameter 3.7 mm and length 13 mm. (2) Dental implant model with diameter 4.1 mm and length 13 mm. (3) Dental implant model with diameter 4.7 mm and length 13 mm. Group II: for parallel design (Zimmer Dental Implant Carlsbad, CA, USA) (4) Dental implant model with diameter 3.7 mm and length 13 mm. (5) Dental implant model with diameter 4.1 mm and length 13 mm. (6) Dental implant model with diameter 4.7 mm and length 13 mm. The 3-D model of the implant was created in the pro-e wildfire 4.0 software by giving various commands. This model was imported to the ANSYS software through IGES (initial graphic exchange specification) file for further analysis. All six models were loaded with a force of 17.1, 114.6 and 23.4 N in a lingual, an axial and disto-mesial direction respectively, simulating average masticatory force in a natural oblique direction, to analyze the stress distribution on these implants. The increase in implant diameter in Group I and Group II from 3.7 to 4.1 mm and from 4.1 to 4.7 mm with constant 13 mm length for screw-vent tapered and parallel design implant resulted in a reduction in maximum value of Von Mises stress in the bone surrounding the implant was statistically significant at 5% level done by student “t” test. The overall maximum value of Von Mises stress was decreased in parallel design implant diameter of 4.7 mm with constant length of 13 mm when compared to screw-vent tapered design implant samples. The results of the FEA computation depend on many individual factors including material properties, boundary conditions interface definition and also on the overall approach to the model. The results depicted that the tapered shape implant design exhibited higher stress levels in bone than the parallel shaped implant design which seemed to be distributing stresses more evenly. The application of a 3-D model simulation with the non-symmetric loading by the masticatory force on a dental implant resulted in a more satisfactory modeling of “clinical reality” than that achieved with 2-D models used in other studies.     

Changes of Hyoid,Tongue and Pharyngeal Airway after Mandibular Setback Surgery by Intraoral Vertical Ramus Osteotomy

Objective:To assess changes in hyoid, tongue, pharyngeal airway, and head posture in patients who had mandibular setback surgery by intraoral vertical ramus osteotomy (IVRO) and to investigate the influence of LeFort I osteotomy.Materials and Methods:Sixty patients with skeletal Class III malocclusion were evaluated. All patients had mandibular setback surgery via IVRO, and 45 patients had additional maxillary impaction surgery via LeFort I osteotomy. Lateral cephalograms were taken before, immediately after, approximately 1 month after, and at least 1 year after surgery. Parameters indicating the hyoid, tongue, pharyngeal airway, and head posture were evaluated.Results:The hyoid significantly moved inferoposteriorly immediately after surgery and relapsed superoanteriorly during observation periods. The tongue significantly moved posteriorly during all periods. The final position of the hyoid and tongue was significantly posterior, and the final pharyngeal airway was significantly narrower compared with its presurgical position. Significant cervical hyperflection occurred during observation periods and was strongly correlated with anterior movement of the hyoid. The hyoid and tongue showed similar positions regardless of the presence of different genders or LeFort I osteotomy after the long-term observation period.Conclusions:The hyoid and tongue moved posteriorly after mandibular setback surgery via IVRO, and there was a tendency to relapse back to its original position. However, the final pharyngeal airway width remained narrower after the long-term observation period. Based on our results, careful monitoring of the airway may be needed after mandibular setback surgery via IVRO.     

不同桩核系统修复上颌第一磨牙的有限元分析

目的：利用有限元法分析不同数目桩、不同材料桩核及不同载荷对磨牙桩核冠修复后剩余牙体组织的应力大小及其分布的影响。方法：采用CT扫描上颌第一磨牙,有限元法建立不同数目桩及不同材料桩核修复上颌第一磨牙后的模型,载荷1以480 N总载荷垂直加载模拟正中咬合,载荷2以200 N总载荷与牙长轴成45°斜向加载模拟咀嚼,采用MSC.Marc软件分析剩余牙体组织的Von Mises应力大小及其分布。结果：随桩核材料弹性模量的增加,牙颈部Von Mises应力峰值减小,牙根内表面的应力值增加;铸造桩组腭根和远中颊根桩修复时,桩周牙本质的应力峰值小于腭根桩修复及腭根和近远中颊根桩修复;载荷2条件下,牙颈部的应力峰值较载荷1条件下的应力峰值小,而牙根内表面的应力峰值较大。结论：桩的数目、桩核材料及载荷大小与方向均对磨牙桩核冠修复后剩余牙本质的应力大小和分布有影响。     

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.     

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.     

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。     

牵引器放置方位对骨-牵引器界面生物力学影响的三维有限元分析

目的：建立双侧下颌骨牵引成骨的三维有限元模型,探讨牵引器不同放置方位对骨一牵引器界面的生物力学影响。方法：模拟牵引器放置平行于下颌骨体部及平行于牵引轴方向两种状况,分析下颌骨牵引延长不同工况下骨一牵引器界面位移、综合应力情况。结果：牵引器放置平行于下颌骨体部时,骨一牵引器界面侧向位移、综合应力均大于牵引器放置平行于牵引轴方向的情况。结论：实验结果提示牵引器应尽量放置平行于牵引轴方向,避免可能发生的不良并发症。     

两种附着体固位的下颌种植覆盖义齿三维有限元应力分析

目的：探讨球形、杆式附着体对全下颌种植覆盖义齿应力分布的影响.方法：应用三维有限元法,对比两种附着体固位的全下颌种植覆盖义齿及支持组织应力分布的差异.结果：①两种固位方式的覆盖义齿对侧向力的抵抗性均差,种植体-骨界面应力峰值高,为垂直载荷的1.6-9.2倍.②剩余牙槽嵴表面应力,球形大于杆式,但两种固位方式均有利于骨组织的生理健康;③球形基桩颈部,杆与种植体、附着体阴型与基托连接处应力集中、峰值高.结论：杆式附着式覆盖义齿的固位、稳定性较好.应通过采用缓冲措施或改变种植体植入部位等方式优化应力分布,提高种植成功率.     

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。     

Evaluation of Stress Distribution in Bone of Different Densities Using Different Implant Designs: A Three-Dimensional Finite Element Analysis

A key factor for the success or failure of a dental implant is the manner in which stresses are transferred to the surrounding bone. This depends on the type of loading, bone–implant interface, the shape and characteristics of the implant surface and the quality and quantity of the surrounding bone. This study was done to evaluate the pattern of stress distribution with two different implant designs in four different densities of bone using 3D finite element analysis. Graphic pre-processing software Ansys version 10 was used for creating the geometric configuration of a section of the mandible with a missing first molar. Eight 3D models of this section restored with implant-supported all ceramic crowns were created. Four of these models were created to simulate a single threaded implant placed in four different densities of bone (D1, D2, D3 and D4). The other four models were created to simulate a single cylindrical implant placed in four different densities of bone (D1, D2, D3, and D4). The Poisson’s ratio (μ) and Young’s modulus (E) of elasticity of the material were incorporated into the model. An average vertical load of 400 N was applied on the occlusal surface of the first molar between the buccal cusp, central fossa and the marginal ridge. Maximum Von Mises stresses in all the eight models were observed at the crestal region or neck of the implant. The stresses observed were more for the threaded implants in all the four densities of bone when compared to that of the cylindrical implants. The study concluded that the cylindrical implant design was more favorable in softer bone than the threaded implant design.     

I类骨质中正畸微种植体支抗直径和长度的优化设计

目的：探讨正畸微种植体支抗长度和直径对I类骨质下颌骨的应力和微种植体稳定性的影响,为临床设计I类骨质中微种植体支抗的最佳长度和直径提供理论依据。方法：建立包含正畸微种植体支抗的颌骨骨块的三维有限元模型,设定微种植体的直径和长度为变量,直径变化范围1.0～1.8mm,长度变化范围5.0～11.0mm。设定颌骨平均主应力峰值和正畸微种植体支抗位移峰值为目标函数。观察设计变量变化对目标函数的影响。结果：随着直径的增加,皮质骨、松质骨应力峰值和种植体位移分别降低了67.98%,64.06%,78.55%;随着长度变化皮质骨、松质骨的应力峰值和种植体位移分别降低了13.94%,61.32%,0.01%。结论：种植体支抗的直径对I类骨质颌骨的应力和种植体支抗稳定性的影响更显著。长度对I类骨质颌骨的应力和种植体支抗稳定性的影响并不显著。从生物力学角度而言,直径大于1.4mm种植体支抗更加适用于I类骨质的颌骨。     

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.     

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.

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°。     

Finite Element Stress Analysis of Tooth-to-Implant Fixed Partial Denture Designs

Purpose The purpose of this study was to conduct a three-dimensional finite element stress analysis to compare models representing a natural tooth and an integrated implant connected with rigid and nonrigid prostheses. Materials and Methods The mathematical models described an integrated implant connected to a second premolar tooth with a three-unit metal-ceramic fixed partial denture. In one model, the tooth and implant were rigidly connected, and in the other, a nonrigid connection was assumed. From a simulated vertical load the computer generated resultant stress contours and values (compressive and tensile) in horizontal and vertical dimensions. Results A comparison of the magnitude and pattern of stresses generated in the models shows minimal differences. Although the maximum stress values were slightly higher in some areas of the rigid prosthesis model, the differences were negligible. Conclusions Based on the similarities in both the patterns of stress contours and the stress values generated in the two models, advocating a nonrigid connection because of a biomechanical advantage may be erroneous.     

A Finite Element Analysis of Stress Distribution in the Bone, Around the Implant Supporting a Mandibular Overdenture with Ball/O Ring and Magnetic Attachment

Today implant dentistry has made great inroads into the treatment modalities that are available in treating an edentulous patient. Popularity of a two implant retained overdenture has created a necessity to examine the various attachment systems being used and the stresses that are transmitted to the alveolar bone. Hence a Three dimensional Finite Element Analysis was done to analyze the stress distribution in the mandibular bone with implant-supported overdenture having Ball/O-ring and Magnet attachments of different diameters. A segment of the anterior region of the mandible was modeled with implant and the overdenture. Four different models were generated having Ball/O-Ring and Magnet Attachments. Forces of 10 N, 35 N and 70 N were applied from the horizontal, vertical and oblique directions respectively and the stress distribution studied. It was concluded that the greatest stress concentrations were seen at the crest of the cortical bone and could be reduced by using smaller sized attachments for implant supported-overdenture.     

Finite Element Stress Analysis of Diastema Closure with Ceramic Laminate Veneers

Purpose: The purpose of this study was to use finite element stress analysis to examine the relative importance of variables such as porcelain laminate veneer (PLV) extensions, loading angle, and loading level for the case of feldspathic ceramic veneering of teeth to manage diastema. Materials and Methods: A 3D maxillary central incisor including its internal anatomy and morphology was constructed with ANSYS software for different extensions of PLV. Internal boundaries defining the dentinoenamel junction, the pulp‐dentinal junction, the interface between the enamel‐luting cement, and the porcelain‐luting cement were well defined. The von Mises stresses distribution and stress intensity were analyzed on the free extension of PLV for varying extensions, various angulations (0°, 30°, and 60°) on the incisal edge, and for different loading levels (50, 150, and 250 N). Results: The numerical values of stress were recorded. A significant difference in stress was observed. Increased stresses occurred with increased extensions, angulations, and loading levels. At 0° angulation, compressive stresses were visualized in finite element analysis for various magnitudes of force. Higher stress values of 182 MPa and 211 MPa were obtained for the 2.5‐mm extension in the mesial surface and in both proximal surfaces for 0° angulation at 250 N magnitude of force. The stress occurring at 30° and 60° angulations was the combination of compressive and tensile stress. Higher values of 261 MPa and 232 MPa were observed when forces were applied on the mesial extension of the PLV and on both the proximal surfaces for 2.5 mm at 30°, 250 N magnitude of force. A maximum stress value of 507 MPa was observed when PLV were increased in mesial width by 2.5 mm for 60° angulation at 250 N magnitude of force. Conclusion: The extensions of PLV in diastema closure have more of an esthetic than functional consideration, but critical factors such as angulations and the loading level acting on the free extension of PLV are important.     

Influence of Apical Root Resection on the Biomechanical Response of a Single-rooted Tooth: A 3-dimensional Finite Element Analysis

Introduction

Apical root resection is a biologically essential component in endodontic microsurgery. However, because it reduces the total root length and supported root surface, it changes the biomechanical response of the tooth. The purpose of this study was to analyze the biomechanical effect of apical root resection and to compare apical root resection with periodontal bone loss from a biomechanical standpoint.

Methods

Finite element models of the maxillary central incisor were reconstructed. First, preoperative and surgically treated models were generated to assess the factors altering the biomechanical response of the tooth. Then, apically resected models with different amounts of resection (3, 4, 5, 6, 7, and 8 mm) were created to estimate the clinically applicable limit of apical root resection. Periodontally destructed models with varying degrees of bone loss (0.5, 1, 1.5, 2, and 3 mm) were also created to compare the effect of apical root resection with periodontal bone loss. Stress distribution, tooth displacement, and effective crown-to-root ratio (α) were analyzed for each condition.

Results

Apical root resection did not significantly alter the maximum von Mises stress or tooth displacement until it reached 6 mm (α = 0.67) when the tooth was supported by normal periodontium. In contrast, periodontal bone loss had a greater impact on biomechanical response change compared with apical root resection.

Conclusions

For a tooth supported by normal periodontium, 3 mm of apical root resection (α = 1.07) appeared to be mechanically acceptable. The biomechanical influence of apical root resection was weak compared with that of periodontal bone loss.