连续动态加载下单种植体周围骨组织应力的三维有限元分析

目的:探讨一个咀嚼周期内连续动态加载对单种植体周围骨组织最大Von Mises应力分布的影响。方法:在同一牙种植体全瓷冠修复的三维有限元模型上模拟一个咀嚼周期0.875 s的连续动态载荷,应用ANSYS软件考察骨组织的最大VonMises应力并与假设的瞬间动态加载结果相比较。结果:一个周期动态加载0.151～0.260 s与0.261～0.300 s时种植体周围骨组织的最大Von Mises应力值比瞬间动态颊斜向舌加载与舌斜向颊加载时增加;卸载后0.574 s时种植体周围骨组织的最大Von Mises应力值在一个周期动态连续加载模式比瞬间动态舌斜向颊加载模式增加。结论:一个周期动态载荷中,力的连续加载使种植体周围骨组织的最大Von Mises应力值增加;在一个咀嚼周期末,最大Von Mises应力累积作用比较明显。     

上颌前牙单个种植体带角度基桩的三维有限元应力分析

目的:单个上前牙缺失的种植修复是种植义齿修复的一种特殊形式,但这种种植修复形式需要辅以带角度基桩来弥补植入体长轴与上部修复体长轴的不一致.从而造成了其应力分布形式的特殊性.方法:本实验运用三维有限元应力分析方法,研究不同角度基桩在相同修复条件下对种植体,周围骨组织应力分布的影响,实验采用美国AIS公司的ALGOR分析软件,通过对离体上颌骨标本CT扫描,建立一个部分上颌三维有限元模型.在模型的右上中切牙位置植入一枚Branemark种植体,上部连接成角度的基桩,在基桩截面上施加一个二维的咬合载荷,同时输入物理参数,在计算机上运行ALGOR软件进行数据计算及处理.结果:三维有限元方法能够比较全面地分析种植义齿结构各部分的应力分布;随着基桩角度增大,加载后,种植体,周围骨组织的应力峰也随之增加,其增加的幅度随基桩角度增大加大,加载后,应力集中于种植体颈部皮质骨区域,最大压应力位于辰侧颈部皮质骨区域;最大拉应力位于腭侧颈部皮质骨区域:从颈部1/3骨质区至根端方向,种植体,周围骨组织应力集中明显减小.结论:运用成角度基桩修复单个上前牙缺失,种植体及周围组织的应力集中于颈部皮质骨区域,应力随基桩角度增大而增加,故临床应用这种修复形式时,应尽量减少基桩的角度,从而使植入体长轴与上部修复体长轴趋向一致.避免过大的应力峰值对种植体造成损害.     

The role of cortical zone level and prosthetic platform angle in dental implant mechanical response: A 3D finite element analysis

ObjectiveThe aim of this study was to evaluate the influence of three different dental implant neck geometries, under a combined compressive/shear load using finite element analysis (FEA). The implant neck was positioned in D2 quality bone at the crestal level or 2 mm below.MethodsOne dental implant (4.2 × 9 mm) was digitized by reverse engineering techniques using micro CT and imported into Computer Aided Design (CAD) software. Non-uniform rational B-spline surfaces were reconstructed, generating a 3D volumetric model similar to the digitized implant. Three different models were generated with different implant neck configurations, namely 0°, 10° and 20°. D2 quality bone, composed of cortical and trabecular structure, was modeled using data from CT scans. The implants were included in the bone model using a Boolean operation. Two different fixture insertion depths were simulated for each implant: 2 mm below the crestal bone and exactly at the level of the crestal bone. The obtained models were imported to FEA software in STEP format. Von Mises equivalent strains were analyzed for the peri-implant D2 bone type, considering the magnitude and volume of the affected surrounding cortical and trabecular bone. The highest strain values in both cortical and trabecular tissue at the peri-implant bone interface were extracted and compared.ResultsAll implant models were able to distribute the load at the bone-implant contact (BIC) with a similar strain pattern between the models. At the cervical region, however, differences were observed: the models with 10° and 20° implant neck configurations (Model B and C), showed a lower strain magnitude when compared to the straight neck (Model A). These values were significantly lower when the implants were situated at crestal bone levels. In the apical area, no differences in strain values were observed.SignificanceThe implant neck configuration influenced the strain distribution and magnitude in the cortical bone and cancellous bone tissues. To reduce the strain values and improve the load dissipation in the bone tissue, implants with 10° and 20 neck configuration should be preferred instead of straight implant platforms.     

下颌前磨牙颈部硬组织非线性接触的应力分布有限元分析

目的:分析下颌前磨牙在不同载荷下牙颈部硬组织的应力分布。方法:建立上、下颌前磨牙釉质各向异性的二维有限元模型,模拟紧咬和咀嚼运动中牙齿的受力情况,对下颌前磨牙颈部硬组织进行非线性接触分析。结果:模拟正中咬合三点接触载荷时,颊、舌侧牙颈部釉质应力均最小,而模拟侧方运动工作侧一点接触载荷时,颊侧牙颈部釉质应力最大;侧方运动接触载荷下,牙颈部出现明显应力集中,颊、舌侧釉牙本质界区域是主要应力集中区。结论:牙颈部硬组织的应力与牙齿所受力的位置和方向密切相关。     

上颌前牙区种植方案中角度设计的三维有限元分析

目的 采用有限元法观察分析不同种植体植入角度与不同角度基台联合运用时种植体周骨组织的应力分布及种植体的位移情况,为上颌前牙区种植修复方案的设计提供依据。方法利用锥形束CT（cone beam computed tomography, CBCT）建立包含部分上颌骨、种植体（4.3 mm×11.5 mm）、基台及上部修复体（氧化锆全瓷冠）的三维有限元模型,以种植体植入角度A,即种植体长轴与理想长轴之间的夹角 (0°、5°、10°、15°、20°、25°)和基台角度B,即基台长轴与种植体长轴之间的夹角(0°、5°、10°、15°、20°、25°)建立有限元模型。在模型上与牙冠长轴呈130°、舌侧切端下2 mm,模拟大小为178 N的力加载,采用Ansys13.0软件观察种植体周围皮质骨、松质骨的最大主应力值、分布情况和种植体的位移。结果建立了16个符合实际情况的不同种植修复方案的上颌中切牙种植义齿的三维有限元模型;各种修复方案的种植体—骨界面应力分布特点相同,应力集中在种植体颈部及根部;在相同的植入角度下,基台角度越大,种植体周围皮质骨、松质骨的最大主应力峰值及种植体位移峰值均越大。在相同的基台角度下,种植体的植入角度越大,种植体周围皮质骨、松质骨的最大主应力峰值及种植体位移峰值均越大;植入角度或基台角度大于20°时,种植体周围皮质骨、松质骨的最大主应力峰值及种植体位移峰值增加幅度较大。结论种植体的植入角度和基台角度均与种植体周围皮质骨、松质骨的最大主应力峰值及种植体位移峰值呈正相关关系,应尽量减小种植体的植入角度和基台角度,尤其是需要严格掌握种植体的植入角度。从应力、位移考虑,前牙区种植体植入角度和基台角度在20°以内为佳。大于20°时,应力有明显升高趋势,增加种植成功的风险。     

不同螺距种植体集中载荷的有限元分析

目的:用三维有限元方法分析不同螺距种植体-骨界面应力分布状况,确定利于应力均匀分布的最佳螺纹参数设计.方法:建立包含上部结构的牙种植体、局部下颌骨块三维有限元模型,利用Cosmos/works软件分析在垂直、斜向45° 2 种集中载荷下螺距分别为0.6、 0.8、 1.0 mm的3 种种植体与骨界面的应力分布状况.结果:螺距为0.8 mm种植体周围Von-Mises应力、拉应力、压应力峰值较小,应力分布最均匀;同一螺距种植体斜向载荷下应力显著高于垂直载荷;应力集中主要出现于种植体颈部、皮质骨上缘和种植体末端最下一个螺纹处.结论:螺纹种植体螺距影响骨界面的应力分布和(牙合)力传导,为避免应力集中种植体末端螺纹应进行适当的截齿处理,种植义齿设计和修复时应尽可能减小或避免非轴向力.     

人工楔状缺损牙颈部硬组织应力分布的有限元接触分析

目的:分析人工楔状缺损患牙颈部硬组织的应力分布。方法:在下颌前磨牙沿釉牙本质界建立三角形缺损,设计楔状缺损模型,模拟紧咬和咀嚼运动中牙的受力情况,对下颌前磨牙颈部硬组织进行非线性接触分析。结果:模拟紧咬和咀嚼运动中牙的受力情况,釉牙本质界缺损的下颌前磨牙缺损区尖端均存在明显的拉应力集中,应力集中区沿釉牙本质界向方延伸,其中尤以侧方运动工作侧一点接触载荷下的应力集中最为明显,应力值最大。结论:釉牙本质界破坏改变了缺损区牙颈部的应力分布。     

Finite element analysis of the influence of implant inclination,loading position,and load direction on stress distribution

The selection of the appropriate alignment of an implant and the position of implantation are vital for its longterm success. Excessive load is generated around inclined implants, causing microcracks in the bone, which result in implant loosening and eventual failure. This study was designed to analyze the stress distribution caused by varying the degree of inclination of an implant body and varying the loading position and direction, using the finite-element method of stress analysis. Buccal and lingual two-dimensional simulation models of a cylinder implant, embedded in the first molar edentulous cross-section of the mandible, were prepared, and the stress distribution and maximum principal stresses were recorded. Regardless of the point and direction of loading, compressive stresses were relatively greater when the implant was inclined. This tendency became more pronounced when a 45° loading direction and eccentric loading were tested. For the inclined model, with a 45° loading direction, the compressive stress was observed on the cortical bone adjacent to the direction of inclination, while tensile stress was observed on the opposite side.     

Stress analysis and factor of safety in three dental implant systems by finite element analysis

ObjectiveThe purpose of this study was to compare the stress distribution and the factor of safety of three dental implant systems using the finite element method.Materials and methodsThree commercial dental implant systems were designed using Solid Works 2020 software: Model A with an internal octagonal connection and matching platform, Model B with an internal hexagon connection and switching platform, and Model C with an internal 15° conical-cylindrical connection and switching platform. A 200 N load was applied to each design in both axial and 30° oblique directions using the finite element method.ResultsIn the three dental implant systems, the maximum von Mises stress was concentrated at the cervical level of the bone-implant interface in all models. Model C showed lower maximum stress values in both axial and 30° oblique loads. The highest maximum stress value was observed with the application of the oblique load in all the study models, and the factor of safety was less than one in Model A when subjected to a 200 N oblique load.ConclusionThe switching platform models generated lower maximum stress values and a factor of safety higher than one which is considered an acceptable value.Clinical relevance: A dental implant system with an internal hexagon or conical connection and a switching platform generates lower maximum von Mises stress values both on the implant components and on the peri-implant tissues.     

3D finite element analysis to detect stress distribution: spiral family implants

Aim  

Spiral family implants are a root-form fixtures with increasing thickness of tread. This characteristic gives a self-tapping and self-condensing bone properties to implants. To study spiral family implant inserted in different bone quality and connected with abutments of different angulations a Finite Element Analysis (FEA) was performed. Once drawn the systems that were object of the study by CAD (Computer Aided Design), the FEA discretized solids composing the system in many infinitesimal little elementary solids defined finite elements. This lead to a mesh formation where the single finite elements were connected among them by nodes. For the 3 units bone-implant-abutments several thousand of tetrahedral elements having 10 parabolic nodes were employed.     

自然牙根支持及种植牙支持式下颌全口覆盖义齿的三维有限元分析

目的研究自然牙根支持和种植基牙支持覆盖义齿在咀嚼过程中其周围骨皮质应力的差异，为改善种植覆盖义齿的修复效果提供依据。方法借助于ＣＴ扫描与计算机辅助设计手段，用三维有限元方法比较自然牙根支持式与种植牙支持式覆盖义齿在采用不同固位装置，不同咬合力状态下，支持组织应力分布的差异。结果①无论自然牙根支持式还是种植牙支持式覆盖义齿，在采用杆卡或按扣式附着体时，骨组织应力分布虽有不同，但这种不同与咬合力方向作用的结果相比是小的。在相同载荷下，２０°斜向加载时基牙周围骨皮质层最大应力值是垂直加载的２２～３倍。②种植基牙支持式覆盖义齿在两种不同上部结构设计，４种不同载荷条件下，基牙颈部周围骨质皮层最大应力值是自然牙支持式覆盖义齿的２５倍～４倍。结论为减少种植基牙周围骨皮质应力峰值，预防压力性骨吸收的产生，种植覆盖义齿设计时，应避免产生过大的侧方咬合力。同时，应考虑增加种植牙数目或在种植基牙上部结构中采用缓冲设计     

下颌骨各向异性材质模型对种植牙有限元分析的影响

目的 建立含螺纹种植体各向异性的完整下颌骨有限元模型,研究各向异性材质模型模拟对牙种植体有限元分析的影响.方法 采用薄层CT扫描和自主开发的软件分别建立各向异性和等效各向同性的完整下颌骨三维有限元模型,其中在后牙区植入两枚牙种植体,分析在颊舌向、斜向加载时,种植体-骨界面主应力和主应变值的变化.结果 在各向异性下颌骨模型中,除骨皮质第一最小主应力减小6.3%～7.6%和骨松质第三最小主应力减小8.7%～46.0%外,骨界面绝大多数主应力和所有主应变值均大于各向同性;骨皮质主应力增加2.1%～74.1%,主应变增加4.7%～57.3%;骨松质主应力增加10.3%～71.4%,主应变值增加19.5%～63.4%,而且骨松质应力的增加比骨皮质明显.结论 下颌骨种植牙有限元分析时,下颌骨各向异性模拟会明显影响骨界面应力和应变值,并以增加为主.在生物力学研究中应更注重下颌骨各向异性的材质力学特性.     

Finite element modeling technique for predicting mechanical behaviors on mandible bone during mastication

PURPOSE

The purpose of this study was to propose finite element (FE) modeling methods for predicting stress distributions on teeth and mandible under chewing action.

MATERIALS AND METHODS

For FE model generation, CT images of skull were translated into 3D FE models, and static analysis was performed considering linear material behaviors and nonlinear geometrical effect. To find out proper boundary and loading conditions, parametric studies were performed with various areas and directions of restraints and loading. The loading directions are prescribed to be same as direction of masseter muscle, which was referred from anatomy chart and CT image. From the analysis, strain and stress distributions of teeth and mandible were obtained and compared with experimental data for model validation.

RESULTS

As a result of FE analysis, the optimized boundary condition was chosen such that 8 teeth were fixed in all directions and condyloid process was fixed in all directions except for forward and backward directions. Also, fixing a part of mandible in a lateral direction, where medial pterygoid muscle was attached, gave the more proper analytical results. Loading was prescribed in a same direction as masseter muscle. The tendency of strain distributions between the teeth predicted from the proposed model were compared with experimental results and showed good agreements.

CONCLUSION

This study proposes cost efficient FE modeling method for predicting stress distributions on teeth and mandible under chewing action. The proposed modeling method is validated with experimental data and can further be used to evaluate structural safety of dental prosthesis.     

Comparative evaluation of peri-implant stress distribution in implant protected occlusion and cuspally loaded occlusion on a 3 unit implant supported fixed partial denture: A 3D finite element analysis study

PURPOSETo assess peri-implant stress distribution using finite element analysis in implant supported fixed partial denture with occlusal schemes of cuspally loaded occlusion and implant protected occlusion.MATERIALS AND METHODSA 3-D finite element model of mandible with D2 bone with partially edentulism with unilateral distal extension was made. Two Ti alloy identical implants with 4.2 mm diameter and 10 mm length were placed in the mandibular second premolar and the mandibular second molar region and prosthesis was given with the mandibular first molar pontic. Vertical load of 100 N and and oblique load of 70 N was applied on occlusal surface of prosthesis. Group 1 was cuspally loaded occlusion with total 8 contact points and Group 2 was implant protected occlusion with 3 contact points.RESULTSIn Group 1 for vertical load , maximum stress was generated over implant having 14.3552 Mpa. While for oblique load, overall stress generated was 28.0732 Mpa. In Group 2 for vertical load, maximum stress was generated over crown and overall stress was 16.7682 Mpa. But for oblique load, crown stress and overall stress was maximum 22.7561 Mpa. When Group 1 is compared to Group 2, harmful oblique load caused maximum overall stress 28.0732 Mpa in Group 1.CONCLUSIONIn Group 1, vertical load generated high implant stress, and oblique load generated high overall stresses, cortical stresses and crown stresses compared to vertical load. In Group 2, oblique load generated more overall stresses, cortical stresses, and crown stresses compared to vertical load. Implant protected occlusion generated lesser harmful oblique implant, crown, bone and overall stresses compared to cuspally loaded occlusion.     

Finite element analysis and fracture resistance testing of a new intraradicular post

Objectives

The objective of the present study was to evaluate a prefabricated intraradicular threaded pure titanium post, designed and developed at the São José dos Campos School of Dentistry - UNESP, Brazil. This new post was designed to minimize stresses observed with prefabricated post systems and to improve cost-benefits.

Material and methods

Fracture resistance testing of the post/core/root complex, fracture analysis by microscopy and stress analysis by the finite element method were used for post evaluation. The following four prefabricated metal post systems were analyzed: group 1, experimental post; group 2, modification of the experimental post; group 3, Flexi Post, and group 4, Para Post. For the analysis of fracture resistance, 40 bovine teeth were randomly assigned to the four groups (n=10) and used for the fabrication of test specimens simulating the situation in the mouth. The test specimens were subjected to compressive strength testing until fracture in an EMIC universal testing machine. After fracture of the test specimens, their roots were sectioned and analyzed by microscopy. For the finite element method, specimens of the fracture resistance test were simulated by computer modeling to determine the stress distribution pattern in the post systems studied.

Results

The fracture test presented the following averages and standard deviation: G1 (45.63±8.77), G2 (49.98±7.08), G3 (43.84±5.52), G4 (47.61±7.23). Stress was homogenously distributed along the body of the intraradicular post in group 1, whereas high stress concentrations in certain regions were observed in the other groups. These stress concentrations in the body of the post induced the same stress concentration in root dentin.

Conclusions

The experimental post (original and modified versions) presented similar fracture resistance and better results in the stress analysis when compared with the commercial post systems tested (08/2008-PA/CEP).     

Three dimensional finite element analysis of the stress distribution around the mandibular posterior implant during non-working movement according to the amount of cantilever

PURPOSE

In case of large horizontal discrepancy of alveolar ridge due to severe resorption, cantilevered crown is usually an unavoidable treatment modality. The purpose of this study was to evaluate the clinical criteria for the placement of the aforementioned implant crown.

MATERIALS AND METHODS

The mandible model with 2 mm thick cortical bone and cancellous bone was fabricated from CT cross-section image. An external connection type implant was installed and cantilevered crowns with increasing offset of 3, 4, 5, 6, and 7 mm were connected. Vertical load and 30° oblique load of 300 N was applied and stress around bone and implant component was analyzed. A total of 14 cases were modeled and finite element analysis was performed using COSMOS Works (Solid works Inc, USA).

RESULTS

As for the location of the vertical load, the maximum stress generated on the lingual side of the implant became larger according to the increase of offset distance. When the oblique load was applied at 30°, the maximum stress was generated on the buccal side and its magnitude gradually decreased as the distance of the offset load increased to 5 mm. After that point, the magnitude of implant component''s stress increased gradually.

CONCLUSION

The results of this study suggest that for the patient with atrophied alveolar ridge following the loss of molar teeth, von-Mises stress on implant components was the lowest under the 30° oblique load at the 5 mm offset point. Further studies for the various crown height and numbers of occusal points are needed to generalize the conclusion of present study.     

根骨内种植体植入牙槽骨吸收的中切牙的有限元应力分析

目的 :研究分析Ⅱ度牙槽骨吸收的上颌中切牙植入根骨内种植体后的种植体 骨界面、牙本质以及牙周膜的应力特点。方法 :二维有限元应力分析法 ,根据王惠芸对中国成人上中切牙形态的统计数据 ,模拟牙根形态 ,建立有限元模型 ;10 0N垂直和斜向静力加载 ,采用Super sap( 1991年版本 )有限元分析软件 ,在PⅢ 5 5 0IBM兼容机上进行运算。结果 :根骨内种植体植入Ⅱ度牙槽骨吸收的单根牙后 ,可显著减小牙齿的松动度 ;垂直载荷作用时 ,可显著降低骨组织、牙周膜的VonMises应力、拉应力和压应力以及牙本质的VonMises应力和压应力水平。牙本质内的拉应力水平稍有增加。骨组织主要受压应力作用 ,应力集中区在种植体的尖端 ;斜向载荷时 ,牙槽嵴顶和牙周膜的应力水平较植入前有明显减小 ;而牙根尖部的牙本质和骨组织的各项应力水平则有显著的提高。结论 :根骨内种植体对牙周损害牙齿具有较好的稳定作用 ,且可改善牙周组织的应力分布形式     

Damping effects on the response of maxillary incisor subjected to a traumatic impact force: a nonlinear finite element analysis

OBJECTIVES: The aim of this study was to evaluate the effects of damping on stress concentration in an impacted incisor. METHODS: Damping ratios of maxillary incisors were tested using an in vivo modal testing method. A finite element model of the upper central incisor was established for dental trauma analysis. To assess the effect of damping properties on induced stresses in the traumatized incisors, equivalent stresses in the finite element model with various damping ratios were calculated for comparison. The mechanisms of cushioning properties of the upper incisors on traumatic injuries were assessed by profiling the stress distributions in the incisor model sequentially with time. RESULTS: The measured damping ratio of maxillary incisors was 0.146+/-0.037. When the incisor was subjected to an impact force, high stresses were concentrated at the labial and lingual incisor edges, cervical ridge, and the area around root apex. When the damping ratios of the incisor model were set at 10- and 50-fold of the measured values, the peak stresses induced near the impact site of the incisor model were reduced from 24.0 to 23.2 and 15.9 MPa, respectively. On the other hand, the peak stress lagged and the stress existence period increased when the damping properties were taken into consideration. CONCLUSIONS: Damping properties of teeth provide protection to the tooth during traumatic injury by decreasing the peak stress magnitude due to release of strain energy over a longer period.     

软衬材料固位的全下颌种植覆盖义齿三维有限元应力分析

目的 探讨弹性缓冲装置对种植覆盖义齿应力分布的影响，为优化种植覆盖义齿设计提供依据。方法 应用三维有限元法，对采用弹性软衬材料和非弹性材料固位的全下颌种植覆盖义齿进行应力分析，对比义齿本身和支持组织应力分布的差异。结果 ①无弹性材料缓冲的覆盖义齿对斜向载荷的抵抗性差，种植体颈部—皮质骨界面应力峰值为垂直载荷的2．4～9．2倍。垂直及斜向载荷，种植体及基托均有较高的应力集中。②弹性软衬材料固位的覆盖义齿，垂直及斜向载荷时，种植体—骨界面及义齿本身应力分布较均匀，避免了较大的应力集中。结论 弹性软衬材料应用于全下颌种植覆盖义齿时，表现了良好的应力缓冲作用，降低了种植体—骨界面应力峰值，减少机械性并发症的发生，有利于提高种植覆盖义齿的远期成功率。     

Finite element analysis in implant dentistry: State of the art and future directions

ObjectiveTo discuss the state of the art of Finite Element (FE) modeling in implant dentistry, to highlight the principal features and the current limitations, and giving recommendations to pave the way for future studies.MethodsThe articles’ search was performed through PubMed, Web of Science, Scopus, Science Direct, and Google Scholar using specific keywords. The articles were selected based on the inclusion and exclusion criteria, after title, abstract and full-text evaluation. A total of 147 studies were included in this review.ResultsTo date, the FE analysis of the bone-dental implant system has been investigated by analyzing several types of implants; modeling only a portion of bone considered as isotropic material, despite its anisotropic behavior; assuming in most cases complete osseointegration; considering compressive or oblique forces acting on the implant; neglecting muscle forces and the bone remodeling process. Finally, there is no standardized approach for FE modeling in the dentistry field.SignificanceFE modeling is an effective computational tool to investigate the long-term stability of implants. The ultimate aim is to transfer such technology into clinical practice to help dentists in the diagnostic and therapeutic phases. To do this, future research should deeply investigate the loading influence on the bone-implant complex at a microscale level. This is a key factor still not adequately studied. Thus, a multiscale model could be useful, allowing to account for this information through multiple length scales. It could help to obtain information about the relationship among implant design, distribution of bone stress, and bone growth. Finally, the adoption of a standardized approach will be necessary, in order to make FE modeling highly predictive of the implant’s long-term stability.