平台转换连接对种植体-骨界面应力分布的影响

目的：探讨平台转换连接对种植体-骨界面应力分布的影响。方法：采用三维有限元分析方法,模拟建立上颌骨前牙区、种植体（直径3.5mm、长度11mm）以及修复体模型。实验模型的种植体-基台连接形式为平台转换连接,对照模型为平齐对接式连接。对模型施以100N的轴向载荷和与牙体长轴呈30°的侧向载荷,分别计算两模型种植体-骨界面的最大等效应力,并进行比较分析。结果：不同加载条件下,两模型的最大等效应力均位于种植体颈部周围颊侧皮质骨中,松质骨中应力较小;相比对照模型,平台转换连接方式的骨应力分布更均匀,且等效应力峰值较小。结论：平台转换连接可减小种植体颈周骨组织的应力,从生物力学角度考虑,建议临床上尽量选择平台转换连接式种植体。     

氧化锆全瓷角度基台的三维有限元应力分析

目的:观察基台倾斜角度对氧化锆全瓷基台及种植体周围骨组织内部应力分布的影响。方法:利用COS-MOS2.85软件包建立14个种植体支持的上颌中切牙三维有限元模型,基台分别设计为与种植体长轴呈0°、5°、10°、15°、20°、25°和30°的氧化锆全瓷基台和钛基台,用178N的与种植体成130°的斜向加载,比较不同模型中基台内部和种植体周围骨组织内应力分布情况。结果:不同倾斜角度时氧化锆全瓷基台和钛基台内应力集中区不同,前者集中在唇侧肩台和唇侧轴壁中上部,钛基台应力集中区为唇侧肩台处。随倾斜角度的增加,基台和种植体周围骨组织内最大Von Mises应力增加,钛基台增加速度相对平稳,而瓷基台的增加速度在倾斜角度大于15°后明显加剧。和钛基台相比,在相同倾斜角度时,瓷基台内应力值较高而骨组织内应力值较低。结论:随着基台倾斜角度的增加,氧化锆全瓷基台和骨组织内应力增加;氧化锆全瓷角度基台的倾斜角度不宜超过15°。     

不同直径种植体与天然牙联合支持固定桥的应力分析

目的:通过三维有限元方法研究种植体直径对天然牙种植体联合固定桥周围骨组织应力的影响。方法:CT扫描获得志愿者DICOM数据,通过Mimics软件、Imageware逆向工程软件及ANSYS软件处理,先建立左侧下颌第二前磨牙和第二磨牙支持的天然牙固定桥三维有限元模型,用不同直径种植体替换下颌第二磨牙得到一系列种植体-天然牙联合支持式固定桥的三维有限元模型。分别在垂直向和斜向45°集中加载下,对比分析天然牙及种植体周围的应力分布情况。结果:相同加载条件下,不同模型的第二前磨牙(天然牙)颈部应力无明显区别。对联合支持式固定桥,当种植体直径由3.5 mm增加为4.3 mm时,种植体颈部和基台的应力明显降低(近1/2);随种植体直径增加,2处应力也继续降低,但降低的幅度明显放缓。结论:随着种植体直径的增大,种植体颈缘处骨组织及基台的von Mises应力逐渐减小,但对天然牙周围的应力影响较小。斜向载荷时,天然牙、种植体周围骨组织及基台受到的von Mises应力显著增大,更易导致固定桥修复的失败。     

氧化锆角度基台及种植体周骨壁应力分布的有限元分析

目的研究氧化锆角度基台及种植体周骨壁应力的分布情况,为临床应用提供参考。方法采用三维有限元分析方法,对氧化锆直基台、15°、20°基台修复时的种植体基台、固定螺丝及种植体周骨壁应力的分布进行分析,并与常规钛基台进行比较。结果角度基台模型的基台、螺丝、种植体周骨壁的等效应力大于直基台;20°基台模型的基台、螺丝、种植体周骨壁等效应力远远大于15°基台模型;氧化锆基台模型与钛基台模型相比,2组无显著差异。结论基台角度对应力分布有影响,并随角度的增大而增大,提示临床上应注意种植体植入方向,尽量使用直基台或小角度基台,以减少种植体颈部骨吸收及修复并发症的发生;基台材料改变对基台、螺丝、种植体周骨壁的应力分布无显著影响,从生物力学考虑,临床上可以放心选用氧化锆角度基台。     

种植义齿缓冲单元材料特性对缓冲效果的影响

目的：探究动态载荷作用下种植义齿缓冲单元不同的材料特性对应力吸收效果的影响。方法：在传统种植体与基台之间设计硅橡胶缓冲单元,利用abaqus有限元分析软件建立三维有限元模型,分别赋予缓冲单元材料不同弹性模量值,分析比较动态载荷作用下种植体-骨界面的应力分布。结果：缓冲材料弹性模量不同,种植体-骨界面的应力分布不同,弹性模量值在10~23MPa范围内时缓冲效果较好。结论：带有缓冲单元的新型种植体系统可减小皮质骨内的应力峰值,并且材料的弹性模量对缓冲效果有影响,在一定范围内,材料的弹性模量越小,缓冲效果越好。     

A finite element analysis of two different dental implants: stress distribution in the prosthesis, abutment, implant, and supporting bone

This study evaluates the influence of 2 commercially available dental implant systems on stress distribution in the prosthesis, abutment, implant, and supporting alveolar bone under simulated occlusal forces, employing a finite element analysis. The implants and abutments evaluated consisted of a stepped cylinder implant connected to a screw-retained, internal, hexagonal abutment (system 1) and a conical implant connected to a solid, internal, conical abutment (system 2). A porcelain-covered, silver-palladium alloy was used as a crown. In each case, a simulated, 100-N vertical load was applied to the buccal cusp. A finite element model was created based on the physical properties of each component, and the values of the von Mises stresses generated in the prosthesis, abutment, implant, and supporting alveolar bone were calculated. In the prostheses, the maximum von Mises stresses were concentrated at the points of load application in both systems, and they were greater in system 1 (148 N/mm2) than in system 2 (55 N/mm2). Stress was greater on the abutment of system 2 than of system 1 on both the buccal (342 N/mm2 x 294 N/mm2) and lingual (294 N/mm2 x 148 N/ mm2) faces. Stress in the cortical, alveolar bone crest was greater in system 1 than in system 2 (buccal: 99.5 N/mm2 x 55 N/mm2, lingual: 55 N/mm2 x 24.5 N/mm2, respectively). Within the limits of this investigation, the stepped cylinder implant connected to a screw-retained, internal hexagonal abutment produces greater stresses on the alveolar bone and prosthesis and lower stresses on the abutment complex. In contrast, the conical implant connected to a solid, internal, conical abutment furnishes lower stresses on the alveolar bone and prosthesis and greater stresses on the abutment.     

Finite‐Element Analysis of Stress on Dental Implant Prosthesis

Background: Understanding how clinical variables affect stress distribution facilitates optimal prosthesis design and fabrication and may lead to a decrease in mechanical failures as well as improve implant longevity. Purpose: In this study, the many clinical variations present in implant‐supported prosthesis were analyzed by 3‐D finite element method. Materials and Method: A geometrical model representing the anterior segment of a human mandible treated with 5 implants supporting a framework was created to perform the tests. The variables introduced in the computer model were cantilever length, elastic modulus of cancellous bone, abutment length, implant length, and framework alloy (AgPd or CoCr). The computer was programmed with physical properties of the materials as derived from the literature, and a 100N vertical load was used to simulate the occlusal force. Images with the fringes of stress were obtained and the maximum stress at each site was plotted in graphs for comparison. Results: Stresses clustered at the elements closest to the loading point. Stress increase was found to be proportional to the increase in cantilever length and inversely proportional to the increase in the elastic modulus of cancellous bone. Increasing the abutment length resulted in a decrease of stress on implants and framework. Stress decrease could not be demonstrated with implants longer than 13 mm. A stiffer framework may allow better stress distribution. Conclusion: The relative physical properties of the many materials involved in an implant‐supported prosthesis system affect the way stresses are distributed.     

Study of Biomechanics of Porous Coated Root Form Implant Using Overdenture Attachment: A 3D FEA

The purpose of this article is to do a three-dimensional finite element stress analysis, in relation to root form implant supported by overdenture attachment, during axial and non-axial loading. Two porous coated Titanium–aluminum–vanadium (Ti–6Al–4V) implants with overdenture abutment were embedded in both simple and 3D model of interforaminal region of mandible. The material properties of tissue ingrowth bonded interface were calculated considering Iso-Strain condition. The masticatory forces: axial load of 35 N, a horizontal load of 10 N, and an oblique load of 120 N, was applied for the two qualities of cancellous bone. It implied that porous topography of the implant led to optimal stress transfer at the tissue ingrowth bonded interface and insignificant punching stress at the apex than a smooth surface implant. The inferior bone quality was deformed even under physiologic loads and showed wider stress pattern. Simulated implant abutment to implant bone interface stress may be significantly affected by the quality of the bone and the surface topography of the implant. The interface is affected to a lesser extent by the prosthetic material properties. Threedimensional anatomical model was more close to reality than the geometry of much simpler altered models.     

Influence of Cusp Inclination on Stress Distribution in Implant‐Supported Prostheses. A Three‐Dimensional Finite Element Analysis

Purpose: The aim of this study was to assess the influence of cusp inclination on stress distribution in implant‐supported prostheses by 3D finite element method. Materials and Methods: Three‐dimensional models were created to simulate a mandibular bone section with an implant (3.75 mm diameter × 10 mm length) and crown by means of a 3D scanner and 3D CAD software. A screw‐retained single crown was simulated using three cusp inclinations (10°, 20°, 30°). The 3D models (model 10d, model 20d, and model 30d) were transferred to the finite element program NeiNastran 9.0 to generate a mesh and perform the stress analysis. An oblique load of 200 N was applied on the internal vestibular face of the metal ceramic crown. Results: The results were visualized by means of von Mises stress maps. Maximum stress concentration was located at the point of application. The implant showed higher stress values in model 30d (160.68 MPa). Cortical bone showed higher stress values in model 10d (28.23 MPa). Conclusion: Stresses on the implant and implant/abutment interface increased with increasing cusp inclination, and stresses on the cortical bone decreased with increasing cusp inclination.     

Micromechanics of implant/tissue interfaces.

A series of finite element models was developed for evaluation of the micromechanics of implant/tissue interfaces. Conventional finite element global models of a dental implant, assuming a continuum implant/bone interface, were developed so that general stress patterns in the implant and surrounding tissue could be obtained. Stresses in bone were concentrated on the alveolar crest and apex region for all global models having a direct bone/implant contact. The addition of a 100-microns-thick layer of fibrous tissue into the bone/implant interface concentrated the stresses in the middle third of the bone adjacent to the implant surface. Stresses in the middle third were ten times higher than in the cases without fibrous tissue. Interfaces modeled under the assumption of a volume-weighted average material stiffness of bone tissue and metal confirmed these general stress patterns, but provided no stress details of the interfacial zone. Finally, the equivalent material constants of the interfacial zone with and without fibrous tissue were calculated by homogenization theory. From these equivalent constants, local strains around single threads were calculated. These equivalent material properties are sensitive to the microstructure. Therefore, it is now possible for stress patterns within the interfacial zone to be quantified and the local micromechanical behavior around individual surface structures for whole implants accounted for.     

Biomechanical analysis on platform switching: is there any biomechanical rationale?

OBJECTIVES: The purpose of this study was to examine the biomechanical advantages of platform switching using three-dimensional (3D) finite element models. MATERIAL AND METHODS: 3D finite element models simulating an external hex implant (4 x 15 mm) and the surrounding bone were constructed. One model was the simulation of a 4 mm diameter abutment connection and the other was the simulation of a narrower 3.25 mm diameter abutment connection, assuming a platform-switching configuration. RESULTS: The stress level in the cervical bone area at the implant was greatly reduced when the narrow diameter abutment was connected compared with the regular-sized one. CONCLUSION: Within the limitations of this study, it was suggested that the platform switching configuration has the biomechanical advantage of shifting the stress concentration area away from the cervical bone-implant interface. It also has the disadvantage of increasing stress in the abutment or abutment screw.     

Implant-abutment interface: biomechanical study of flat top versus conical

Background: Overloading has been identified as a primary factor behind dental implant failure. The peak bone stresses normally appear in the marginal bone. The anchorage strength is maximized if the implant is given a design that minimizes the peak bone stress caused by a standardized load. Clinical studies have shown that it is possible to obtain a marginal bone level close to the crest of the implant. Different implant systems make use of different designs of the implant‐abutment interface. Different implant‐abutment interfaces imply that the functional load is distributed in different ways upon the implant. According to Saint‐Venant's principle, this will result in different stress patterns in the marginal bone when this reaches levels close to the implant crest. Purpose: One aim of the study was to theoretically investigate if a conical implant‐abutment interface gives rise to a changed stress pattern in the marginal bone, as compared to a flat top interface, for an axially loaded mandibular titanium implant, the neck of which is provided with retention elements giving effective interlocking with the bone. Further aims were to investigate if the way in which the axial load is distributed on the flat top and on the inner conus respectively affects the stress pattern in the marginal bone. The pertinent stress was considered to be the bone‐implant interfacial shear stress. It was assumed that the marginal bone reached the level of the implant–abutment interface. Method: The investigation was performed by means of axisymmetric finite element analysis. Results: The conical implant‐abutment interface of the type studied brought about a decrease in the peak bone‐implant interfacial shear stress as compared to the flat top interface of the type studied. This peak interfacial shear stress was located at the top marginal bone for the flat top implant‐abutment interface whereas it was located more apically in the bone for the conical implant‐abutment interface. The way in which the axial load was distributed on the flat top and on the inner conus respectively affected the peak interfacial shear stress level. Conclusion: The design of the implant‐abutment interface has a profound effect upon the stress state in the marginal bone when this reaches the level of this interface. The implant with the conical interface can theoretically resist a larger axial load than the implant with the flat top interface.     

Effects of the Implant Design on Peri‐Implant Bone Stress and Abutment Micromovement: Three‐Dimensional Finite Element Analysis of Original Computer‐Aided Design Models

Background: Occlusal overloading causes peri‐implant bone resorption. Previous studies examined stress distribution in alveolar bone around commercial implants using three‐dimensional (3D) finite element analysis. However, the commercial implants contained some different designs. The purpose of this study is to reveal the effect of the target design on peri‐implant bone stress and abutment micromovement. Methods: Six 3D implant models were created for different implant–abutment joints: 1) internal joint model (IM); 2) external joint model (EM); 3) straight abutment (SA) shape; 4) tapered abutment (TA) shapes; 5) platform switching (PS) in the IM; and 6) modified TA neck design (reverse conical neck [RN]). A static load of 100 N was applied to the basal ridge surface of the abutment at a 45‐degree oblique angle to the long axis of the implant. Both stress distribution in peri‐implant bone and abutment micromovement in the SA and TA models were analyzed. Results: Compressive stress concentrated on labial cortical bone and tensile stress on the palatal side in the EM and on the labial side in the IM. There was no difference in maximum principal stress distribution for SA and TA models. Tensile stress concentration was not apparent on labial cortical bone in the PS model (versus IM). Maximum principal stress concentrated more on peri‐implant bone in the RN than in the TA model. The TA model exhibited less abutment micromovement than the SA model. Conclusion: This study reveals the effects of the design of specific components on peri‐implant bone stress and abutment displacement after implant‐supported single restoration in the anterior maxilla.     

种植体长度与直径对骨界面应力分布影响的三维有限元分析

目的　比较不同直径、长度的种植体对种植体-骨界面应力分布的影响。方法　按照种植体不同长度与直径,建立种植义齿的三维有限元模型。以美国3I种植体系统为参考,在Solidworks三维制图软件中绘制包含种植体、相应基台及牙冠的三维实体模型。种植体长度分别设为8、10、12、14 mm,直径分别设为3.5、4.0、4.5、5.0 mm,通过不同长度与直径交叉组合,共得到16种模型。对每个模型进行垂直向及斜向加载负荷,运用Ansys Workbench 13.0分析比较各模型受力后应力分布情况。结果　两种载荷下应力集中出现在种植体颈部皮质骨区和根尖松质骨区,随着种植体长度增加,根尖松质骨区应力集中缓慢下降;随着种植体直径的增大,根尖松质骨区应力集中明显减小。结论　在种植体长度与直径的选择中,直径与长度越大,种植体-骨界面的应力集中越小,但与长度相比,直径的影响更加显著。     

Influences of internal tapered abutment designs on bone stresses around a dental implant: three-dimensional finite element method with statistical evaluation

Background: The aim of this study is to determine the effects of various designs of internal tapered abutment joints on the stress induced in peri‐implant crestal bone by using the three‐dimensional finite element method and statistical analyses. Methods: Thirty‐six models with various internal tapered abutment–implant interface designs including different abutment diameters (3.0, 3.5, and 4.0 mm), connection depths (4, 6, and 8 mm), and tapers (2°, 4°, 6°, and 8°) were constructed. A force of 170 N was applied to the top surface of the abutment either vertically or 45° obliquely. The maximum von Mises bone‐stress values in the crestal bone surrounding the implant were statistically analyzed using analysis of variance. In addition, patterns of bone stress around the implant were examined. Results: The results demonstrate that a smaller abutment diameter and a longer abutment connection significantly reduced the bone stresses (P <0.0001) in vertical and oblique loading conditions. Moreover, when the tapered abutment–implant interfaced connection was more parallel, bone stresses under vertical loading were less (P = 0.0002), whereas the abutment taper did not show significant effects on bone stresses under oblique loading (P = 0.83). Bone stresses were mainly influenced by the abutment diameter, followed by the abutment connection depth and the abutment taper. Conclusion: For an internal tapered abutment design, it was suggested that a narrower and deeper abutment–implant interface produced the biomechanical advantage of reducing the stress concentration in the crestal region around an implant.     

口腔种植体-基台微间隙充填对种植修复系统及周围骨力学的影响

目的:探讨口腔种植体-基台微间隙充填对种植修复系统及周围骨力学的影响.方法:建立第一磨牙缺失的下颌骨有限元模型,模拟植入1颗Straumann种植体.建立对不同大小种植体-基台微间隙(5、6、7、8、9μm)胶质充填后的种植系统模型,于面垂直向加载100 N咬合力和斜向45°加载100 N咬合力,分析种植体系统各部件...     

Biomechanical effect of abutment on stability of orthodontic mini-implant. A finite element analysis

The biomechanical influences of primary factors on titanium mini-implant, which is used as an anchorage for orthodontic tooth movement, were quantified using the three-dimensional finite element method. Six types of finite element models were designed to show various thread pitches from 0.5 to 1.5 mm. Three models were designed with abutment and three other models without abutment. A traction force of 2 N was applied to the head of the mini-implant or abutment to be at 45 degrees to the bone surface. No remarkable differences were observed in the stress distribution patterns regardless of thread pitch variance. However, the stress distribution was remarkably different between models with abutment and without abutment. The maximum stress of the model with abutment and thread pitch 0.5 mm was the least as compared with the other models. Areas of high-level stress were obviously smaller than in the models without abutment. The plots of the displacement distributions of the models with abutment also presented significant pattern differences as compared with the models without abutment. The high-level area was localized to the head of the implant and the abutment in models with abutment. Therefore, the existence of the abutment is significantly useful in decreasing the stress concentration on the bone, while the effect of thread pitch was uncertain.     

Finite element analyses of two antirotational designs of implant fixtures

The purpose of this study was to compare the effect of cyclic compressive forces on loosening of the abutment retaining screw of dental implant fixtures with two different antirotational designs using the finite element analysis. A three-dimensional model of externally hexed and trichannel dental implant fixtures with their corresponding abutments and retaining screws was developed. Comparison between the two designs was carried out using finite element analysis. The results revealed that the externally hexed design has significantly higher overall stress, contact stress, and deflection compared with the trichannel design. The trichannel antirotational design has the least potential for fracture of the implant/abutment assembly in addition to its capability for preventing rotation of the prosthesis and loosening of the screw.     

Predicting Peri-implant Stresses Around Titanium and Zirconium Dental Implants—A Finite Element Analysis

Due to anatomical and surgical constrains the implant placement may not be parallel to each other always. Non-parallel implants are subjected to detrimental stresses at implant bone interface. Also depending on type of implant material i.e. titanium or zirconium, stresses tend to vary due to change in physical and mechanical properties. Hence stress analysis at implant bone interface between different parallel and non-parallel implants becomes significant. Evaluation and comparison of stress distribution in the bone around two parallel and non-parallel titanium and zirconium dental implants on axial and non-axial loading supporting three unit fixed prosthesis. Three dimensional finite element models (M1, M2, M3) were made of three differently angulated implants in ANSYS (11.0 Version) software and P4 processor with a speed of 3 GHz and 3 Gb RAM hardware, common for titanium and zirconium implants. Stress around the implants was analyzed on an axial load of 200 N and a non-axial load of 50 N. In both titanium and zirconium implants on axial loading in cortical bone, higher stresses were observed in M3 followed by M2 and M1. On non-axial loading higher stresses were observed in M2, followed by M3 and M1. In both titanium and zirconium implants on axial and non-axial loading in cancellous bone stresses were higher in M3 followed by M2 and M1. Zirconium implants showed lower stresses in cortical bone and higher stresses in cancellous bone compared to titanium implants. Over all Stresses in the bone were more due to titanium implants than zirconium implants. Zirconium implants led to lower peri-implant stresses than titanium implants.     

Nonlinear finite element analysis of a splinted implant with various connectors and occlusal forces

PURPOSE: The aim of this study was to analyze the biomechanics in an implant/tooth-supported system under different occlusal forces with rigid and nonrigid connectors by adopting a nonlinear finite element (FE) approach. MATERIALS AND METHODS: A model containing 1 Frialit-2 implant (placed in the second molar position) splinted to the mandibular second premolar was constructed. Nonlinear contact elements were used to simulate a realistic interface fixation between the implant body and abutment screw and the sliding keyway stress-breaker function. Stress distributions in the splinting system with rigid and nonrigid connectors were observed when vertical forces were applied to the tooth, pontic, implant abutment, or complete prosthesis in 10 simulated models. RESULTS: The displacement obtained from the natural tooth increased 11 times than that of the implant, and the peak stress values within the implant system (sigmaI, max) increased significantly when vertical forces acted only on the premolar of a fixed prosthesis with a rigid connector. The sigmaI, max values seen in the splinting prosthesis were not significantly different when vertical forces (50 N) were applied to the pontic, molar (implant) only, or the entire prosthesis, respectively, regardless of whether rigid or nonrigid connectors were used. Moreover, the peak stress values in the implant system and prosthesis were significantly reduced in single- or multiple-contact situations once vertical forces on the pontic were decreased. DISCUSSION: The compensatory mechanism between the implant components and keyway sliding function of the implant/tooth-supported prosthesis could be realistically simulated using nonlinear contact FE analysis. The nonrigid connector (keyway device) significantly exploited its function only when the splinting system received light occlusal forces. CONCLUSION: Minimization of the occlusal loading force on the pontic area through occlusal adjustment procedures to redistribute stress within the implant system in the maximum intercuspation position for an implant/tooth-supported prosthesis is recommended.