Analysis of bone-implant interaction phenomena by using a numerical approach

OBJECTIVES: The purpose of the present work is to investigate the interaction phenomena occurring between endosseus dental implants and peri-implant bone tissue. MATERIAL AND METHODS: Detailed finite element models are adopted in order to analyze the actual behavior of bone-implant system depending on implant and anatomical site configuration and loading conditions. Different types of titanium dental implants are considered. Implant finite element models are obtained through a reverse engineering procedure and adopting specific software for the reconstruction of geometrical configuration. Anatomical sites are modeled starting from computerized tomography data, according to specific image processing procedures. RESULTS: Occlusal static forces are applied to the implants and their effects on the bone-implant interface region are evaluated. The influence of several parameters, such as morphometry of anatomical site or loading condition, on the biomechanical response of bone-implant system is considered. CONCLUSIONS: The evaluation of the biomechanical response of implant-bone compound necessarily requires the adoption of accurate numerical models, accounting for the complex geometry of threaded implants, as well as of the anatomy of the patients to be able to provide for reliable results pertaining to stress/strain path on peri-implant bone tissue.     

Machined and sandblasted human dental implants retrieved after 5 years: A histologic and histomorphometric analysis of three cases

Objective: Human retrieved implants with an intact bone-implant interface play a pivotal role in validating data obtained from in vitro studies and animal experiments. This study presents a histologic and histomorphometric analysis of peri-implant tissue reactions and of the bone-titanium interface in three machined and sandblasted dental implants retrieved after a 5-year loading period. Method and Materials: Three implants, with an intact bone-implant interface, were found in the Archives of the Implant Retrieval Center of the Dental School of the University of Chieti-Pescara, Chieti, Italy. The three implants had been used in a two-stage submerged procedure and loaded as part of a small prosthetic restoration. One implant had been retrieved because of an abutment fracture, while there was a fracture of the connecting screw in the other two. One implant was in the maxilla (sandblasted surface), and two were in the mandible (one with a machined surface and the other with a sandblasted surface). All implants had been processed for histology. Results: All three implants presented mature, compact, lamellar bone at the interface. Many remodeling areas were present in the peri-implant bone, especially inside the implant threads. The bone was always in close contact with the implant surface. The bone-implant contact percentage of the machined implant was 92.7%, while the two sandblasted implants showed bone-implant contact percentages of 85.9% and 76.6%. Conclusion: The present histologic results confirmed that these implants with different surfaces maintained a good level of osseointegration over a 5-year loading period, with continuous remodeling at the interface, and showed high bone-implant contact percentages. (Quintessence Int 2012;43:287?292).     

Threaded versus porous-surfaced implants as anchorage units for orthodontic treatment: three-dimensional finite element analysis of peri-implant bone tissue stresses

PURPOSE: A 3-dimensional finite element model was developed to investigate the cause of different crestal bone loss patterns observed around sintered porous-surfaced and machined (turned) threaded dental implants used for orthodontic anchorage in a previously reported animal study. MATERIALS AND METHODS: Twenty-noded structural solid elements with parabolic interpolation between nodes were used for modeling the bone-implant interface zone. A 3-N traction force acting between either 2 porous-surfaced or 2 machined threaded implants placed in canine premolar mandibular sites and bone profiles observed at initiation and 22 weeks of orthodontic loading were modeled. RESULTS: Higher maximum stresses in peri-implant bone next to the coronal region of the implants were predicted with the machined threaded implants at both the initial and final time points, with the values 20% greater than those predicted after the 22-week loading period. These values were approximately 200% greater than those predicted for the porous-surfaced implants, for which a more uniform stress distribution was predicted. DISCUSSION: The finite element model results indicated that the observed greater retention of crestal bone next to the porous-surfaced implants was attributable to lower peak stresses developing in crestal peri-implant bone with this design, which decreased the probability of bone loss related to local overstressing and bone microfracture. CONCLUSION: The predicted lower stresses were a result of the more uniform transfer of force from implant to bone with the porous-surfaced implants, which was a consequence of the interlocking of bone and implant possible with this design.     

Anisotropic elasticity of cortical and cancellous bone in the posterior mandible increases peri-implant stress and strain under oblique loading

The aim of this study was to compare implant-bone interface stresses and peri-implant principal strains in anisotropic versus isotropic three-dimensional finite element models of an osseointegrated implant in the posterior mandible. We obtained anisotropic (transversely isotropic) elastic constants for mandibular bone and derived equivalent isotropic constants by averaging over all possible spatial orientations. A finite element model was constructed using ten-node tetrahedral p-elements, providing curved edges where necessary and increasing the accuracy of the results in regions of high stress gradients. Perfect bonding was assumed at the implant-bone interface. An oblique load was applied at the coronal aspect of the crown with 100 N vertical and 20 N bucco-to-lingual components. Implant-bone interface stresses exceeded reported bond strengths and principal strains reached yield strain levels in the cortical crest. Anisotropy increased what were already high levels of stress and strain in the isotropic case by 20 to 30% in the cortical crest. In cancellous bone, anisotropy increased what were relatively low levels of interface stress in the isotropic case by three- to four-fold to exceed bond strength levels. Anisotropy has subtle, yet significant effects on interface stresses and peri-implant strains and careful consideration should be given to its use in finite element studies of dental implants.     

眶部种植体长度对骨界面应力影响的三维有限元研究

目的 探讨不同长度的眶部种植体对骨界面应力分布的影响。方法 建立直径3.75 mm,长度分别为3、4、6、10 mm的眶部种植体-颅颌面骨三维有限元模型,分别给予沿种植体轴向和与轴向成45°的载荷,载荷大小20 N,记录两种方向载荷下种植体及骨界面的Von-Mises应力峰值和位移峰值,分析其应力分布。结果 施加沿种植体轴向载荷时,种植体周围应力集中于根部,种植体受力大于骨面;施加与轴向成45°载荷时,应力集中于种植体颈部与第一螺纹之间,种植体受力大于骨面。施加两个方向的载荷时,3 mm种植体的应力峰值明显大于其他长度种植体,而位移峰值无明显变化。在相同长度下,施加沿种植体轴向载荷时的应力峰值及位移峰值均明显低于与轴向成45°载荷时,载荷方式对界面应力分布有明显的影响。结论 临床上尽量选择4 mm以上的眶部种植体;应用3 mm种植体时,应选择骨密质较厚的区域植入。     

The staggered installation of dental implants and its effect on bone stresses

Purpose: The aim of this study was to investigate the effect of offsetting the middle or peripheral implant on the compressive stress values in the crestal bone around the neck of the dental implant. Materials and Methods: Three finite element models describing three titanium implants installed in quadrilateral pieces of bone was executed. A 2‐mm nickel chromium superstructure representing a bridge was modeled over the implant abutments. In model 1, implants were installed along a straight line. Model 2 had the middle implant installed outside the line connecting the two peripheral implants buccally. Model 3 had the mesial implant installed out of alignment. Six 100‐N loads were modeled on top of the mesial and middle implants of the three models individually. Loads 1 and 2 were directed vertically on the mesial and middle implants, while loads 3 and 4 represented the horizontal loads in the buccal direction. Loads 5 and 6 were directed mesially on the mesial and central implants. Maximal compressive stress levels in the crestal bone of the three models were then investigated. Results: The results demonstrated that offset implant installation revealed slightly lower bone stresses under buccally or lingually directed horizontal forces. Slightly higher bone stresses under vertical loads were observed. Horizontal mesial or distal loads resulted in slightly higher bone stresses than those caused by buccal or lingual loading. Conclusions: The in‐line implant alignment clearly had the safest compressive stress outcome on the surrounding structure under vertical loads. Under buccolingual loads, implant alignment with peripheral offset would have, relatively, the safest compressive stress outcome on bone.     

螺距对即刻负载种植体和周围骨组织影响的三维有限元研究

目的探讨在即刻种植负载条件下,种植体形成骨结合后,梯形螺纹螺距对种植体和周围骨组织的影响,为种植体结构的优化提供依据。方法运用计算机辅助设计j维建模软件Solidworks,建立螺距分别为0．6mm、0．7mm、0．8mm、1．0mm、1．2mm、1．3mm、1．4mm、1．6mm的圆柱状梯形螺纹种植体模型,再将其分别与利用CT扫描数据蓖建的下颌骨组织模型进行仿真结合,在即刻加载情况下且种植体形成骨结合后,分别施加垂直向和与种植体长轴成15°的颊舌向力150N。运用ANSYSWorkbench有限元分析软件进行模拟仿真分析,比较种植体和周围牙槽骨组织,随种植体螺距改变而引起的应力、应变的变化。结果即刻负载且种植体与骨结合完成后,垂直向加载,皮质骨在种植体螺距为0．8mm和1．0mm时,Von—Mise应力、应变均较小;松质骨在螺距为0．7mm、0．8mm、1．0mm时,Von—Mise应力、应变较小;种植体在螺距为1．6mm时应力最小为44．18MPa,螺距为0．8mm时应变最小为11．04μm。颊舌向加载,皮质骨在螺距为0．7mm、0．8mm时,Von-Mise应力、应变较小;松质骨在螺距为0．6mm、0．7mm、0．8mm时,Von—Mise应力、应变均较小;种植体在螺距为0．8mm时应力最小为188．23MPa,螺距为0．6mm时应变最小为23．69μm。结论对于圆柱状梯形螺纹种植体,螺距选取1．0mm、1．2mm、1．3mm或1．4mm时,在即刻负载情况下,当种植体与骨结合完成后,种植体-骨组织系统各主要零件的综合力学性能较好、形变较小,对骨的破坏小,有利于种植稳定性的提高。     

Effect of Compromised Cortical Bone on Implant Load Distribution

Purpose: To investigate photoelastically the difference in load distribution of dental implants with different implant neck designs in intact and compromised bone. Materials and Methods: Composite photoelastic models were fabricated using two different resins to simulate trabecular bone and a 1‐mm thick layer of cortical bone. The following parallel‐sided, threaded implants were centrally located in individual models representing intact and compromised cortical bone: Straumann (4.1‐mm diameter × 12‐mm length), AstraTech (4.0‐mm diameter × 13‐mm length), and 3i (3.75‐mm diameter × 13‐mm length). The compromised cortical bone condition was simulated by contaminating a 1‐mm neck portion with Vaseline to impair the implant–resin interface. Vertical and oblique static loads were applied on the abutments, and the resulting stresses were monitored photoelastically and recorded photograhphically. Results: For the fully intact condition, the highest stresses were observed around the crest and apical region for all implant designs under vertical and inclined loads. There were no appreciable differences in magnitude or distribution between implant types. With compromised cortical bone, for all designs and load directions, higher stresses in the supporting structures were observed. Increased stresses were noted especially at the cortical bone–trabecular bone interface. Somewhat lower stress levels were observed with the 3i implant. Conclusions: The condition of implant–cortical bone contact has considerable influence on stress distribution. A compromised cortical bone condition caused higher level stresses for all implant designs tested.     

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.     

Comparative evaluation of implant designs: influence of diameter, length, and taper on strains in the alveolar crest. A three-dimensional finite-element analysis

OBJECTIVES: Our aim was to analyze and compare systematically the relative and interactive effects of implant diameter, length, and taper on calculated crestal bone strains. MATERIAL AND METHODS: Three-dimensional finite-element models were created of a 20-mm premolar section of the mandible with a single endosseous implant embedded in high- or low-density cancellous bone. Oblique (200-N vertical and 40-N horizontal) occlusal loading was applied. Cortical and cancellous bone were modeled as transversely isotropic and linearly elastic. Perfect bonding was assumed at all interfaces. A two-level factorial statistical design was used to determine the main and interactive effects of four implant design variables on maximum shear strains in the crestal alveolar bone: diameter, length of tapered segment, length of untapered segment, and taper. Implant diameter ranged from 3.5 to 6 mm, total implant length from 5.75 to 23.5 mm, and taper from 0 to 14 degrees , resulting in 16 implant designs. RESULTS: Increasing implant diameter resulted in as much as a 3.5-fold reduction in crestal strain, increasing length caused as much as a 1.65-fold reduction, whereas taper increased crestal strain, especially in narrow and short implants, where it increased 1.65-fold. Diameter, length, and taper have to be considered together because of their interactive effects on crestal bone strain. CONCLUSION: If the objective is to minimize peri-implant strain in the crestal alveolar bone, a wide and relatively long, untapered implant appears to be the most favorable choice. Narrow, short implants with taper in the crestal region should be avoided, especially in low-density bone.     

Three-dimensional numerical simulation of dental implants as orthodontic anchorage

Endosseous oral implants have been used as orthodontic anchorage in subjects with multiple tooth agenesis, and their application under orthodontic loading has been demonstrated clinically and experimentally. The aim of this investigation was to examine three-dimensional (3D) bone and implant finite element (FE) models. The first model assumed that there was no osseointegration and the second that full osseointegration had occurred. These models were used to determine the pattern and distribution of stresses within the ITI-Bonefit endosseous implant and its supporting tissues when used as an orthodontic anchorage unit. The study examined a threaded implant placed in an edentulous segment of a human mandible with cortical and cancellous bone.The results, using both models, indicated that the maximum stresses were always located around the neck of the implant, in the marginal bone. Thus, this area should be preserved clinically in order to maintain the bone-implant interface structurally and functionally.     

Ultimate masticatory force as a criterion in implant selection

Osseointegrated implants often fail because of excessive masticatory forces that cause extremely large stresses in bone tissue. We hypothesized that a proper dental implant could be selected by comparing the ultimate masticatory forces of a wide range of commercially available implants. We determined ultimate oblique masticatory forces for different cylindrical implants, taking into consideration the biomechanical correlation between implant dimensions and stresses in supporting bone. For this purpose, we used the finite element (FE) method and studied von Mises stresses in implant-bone interface areas to evaluate the influence of implant dimensions on stress concentration and on the value of an implant's ultimate masticatory load. Geometric models of a mandibular segment were generated from computed tomography (CT) images and were analyzed with osseointegrated cylindrical implants. Masticatory forces were applied in their natural direction. All materials were assumed to be linearly elastic and isotropic. Critical point in the peri-implant area of bone was determined. The ultimate value of the masticatory load, which generates ultimate stresses at the critical point, was calculated for each implant. These findings provide correct selection of implant dimensions in clinical cases, because corresponding ultimate values of masticatory force were used as a criterion for assessment of their load-carrying capacity and applicability.     

紧咬型磨牙对后牙游离端种植体周围骨组织应力分布的有限元研究

目的　采用三维有限元分析法,分析紧咬型磨牙对种植体及周围骨组织应力分布的影响。方法　采用锥体束CT扫描一成年磨牙症志愿者,通过轮廓提取、三维重建、布尔运算建立带咬合关系的游离端缺失模型。采用参数化建模,建立Ankylos C/X 4.5×11 mm种植体模型。完成模型装配后,模拟紧咬型磨牙载荷与正常咀嚼载荷对模型进行加载,分析种植体与周围骨组织的von Mises应力分布情况。结果　两种载荷下种植体、基台中应力主要集中在其颊舌侧颈部周围,种植体周围骨组织应力主要集中于与种植体颈部接触的颊舌侧骨皮质。紧咬型磨牙载荷下种植体及骨组织的von Mises峰值与高应力分布区均大于正常咀嚼载荷。紧咬型磨牙载荷与正常咀嚼载荷下第一磨牙区种植体周围骨组织von Mises峰值分别为163.27 MPa与24.02 MPa,第二磨牙区分别为135.52 MPa与16.94 MPa。结论　与正常的咀嚼负荷相比,紧咬型磨牙可能导致种植体与其周围骨组织的应力过度集中。     

Biomechanical effect of a zirconia dental implant-crown system: a three-dimensional finite element analysis

Purpose: The objective of this study was to analyze and compare the stresses in two different bone-implant interface conditions in anisotropic three-dimensional finite element models (FEMs) of an osseointegrated implant of either commercially pure titanium or yttrium-partially stabilized zirconia (Y-PSZ) in combination with different superstructures (gold alloy or Y-PSZ crown) in the posterior maxilla. Materials and Methods: Three-dimensional FEMs were created of a first molar section of the maxilla into which was embedded an implant, connected to an abutment and superstructure, using commercial software. Two versions of the FEM were constructed; these allowed varying assignment of properties (either a bonded and or a contact interface), so that all experimental variables could be investigated in eight groups. Compact and cancellous bone were modeled as fully orthotropic and transversely isotropic, respectively. Oblique (200-N vertical and 40-N horizontal) occlusal loading was applied at the central and distal fossae of the crown. Results: Maximum von Mises and compressive stresses in the compact bone in the two interfaces were lower in the zirconia implant groups than in the titanium implant groups. A similar pattern of stress distribution in cancellous bone was observed, not only on the palatal side of the platform but also in the apical area of both types of implants. Conclusion: The biomechanical parameters of the new zirconia implant generated a performance similar to that of the titanium implant in terms of displacement, stresses on the implant, and the bone-implant interface; therefore, it may be a viable alternative, especially for esthetic regions.     

The influence of bone mechanical properties and implant fixation upon bone loading around oral implants.

Finite element models were created to study the stress and strain distribution around a solitary BAnemark implant. The influence of a number of clinically relevant parameters was examined: bone-implant interface (fixed bond versus frictionless free contact), bone elastic properties, unicortical versus bicortical implant fixation and the presence of a lamina dura. Bone loading patterns in the vicinity of the implant seem to be very sensitive to these parameters. Hence they should be integrated correctly in numerical models of in vivo behaviour of oral implants. This necessitates the creation of patient-dependent finite element models.     

无牙下颌固定种植义齿带末端悬臂的应力分析

目的:比较不同悬臂设计下颌种植支持全口义齿的骨及种植体应力分布特点,为临床种植修复提供生物力学分析依据。方法:建立3组下颌6个种植支持全口义齿的三维有限元模型,悬臂分别为3、6、9 mm。在悬臂末端垂直加载100 N的力。结果:种植全口义齿悬臂末端垂直加载时,末端种植体骨应力集中,易发生松动失败;末端种植体及中间种植体颈部应力集中,易发生植入体与基桩连接失败;连梁应力集中在与末端种植体连接处,此处易发生折断。悬臂长度增加骨应力、种植体应力及连梁应力明显增加。结论:悬臂越短越有利于力的均匀分布。6个种植体支持短悬臂修复设计较符合生物力学分布原理。     

植术区邻牙牙周-牙髓联合病变伴角形骨缺损的综合治疗：2年临床观察病例报告一例

本研究报道了一例邻牙牙周-牙髓联合病变伴角形骨缺损患者的种植治疗过程,以及随访2年后的治疗效果。该患者左下第一、第二双尖牙缺失,左下尖牙重度牙周病伴有角形骨吸收至根尖1/3,冷热测牙髓反应迟钝,诊断为牙周-牙髓联合病变。种植术前首先对左下尖牙进行了根管治疗,然后局部切开翻瓣、彻底清创、Nd：YAP激光处理,并于骨缺损处植入胶原骨（Bio-Oss Collagen,Geistlich Pharma AG,Wolhusen,Switzerland）。植骨术后6个月,二次暴露,见左下尖牙骨缺损消失,植骨区成骨良好,遂直接行种植体植入手术,采用一次法植入两颗种植体（Camlog Screw Line,Camlog Biotechnologies）,初期稳定性好,愈合3个月后行永久修复。种植术后2年时复查,临床及X线检查见种植体周围软、硬组织稳定,健康;左下尖牙牙周状况健康,角形骨吸收消失。本研究提示,种植术区邻牙虽存在重度牙周病及较大骨缺损,若处理得当、综合治疗,不会影响种植治疗的长期效果。     

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目的系统地分析和比较支抗种植体骨内段的直径、长度和锥度(锥体直径/锥体长度)对种植体与骨界面应力分布的影响及相互作用。方法2007年10月至2008年12月在烟台市口腔医院、山东大学机械工程学院,通过三因素两水平析因设计建立包含不同直径、主体长度和锥度的支抗种植体的上颌骨前磨牙区域骨块模型共8个,分别对种植体施加1.96N(200gf)与种植体成90°角的拉力,得到8种植体与骨界面的VonMises应力。比较三种设计因素(直径、长度、锥度)对种植体与骨界面应力分布的影响及相互作用关系。结果随着种植体直径和锥度的增加,骨组织内的应力明显降低,具有统计学意义。种植体长度的改变对应力的影响则不具有统计学意义。结论使用直径较粗、具有锥度的种植体可以降低种植体周围骨界面应力。     

种植体数目与分布对下颌种植覆盖义齿骨组织应力变化的影响

目的：建立下颌种植覆盖义齿三维有限元模型,研究咬合力作用下种植体数目与位置分布对牙槽骨组织应力分布的影响因素。方法：临床采集患者下颌骨及其原有义齿CT数据,使用逆向工程软件建立种植体数目与位置不同的下颌种植覆盖义齿实体模型。通过Abaqus有限元软件分析咬合力作用下种植体数目与位置分布对种植体周围以及下颌后端牙槽骨应力变化的影响。结果：在咬合力作用下,下颌骨Mises应力主要分布在种植体周围骨组织,种植体远中颈部呈现应力集中,下颌后端区域应力较小且分布均匀。随着种植体数目的增加,后端种植体周围骨应力上升,远端牙槽骨应力降低。当牙弓前、后端种植体距离增加时,种植体周围骨应力增大,远端牙槽骨应力降低。结论：采用2植体支持的下颌种植覆盖义齿种植体周围骨吸收风险较小,但远端牙槽嵴骨吸收风险增大。4植体义齿所承受的咬合力主要由植体承担,修复时应注意前后植体的距离和咬合力在义齿上的合理分布。     

A 5‐year randomized clinical trial on the influence of splinted and unsplinted oral implants in the mandibular overdenture therapy. Part I: peri‐implant outcome.

Thirty-six completely edentulous patients were enrolled for a 5-year prospective study testing the treatment outcome between splinted and unsplinted implants retaining a mandibular hinging overdenture. The patients were randomized into 3 groups of equal size depending on the attachment system used such as: magnets, ball attachments or bars (reference group). Only 1 implant out of the 72 had failed at the abutment stage. Not a single implant failed during the 5-year loading period. The accumulation of plaque was significantly higher for the Magnet than for the Ball group. Bleeding on probing, as well as marginal bone level, attachment level and Periotest values did not statistically differ among the groups, neither at year 1 nor at year 5. However, the Periotest values were significantly lower at year 5 compared to year 1 for all groups, which indicates a higher rigidity at the bone-implant interface. No correlation was found between bleeding on probing and marginal bone loss. We conclude that the connection state of 2 implants retaining a hinging overdenture did not influence the peri-implant outcome.