不同弹性模量的基台--种植体组合对周围成骨性能的影响

利用有限元分析软件计算了不同静力作用下的多种基台-种植体周围骨组织的应力分布.模拟结果显示,基台-种植体组合中Ti6Al4V钛合金-聚醚醚酮(TC4-PEEK)相对于其他实验组其应力集中程度现象可以有效降低,周围骨组织的应力分布较为均匀,最大应力值为40～60 MPa.在轴向加载条件下,不同基台-种植体系统中PEEK种植体的应力水平较小,而周围骨组织应力水平较大;在斜向45°加载条件下,相对于其他两种基台-种植体系统,TC4-PEEK的应力水平更低,其周围骨组织中的皮质骨承受的最大应力值为55 MPa,松质骨承受的最大应力值为5 MPa,综合来看的应力水平最小,有助于骨沉积和成骨量增加,从而有效提高种植体的界面稳定性.     

动静组合荷载下岩石特性的三维数值模拟研究

针对深部岩石工程中,围岩在动荷载压力作用之前就已经承受高静应力或地应力,因此对三维动静荷载联合作用下的岩石变形及破坏特性展开研究具有重要意义。为了探究三维动静组合加载下岩石的力学特性,采用FLAC3D数值模拟方法对岩样进行模拟,以岩石单轴抗压强度的0%、20%、50%和80%作为轴压值,分别设置0 MPa、2 MPa、4 MPa、6 MPa、8 MPa为围压进行加载。得出以下结论:在轴向静压固定、围压变化下,试件的组合强度逐渐升高;当对岩石试件的径向进行加载,增强岩石的整体强度,表现出等效应力逐渐变大;当围压不变,轴向静压变化的情况下,轴向静压值成为岩石试件毁坏程度和破碎速度的主要条件,当压力值增大到一定程度,试件将发生破碎。     

奥氏体钢四点弯曲疲劳行为的数值模拟与试验

采用有限元方法对奥氏体钢四点弯曲疲劳试验的加载过程进行了数值模拟,分析了疲劳试样的应力分布与疲劳寿命,确定了受力分布相对均匀的试样的合理尺寸范围,并对一种Cr-Mn奥氏体钢进行了四点弯曲疲劳试验研究,对比分析了有限元模拟与试验结果间的差别与原因。结果表明,试样尺寸不同,两加载辊之间的应力分布规律不同;当t/h(材料厚度/加载辊距)1.4时,最大应力出现在靠近加载辊的内侧,距加载辊0.4~0.5 mm;当t/h=1.2~1.4时,两加载辊之间的应力分布比较均匀,最大模拟应力与加载应力(理论值)的误差小于5%;当t/h1.2时,最大应力出现在两加载辊中间,其中t/h=0.7~0.8时,模拟值最大应力与加载应力比较接近,但应力分布均匀性较低;采用t/h≈1.3的试样进行疲劳试验研究,试验后的疲劳裂纹均产生在两加载辊中间,在加载辊外侧未发现疲劳裂纹,这与模拟结果相一致;模拟疲劳极限为498 MPa,循环4.0×10~6周次,试验测定疲劳极限为505MPa,循环3.6×106周次,模拟值略小于试验值,可见有限元方法可以较准确地预测材料的疲劳寿命。     

铁磁试件静载拉伸时应力磁化的反转效应

 以20钢含V型缺陷平板试样为研究对象,通过试验方法和ANSYS仿真方法对试样在拉伸载荷下的应力分布进行反复加载卸载分析,测量了试样表面规定路径的切向和法向的漏磁场分布;分析了V型缺陷对磁记忆信号的影响以及固定位置的磁场值随应力的变化关系;最后将试验结果与模拟结果进行对比,发现试验结果与模拟结果具有很好的一致性。在应力小于50MPa时磁场值随应力的增加而减小,在应力大于50MPa时磁场值随应力的增加而增加。变化关系表现出了明显的应力磁化反转现象,磁化反转位置在50MPa(约是最大应力的30%)。     

外科植入物用新型TAMZ合金的生物学性能（Ⅱ）

3　TAMZ合金的骨组织相容性应用于骨内种植的生物材料 ,由于其特殊的应用部位及目的 ,有它特定的生物相容性要求 ,即骨组织生物相容性。早期的研究多采用动物体内实验方法来了解种植体与骨组织的相互作用。然而这种方法并不能对骨组织 -种植体界面的生物作用机制作出确切的描述 ,因为骨组织与种植体界面的生物作用是发生在细胞和分子的微观水平上 ,由于缺少有效的手段保护种植材料表面脆弱的细胞结构和制备足够薄的组织切片供结构分析 ,透射电子显微镜等分析工具的应用也受到了限制。近年来 ,由于细胞培养和分化提纯技术的研究进展 ,成骨…     

7475-T7351铝合金抗疲劳性能研究

采用旋转弯曲疲劳试验、轴向加载疲劳试验、疲劳裂纹扩展速率试验等疲劳性能测试方法,研究了7475-T7351铝合金厚板的疲劳性能.并通过透射电镜(TEM)和扫描电镜(SEM)分析了该合金的显微组织和疲劳断口形貌.结果表明:7475-T7351铝合金具有良好的耐疲劳损伤性能,光滑试样(Kt=1)在室温旋转弯曲和高温轴向加载条件下的疲劳极限分别为180.0和345.0 MPa,缺口试样(Kt=2.2)在室温旋转弯曲加载条件下的疲劳极限为91.9 MPa;合金厚板材料在高温下缺口敏感性有所降低;国产材料裂纹扩展速率随应力比增加而增大,裂纹扩展门槛值减小;国产7475铝合金与进口材料在裂纹稳定扩展阶段裂纹扩展行为基本相当;在近门槛值附近不同应力比下的裂纹扩展门槛值略有差别.     

大方坯结晶器铜板热应力数值分析

本文采用Fluent与Ansys软件对结晶器铜板进行了"热-应力"耦合计算,模拟计算中考虑了钢液流动对铜板温度分布的影响,在此基础上得出较精确的热应力分布。分析结果表明,最大应力点位于结晶器铜板外侧壁面的角部区域,最大应力值为135 MPa,低于材料的最大许用应力。为进一步降低应力集中,对结晶器水缝宽度、水速等浇注参数进行了适当调整,使得应力点最大应力值降到了110 MPa以下。     

镁合金板材挤压工艺的有限元模拟

采用有限元模拟方法对AZ31B镁合金板材挤压过程中的应力场、应变场和挤压力随工艺参数的变化规律进行研究.所研究的挤压工艺参数包括:挤压温度、挤压比和挤压速度等。结果表明:随着坯料挤压温度的升高,最大等效应变值从17. 6逐渐增大至26. 4;最大等效应力值由133. 2 MPa减小至43. 4 MPa;挤压温度高于350℃后,挤压力变化不大.随着挤压比的增加,挤压力由7. 328 MN增大至8. 808 MN;最大等效应变值先减小后增大;最大等效应力值由87 MPa增加至119 MPa.随着挤压速度的增加,挤压力从2. 14 MN增加至3. 42 MN;最大等效应变值先增大后减小;最大等效应力值由72. 3 MPa逐渐增大至104. 2MPa.     

不同组织状态TC4 ELI钛合金动态力学性能研究

利用分离式霍普金森压杆装置(SHPB)对低间隙Ti-6Al-4V(TC4 ELI)合金的等轴组织、双态组织和魏氏组织试样进行了动态压缩试验。应变率分别为ε=2000,3000,4000 s-1,得到了动态压缩真应力-应变(σ-ε)曲线,并对试验后发生剪切失效破坏的试样沿纵剖面切开,利用金相显微镜(OM)进行显微组织观察。结果表明:动态压缩条件下TC4 ELI合金3种组织试样的真应力-应变曲线大致分为弹性阶段和塑性阶段,没有明显的屈服平台,3种组织状态下的试样在高应变率下应变强化效应不明显,表现出一定的应变率强化效应;在4000 s-1应变率加载条件下,平均动态流变应力(σ)、均匀动态塑性应变(ε)以及冲击吸收功(E)按等轴组织、双态组织和魏氏组织顺序依次减小,等轴组织试样的σ,ε和E分别达到了1400 MPa,0.34%和470 kJ.m-3,具有较好的动态力学性能;在4000 s-1应变率加载条件下3种组织状态的试样均发生了剪切失效破坏,并在其纵剖面上都观察到了一条白亮的绝热剪切带(ASB),裂纹沿着绝热剪切带由圆柱试样的圆柱面向中心扩展,与ASB形成和扩展的方向一致,剪切带与导致断裂的裂纹密切相关。     

局部加载拉应力对圆柱薄壳焊接残余应力场分布的影响

采用有限元模拟技术,从理论上论证了通过局部加载减小焊接残余应力技术路线的可行性.比较了焊接过程中拉伸与焊后拉伸降低应力在机理上的不同,研究表明,焊接过程中拉伸远比焊后拉伸效果好.200 MPa外力拉伸时,焊后拉伸残余应力最大值由常规焊条件下的235 MPa降至90 MPa左右,焊接过程中拉伸残余应力最大值可降至30 MPa左右.     

Quantitative histologic evaluation of LTI carbon, carbon-coated aluminum oxide and uncoated aluminum oxide dental implants

The response of mandibular bone to identical geometry LTI carbon, carbon-coated aluminum oxide, and uncoated aluminum oxide blade-type dental implants in baboons for 2 years was evaluated using histologic, microradiographic, and scanning electron microscopic methods. In addition, a quantitative histologic analysis was performed identifying the type, amount, and distribution of tissue surrounding the dental implant systems. This is the final phase of a study investigating the effect of implant elastic modulus and implant surface chemical composition on the performance of dental implants. Previous studies have utilized clinical and radiographic evaluations, postretrieval mechanical testing, and finite element stress analysis to evaluate the dental implant performance. The results of the histologic study revealed a direct implant-bone interface with no intervening soft tissue in 16 of the 21 implants (76%). A fibrous tissue interface was observed in 5 of 21 implants (24%). Quantitative histologic results for the implants with a direct implant-bone interface showed statistically larger crestal cortical plates (p less than 0.05) and greater area fraction crestal cancellous bone (p less than 0.05) in the LTI carbon implant compared to the carbon-coated and uncoated aluminum oxide implants. The carbon-coated and uncoated aluminum oxide implants demonstrated statistically greater area fraction cancellous bone at the inferior region of the implant (p less than 0.05) and thinned and reduced crestal cortical plates when compared to the LTI carbon implants. The results indicate that significant stress shielding of the crestal bone had occurred with the rigid carbon-coated and uncoated aluminum oxide implants when compared to the LTI carbon implants which had a material elastic modulus similar to cortical bone. Based upon the histologic results, it appears that the LTI carbon implants with the direct implant-bone interface exhibited a greater potential for long-term successful performance compared to the aluminum oxide substrate implants.     

Experimental protocol for mechanical characterization of a femoral implant of carbon-Peek composite hip prosthesis in fatigue

This study concerns the fatigue behavior of a C/Peek hip implant. It is now well-established that the extent of bone loss around a total hip arthroplasty stem is related to stress shielding process. Due to a modulus mismatch between the bone and the implant material, the load transfer to the stem decreases the mechanical stimulus needed by the bone to maintain its structure. Because of its low modulus of elasticity and its good resistance to fatigue in aeronautical applications, the Fiber Carbon/Peek composite could potentially replace some of the metal alloys used in hip stem implant. After a literature survey on biomechanical performances of some fiber carbon composites, including AS4/Peek, experimental quasi-static and fatigue compression tests have been performed on AS4/Peek hip implants. The structural and mechanical characterization of the injection moulded composite material has been realized. The prosthesis compression and fatigue behaviour have been studied with a joint-stimulating apparatus immersed in a physiological solution temperature controlled. Instead of the low specimen homogeneity, no fatigue damage has been revealed either by X-ray observations of stiffness measurements, till ten millions of cycles. The quasi-static compressive fracture morphology has been analyzed by S.E.M. and have shown a good fiber matrix bonding. This mechanical results would suggest that AS4/Peek hip stem are worthy of further investigation as implantable prostheses.     

Influence of bone quality on stress distribution for endosseous implants

The present study examined the influence of bone quality on the transmission of occlusal forces for endosseous dental implants. Employing the finite element method, the study modeled a 3.75 x 10-mm threaded implant placed in a 12 x 11 x 8-mm section of bone. By varying the elastic parameters assigned to the bone elements, four bone quality categories were established. A load of 100 N was applied at the occlusal surface of the restoration at a 30 degrees angle to the vertical axis of the implant. Maximum von Mises stress concentrations (sigma Emax) were observed to be located in the marginal bone at the coronal aspect of the implant fixture in all four cases. Values of sigma Emax were 13.7 MPa for type 1 bone, 15.8 MPa for type 2 bone, 20.1 MPa for type 3 bone, and 26.5 MPa for type 4 bone. Magnitude of the stresses in bone was strongly correlated (r = 0.997) with computed displacement of the implant system. This analysis predicts that placement of implants in bone with greater thickness of the cortical shell and greater density of the core will result in less micromovement and reduced stress concentration, thereby increasing the likelihood of fixture stabilization and tissue integration.     

Fixed temporization and bone-augmented ridge stabilization with transitional implants

Utilization of dental implants in full-mouth restorations is now a well-accepted treatment modality, with numerous modifications and implant systems documented in the literature. The efficacy of the treatment procedure generally requires an extended postplacement healing period prior to loading the implant fixture with the stress of mastication. Until recently, clinicians have not been able to address patient comfort requirements during the healing period. The teaching objective of this article is to present and evaluate a transitional implant system used to provide function during the healing phase. The system consists of thin titanium transitional implants and a three-component overdenture that is intended to absorb the pressure during function and protect the augmented implant site and the definitive implant fixtures from the stress of immediate loading. Treatment objectives for the transitional and definitive implants are made during the initial treatment planning. Three cases are presented to document and illustrate the clinical procedure.     

Osteogenesis at the dental implant interface: high-voltage electron microscopic and conventional transmission electron microscopic observations

The osteogenesis of mandibular bone to endosteal dental implants was examined using an in vivo dog model. One half of the implants examined were unloaded implants, with the remaining one half prosthodontically loaded for 6 months. Undecalcified mandibular implant samples were examined with both high-voltage electron microscopy (HVEM) stereology and routine transmission electron microscopy. The osseous interface to integrated implants was shown to vary in its morphology. Mineralized bone was observed directly apposing the implant, often separated from the implant by an electron-dense deposit of approximately 50 nm. Within this densely mineralized matrix, osteocytes were routinely observed. Adjacent areas were shown to contain slightly wider zones of either a less dense mineralized matrix or, alternatively, unmineralized tissue. Other zones consisted of wider unmineralized matrices containing collagen fibers and osteoblasts. These latter zones were consistent with the appearance of an appositional type of bone growth. Because bone is a dynamic, actively remodeling tissue, a varied morphology of the support tissues to dental implant is not unexpected. Areas of mature bone interfacing with successfully integrated implants were demonstrated, as well as areas adjacent to the mature bone that were undergoing remodeling or mineralization. This study has also shown that HVEM stereology is a valuable research tool to investigate the oral tissue interface with dental implants.     

Biodegradable interlocking nails for fracture fixation

Serious problems such as stress shielding, allergic reactions, and corrosion are associated with the use of metallic fracture fixation devices in fractured long bones. Metal implants often are removed during a second retrieval operation after fracture healing has completed. A biocompatible implant that degrades slowly during implantation would obviate the need for a second operation and save the patient from considerable physical, psychologic, and financial discomfort. The biodegradable implant must provide the fractured limb sufficient support for a certain time, allowing early loading. A gradual transfer of load from the biodegradable implant to the bone would result in a better product of bone healing and avoid stress shielding. In an animal model using adult sheep, two types of biodegradable polymer interlocking nails were tested in comparison with a stainless steel interlocking nail. Fracture healing, mechanical properties of the bones, degradation behavior in vivo and in vitro, and tissue response were monitored during a 2 1/2-year followup study. To detect shifts in acid base relations caused by the release of acid compounds, pH measurements were performed. Fracture healing was unimpaired, and the mechanical test results of all three groups were excellent. Histologic analysis showed a mild inflammatory response, but no pH shifts were observed. The results of this study justify additional research on these promising materials.     

Homogenized stress analysis in a dental implant system

In this study, the stress state occurring at each trabecular due to three different types of dental implant is investigated by a homogenization technique, in which the trabecular structure is assumed to be composed of repeating hexagonal units. This technique helps make a proper material model of bone and to analyse such a non-homogeneous structure at the level of an individual microstructural unit. Stress analyses with the homogenization technique show a much higher stress level in the sponge bone, compared to those with conventional FEM. It also shows that even a minor lateral force results in crucial stresses in the dental implant system. The stress states of the mandible with a hemisphere-rooted implant and a wedge type implant show similar levels, while those with a rectangular-rooted implant result in higher stresses. It is suggested that the distance between the implant tip and cortical bone be kept far enough apart to prevent stress concentrations in the mandible.     

仿生结构钛合金植入材料的研究和应用

仿生结构钛合金植入材料拥有良好的力学性能和生物相容性,且弹性模量与人体骨骼较为相近,具有广阔的应用前景.为此,介绍了表面仿生结构和梯度仿生结构两大类仿生结构钛合金植入材料的研究现状,其中,表面仿生结构钛合金植入材料的制备方法主要有电化学沉积法、激光熔覆法以及复合改性技术等;梯度仿生结构钛合金的制备方法主要有粉末冶金法、...     

Cloning, characterization, and chromosomal localization of human superillin (SVIL)

The specific aim of this study was to determine the response of alveolar bone after it was augmented vertically using distraction osteogenesis and subsequently loaded with implant restorations. Four dogs each had four implants placed horizontally into an edentulous mandibular quadrant and, after integration, a distraction osteogenesis device was fabricated in the laboratory. An osteotomy was made to allow the crest of the alveolar ridge to be distracted vertically. After 10 mm of vertical distraction, the device was stabilized with light cured resin. Following bone fill confirmation of the distraction gap at 10 weeks, two implants were placed into the ridges, one in distracted bone and one in nondistracted bone. After 4 months for implant integration, freestanding prostheses were fabricated. Crestal bone levels were evaluated throughout the period of function. Animals were sacrificed after 1 year of loading, for histologic evaluation of the bone. The vertical ridge augmentation averaged 8.85 +/- 1.05 mm after 10 weeks of healing following distraction, without change over 1 year of implant loading. Histologic examination showed that bone had formed between the distracted segments, creating an augmented ridge. The average thickness of the labial cortex in the distraction gap was significantly thinner than the lingual cortex in distracted bone and the lingual and labial nondistracted cortical bone. The presence of the dental implant did not significantly affect cortical bone thickness. Serial sections showed that implants remained integrated and functional without soft tissue inflammation. Dental implants placed into alveolar ridges augmented with the technique of distraction osteogenesis maintained bone and were functional for the length of this study.     

Dry-process surface modification for titanium dental implants

Because dental implants contact many different tissues, the implant material must have optimum surface compatibility with the host bone tissue, subepithelial connective tissue, and epithelial tissue. In addition, dental implant surfaces exposed to the oral cavity must remain plaque-free. Such materials can be created under well-controlled conditions by modifying the surfaces of metals that contact those tissues. “Tissue-compatible implants,” which are compatible with all host tissues, must integrate with bone tissue, easily form hemidesmosomes, and prevent bacterial adhesion. This research was aimed at developing such tissue-compatible implants by modifying titanium surfaces using a dry process for closely adhering to the titanium substrate and ensuring good wear resistance. The process includes ion beam dynamic mixing (thin calcium phosphates), ion implantation (Ca⁺, N⁺, F⁺), titania spraying, ion plating (TiN, alumina), and ion beam mixing (Ag, Sn, Zn, Pt) with Ar⁺. At the bone tissue/implant interface, a thin calcium phosphate coating and rapid heating with infrared radiation were effective in controlling the dissolution without cracking the coating. This thin calcium phosphate coating may directly promote osteogenisis, but it may also enable immobilization of functional proteins or drugs. At the oral fluid/implant interface, an alumina coating and F⁺ implantation were responsible for inhibiting the adhesion of microbial plaque. In conclusion, dry-process surface modification is useful in controlling the physicochemical nature of surfaces, including the surface energy and the surface electrical charge, and in developing tissue-compatible implants.