Mixed oxides prosthetic ceramic ball heads. Part 1: effect of the ZrO2 fraction on the wear of ceramic on polythylene joints.

Although mixed oxides ceramics have been indicated in the literature as a promising compromise between strength and wear, to the authors' knowledge no reports are available on the influence of the percentage of zirconia in ceramic femoral heads when sliding against polyethylene cups. Two types of mixed oxides ceramic ball heads (alumina plus, respectively, 60 and 80% of zirconia) were compared to pure zirconia and pure alumina heads in terms of wear behaviour against UHMWPE in a hip joint simulator. Polyethylene cups and ceramic femoral heads were fixed on a simulator apparatus with a sinusoidal movement and load in presence of bovine calf serum. The experimental results did not show significant difference between the two experimental ceramic materials or in comparison with pure materials. Considering that all specimens, regardless of the material, had the same level of surface roughness, this roughness factor seems to have a more relevant role than the mix of oxides used to manufacture the ceramic head. Wear tests are conducted on materials used in prosthetic hip implants in order to obtain quality control and to acquire further knowledge of the tribological processes that involve joint prostheses, therefore reducing the risk of implant failure of innovative prostheses.     

Mixed oxides prosthetic ceramic ball heads. Part 3: effect of the ZrO2 fraction on the wear of ceramic on ceramic hip joint prostheses. A long-term in vitro wear study

Using ceramic materials it is possible to obtain a number of beneficial mechanical properties such as considerable hardness, good chemical resistance, high tensile strength, and a good fracture toughness. The use of ceramic-on-ceramic as bearing surfaces for hip joint prostheses has been reported to produce a lower wear rate than other combinations (i.e. metal-on-polyethylene and ceramic-on-polyethylene) in total hip artroplasty. These advantages may increase the life expectancy of hip implants and improve the life of patients. Two new types of mixed-oxide ceramics (alumina and yttria-stabilised zirconia) femoral heads and acetabular cups containing different ratios of alumina and zirconia were compared with pure commercial alumina in terms of wear behaviour in a hip joint simulator. Hip joint wear simulator studies were carried out with a full-peak load of 2030 N and a frequency of 1 Hz in bovine calf serum. After 10 million cycles the measured weight loss of all specimens was very low. However, the experimental results did not show any significant difference between the new experimental mixed-oxide ceramics prototype and the commercial ceramic material couplings.     

Protein characterisation of salivary and plasma biofilms formed in vitro on non-corroded and corroded dental ceramic materials

Dental ceramics are generally regarded as low-adhesive materials. Different ceramics may, however, differ in composition and physico-chemical surface properties, which may be changed after corrosion. The aim of this study was to examine the adsorption of proteins onto specimens of different ceramic materials after the incubation in saliva and plasma before and after in vitro corrosion. In addition, the topography of the biofilm was examined by AFM. Surface-bound proteins were desorbed and analysed by polyacrylamide gel electrophoresis (PAGE) and immunoblotting using antibodies to saliva and plasma proteins. Silver-stained gels indicated differences in the adsorption of proteins. Differences in surface roughness at the nanometer level did not, however, seem to be correlated to the protein adsorption. After corrosion, unchanged or increased protein staining was generally seen in the gels and Western blots. The reactions for salivary amylase and proline-rich proteins varied between the different materials. Albumin and fibrinogen were identified in samples from all materials tested. Fibronectin and in specific IgA were more sparsely seen. No saliva but all plasma proteins were identified in the alumina and yttria-stabilised zirconia samples and reduced protein reactions were obtained after corrosion.     

Alumina and zirconia coated vitallium oral endosteal implants in beagles.

The purpose of this study was to assess the addition of a ceramic coating upon a Vitallium implant to increase the implant's biologic acceptability in the oral environment. The mandibular premolar teeth in 9 adult beagle dogs were removed bilaterally and these areas allowed to heal for 6 weeks. Ceramic coating with either Al2O3 or ZrO2 was carried out by flame spray deposition upon Vitallium anchor implants (9 of each), and the implants placed into the 18 healed premolar areas. Clinical and radiographic evaluation was conducted by 2 independent investigators over a 32 week period. Implants which exhibited mobility greater than II on a scale of 0 to III, at intervals of one-half, were judged unsatisfactory. After 19 weeks, all 9 Al2O3 coated implants and 5 ZrO2 coated implants were rated unsatisfactory. After 32 weeks, 4 ZrO2 coated implants were in situ with 0 or I mobility. Radiographically the width of the peri-implant space increased in direct proportion to both time and mobility. Histologic sections demonstrated encapsulating dense fibrous connective tissue which was oriented parallel to both ZrO2 and Al2O3 implants. Results suggest the zirconia used is a superior ceramic coating to the alumina. Neither seemed to increase biologic acceptability over uncoated Vitallium implants.     

Crack growth resistance of alumina, zirconia and zirconia toughened alumina ceramics for joint prostheses.

Mono-phase bio-ceramics (alumina and zirconia) are widely used as femoral heads in total hip replacements (THR) as an alternative to metal devices. Unfortunately, the orthopaedic community reports significant in-vivo failures. Material scientists are already familiar with composites like alumina zirconia. Since both are biocompatible, this could prove to be a new approach to implants. This paper deals with a new generation of alumina-zirconia nano-composites having a high resistance to crack propagation, and as a consequence may offer the option to improve lifetime and reliability of ceramic joint prostheses. The reliability of the above mentioned three bio-ceramics (alumina, zirconia and zirconia toughened alumina) for THR components is analysed based on the study of their slow crack-growth behaviour. The influence of the processing conditions on the microstructure development, of the zirconia toughened alumina composites and the effect of these microstructures, on its mechanical properties, are discussed.     

Wear properties of alumina/zirconia composite ceramics for joint prostheses measured with an end-face apparatus

While only alumina is applied to all-ceramic joint prostheses at present, a stronger ceramic is required to prevent fracture and chipping due to impingement and stress concentration. Zirconia could be a potential substitute for alumina because it has high strength and fracture toughness. However, the wear of zirconia/zirconia combination is too high for clinical use. Although some investigations on composite ceramics revealed that mixing of different ceramics was able to improve the mechanical properties of ceramics, there are few reports about wear properties of composite ceramics for joint prosthesis. Since acetabular cup and femoral head of artificial hip joint are finished precisely, they indicate high geometric conformity. Therefore, wear test under flat contact was carried out with an end-face wear testing apparatus for four kinds of ceramics: alumina monolith, zirconia monolith, alumina-based composite ceramic, and zirconia based composite ceramic. Mean contact pressure was 10 MPa and sliding velocity was 40 mm/s. The wear test continued for 72 hours and total sliding distance was 10 km. After the test, the wear factor was calculated. Worn surfaces were observed with a scanning electron micrograph (SEM). The results of this wear test show that the wear factors of the both composite ceramics are similarly low and their mechanical properties are much better than those of the alumina monolith and the zirconia monolith. According to these results, it is predicted that joint prostheses of the composite ceramics are safer against break down and have longer lifetime compared with alumina/alumina joint prostheses.     

氧化锆陶瓷材料的生物相容性

背景：已有大量研究表明,氧化锆陶瓷具有优良的生物学性能,但作为牙种植基台的研究在国内还鲜见报道,将其应用于种植牙基台上的生物学性能还需要进一步的验证。 目的：评价牙种植基台制作材料氧化锆陶瓷的生物相容性。 方法：将氧化锆陶瓷圆形试件固定在Wistar大鼠左颊黏膜表面,右侧用牙胶试件作为对照,使两组试件与颊黏膜紧密贴合但无压迫,术后2周应用大体观察和组织学方法观察口腔黏膜与氧化锆陶瓷材料的生物学反应;将氧化锆陶瓷棒形试件植入Wistar大鼠背部皮下组织内,于植入后1,2,4,8周应用大体观察和组织学方法动态观察皮肤组织与氧化锆陶瓷材料的生物学反应。 结果与结论：氧化锆陶瓷圆形试件固定后,大鼠颊黏膜局部组织未见异常,与对照组比较差异无显著性意义;氧化锆陶瓷棒形试件植入第1周可见局部组织轻微红肿,组织切片可见少量炎性细胞,2~8周红肿消退,组织切片见纤维包膜形成并逐渐变薄,到8周时包膜形成致密纤维,未见炎性细胞。提示氧化锆陶瓷材料与口腔黏膜、皮肤及皮下组织具有良好的生物相容性。     

Biological reactivity of zirconia-hydroxyapatite composites

Materials and devices intended for end-use applications as implants and medical devices must be evaluated to determine their biocompatibility potential in contact with physiological systems. The use of standard practices of biological testing provides a reasonable level of confidence concerning the response of a living organism to a given material or device, as well as guidance in selecting the proper procedures to be carried out for the screening of new or modified materials. This article presents results from cytotoxicity assays of cell culture, skin irritation, and acute toxicity by systemic and intracutaneous injections for powders, ceramic bodies, and extract liquids of hydroxyapatite (HA), calcia partially stabilized zirconia (ZO), and two types of zirconia-hydroxyapatite composites (Z4H6 and Z6H4) with potential for future use as orthopedic and dental implants. They indicate that these materials present potential for this type of application because they meet the requirements of the standard practices recommended for evaluating the biological reactivity of ATCC cell cultures (CCL1 NCTC clone 929 of mouse connective tissue and CCL 81 of monkey connective tissue) and animals (rabbit and mouse) with direct or indirect patient contact, or by the injection of specific extracts prepared from the material under test. In addition, studies involving short-term intramuscular and long-term implantation assays to estimate the reaction of living tissue to the composites studied, and investigations on long-term effects that these materials can cause on the cellular metabolism, are already in progress.     

Protein interaction with tantalum: changes with oxide layer and hydroxyapatite at the interface.

For metallic implants the surface nature is extremely important because blood and tissue interactions with metal depend upon it. Protein adsorption is the initial reaction that takes place when an implant comes in contact with blood or tissue. We attempted to coat different thicknesses of oxide layers and hydroxyapatite on tantalum and examined the changes in water contact angle and adsorption of albumin and fibrinogen. Protein adsorption studies were performed with 125I-labeled proteins. A decrease in water contact angle was observed as the oxide layer thickness of tantalum increased. Fibrinogen adsorption increased on oxide layer coated and hydroxyapatite coated surfaces, compared to bare tantalum.     

Isolation and morphological characterisation of UHMWPE wear debris generated in vitro

Wear tests are generally carried out on materials used in prosthetic hip implants, in order to obtain a better understanding of the tribological processes involved and improve the quality control of joint prostheses, directed towards reducing the risk of implant failure of innovative prostheses. Ceramic femoral heads of mixed alumina-zirconia oxides as well as zirconia and alumina single oxide heads were tested against UHMWPE acetabular cups in a hip joint simulator. Polyethylene cups and ceramic femoral heads were mounted in a simulator apparatus moving according to a sinusoidal function, under load and in the presence of bovine calf serum as lubricant. Wear particles were isolated from the bovine calf serum collected during the wear tests. An easy to follow method was used to separate the wear particles from the lubricant. Chemical digestive methods were used to separate the wear particles from the lubricant and the isolated particles were studied using scanning electron microscopy. The morphologies of the polyethylene debris showed considerable differences, both in size and shape of the particles, as a function of the coupled head material.     

Plasma protein adsorption pattern on characterized ceramic biomaterials.

The protein/biomaterial interactions of three biomaterials used in hard tissue surgery were studied in vitro. A dynamic flow system and two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) were used to investigate the adsorption of proteins from diluted human plasma on hydroxyapatite, alumina and zirconia, with regard to total protein binding capacity, relative binding capacity for specific proteins and flow-through and desorption patterns. The ceramics were characterized regarding physicochemical properties; namely, chemical composition by elementary analyses and specific surface, pore volume and pore size distribution using the BET-method and Hg-porosimetry. The materials were found to adsorb a surprisingly low amount of plasma proteins, leaving more than 70% of the surface free. The cellular response will therefore be highly affected by the physico-chemical properties of the material, in contrast to a surface fully covered with proteins. Regarding the adsorption of proteins, most proteins exhibited similar flow-through patterns on the three adsorbents. The exceptions with different flow-through patterns were apolipoprotein D (Apo D), apolipoprotein J (Apo J), complement factor C1s (C1s), complement factor C3 (C3), ceruloplasmin, fibrinogen, alpha1 B glycoprotein and alpha2 HS glycoprotein and serum retinal-binding protein (SRBP). The role of these proteins on acceptance or rejection of implants has to be investigated.     

比较4种CAD/CAM氧化锆抗压强度和断裂模式

目的 通过赫兹触压实验分析比较4种牙科CAD/CAM系统氧化锆材料的抗压强度和断裂模式。方法 制作Cercon smart、Lava、Porcera、CEREC 3 共4种CAD/CAM系统氧化锆平板试件各6个。通过赫兹触压实验及数字图像相关法,对各组试件的临界载荷值、破坏载荷值及断裂模式进行分析。结果 平板试件均在饰瓷内部以中位裂纹的形式起裂,以弧形方式传递至核瓷表面,沿饰瓷和核瓷界面分层;4种系统之间临界载荷值差异不具有统计学意义（P＞0.05）,破坏载荷值差异具有统计学意义（P＜0.05）,其中CEREC 3系统最高。结论 4种CAD/CAM系统氧化锆材料抗压强度能基本满足临床运用中口内最大咬合力的需要;其破坏模式相似,出现微裂纹及完全断裂仅发生于饰瓷,饰瓷强度仍需加强。     

In vitro reactions of human osteoblasts in culture with zirconia and alumina ceramics.

The biocompatibility of two implantable materials, zirconia and alumina ceramics, was investigated in vitro using human osteoblast cell cultures. The viability of osteoblast cells with the materials was evaluated by the methylthiazole sulfate test that revealed an absence of any cytostatic or cytotoxic effect. Cell proliferation kinetic and total protein synthesis in osteoblasts with zirconia or alumina were similar to that observed in control cells cultured on glass coverslips. Light and scanning electron microscopic examinations showed an intimate contact between osteoblasts and the substrates; well-spread cells were observed on the surfaces of both materials. Adhesion ability and morphological characteristics were preserved in osteoblast cultures with these substrates. Moreover, immunohistochemical staining in osteoblasts with zirconia and alumina showed the capacity of these cells to elaborate the extracellular matrix composed of types I and V collagen, osteocalcin, osteonectin, bone sialoprotein, and cellular fibronectin. Finally, DNA image cytometry and interphase silver-nucleolar organizer regions quantification were applied as complementary biocompatibility tests to detect any changes in DNA synthesis and cell proliferation, respectively. The results showed that neither material altered cell ploidy or cell growth rate in accordance with the absence of any inducing effect on DNA synthesis or proliferation.     

The role of whole blood in thrombin generation in contact with various titanium surfaces

Understanding of the thrombotic response (activation of the intrinsic coagulation system followed by platelet activation) from blood components upon contact with a titanium dental implant is important and not fully understood. The aims of this study were to evaluate: (1) the thrombogenic response of whole blood, platelet-rich plasma (PRP) and platelet-poor plasma (PPP) in contact with a highly thrombogenic surface as titanium, (2) the thrombogenic response of clinically used surfaces as hydroxyapatite (HA), machined titanium (mTi), TiO2 grit-blasted titanium (TiOB) and fluoride ion-modified grit-blasted titanium (TiOB-F). An in vitro slide chamber model, furnished with heparin, was used in which whole blood, PRP or PPP came in contact with slides of the test surfaces. After incubation (60 min rotation at 22 rpm in a 37 degrees C water bath), blood/plasma was mixed with EDTA or citrate, further centrifuged at +4 degrees C (2200 g at 10 min). Finally, plasma was collected pending analysis. Whole blood in contact with Ti alloy resulted in the binding of platelets to the material surface and in the generation of thrombin-antithrombin (TAT) complexes. With whole blood TAT levels increased 1000-fold compared with PRP and PPP, in which both almost no increase of TAT could be detected. In addition, the platelet activation showed a similar pattern with a 15-fold higher release of beta-TG in whole blood. In the in vitro chamber model with the clinically relevant materials, the fluoride-modified surface (TiOB-F) showed pronounced TAT generation compared with TiOB, mTi and HA. Similar results were achieved for platelet consumption and activation markers of the intrinsic coagulation system. Taken together these results implicate first that whole blood is necessary for sufficient thrombin generation and platelet activation during placement of implants. Second, a fluoride ion modification seems to augment the thrombogenic properties of titanium.     

不同材料烤瓷冠在后牙种植修复中的对比

背景：种植体上部结构牙冠材料的选择十分重要,其临床修复效果直接影响到种植体的寿命和患者的牙周健康状况。 目的：比较Lava氧化锆全瓷、金铂合金烤瓷与银钯合金烤瓷冠在后牙单颗缺失口腔种植修复中的临床效果。 方法：选择60例120颗第一磨牙缺失病例,完成单颗牙缺失种植牙修复治疗,上部结构修复牙冠材料分别为Lava氧化锆全瓷冠、金铂合金烤瓷冠与银钯合金烤瓷冠,每种材料40颗,比较3种修复体的临床修复效果。 结果与结论：通过6-48个月的随访发现,Lava氧化锆全瓷冠组和金铂合金烤瓷冠组的牙龈边缘着色、龈缘密合度、修复体颜色优于银钯合金烤瓷冠组,Lava氧化锆全瓷冠组的牙龈边缘着色和修复体颜色优于金铂合金烤瓷冠组,金铂合金烤瓷冠组的龈缘密合度优于Lava氧化锆全瓷冠组;银钯合金烤瓷冠抗折程度最强,最具临床优越性,但其牙龈指数最高,牙龈健康程度最差,菌斑形成速度最快、程度最重。由此可见,在种植修复完成后需要选择较为适合的冠部修复体进行种植修复,Lava氧化锆全瓷冠具有卓越的生物相容性,而金铂合金烤瓷冠在边缘密合性方面更具优势,此两种修复体在临床治疗中具有一定的优势。中国组织工程研究杂志出版内容重点：生物材料;骨生物材料; 口腔生物材料; 纳米材料; 缓释材料; 材料相容性;组织工程全文链接：     

In vitro evaluation of the mutagenic and carcinogenic power of high purity zirconia ceramic

Tetragonal zirconia polycrystal (TZP) is a new interesting ceramic for the manufacture of medical devices. Its wide use in orthopedic and odontoiatric implants was limited till now by the high chemical and radiochemical impurities of the raw materials. Purification processes now available allow to obtain high purity ceramic grade powders suitable for TZP ceramics manufacture, even if their possible mutagenic and transforming effects are still unclear. The aim of this work is to study in vitro the mutagenic and oncogenic effects of a new zirconia ceramic stabilized by yttria (Y-TZP). This ceramic was sintered from high purity powders obtained by a process developed under a project carried out within the Brite EuRam programme. For comparison, ceramics made from unpurified zirconia powder were also tested. Fibroblasts irradiated by a linear accelerator were used as positive control. The results obtained show that Y-TZP ceramic does not elicit either mutagenic or transforming effect on C3H/10T(1/2) (10T(1/2)) cells and demonstrate that ceramic from high purity powders can be considered suitable for biomedical applications from the point of view of the effects of its radioactive impurity content.     

On the kinetics and impact of tetragonal to monoclinic transformation in an alumina/zirconia composite for arthroplasty applications

Latest trends in load-bearing materials for arthroplastic applications involve the development of highly fracture resistant alumina/zirconia composites, as an alternative choice to alumina and zirconia monolithic ceramics. Composite materials are designed from both chemical and microstructural viewpoints in order to prevent environmental degradation and fracture events in vivo, whose shadow yet hampers the full exploitation of ceramic materials in the field of arthroplasty. The aim of this paper is to evaluate the resistance to environmental degradation in an alumina/zirconia composite (Biolox Delta^®), which represents a primary candidate for hip and knee joint applications. Our approach consists first in the experimental determination of an activation energy value for environmentally driven tetragonal to monoclinic (t–m, henceforth) polymorphic transformation in the zirconia phase of the material; then, based on such an experimental value, a prediction is given for the long-term in vivo environmental resistance of prostheses made of the composite material. The present evaluation clarifies the in vivo performance of this new composite for orthopedic applications.     

Dental implants stimulate expression of Interleukin-8 and its receptor in human blood--an in vitro approach

Interleukin (IL)-8 secreted from osteoblasts and peripheral blood monocytes increases in patients with aseptic hip-implant loss and in patients with mucositis after dental implant insertion. We explored in vitro the possibility of an IL-8-mediated inflammatory response as a consequence of contact between different dental implant surfaces and human blood. Titanium and zirconia implants were incubated in human blood. Nonstimulated blood served as negative, while blood stimulated with bacterial lipopolysaccharides (LPS) served as positive control. After depyrogenization, to examine the possible role of LPS, implants were again submerged in blood. Gene-expression of IL-8 and its receptor was measured by real-time quantitative polymerase chain reaction. In a receptor mediated, but LPS-independent manner, titanium implants led to a more pronounced increase in IL-8 gene expression when compared with zirconia implants. Depyrogenization resulted after 24 h in zirconia implants in decreased IL-8 gene expression. Altered IL-8 expression could indicate aseptic, at least LPS-independent implant loss, which may be an additional feature in the manifestation of peri-implantitis, possibly triggered by microscopically small implant-particles. Hence, opening a new field of investigations to further understand the possible mechanism underlying the manifestation of implant failure.     

Increased viable osteoblast density in the presence of nanophase compared to conventional alumina and titania particles

In the present in vitro study, osteoblast (bone-forming cells) viability and cell density were investigated when cultured in the presence of nanophase compared to conventional (i.e. micron) alumina and titania particles at various concentrations (from 10,000 to 100 microg/ml of cell culture media) for up to 6h. Results confirmed previous studies of the detrimental influences of all ceramic particulates on osteoblast viability and cell densities. For the first time, however, results provided evidence of increased apoptotic cell death when cultured in the presence of conventional compared to nanophase alumina and titania particles. Moreover, since material characterization studies revealed that the only difference between respective ceramic particles was nanometer- and conventional-dimensions (specifically, phase and chemical properties were similar between respective nanophase and conventional alumina as well as titania particles), these results indicated that osteoblast viability and densities were influenced solely by particle size. Such nanometer particulate wear debris may result from friction between articulating components of orthopedic implants composed of novel nanophase ceramic materials. Results of a less detrimental effect of nanometer--as compared to conventional-dimensioned particles on the functions of osteoblasts provide additional evidence that nanophase ceramics may become the next generation of bone prosthetic materials with increased efficacy and, thus, deserve further testing.     

Soft tissue response to four dense ceramic materials and two clinically used biomaterials.

Disk-shaped implants of spinel, alumina, mullite, zircon, a cast Co-Cr-Mo alloy, and ultra-high molecular weight polyethylene (UHMWPE), were implanted in the paraspinalis muscle of 12 adult, male, white New Zealand rabbits. Prior to implantation the implants were characterized with respect to size and shape, weight and surface roughness. After periods of 1 month, 2 months, and 4 months, the rabbits were sacrificed and the tissue specimens were retrieved with the implants still intact. Histological examination of the tissues surrounding the implants along with changes in the size and shape, weight, and surface roughness of the implants were used as criteria for evaluating these materials for implant purposes. No surfaces degradation of any of the materials was detected using scanning electron microscopy. Fibrous tissue seemed to adhere to the UHMWPE implants more than any other material used in this study. Large amounts of fibrous tissue were also found to adhere to the cast Co-Cr-Mo alloy implants. The histological results indicated that within the limits of this investigation, the biocompatibility of the ceramic materials used in this study compared favorably with the clinically used Co-Cr-Mo alloy implants and the UHMWPE implants.