Effects of Endoprosthesis Head Material on Acetabular Cartilage Metabolism: An Animal Study Using Crossbred Pigs.

BACKGROUND: Hip endoprosthesis is one option for the treatment of displaced femoral neck fractures and avascular necrosis of the femoral head. Few reports are available describing acetabular cartilage metabolism after endoprosthesis surgery of the hip. The purpose of this study was to compare the biological effects on cartilage between cobalt-chrome (Co-Cr) and alumina ceramic heads wherein the cartilage articulates directly. METHODS: We used the acetabular cartilage from six hips of three immature crossbred pigs to examine the effects on cytokines, the amount of hyaluronic acid (HA), and cartilage mRNA expression of ceramic head and Co-Cr head endoprosthesis. Mechanical loading of materials of Co-Cr and ceramic heads was performed on the acetabular cartilage in culture media as an organ culture model. Thereafter, protein levels of cytokines (MMP-1, 3, TNF-alpha (α), Interleukin (IL)-1 alpha (α), and IL-1 beta (ß)) and the amount of HA were measured from the culture media. Cartilage RNA extraction was performed, and quantitative reverse transcriptase-polymerase chain reaction was performed with primer sets for type I, II, and III collagens; aggrecan; MMP-1, 3, 13; TNF-α; and IL-1 α, IL-1 ß. RESULTS: Protein level of IL-1 ß and amount of HA in the Co-Cr group were significantly higher than those of the Ceramic group. Type II collagen mRNA expression in the Ceramic group was significantly higher than in the Co-Cr group. IL-1 ß mRNA expression was significantly higher in the Co-Cr group than in the Ceramic group. CONCLUSIONS: The present study showed that ceramic bipolar produces smaller adverse effects on cartilage cells compared to Co-Cr bipolar. These results could have significant implications for implant usage not only in hip joints, but also in other joints, including the shoulder, talus and radial head.

Characteristics of Cobalt-Related Cardiomyopathy in Metal Hip Implant Patients: An Evaluation of 15 Published Reports.

Over 300,000 hip replacements occurred in the USA in 2010, and the frequency is likely increasing annually. Blood Cobalt (Co) concentrations in patients with well-functioning cobalt-chromium (Co-Cr) hip implants are usually elevated above background concentrations relative to the general population. Excessive Co exposure, in rare cases, can result in cardiomyopathy. The purpose of this review was to identify cases of cardiomyopathy in metal-containing hip implant patients and to evaluate the possible cause of each patient's cardiomyopathy. We evaluated 15 cases published between 2009 and 2016, and, based on a review of the preexisting risk factors, blood Co concentrations, and histopathological information published for each patient, they were stratified into one of four categories regarding the association between Co exposure and the development of cardiomyopathy: (1) Co was causal (five cases); (2) Co was contributory (two cases); (3) Co was possibly contributory (six cases); and (4) Co was non-causal (two cases). In all 15 cases, blood Co concentrations (14-6521 µg/L) were elevated beyond levels associated with the majority of metal-containing implant patients (0.1-10 µg/L), and, in many cases, there was evidence of a malfunctioning implant. The data indicate that individuals with well-functioning implants, even those with preexisting risk factors, are at no risk of developing cardiac effects. We conclude that blood Co measurements are informative, but should be interpreted with caution, and in context of other factors evaluated in this analysis. The mere presence of elevated Co is not sufficient to indicate causation for a patient's cardiomyopathy.

Detection of metallic cobalt and chromium liver deposition following failed hip replacement using T2* and R2 magnetic resonance.

BACKGROUND: Failed hip prostheses can cause elevated circulating cobalt and chromium levels, with rare reports of fatal systemic organ deposition, including cobalt cardiomyopathy. Although blood cobalt and chromium levels are easily measured, organ deposition is difficult to detect without invasive biopsy. The T2* magnetic resonance (MR) method is used to quantify tissue iron deposition, and plays an important role in the management of iron-loading conditions. Cobalt and chromium, like iron, also affect magnetism and are proposed MR contrast agents. CASE PRESENTATION: We describe a case of a 44-year-old male with a failed hip implant and very elevated blood cobalt and chromium levels. Despite normal cardiac MR findings, liver T2* and R2 values were abnormal, triggering tissue biopsy. Liver tissue analysis, including X-ray fluorescence, demonstrated heavy elemental cobalt and chromium deposition in macrophages, and no detectable iron. CONCLUSIONS: Our case demonstrates T2* and R2 quantification of liver metal deposition in a patient with a failed hip implant. Further work is needed to investigate the role of T2* and R2 MR in the detection of metal deposition from metal on metal hip prostheses.

Corrosion resistance assessment of Co-Cr alloy frameworks fabricated by CAD/CAM milling, laser sintering, and casting methods.

STATEMENT OF PROBLEM: The effects of fabrication methods on the corrosion resistance of frameworks produced with Co-Cr alloys are not clear. PURPOSE: The purpose of this in vitro study was to evaluate the electrochemical corrosion resistance of Co-Cr alloy specimens that were fabricated by conventional casting, milling, and laser sintering. MATERIAL AND METHODS: The specimens fabricated with 3 different methods were investigated by potentiodynamic tests and electrochemical impedance spectroscopy in an artificial saliva. Ions released into the artificial saliva were estimated with inductively coupled plasma-mass spectrometry, and the results were statistically analyzed. The specimen surfaces were investigated with scanning electron microscopy before and after the tests. RESULTS: In terms of corrosion current and Rct properties, statistically significant differences were found both among the means of the methods and among the means of the material groups (P<.05). With regard to ions released, a statistically significant difference was found among the material groups (P<.05); however, no difference was found among the methods. Scanning electron microscopic imaging revealed that the specimens produced by conventional casting were affected to a greater extent by etching and electrochemical corrosion than those produced by milling and laser sintering. CONCLUSIONS: The corrosion resistance of a Co-Cr alloy specimens fabricated by milling or laser sintering was greater than that of the conventionally cast alloy specimens. The Co-Cr specimens produced by the same method also differed from one another in terms of corrosion resistance. These differences may be related to the variations in the alloy compositions.

CoCr wear particles generated from CoCr alloy metal-on-metal hip replacements, and cobalt ions stimulate apoptosis and expression of general toxicology-related genes in monocyte-like U937 cells.

Cobalt-chromium (CoCr) particles in the nanometre size range and their concomitant release of Co and Cr ions into the patients' circulation are produced by wear at the articulating surfaces of metal-on-metal (MoM) implants. This process is associated with inflammation, bone loss and implant loosening and led to the withdrawal from the market of the DePuy ASR™ MoM hip replacements in 2010. Ions released from CoCr particles derived from a resurfacing implant in vitro and their subsequent cellular up-take were measured by ICP-MS. Moreover, the ability of such metal debris and Co ions to induce both apoptosis was evaluated with both FACS and immunoblotting. qRT-PCR was used to assess the effects on the expression of lymphotoxin alpha (LTA), BCL2-associated athanogene (BAG1), nitric oxide synthase 2 inducible (NOS2), FBJ murine osteosarcoma viral oncogene homolog (FOS), growth arrest and DNA-damage-inducible alpha (GADD45A). ICP-MS showed that the wear debris released significant (p<0.05) amounts of Co and Cr ions into the culture medium, and significant (p<0.05) cellular uptake of both ions. There was also an increase (p<0.05) in apoptosis after a 48h exposure to wear debris. Analysis of qRT-PCR results found significant up-regulation (p<0.05) particularly of NOS2 and BAG1 in Co pre-treated cells which were subsequently exposed to Co ions+debris. Metal debris was more effective as an inducer of apoptosis and gene expression when cells had been pre-treated with Co ions. This suggests that if a patient receives sequential bilateral CoCr implants, the second implant may be more likely to produce adverse effects than the first one.

F-actin and α-actinin reorganization mediates initial fibroblast interaction with CoCr alloy particles in vitro.

Asceptic loosening remains the primary cause for failure of joint implant. The active role of fibroblasts in mediating asceptic loosening is however not well documented. In this study the initial interactions of fibroblasts with metal particles was studied by evaluating changes in the cytoskeletal structure and cytokine level. Murine L929 fibroblasts cultured with cobalt chromium particles were observed by phase contrast and scanning electron microscopy (SEM). Changes in the cytoskeletal rearrangement of F-actin and α-actinin focal adhesion plaques were studied by confocal microscopy. Expression of the proinflammatory cytokines IL-6 and IL-1α were analyzed by ELISA. The role of actin filaments and microtubules in particle uptake were determined at low temperature and in presence of colchicine and cytochalasin B. Phase contrast and SEM studies reveal that the metal particles adhere to the fibroblasts. The cellular cytoplasm was observed to grow over the particles and is suggestive of particle uptake. Confocal microscopy shows the presence of voids within the F-actin cytoskeletal framework corresponding to areas occupied by the metal particles, indicating the possible uptake of these particles. Aggregates of α-actinin into patches at the cell surface were also noted. Adherence and uptake of particles did not occur at low temperature and in presence of cytochalasin B, indicating that it is an active energy-dependent process involving actin filaments. Changes in the levels of cytokine IL-6 and IL-1α were not observed suggesting the role of other cytokine molecules in mediating the inflammatory response to wear debri by fibroblasts.

Distribution of metal released from cobalt-chromium alloy orthopaedic wear particles implanted into air pouches in mice.

Metal-on-metal hip replacement implants generate wear debris and release ions both locally and systemically in patients. To investigate dissemination of metal, we determined blood and organ levels of cobalt (Co), chromium (Cr), and molybdenum (Mo) following the implantation of Co-Cr alloy wear debris in mice using skin pouches as a model system. We observed increased metal levels in blood for up to 72 h; the levels of Co were highest and remained elevated for 7 days. Co levels were elevated in all organs studied (liver, kidney, spleen, lung, heart, brain, and testes), with the peak at 48 h; highest levels were measured in liver and kidney (838.9 ± 223.7 ng/g in liver, and 938.8 ± 131.6 ng/g in kidney). Organ Cr levels were considerably lower than Co levels, for example, Cr in kidney was 117.2 ± 12.6 ng/g tissue at 48 h. Co is more mobile than Cr, reaching higher levels at earlier time points. This could be due to local tissue binding of Cr. Exposure to Co-Cr particles in vivo altered antioxidant enzyme expression and activities. We observed induction of catalase protein in the liver and glutathione reductase (GR) and peroxidase (GPx) proteins in the spleen. Activities of catalase and GPx in the liver were significantly increased while that of GR was decreased in the kidney. Organs of mice with Co-Cr particle implantation were exposed to increased metal levels capable of inducing reactive oxygen species scavenging enzymes, suggesting the tissue may be subjected to oxidative stress; however, the overall antioxidant defence system was not markedly disturbed.

Signalling of DNA damage and cytokines across cell barriers exposed to nanoparticles depends on barrier thickness.

The use of nanoparticles in medicine is ever increasing, and it is important to understand their targeted and non-targeted effects. We have previously shown that nanoparticles can cause DNA damage to cells cultured below a cellular barrier without crossing this barrier. Here, we show that this indirect DNA damage depends on the thickness of the cellular barrier, and it is mediated by signalling through gap junction proteins following the generation of mitochondrial free radicals. Indirect damage was seen across both trophoblast and corneal barriers. Signalling, including cytokine release, occurred only across bilayer and multilayer barriers, but not across monolayer barriers. Indirect toxicity was also observed in mice and using ex vivo explants of the human placenta. If the importance of barrier thickness in signalling is a general feature for all types of barriers, our results may offer a principle with which to limit the adverse effects of nanoparticle exposure and offer new therapeutic approaches.

Estimation of nickel and chromium in saliva of patients with fixed orthodontic appliances.

AIM: To examine whether orthodontic treatment induces an increase in salivary nickel and chromium concentration. METHODS: Ten new patients (7 females and 3 males) beginning fixed orthodontic treatment were included in the study. The mean age of the sample was 17.5 years (range 14 to 24 years). Three samples of stimulated saliva were collected from each orthodontic patient, 1 at each of the following times: before insertion of the fixed appliance (which served as a baseline/reference level for salivary nickel and chromium content), 1 week after insertion of the appliance, and 3 weeks after insertion of the appliance. These samples were analyzed for nickel and chromium content using the atomic absorption spectrometer and their values recorded in ng/mL. The Friedman test was used to test the statistical significance of differences in concentrations of each metal before and after insertion of orthodontic appliances. Post-hoc comparisons were performed using the Wilcoxon signed rank test and Mann-Whitney U test. RESULTS: This study showed that there was a statistically significant difference in salivary nickel and chromium concentrations before and 1 week and 3 weeks after insertion of fixed orthodontic appliances. The highest concentrations of nickel and chromium were found after 1 week. The salivary nickel and chromium concentrations tapered off 3 weeks after insertion but were significantly higher than baseline levels. CONCLUSION: The salivary nickel and chromium concentrations significantly increased after insertion of fixed orthodontic appliances as compared to baseline levels, with the maximum concentration seen in the first week after placement of fixed orthodontic appliances.

The combined role of wear particles, macrophages and lymphocytes in the loosening of total joint prostheses.

This review considers the causes of loosening of prosthetic joint replacement paying attention to the biological mechanisms rather than other effects that are physical, such as component fracture and other failure related to mechanical problems. Infection accounts for approximately 1.5 per cent of joint loosening and when it occurs it is a cause of serious concern to the surgeon. The loosening of prosthetic joints in the absence of infection is by far the most common reason for revision surgery and is known as aseptic loosening. While this may be multifactorial in terms of causation, and non-biological factors may contribute significantly in a particular individual, a significant part is undoubtedly played by the generation of wear debris, mainly from the bearing surfaces of the joint, and the cellular reaction to this in the implant bed. Phagocytic cells (macrophages and multinucleated giant cells) are the ones that remove foreign material from the tissues, and the ways in which these cells function in the interface between implant and bone are described. Mediators produced locally include numerous cytokines, enzymes and integrins. There is evidence for interactions between macrophages and locally recruited lymphocytes, which may or may not give rise to an immunologically mediated process.Sensitization of individuals having metal implants in place has been shown by positive skin tests or blood lymphocyte transformation tests and in these cases has been accompanied by loosening and failure of the replacement joint. The question remains as to whether this process is also present in a proportion of individuals with aseptic loosening in the absence of clearly defined clinical evidence of sensitization.Numerous studies performed by the author's group and, latterly, by others suggest that the cellular reactions detected in the tissues in cases of aseptic loosening are indeed those of contact sensitization. There is good evidence to show that a type IV cell-mediated immune reaction is taking place, with TH1 cell involvement and active antigen presentation. The extent to which sensitization is present in individual cases of aseptic loosening remains a subject for further work and this needs all the sophisticated molecular methods now available to modern biology to be applied in appropriate prospective clinical studies coupled with experimental models in vitro and in vivo. Immunological processes may play a more important part in joint loosening than previously considered.

A model system to assess key vascular responses to biomaterials.

PURPOSE: To establish a reproducible laboratory test to evaluate prospective vascular biomaterials with respect to their thromboinflammatory properties by examining fibrinogen, platelet, and monocyte binding. Endothelial migration onto these surfaces was used as an index of vascular healing. METHODS: To evaluate biomaterials for potential thrombogenicity and inflammation, binding assays of radiolabeled human fibrinogen, platelets, and monocytes were performed on standard pieces of vascular biomaterials, including metals and polymeric and ceramic-coated materials. Using an established in vitro endothelial cell migration model, the relative migration rate of cultured human aortic endothelial cells onto these vascular biomaterials was measured and compared. The fibrinogen, platelet, and monocyte binding results were combined along with the migration results to create an overall score of biocompatibility. RESULTS: A significant direct relation of platelet and monocyte binding to the amount of adsorbed fibrinogen was observed. In contrast, migration rates of cultured human aortic endothelial cells onto the same biomaterial surfaces were found to be inversely related the amount of bound fibrinogen. Among the materials tested, stainless steel received the highest score of biocompatibility, while turbostratic carbon scored the lowest. CONCLUSIONS: Fibrinogen, platelet, and monocyte binding levels, as well as endothelial migration rates onto vascular material surfaces, provide a basis for evaluating thrombogenicity, inflammatory potential, and endothelialization in the laboratory prior to in vivo testing.

An orthologue of the cor gene is involved in the exclusion of temperate lambdoid phages. Evidence that Cor inactivates FhuA receptor functions.

A new set of lambdoid phages (mEp) classified into different immunity groups was previously described. Phages mEp213, mEp237, and mEp410 were unable to grow in mEp167 lysogenic cells, presumably due to an exclusion mechanism expressed constitutively by the mEp167 repressed prophage. In this work, to analyze the exclusion phenomenon, we constructed a genomic library from mEp167 phage in a pPROEX derivative plasmid. A DNA fragment containing an open reading frame for a 77 amino acid polypeptide was selected by its ability to confer resistance to heteroimmune phage infection. This ORF shows high amino acid sequence identity with putative Cor proteins of phages HK022, phi80 and N15. Cells expressing the mEp167 cor gene from a plasmid (Cor(+) phenotype) excluded 13 of 20 phages from different infection immunity groups. This exclusion was observed in both tonB(-) and tonB(+) cells. Lambdoid mEp phages that were excluded in these cells were unable to infect cells defective in the outer membrane FhuA receptor (fhuA(-)). Thus, Cor-mediated exclusion was only observed in fhuA(+) cells. Phage production after DNA transfection or the spontaneous induction of mEp prophage in Cor(+) cells was not blocked. In addition, ferrichrome uptake, which is mediated by FhuA, was inhibited in Cor(+) cells. Our results show that not only phage infection via FhuA but also a FhuA transport activity (ferrichrome uptake) are inhibited by Cor, presumably by inactivation of FhuA.

In vitro biocorrosion of Co-Cr-Mo implant alloy by macrophage cells.

We hypothesized that macrophage cells and their released reactive chemical species (RCS) affect Co-Cr-Mo alloy's corrosion properties and that alloy corrosion products change macrophage cell behavior. A custom cell culture corrosion cell was used to evaluate how culture medium, cells, and RCS altered alloy corrosion in 3-day tests. Corrosion was evaluated by measuring total charge transfer at a constant potential using a potentiostat and metal ion release by atomic emission spectroscopy. Viability, proliferation, and NO (nitric oxide) and IL-1beta (interlukin-1beta) release were used to assess cellular response to alloy corrosion products. In the presence of activated cells, total charge transfers and Co ion release were the lowest (p < 0.05). This was attributed to an enhancement of the surface oxide by RCS. Cr and Mo release were not different between cells and activated cells. Low levels of metal ions did not affect cell viability, proliferation, or NO release, though IL-1beta released from the activated cells was higher on the alloy compared to the controls. These data support the hypothesis that macrophage cells and their RCS affect alloy corrosion. Changes in alloy corrosion by cells may be important to the development of host responses to the alloy and its corrosion products.

Relating nickel-induced tissue inflammation to nickel release in vivo.

Nickel has a number of adverse biological effects that have made the use of nickel in biomedical implants controversial. Yet information about the distribution of nickel in tissues around nickel-containing implants is scarce. The purpose of the current study was to use a laser ablation technique, combined with inductively coupled mass spectroscopy, to assess the spatial distribution of nickel around nickel-containing implants in vivo. Polyethylene, pure nickel wire, or a nickel-containing alloy (Ni-Cr) were implanted subcutaneously into rats for 7 days. The tissues were analyzed for Ni content and inflammation at 1-mm intervals up to 5 mm away from the implants. The sham surgery sites and the polyethylene caused mild to moderate inflammation 1-2 mm from the implant site with no detectable nickel in the tissue. The nickel wire caused severe inflammation up to 5 mm away from the implant site with necrosis for 1 mm around the implant. Nickel concentrations reached 48 microg/g near the implants, falling exponentially to undetectable levels at 3-4 mm from the implants. The Ni-Cr wire caused inflammation equivalent to polyethylene, with less than 4 microg/g of nickel present in the tissue for 1-2 mm around the implants. The current study showed that the laser-ablation technique was well suited for the analysis of soft tissues for metal-ion content, and that the nickel distribution in tissues correlated well with overt tissue inflammation.

Selective association between a macrocyclic nickel complex and extrahelical guanine residues.

Nickel-dependent recognition and oxidation of guanine have been linked in part through the paramagnetic effects of nickel on the NMR of model oligonucleotide duplexes. Direct interaction between nickel and guanine N7 had originally been postulated from correlations between the efficiency of guanine oxidation and the environment surrounding its N7 position. (1)H and (31)P NMR spectra of DNA containing a single, isolated extrahelical guanine are consistent with selective binding of nickel to the N7 of this unique base over a background of nonspecific association to the phosphate backbone. The presence of a macrocyclic complex or simple salt of nickel did not detectably alter the structure of the duplex or extrahelical residue. Accordingly, nickel appeared to bind the extrahelical guanine N7 within the major groove as indicated by paramagnetic effects on the proton signals of nucleotides on the 5' but not 3' side of the nickel binding site. Similar (1)H NMR analysis of DNA containing a dynamic equilibrium of extrahelical guanine residues also suggested that the nickel complex did not affect the native distribution of structures. Oxidation of these sites by a nickel-mediated pathway consequently reflected their solvent accessibility in a general and metal-independent manner. The close proximity of the extrahelical guanines produced a composite of paramagnetic effects on each adjacent nucleotide resulting from both direct and proximal coordination of nickel.

Distribution of cobalt chromium wear and corrosion products and biologic reactions.

Replacement hip arthroplasty with the use of ultrahigh molecular weight polyethylene for the cup articulating with a metal head has provided a low friction arthroplasty with years of success. However, the search for improved materials and designs for articulating surfaces continues. The use of metallic heads articulating with metallic cups is now being reconsidered for total hip replacements. Success will be enhanced if wear and corrosion of the articulating surfaces can be kept below that of the metal on ultrahigh molecular weight polyethylene couple. Concern has been raised about the release, and biologic fate, of metal species from corrosion and wear. Titanium alloys have been shown to have limitations as an articulating surface showing significant wear, and the alloy per se should not be considered for wear couples in total hip replacements. The cobalt chromium alloys are known to have reasonable wear and corrosion properties and continue to be evaluated. The issue of cobalt chromium wear and corrosion products and how this relates to the biologic performance of total hip replacement devices is reviewed. Under the condition of wear as currently experienced at the articulating surfaces of cobalt chromium alloys and ultrahigh molecular weight polyethylene, the amount of metallic products transferred to the tissues is sufficiently low to be well tolerated by the biologic system. Nickel and cobalt ions arc, rapidly transported from the implant site and eliminated in the urine. Chromium is stored in the tissue and eliminated more slowly. The issue of host hypersensitivity to these elements remains of concern. All 3 elements, in ionic form, are known to cause contact dermatitis. Untoward biologic reactions, including hypersensitivity, should be minimized if wear and corrosion phenomena are minimized.

In vitro study of biodegradation of a Co-Cr alloy using a human cell culture model.

The evaluation of a potential biomaterial is based on two approaches: firstly, the study of the local and systemic effects of the biomaterial implanted in the host; and secondly the study of the behaviour of the biomaterial itself with increasing time. The progress achieved in human cell culturing allows in vitro evaluation of a new biomaterial using the human cell(s) system(s) characteristic of the tissue which it will be exposed to in vivo. This kind of approach permits the assessment of the biodegradation of a biomaterial whatever it is: metal; alloy; ceramic; glass; polymer; with or without specialized coating.... The experimental approach is as follows: discs representative of the biomaterial (surface state, cleaning, sterilization process) are manufactured in order to cover the bottom of the culture wells. Thereafter, they are either brought in the presence of complete culture medium alone, or in the presence of a subconfluent cell layer. A kinetic analysis is performed using various incubation periods at 37 degrees C. Released biodegradation products are identified and quantified, in both the medium and cell compartment, and on the other hand cytotoxicity is assessed. A Co-Cr alloy was studied over a 9-day period according to the experimental schedule, and showed a higher corrosion rate in the presence of osteoblasts in the range of 25-30%. Moreover, an intracellular uptake of both Cr and Co was detected, which will have physiological importance.

Surface composition of orthopaedic implant metals regulates cell attachment, spreading, and cytoskeletal organization of primary human osteoblasts in vitro.

The nature of orthopaedic implant surfaces affects the interaction between bone and the implant. To analyze this interaction at a cellular level, this study examined the early phase of cell adhesion to implant surfaces. Using an in vitro model, the cell adhesion of primary human osteoblasts cultured on Ti6A14V (Ti), CoCrMo (CC), and tissue culture polystyrene (PS) was characterized. The osteoblasts were found to adhere in greater numbers to Ti compared with PS and CC during a 12 hour period. Other cellular characteristics related to cell adhesion, such as cell spreading, cytoskeletal organization, and focal contact formation, were also examined. Osteoblasts cultured on Ti were significantly larger, and spread better, compared with those on PS and CC. Also, the rate of cytoskeletal reorganization was enhanced on Ti. Focal contacts remained peripherally located in cells on Ti and CC as cytoskeletal reorganization proceeded. However, for cells on PS, the focal contacts quickly became dispersed along actin filaments. There was no difference between surfaces in the number of cells forming focal contacts, although the cells used a larger percentage of their membrane to attach to CC. These data suggest that osteoblast attachment to Ti is greater because cell spreading and cytoskeletal organization are enhanced. Furthermore, the mechanisms of osteoblast attachment to the underlying substrate may be significantly different between biometals and tissue culture plastic. Substrate specific information regarding the characteristics and mechanisms of cell adhesion may be helpful in the design of implants to optimize bone growth at the interface.

Averiguaçäo radiográfica de possíveis defeitos de fundiçäo em armaçöes de próteses parciais removíveis / Quality evaluation of removable partial denture framework by x-rays

Cientes das grandes variáveis que podem determinar a ocorrência de fraturas em armaçöes de cobalto-cromo no momento de sua adaptaçäo pelo cirurgiäo-dentista e/ou durante o uso pelos pacientes, procurou-se, por meio de uma técnica radiográfica simples, identificar a presença de defeitos estruturais (áreas de maior ou menor radioluscência), a fim de evitar perda de tempo e despesas envolvidas com o uso de laboratório, protético, ou a responsabilizaçäo do paciente pela fratura. Foram realizadas armaçöes de P. P. R. para os pacientes atendidos na Clínica de Prótese da Faculade de Odontologia de Bauru-USP, utilizando-se as ligas Still-Dent e Alloy, respectivamente nos anos de 1990 e 1991, tendo sido radiografadas 82 armaçöes previamente identificadas e numeradas. O processamento das películas radiográficas expostas foi realizado, obedecendo-se rigorosamente às recomendaçöes do fabricante, e as películas foram avaliadas por 2 examinadores previamente calibrados. As armaçöes fundidas com liga Alloy apresentaram uma melhor qualidade que as em Still-Dent. Somente por intermédio de radiografias das armaçöes, feitas rotineiramente, poder-se-ía identificar possíveis defeitos estruturais que culminariam em fracasso do aparelho