Co-Cr Alloy Research Articles

Recent Advancements in Surface Modification, Characterization and Functionalization for Enhancing the Biocompatibility and Corrosion Resistance of Biomedical Implants

Metallic materials are among the most crucial engineering materials widely utilized as biomaterials owing to their significant thermal conductivity, mechanical characteristics, and biocompatibility. Although these metallic biomedical implants, such as stainless steel, gold, silver, dental amalgams, Co-Cr, and Ti alloys, are generally used for bone tissue regeneration and repairing bodily tissue, the need for innovative technologies is required owing to the sensitivity of medical applications and to avoid any potential harmful reactions, thereby improving the implant to bone integration and prohibiting infection lea by corrosion and excessive stress. Taking this into consideration, several research and developments in biomaterial surface modification are geared toward resolving these issues in bone-related medical therapies/implants offering a substantial influence on cell adherence, increasing the longevity of the implant and rejuvenation along with the expansion in cell and molecular biology expertise. The primary objective of this review is to reaffirm the significance of surface modification of biomedical implants by enlightening numerous significant physical surface modifications, including ultrasonic nanocrystal surface modification, thermal spraying, ion implantation, glow discharge plasma, electrophoretic deposition, and physical vapor deposition. Furthermore, we also focused on the characteristics of some commonly used biomedical alloys, such as stainless steel, Co-Cr, and Ti alloys.

Evaluation of microleakage and push-out bond strength of various composite resins for sealing the screw-access channel in implant-supported restorations

Statement of problemMicroleakage and loss of the composite resin sealing the screw-access channel are frequent complications of screw-retained implant-supported prostheses. How the screw-access channel should be best restored to reduce such complications is unclear. PurposeThe purpose of this in vitro study was to evaluate the microleakage and bond strength of 3 types of composite resins (flowable, packable, and bulk-fill) with or without a bonding agent treatment to seal the screw-access channel of 2 types of restorative materials (zirconia and Co-Cr alloy) with or without thermocycling. Material and methodsIn total, 240 yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) specimens (IPS e.max ZirCAD) and 240 Co-Cr alloy (Vera PDS) specimens were prepared with a Ø3×3-mm cylindrical cavity at the center to simulate the screw-access channel. Three types of composite resins (flowable, packable, and bulk-fill resin) (Filtek Z350 XT Flowable Restorative, Filtek Z350 XT Universal Restorative, and Filtek One Bulk Fill Restorative) were applied to restore the access channel of the zirconia and Co-Cr specimens with or without a bonding agent (Single Bond Universal Adhesive). Microleakage and push-out bond strength were determined and compared by dividing the specimens into experimental groups with or without thermocycling (1000 times with 30 seconds at 5 ±2 °C and 55 ±2 °C). The results were analyzed by using a 1-way ANOVA and 4-way ANOVA. Adjustment for multiple comparisons was made with the Tukey Honestly Significant Difference (HSD) test. ResultsThe specimens subjected to thermocycling showed a lower bond strength (P<.001) and higher microleakage (P<.001) than specimens stored in a constant-temperature water bath. Specimens treated with bonding agents showed a higher bond strength (P<.001) and lower microleakage (P<.001) than specimens not treated with a bonding agent. Higher bond strengths were observed in the order of bulk-fill resin, packable resin, and flowable resin (P<.001). Packable resin showed higher microleakage than flowable resin and bulk-fill resin (P<.05). No significant difference in microleakage was found between the flowable resin and bulk-fill resin (P>.05). ConclusionsHigher bond strengths were observed in the order of bulk-fill resin, packable resin, and flowable resin. Less microleakage was observed in the flowable resin and bulk-fill resin than in the packable composite resin. Bonding agent treatment was effective in increasing bond strength and decreasing microleakage. Zirconia and Co-Cr showed a bond strength similar to that of composite resins, but zirconia showed higher microleakage than Co-Cr. Restoring the screw-access channel with the bulk-fill resin should increase bond strength and reduce microleakage.

Additive manufacturing of a Co-Cr-W alloy by selective laser melting: In-situ oxidation, precipitation and the corresponding strengthening effects

• The in-situ oxidization and precipitation behaviors in laser powder bed fusion (LPBF) processed Co-Cr-W alloy were investigated. • The corresponding strengthening behaviors of observed nano-oxide inclusions and nano-precipitates were studied. • A nano-oxide with high Si content, together with a bcc type Co5Cr3Si2 nano-precipitates were reported for the first time in LPBF Co-Cr-W alloys. • The strengthening mechanism of widely dispersed nano-oxides was disclosed, whose strengthening contribution was calculated to be ∼158 MPa. Additive manufacturing exhibits great potentials for the fabrication of novel materials due to its unique non-equilibrium solidification and heating process. In this work, a novel nano-oxides dispersion strengthened Co28Cr9W1.5Si (wt.%) alloy, fabricated by laser powder bed fusion (LPBF), was comprehensively investigated. During the layer-by-layer featured process, in-situ formation of Si rich, amorphous, nano-oxide inclusions was observed, whose formation is ascribed to the high affinity of Si to oxygen. Meanwhile, distinctive body-centered cubic (BCC) Co5Cr3Si2 nano-precipitates with an 8-fold symmetry were also confirmed to appear. The precipitates, rarely reported in previous studied Co-Cr alloys, were found to tightly bond with the in-situ oxidization. Furthermore, the morphologies, the size distributions as well as the microstructure of the interface between the matrix and the inclusions were investigated in detail and their influence on the tensile deformation was also clarified. The existence of transition boundaries between these inclusions and the matrix strongly blocked the movement of dislocations, thereby increasing the strength of the alloy. It was understood that when the plastic deformation proceeds, the fracture occurs in the vicinity of the oxide inclusions where dislocations accumulate. A quantitative analysis of the strengthening mechanism was also established, in which an additional important contribution to strength (∼ 169 MPa) caused by the effects of in-situ formed oxide inclusions was calculated.

Sensitivity of surface roughness to laser parameters used for polishing additively manufactured Co-Cr alloy

Poor fatigue life, which is impacted by a rough and irregular surface, is a critical challenge that additive manufacturing needs to overcome to facilitate widespread engineering use. Laser polishing, in which a laser irradiates, melts, and smooths a surface through surface tension, is one solution. This work studies the laser polishing of laser powder bed fusion cobalt‑chromium samples through experimentation and microscopy of the surface before and after polishing. The laser processing parameters that contribute to the smoothing performance of four different surface texture parameters are analyzed. It is found that laser power plays an outsized role in smoothing the surface, followed by hatch spacing, scanning velocity, and beam diameter. The greater role of power compared to beam diameter and velocity is explained using analytical temperature models of a Gaussian heat flux on a semi-infinite surface. The influence of the starting surface is also discussed, and the variability in the final laser polished surfaces is partially attributed to the variability that occurs on the original printed surface due to the sporadic adherence of particles and particle agglomerates. This work provides an overview of important processing aspects for furthering the commercialization of the technology for the finishing of additively manufactured parts.

Metal-Seramik Diş Restorasyonlarının Üretiminde Farklı Yüzey İşlemlerinin Makaslama Bağlanma Dayanımına Etkilerinin Araştırılması

Aim: The bond strength between metal and porcelain is an essential factor for the success of metal-ceramic restorations. Therefore, this study evaluated the shear bond strength (SBS) between ceramic and cobalt-chromium (Co-Cr) alloys after oxidation treatment.&#x0D; Material and Methods: A total of 150 Co-Cr samples, 50 samples each, were produced from casting, laser sintering, and milling techniques. The primary group samples produced were divided into five subgroups. One of the subgroups is sandblasted with 110 µm Al2O3, and the others are ground with carbon separator disc, sintered diamond bur, tungsten carbide bur, and pink stone in one direction. SBS test was applied after the oxidation and veneering process. After debonding, digital microscopy investigated the surface characterizations of Co-Cr alloys. For the normality distribution of SBS measurements, the Kolmogorov-Smirnov test was used. According to the results, non-parametric tests were used in the study because the distribution was not suitable for the normal distribution, and the number of samples within the group was low in the subgroups. Kruskal Wallis and All pair-wise post hoc test (α = 0.05) were used for analysis.&#x0D; Results: There was a statistical difference between the laser sintering and milling groups according to the fabrication techniques. The highest SBS value was found in the Al2O3 laser group (34.35) and the lowest in the Al2O3 casting group (17.68). Surface treatments significantly altered ceramic adhesion. Almost all subgroups exhibited mixed failure. All of the SBS values found in this study were almost clinically acceptable.&#x0D; Conclusion: As different abrasives in the leveling and finishing of metal substructures may affect the metal-ceramic bonding, care should be taken in their use as much as possible.

Marginal Misfit of 3D-Printed (Selective Laser Sintered), CAD-CAM and Lost Wax Technique Cobalt Chromium Copings with Shoulder and Chamfer Finish Lines: An In-Vitro Study.

Background and Objectives: The aim was to compare the Misfit of 3D-Printed, Selective laser melting (SLM), milled (Computer aided design-Computer aided manufacture CAD-CAM) and Lost wax technique (LWT) fabricated Cobalt chromium (CoCr) alloy copings on shoulder (SH), radial shoulder (R-SH) and chamfer (CH) finish line configuration. Materials and Methods: Ninety resin, second maxillary premolar teeth were prepared for metal-ceramic crowns, equally divided into (n = 30) SH, R-SH and CH margin preparations. For each preparation design (SH, R-SH and CH), CoCr copings were prepared using SLM, CAD-CAM and LWT. This resulted in nine study groups with 10 CoCr copings each. The marginal misfit of specimens was assessed with a high-resolution digital microscope. Misfit was evaluated in vertical and horizontal dimensions in μm. Data were analyzed using ANOVA and a post hoc multiple comparisons test. Results: For vertical misfit, the highest was observed in SLM samples with chamfer margin (167.96 ± 24.1), and the least was shown by CAD-CAM samples with radial shoulder (58.8 ± 12.53). CAD-CAM and shoulder margins showed the least vertical misfit. For horizontal misfit, the maximum was observed in SLM samples with shoulder margin (137.94 ± 37.85) and the least by LWT samples with chamfer (89.38 ± 14.81). Chamfer margins and LWT samples showed the least horizontal misfit among the group samples. Fabrication technique and finish line design play a critical role in reducing the marginal misfit of CoCr copings. Conclusions: For vertical misfit, SLM copings showed poor outcomes compared to CAD-CAM specimens, however comparable outcomes to Cast specimens. SLM copings showed comparable horizontal misfit outcomes to CAD-CAM specimens and low misfit compared to Cast copings, respectively. Vertical misfit was low with shoulder margins, and horizontal misfit was better with chamfer marginal configuration.

Wear rate and biocompatibility of pre and post UV irradiated UHMWPE for tribo-pair in total knee replacement application

Ultra-high molecular weight polyethylene (UHMWPE) and CoCr alloy are popular tribo-pair in total knee replacement. Wear in the liner is a major failure reason for knee implant. Therefore, this work focuses on an approach for reducing the wear rate by irradiating the UHMWPE specimens using Ultraviolet (UV) radiation. The powder of UHMWPE was molded into a plate by microwave-assisted compression (MAC) molding. The UV radiations of intensity 0.025 J/cm2 were irradiated on the MAC molded UHMWPE specimens. The wear rate was determined using a pin on the disc wear tribometer using the pre and post-irradiated UHMWPE specimens as a pin and CoCr alloy as the disc. The pre and post-irradiated UHMWPE sliding was done at the load of 40 N for 1500 m under dry conditions. The reduction in the wear rate recorded was 56% after UV irradiation. The surface morphology of the worn specimens was done using scanning electron microscopy (SEM) and the 3D surface mapping technique. The obtained results of wear rate were validated numerically by implementing the contact problem solution in Archard’s wear law using user-subroutine on Python. The experimental and numerically obtained results were in good agreement. The biological response of pre and post-irradiated specimens was evaluated by hemolysis assay, cellular compatibility against peripheral blood mononuclear cells, platelet adhesion, and in vitro degradation under a simulated blood fluid environment.

Printability for additive manufacturing with machine learning: Hybrid intelligent Gaussian process surrogate-based neural network model for Co-Cr alloy

AM has revolutionized the manufacturing industry, involving several operating parameters that may affect the properties of the final manufactured part. In AM, LPBF has proved its reliability in producing dense components; however, process development for every material necessitates extensive testing. Even the tiniest change can negate all the data for the same material. It is vital to have a P-P correlation that can train itself following a change in powder or machine to achieve defects-free parts and optimal properties. These goals cannot be met alone by multi-physics. One of the ways to address this issue is to apply ML, but it requires a huge data set for training and testing purposes. A framework has been developed for Co-Cr S-S curves to resolve this issue. Twenty-two experimental S-S curves have been generated to produce YS, TS, and EL data points. In combination with DNN, these data points have been applied to the validated and tested GPS-surrogate model to develop a smart processing window to achieve desired YS, TS, and EL. LP, LSS, HD, and PLT have been selected during the whole framework as inputs, while YS, TS, and EL have been classified as outputs. The output of the smart window was verified experimentally. It is found that the highest YS (1110.91 MPa) is attained using LP = 180 W, LSS = 600 mm/s and HD = 70 μm, while least YS (645.05 MPa) is identified using LP = 160 W, LSS = 900 mm/s and HD = 70 μm. For TS, the maximum (165.91 MPa) and minimum (689.73 MPa) values have been achieved using LP = 180 W, LSS = 900 mm/s and HD = 70 μm, and LP = 180 W, LSS = 1000 mm/s and HD = 70 μm, respectively. In the case of EL, LP = 180 W, LSS = 700 mm/s and HD = 70 μm, and LP = 180 W, LSS = 600 mm/s and HD = 70 μm, resulted 23.04% and 0.789% EL, respectively. Using CC, LP and HD did not significantly affect the TS, YS, and EL, while a negative relationship has been found for LSS with TS, YS, and EL. The smart processing window showed that the YS and TS could be achieved at low-high LP and low LSS at the cost of EL. This study provides a technique for framework development in the case of P-P relation based on the provided inputs and the corresponding outputs, leading toward process smartification.

Toxicological Risks of the Cobalt-Chromium Alloys in Dentistry: A Systematic Review.

Background: The toxicological risk of Co-Cr dental alloys is actually a sensitive subject with the European regulatory changes, namely regulation (EU) 2017/745 and annex VI to the CLP regulation (EC) 1972/2008. Objectives: The objective of this review is to conduct a rigorous analysis of the cytocompatibility of cobalt–chromium (Co-Cr) dental alloys. Considering various parameters such as cytotoxicity, type IV hypersensitivity reaction, sensitization, and irritation, we investigated evidence of toxicity of Co-Cr in human dental applications. Data sources: Specific search strategies were performed in three electronic databases, namely Medline, Embase, and Web of Science, using a main restriction in the search regarding the publication date (1995–2022). Study selection: Out of a total of 836 articles, only 21 studies were selected and analyzed according to PRISMA methodology. Results: Among them, 10 in vitro studies using human samples and 11 in vivo studies on human patients were distinguished. Most of the in vitro studies confirmed that Co-Cr alloys have a good cytocompatibility compared to Ni alloys. Regarding the in vivo studies, it appeared that Co-Cr could rarely cause sensitization, irritation, and allergic reactions. Reactions were mainly observed for people allergic to Co or Cr. Nevertheless, titanium-based materials showed better results. Conclusions: This study proposes a new state of the art on Co-Cr dental alloys and will thus be very useful for carrying out additional studies. Relevance: This review will help practitioners in their daily clinical choice.

Influence of Filler Metal on Electrochemical Characteristics of a Laser-Welded CoCrMoW Alloy Used in Prosthodontics.

This paper sought to determine corrosion resistance changes in the artificial saliva of a CoCrMoW-based alloy used for dental prostheses under Nd:YAG laser welding with CoCr alloy and stainless steel wire filler metals. The paper presents the corrosion characteristics of such joints, including the next stage of porcelain-fused-to-metal (PFM) firing. Corrosion tests were performed by electrochemical methods registering anodic polarization curves and electrochemical impedance spectroscopy (EIS). The microstructures were assessed by scanning microscopy (SEM) and chemical composition analysis (EDS) at the connection and heat-affected zones. Welding CoCrMoW alloy with and without a filler material increased the open circuit potential of the samples by 40–100 mV compared to unwelded base alloy. At the same time, a potentiodynamic test showed a polarization resistance Rpol reduction in welded samples, both for CoCr and stainless steel wires, as compared to the base CoCrMoW material. On the other hand, when comparing the current density and polarization resistance between materials welded with two different filler metals, better results were obtained for samples welded with stainless steel wire. The polarization resistance Rpol for the base alloy was 402 kΩ·cm2, for the CoCr wire weld it was 436 kΩ·cm2, and the value was 452 kΩ·cm2 for stainless steel wire welds. Comparing polarization resistance Rpol from the Tafel analysis and the total charge transfer resistance from Rp(EIS) from EIS, the CoCrMoW alloy welded with a stainless steel wire after heat treatment equaled or even slightly exceeded the corrosion resistance of the base alloy and alloy welded with dedicated CoCr wire after heat treatment. These results indicated the possibility of using stainless steel wire for the laser welding of CoCrMoW alloys dental prostheses, including the next stage of PFM, without sacrificing the corrosion resistance of such connections, and this was confirmed by most electrochemical parameters.

5. Reducing set screw loosening failures: an analysis of final tightening technique

<h3>BACKGROUND CONTEXT</h3> A 5% rate of S2AI screw failure consisting of rod slippage/set screw displacement has been reported. Fixation construct strength is largely dependent on the set screw's locking torque. Both the magnitude (how much torque is applied) and the rate (how fast the torque is applied) can impact set screw loosening failure. <h3>PURPOSE</h3> To evaluate the effect of set screw locking torque on the strength of the fixation construct. <h3>STUDY DESIGN/SETTING</h3> Benchtop biomechanical testing. <h3>METHODS</h3> Commercially available, Ti alloy 5.5mm polyaxial pedicle screws and set screws were used. To test the effect of the locking torque magnitude on construct strength, the set screws were tightened onto a Ti alloy rod at 85 and 105 in-lbs (N=8 each). A torque meter (TM) [Transducer Techniques, SWS-20] was attached to the driver to record both the locking and loosening torque. To test the effect of the rod alloy, the same implants were tested with 5.5 CoCr and Ti alloy rods (N=8 each). The set screws' locking and loosening torque were measured. Also, six torque limiting handles from five suppliers were attached to the same TM. To test the effect of torque application rate, an experienced user torqued the handle until the device's internal limit was reached. The resulting torque was measured. Each handle was subjected to 11 actuations at two rates fast (defined by taking less than one second to click over after resistance is felt) and slow (defined by taking 1-2 seconds to click over after resistance is felt). <h3>RESULTS</h3> Set screws tightened to 105.8(±.54)in-lbs retained 39.6% more torque than those tightened to 85.4(±.57)in-lbs(p <0.001), demonstrating that more torque applied results in more torque retained. Set screws tightened onto a Ti alloy rod retained 15.0% more torque than those tightened onto a CoCr rod (p < .003). When torque limiting handles are actuated at a slow rate, the resulting torque output produced is 22.6% higher than when actuated at a fast rate, demonstrating the magnitude of the torque applied is dependent on the rate at which the handle is rotated (p <0.05). <h3>CONCLUSIONS</h3> The choice of spinal rod alloy used may affect set screw security. More torque applied results in more torque retained; therefore, we recommend the final locking torque be applied in a slow and controlled manner to ensure the intended locking torque magnitude is applied. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.

Effect of Chemically Modified Carbon-Coated Iron Nanoparticles on the Structure of Human Atherosclerotic Plaques Ex Vivo and on Adipose Tissue in Chronic Experiment In Vivo.

The high mortality rate caused by atherosclerosis makes it necessary to constantly search for new and better treatments. In previous reports, chemically modified carbon-coated iron nanoparticles (Fe@C NPs) have been demonstrated a high biocompatibility and promising anti-plaque properties. To further investigate these effects, the interaction of these nanoparticles with the adipose tissue of Wistar rats (in vivo) and human atherosclerotic plaques (ex vivo) was studied. For the in vivo study, cobalt–chromium (CoCr) alloy tubes, which are used for coronary stent manufacturing, were prepared with a coating of polylactic acid (PLA) which contained either modified or non-modified Fe@C NPs in a 5% by weight concentration. The tubes were implanted into an area of subcutaneous fat in Wistar rats, where changes in the histological structure and functional properties of the surrounding tissue were observed in the case of coatings modified with Fe@C NPs. For the ex vivo study, freshly explanted human atherosclerotic plaques were treated in the physiological solution with doses of modified Fe@C NPs, with mass equal to 5% or 25% relative to the plaques. This treatment resulted in the release of cholesterol-like compounds from the surface of the plaques into the solution, thus proving a pronounced destructive effect on the plaque structure. Chemically modified Fe@C NPs, when used as an anti-atherosclerosis agent, were able to activate the activity of macrophages, which could lead to the destruction of atherosclerotic plaques structures. These findings could prove the fabrication of next-generation vascular stents with built-in anti-atherosclerotic agents.

Robust Co alloy design for Co interconnects using a self-forming barrier layer

With recent rapid increases in Cu resistivity, RC delay has become an important issue again. Co, which has a low electron mean free path, is being studied as beyond Cu metal and is expected to minimize this increase in resistivity. However, extrinsic time-dependent dielectric breakdown has been reported for Co interconnects. Therefore, it is necessary to apply a diffusion barrier, such as the Ta/TaN system, to increase interconnect lifetimes. In addition, an ultrathin diffusion barrier should be formed to occupy as little area as possible. This study provides a thermodynamic design for a self-forming barrier that provides reliability with Co interconnects. Since Cr, Mn, Sn, and Zn dopants exhibited surface diffusion or interfacial stable phases, the model constituted an effective alloy design. In the Co-Cr alloy, Cr diffused into the dielectric interface and reacted with oxygen to provide a self-forming diffusion barrier comprising Cr2O3. In a breakdown voltage test, the Co-Cr alloy showed a breakdown voltage more than 200% higher than that of pure Co. The 1.2 nm ultrathin Cr2O3 self-forming barrier will replace the current bilayer barrier system and contribute greatly to lowering the RC delay. It will realize high-performance Co interconnects with robust reliability in the future.

Stress Distribution Pattern in Zygomatic Implants Supporting Different Superstructure Materials.

The aim of this study was to assess and compare the stress–strain pattern of zygomatic dental implants supporting different superstructures using 3D finite element analysis (FEA). A model of a tridimensional edentulous maxilla with four dental implants was designed using the computer-aided design (CAD) software. Two standard and two zygomatic implants were positioned to support the U-shaped bar superstructure. In the computer-aided engineering (CAE) software, different materials have been simulated for the superstructure: cobalt–chrome (CoCr) alloy, titanium alloy (Ti), zirconia (Zr), carbon-fiber polymers (CF) and polyetheretherketone (PEEK). An axial load of 500 N was applied in the posterior regions near the zygomatic implants. Considering the mechanical response of the bone tissue, all superstructure materials resulted in homogeneous strain and thus could reconstruct the edentulous maxilla. However, with the aim to reduce the stress in the zygomatic implants and prosthetic screws, stiffer materials, such Zr, CoCr and Ti, appeared to be a preferable option.

Simultaneously Embedding Indomethacin and Electrodeposition of Polypyrrole on Various CoCr Alloys from Ionic Liquids.

The aim of the present investigation is the electrochemical deposition of polypyrrole films from choline chloride-based ionic liquids at various potential, period times and simultaneously an indomethacin embedding and release. The electrodeposition films were performed on CoCr commercial type Wirobond C (WBC) and, Heraenium CE (Hera) using as electroprocedures for deposition cyclic voltammetry and chronoamperometry. The morphology of obtained films was investigated using scanning electron microscopy (SEM). An FT-IR investigation of CoCr alloys before and after electrodeposition was able to identify the presence of polymer and drug. The research included an evaluation of the hydrophilic character of all studied samples and their electrochemical characterization in Tanni Zuchi artificial saliva. In the electrochemical study, the following methods have been used: open circuit potential, electrochemical impedance spectroscopy and potentiodynamic polarization. Indomethacin release from the polymeric film was determined using UV-VIS spectra. Based on Fick’s law of diffusion and indomethacin release profile, a kinetic law for release was established and discussed.

Investigation of Mechanical Behavior of Scaffolding Structures Produced Using CoCr Alloy by Selective Laser Melting Method

Vücuttaki kullanım yerlerine bağlı olarak implant üretiminde kullanılan malzeme türü değişmektedir. CoCr alaşımı yüksek dayanım, aşınma ve korozyon direnci gibi avantajlarından dolayı kalça implantlarında oldukça sık kullanılmaktadır. Gelişen eklemeli imalat teknolojisi sayesinde farklı yoğunluklara sahip gözenekli kalça implantları üretilebilmektedir. Üretilen gözenekli kalça implantları daha düşük elastisite modülüne sahip olduğundan kemik ve implant arasında oluşan gerilmeler azaltılabilmektedir ve böylelikle implant üzerinde meydana gelen gevşeme, kırılma, deformasyon gibi problemler ortadan kaldırılabilmektedir. Tasarlanan iskelelerin, yeni oluşturulan hücrelerin iç mimarisini desteklemesi gerekir. Bu nedenle vücutta kullanılan iskele yapılar kemiğin mekanik dayanımını korumak zorundadır. Bir kemik iskelesinin elastik modül, basınç ve gerilme dayanımı, maksimum gerilme ve bükülme modülü gibi mekanik özellikleri kemiklerin ve sert bağ dokularının yerine başarıyla geçebilecek şekilde olmalıdır ve hastanın kullanımında ya da düzenli faaliyetleri sırasında çökmemelidir. Bu yüzden yapılan bu çalışmada farklı birim hücre modelleri kullanılarak, hücre yoğunluğu ve şekil geometrisi belirlenip basma testine tabi tutulmuştur. Yapılan testler sonucunda iskeleler boyunca deformasyonun nasıl dağıldığı araştırılmış, değişen hücre modellerinin sonuçları karşılaştırılmıştır. Mekanik testler sonucunda iskele yapılarda farklı porozite oranları ve birim hücreler kullanıldığı için modeller birbirinden farklı mekanik özellikler göstermiştir. İskele modellerde maksimum gerilme Body Diagonalw With Nodes modelinde 247,58 MPa olarak ölçülürken, Dode Thick modelinde 240.7 MPa, Dode Thin modelinde 227.19 MPa olarak ölçülmüştür. Anahtar Kelimeler: Gözenekli yapı, Mekanik Test,Ansys Analiz

Analysis of microstructure and fatigue of cast versus selective laser-melted dental Co-Cr alloy

Statement of problemThe forces exerted on teeth and prostheses during mastication are repeated and dynamic, resulting in fatigue damage to dental prostheses. Most fractures of dental restorations are fatigue failure. The 4-point bend fatigue behavior of Co-Cr-Mo-W alloys manufactured by investment casting (CAST) and selective laser melting (SLM) has received little attention. PurposeThe purpose of this in vitro study was to evaluate the 4-point bend fatigue property of dental Co-Cr alloys and determine the relationship between microstructure and the 4-point bend fatigue property of Co-Cr alloys created by traditional casting and SLM. These can guide the use of Co-Cr alloy in dentistry. Material and methodsCo-Cr-Mo-W alloys were fabricated with a dimension of 45×2×2 mm by investment casting and SLM. The 3-point bend test measured the ultimate bend strength with 3 specimens in each group. The 4-point bend fatigue test evaluated the fatigue life under various stresses, with 6 specimens in each group. The specimens were mechanically ground, polished, and electrochemically etched. Scanning electron microscopy was used to identify the microstructures of both etched specimens and fracture surfaces. X-ray diffraction investigations were used to determine the phases. Significant differences in the bend strength were analyzed by using the independent samples t test (α=.05), and the fatigue test was analyzed with ANCOVA (α=.05). ResultsThe mean ±standard deviation bend strength of SLM specimens was 1837 ±3 MPa, higher than the 1200 ±6 MPa for CAST specimens (P<.05). The maximum bend stress of the SLM specimens without fatigue failure was 735 MPa, which was statistically higher than the 394 MPa for CAST specimens (P<.05). The microstructure characteristics of the SLM alloy contributed to its excellent fatigue performance. In SLM alloy, the γ phase constituted the majority with some ε and Laves phases, while the cast alloy possessed higher ε and Laves phases. The grains of SLM alloy were equiaxed and fine, and the second phases were fine and dispersive. In contrast, the cast alloy possessed clear dendrites, and the second phases were sizable. ConclusionsThe SLM dental Co-Cr-Mo-W alloy had statistically better 4-point bend fatigue properties than cast alloy, which was associated with an improved microstructure.

Effect of Indented Structures on the Retention of Cement-Retained Implant-Supported Crowns by Provisional Cement

Purpose: The objective of this study was to investigate the effect of indented structures, such as dimples and retention groove formations, on the retention of titanium abutment walls when cementing cobalt-chromium (Co-Cr) alloy crowns with zinc oxide-eugenol cement. Materials and Methods: Forty-eight titanium abutments (n = 6) were prepared, of which 24 abutments were 4.0 mm and the other 24 were 6.0 mm in height. These 4.0 mm and 6.0 mm abutments were organized into eight groups: no-dimple, 2-dimple, 4-dimple, and axial retention groove groups. The position and dimensions of the dimples and axial retention grooves were the same for all prepared abutments. Laser-sintered cobalt-chromium (Co-Cr) alloy crowns were cemented using a provisional cement. After thermocycling, a retention test was performed using a universal testing machine. Statistical analysis was performed using the nonparametric Kruskal–Wallis test and post-hoc Mann–Whitney U test (𝛼= .05) to compare the mean retentive force. Results: The lowest retentive force recorded was from the 4.0 mm no-dimple group (112.03 ± 20.30). Forming dimples and retention grooves increased the retentive force for the 4.0 mm groups, but the difference was not statistically significant (p > .05). A statistically significant difference was displayed by the 6.0 mm abutment with the 4-dimple group compared to the 6.0 mm no-dimple group (p < .05). Conclusion: Within the limitations of this in vitro study, the mean retentive force was higher with dimples and axial retention grooves for 4.0 mm titanium abutments but was statistically insignificant (p > .05). An increase in abutment height was statistically correlated with an increase in retentive force within the same number of dimple-groups (p < .05).

Structure and properties of additive products manufactured from electroerosion powders

The paper considers the possibility of using electroerosion metal powders based on the Co-Cr alloy with different properties in additive technologies. Use of these powders opens up great opportunities for improving the technical and economic characteristics of products, and will contribute to a significant increase in their reliability, durability, weight reduction, reduction of manufacture and operation costs. The economic efficiency of the use of electroerosion cobaltchromium powders is due to the use of waste and low energy-intensive technology for their production. The aim of this work is studying the technology of powder fusion obtained by electroerosion dispersion of cobaltchromium alloy waste in alcohol, on porosity, microhardness and roughness of additive products. The process of electrodispersion, i.e. grinding of the KKhMS "Cellite" alloy (63 % Co, 27 % Cr, 5 % Mo, 2 % Ni, 2 % Fe) was carried out on an original patented installation. After dispersion of cobalt-chromium alloy waste, its destruction occurred as a result of local exposure to short-term electrical discharges between the electrodes located in the working fluid, with formation of powder particles. Butyl alcohol was used as the working fluid. The fusion of electroerosion cobalt-chromium powders was carried out by plasma on the original installation for layer-by-layer deposition, which allows varying the technological parameters of the process: the nozzle transition speed (mm/min), the distance between the nozzle and the construction zone (mm), and the fusion temperature (&deg;C). Based on a set of experimental studies, it was found that the melting temperature of particles of electroerosion cobaltchromium powder practically does not effect on varying in the elemental and phase composition of samples; at the same time, with an increase of the melting temperature, the pores size and their number decrease, as well as an increase of microhardness with decrease of the height of irregularities and roughness in general are observed. The research was conducted under financial support&nbsp;of the Russian scientific fund. The project number&nbsp;17-79-20336P.

Corrosion properties of low carbon CoCrMo and additively manufactured CoCr alloys for dental applications

ObjectivesAdditive manufacturing (AM) is being applied to metallic biomaterials and dental alloys, including CoCrMo. CoCrMo mechanical properties and corrosion resistance are vital to the structural integrity of implants and dental appliances. The goal of this work is to assess the resistivity of AM cobalt chromium alloys by comparing them with traditional CoCrMo, regarding electrochemical properties resulting from microstructural and oxide film differences. MethodsIn this work, selective laser melting (SLM), was used to manufacture CoCrMoW. The corrosion characteristics of AM alloy were compared to that of wrought LC CoCrMo (ASTM F-1537) in both phosphate buffered saline (PBS) and PBS with 10 mM H2O2 to simulate increased inflammatory conditions. Anodic polarization and electrochemical impedance spectroscopy (EIS) were performed. ResultsBoth alloys were substantially similar in corrosion behavior in both solutions. They exhibited changes with the different solutions. Polarization resistances were statistically lower (RpAM = 1.4 MΩcm2 (PBS) vs. 0.72 MΩcm2 (H2O2), RpLC = 1.86 MΩcm2 (PBS) vs. 0.55 MΩcm2 (H2O2)), and open circuit potentials (OCP’s) were statistically higher in 10 mM H2O2 for both alloys (0.20 V (in H2O2) vs. − 0.09 V in PBS). Chemistry variations were revealed by the corrosion tests indicating that wrought LC CoCrMo retained its casting-based chemical heterogeneity, while AM CoCrMoW had sub-cell structures within the solidified grains. SignificanceAs novel production methods like AM arise, it is necessary to understand any microstructural differences that may diminish the corrosion resistance properties. AM CoCrMoW alloys hold significant promise for use in dentistry where complex geometries are required.