Co-Cr Alloy Research Articles

Effect of Heat Treatment Duration and Cooling Conditions on Flexural Strength and Surface Roughness of Cobalt-Chromium Alloys produced by Selective-Laser-Melting

Post-heat treatment may enhance mechanical properties of selective laser melting (SLM) Cobalt chromium (Co-Cr) alloys, however it is unknown what duration the heat treatment needs to last and how the rate of cooling impacts the alloy's flexural strength and surface roughness. In this study, SLM Co-Cr alloy specimens were heated at 1150 C for 1 or 6 hours and subsequently cooled by air cooling (AC), furnace cooling (FC), or water quenching (WC). Flexural strength and surface roughness were then tested. Aim of this study: Investigate the effect of heat treatment and different cooling conditions on the flexural strength and surface roughness of SLM Co-Cr alloy specimens. The heat treatment will be conducted at 1150 C for two different durations (1-hour and 6-hours) and under three cooling conditions (AC, FC, and WC). Materials and methods: A total of forty-two rectangular specimens, measuring (34×13×1.5 mm) were manufactured through SLM and divided into seven groups, six specimens for each group as follows: The first group denoted as control with no heat treatment and no cooling applied, second and third groups heated for 1 or 6 hours then cooled in the air (AH-1 and AH-6), fourth and fifth groups heated for 1 or 6 hours and left inside the furnace until they cooled (FH-1 and FH-6), sixth and seventh groups heated for 1 or 6 hours and cooled by water quenching (WH-1 and WH-6). Flexural strength and surface roughness tests were performed on the specimens. A flexural strength value of (2147.33 MPa) was indicated that the control group exhibited the highest flexural strength, whereas the FH-6 group exhibited the lowest flexural strength value (1282.66 MPa). The control group showed the worst surface roughness (1.63 μm) while all other groups demonstrated no significant differences in surface roughness ranging from (0.32 to 0.49 μm) with a slight increase in the 6-hours heated groups. Conclusions: Slow cooling rate inside the furnace affects flexural strength negatively. Therefore, a high cooling rate is recommended to get a better flexural strength. On the other hand, surface roughness results suggests that 1-hour is better than 6-hours in terms of heat treatment duration and time saving

Evaluation the Effect of Heat Treatment on Corrosion Resistance of Cobalt Chromium Alloys

The purpose of present study is to evaluate and comparison the effect of different milling technique surface of CAD/CAM for milled Co-Cr alloy specimens.Material and Methods: The diagnostic divides 20 disc-shaped specimens into 2 main groups, each consisting of 10 specimens for Co/Cr alloys according to their construction, the material used in hard milling and soft milling. All samples for further examination were prepared as drilled discs (diameter 15 mm, height 3 mm) whose surfaces were then finished and polishing with a diamond polisher. Scanning electron microscopy (SEM) images with energy-dispersive beam spectroscopy (EDS) were acquired for one sample in each set to assess the surface topography of the metal framework. All samples were degreased, and steam cleaned samples and heat treated in accordance with the complete firing procedure. Then scanning electron microscopy (SEM) after heating. Samples prepared in the lab for electrochemical corrosion testing were polarized and corroded in accordance with their electrical potential. Results were recorded using Levenes test and anova, with appropriate data analyzed for differences between groups. Results: The results of this study presented that the Descriptive statistics for corrosion test (mmpy) for all experimental groups revealed that the hard milling group mean was the lowest among all groups of the study is recorded (0005), followed, Group soft milling (.0071). The data were statistically analyzed using Welch’s ANOVA and Levene’s test which revealed highly significant differences (p<0.01) among groups. Conclusion: Corrosion resistance decreases in the following order: soft metal milling > hard metal milling, according to the obtained corrosion parameter values.

Experimental and numerical study on micro-milling of CoCrW alloy produced by selective laser melting and casting

CoCrW can be produced using Additive Manufacturing (AM), while casting methods are commonly used for applications such as dental prostheses. However, rapid heating and cooling during AM production can lead to internal defects, micro-cracks, and shrinkage. Micro-milling can help enhance the material’s structure and impart micro-scale properties. This study aimed to investigate the micro-milling properties of CoCrW products manufactured using AM and compare them with materials produced by casting. Numerical models and experimental studies were conducted to examine the differences. Results showed that CoCr alloys produced with AM exhibited 25%–30% lower burr formations, while CoCrW produced by casting had 2%–5% lower surface roughness. Micro-milling experiments demonstrated that a feed rate of 2.5 μm/tooth resulted in 35%–40% more burr formation and surface roughness compared to a feed rate of 5 µm/tooth in both SLM and casting methods, attributed to the cutting edge radius. The cutting temperature and top burr height were analyzed using finite element simulations and experimental methods. It was observed that the maximum temperature in CoCrW produced by casting was 6%–15% higher than that in the SLM method. The finite element analyses and experiments revealed a difference of 4%–7% in maximum temperatures and top burr height.

Investigation of the Chemical Composition, Microstructure, Density, Microhardness, and Elastic Modulus of the New β Ti-50Nb-xMo Alloys for Biomedical Applications.

β-type titanium alloys with a body-centered cubic structure are highly useful in orthopedics due to their low elastic modulus, lower than other commonly used alloys such as stainless steel and Co-Cr alloys. The formation of the β phase in titanium alloys is achieved through β-stabilizing elements such as Nb, Mo, and Ta. To produce new β alloys with a low modulus of elasticity, this work aimed to produce our alloy system for biomedical applications (Ti-50Nb-Mo). The alloys were produced by arc-melting and have the following compositions Ti-50Nb-xMo (x = 0, 3, 5, 7, and 12 wt% Mo). The alloys were characterized by density, X-ray diffraction, scanning electron microscopy, microhardness, and elastic modulus. It is worth highlighting that this new set of alloys of the Ti-50Nb-Mo system produced in this study is unprecedented; due to this, there needs to be a report in the literature on the production and structural characterization, hardness, and elastic modulus analyses. The microstructure of the alloys has an exclusively β phase (with bcc crystalline structure). The results show that adding molybdenum considerably increased the microhardness and decreased the elastic modulus, with values around 80 GPa, below the metallic materials used commercially for this type of application. From the produced alloys, Ti-50Nb-12Mo is highlighted due to its lower elastic modulus.

Establishment of an Animal Model of Dog Bite Injuries.

Nowadays dog bite is becoming a world public health problem. Therefore, the study aimed to develop a dog bite animal model that is helpful to solve these problems. In this study, the skull of an adult dog was scanned. The three-dimensional model of the dog maxillofacial bones and dentition was built by MIMICS. Next, the model was printed with Co-Cr alloy by using selective laser sintering technology to develop the dog bite simulation pliers. Then, to simulate dog bite to most, the maximum bite force of the pliers was measured and actions contained in dog bite process was analyzed. Afterwards, according to action analysis results, rabbits were bitten by the prepared instrument in actions that simulate dog's bite. Finally, the reproducibility and controllability of this animal model of dog bite injuries was validated in an in vivo study. The results showed a reliable animal model of dog bite injuries has been developed in this study. The sites and severities of the injuries could be adjusted as the operator wishes and the animal model of dog bite injuries was highly repeatable. This study also indicates the feasibility of using digital technology in establishing animal bite models.

DED-LB/M and in-situ alloying of a Co-Cr alloy with elemental powders: defect formation, microstructure and mechanical properties

Many industrial sectors are facing regulations to reduce particulate pollution and avoid environmentally harmful manufacturing processes. At the same time, service lifetime of products needs to be improved. All these cases require high-performance materials and advanced processes to meet the requirements. Co-Cr alloys are considered promising materials for a wide range of respective applications due to their excellent wear and corrosion resistance. In this study, Additive Manufacturing by Laser Directed Energy Deposition of Metals in combination with the innovative approach of in-situ alloying was investigated to modify the resulting material properties of a Co-Cr alloy by additions of elemental Cr and Mo. First, the generated specimens were analyzed regarding cracks and relative density. Chemical composition was determined using optical emission spectrometry and energy dispersive X-ray spectroscopy. The microstructure was investigated by means of light microscopy and material hardness profiles were generated. It was found that the resulting properties can be specifically and flexibly adapted by in-situ alloying.

Characteristics of dental materials in the oral cavities of Asian individuals between their 20s and early 40s living temporarily in Japan based on 38 case studies.

Characterization of materials used in dental restorations and fixed prostheses is useful for personal identification. This study investigated the dental treatment trends and use of metal materials among non-Japanese Asian temporary residents and Japanese individuals aged from 20 to 40 years living in a city in Japan. Analysis of 38 participants from different Asian countries showed prominent use of resin fillings, with metal element analysis revealing nickel-chromium (Ni-Cr) or cobalt-chromium (Co-Cr) alloys. Among five Japanese participants of the same age with dental metal treatment scars, resin fillings and silver-palladium-copper-gold (Ag-Pd-Cu-Au) or silver-indium (Ag-In) alloys were observed. This study suggested some regional differences in dental material choices in Asia.

Radial Head Replacement: Management of Elbow and Forearm Instability after Comminuted Radial Head Fractures Associated with Elbow Dislocation

This manuscript aims to identify an indication algorithm for the surgical treatment of radial head fractures associated with elbow dislocation. The study compares the mid-term functional outcomes of patients with multifragment radial head fracture treated by resection with the outcomes of patients treated with radial head replacement. The cohort of 34 patients who sustained a radial head fracture at the mean age of 42.5 years (age range 20-81 years) was broken down into two groups by type of surgery. The EXT group consists of 20 patients with the radial head fracture treated by radial head resection. The END group includes 14 patients treated with the radial head replacement. In all patients, the radial head fracture was associated with elbow dislocation (type IV fracture according to the Mason-Johnston classification). The modified Kocher's surgical approach was used in all patients of both the groups. In the EXT group, resection of the fragmented radial head was performed. In the END group, the ExploR® Modular Radial Head System (Zimmer, Biomet, USA) was used, consisting of a CoCr (cobalt chromium) alloy head and a titanium stem. The pain and the range of motion of the elbow and forearm were evaluated after the completion of the outpatient rehabilitation (the mean follow-up period was 2.4 years). Simultaneously, the elbow joint stability was assessed. Radiographs were taken to detect heterotopic ossifications, proximalization of the radius, and any signs of prosthesis loosening. The frequency of reoperations was followed-up. The MEPS (Mayo Elbow Performance Score) was calculated. In the EXT group, the mean elbow flexion was 117.5° and the mean pronation/supination was 166.9°. In 50% of patients, the MEPS obtained was greater than 90 points, which means an excellent functional outcome. In 1 patient (5%), recurrent elbow dislocation occurred which was the reason for revision surgery (elbow transfixation with the Kirschner wires and medial collateral ligament suture). Revision surgery was also performed in 2 patients (10%) in whom not all the radial head fragments were removed. Moreover, also observed was elbow joint instability (2 patients) and temporary radial nerve paralysis (1 patient). In 1 case discrete proximalization of the radius developed. The patients in the END group showed the mean elbow flexion of 112° and the mean pronation/supination of 135°. The MEPS obtained from 69% of patients was greater than 90 points, which means an excellent outcome. The pain under load was reported by 3 patients (21%). In 5 patients (35%), the X-rays showed radiolucent zone around the stem of the prosthesis. Neither revision surgery, nor prosthesis removal has been performed yet in any patient. No instability, neurological complications or infections have been reported. In both EXT and END group heterotopic ossifications have developed in 4 patients. Radial head replacement compared to the radial head resection in the management of multifragment fractures associated with elbow dislocations increase the elbow and forearm stability. The group of patients with an implanted radial head prosthesis shows a higher percentage of patients achieving excellent functional outcome than the group of patients with radial head resection. radial head, elbow, fracture, dislocation, resection, prosthesis.

Influence of stress-relieving heat treatments on the efficacy of Co-Cr-Mo-W alloy copings fabricated using selective laser melting.

Purpose This study aimed to evaluate the influence of stress-relieving heat treatments on the metal-ceramic bond strength and fitness accuracy of selective laser melting (SLM)-fabricated Co-Cr alloy copings.Methods SLM-manufactured Co-Cr samples were stress-relieved at 750 (Ht-750) and 1150 °C (Ht-1150). The microstructure, surface roughness, metal-ceramic bond strength, marginal and internal fit, Vickers hardness, and residual stress were then compared with those of the non-heat-treated group (As-built). The results were analyzed using one-way ANOVA and post-hoc tests (Tukey's or Student's t test) (P = 0.05).Results The microstructure of the Ht-1150 samples had a brittle oxide layer and lower surface roughness, resulting in significantly lower bond strength values than those of the other groups. The As-built group exhibited significantly lower marginal gap values than the Ht-750 and Ht-1150 groups. Therefore, the post-heat treatments degraded the marginal fitness. The surface residual stress in all sample groups were compressive because of the sandblasting effect. The compressive stresses were larger in Ht-1150 than in As-built and Ht-750 owing to their low hardness values.Conclusions Stress-relief annealing porcelain-fused-to-metal single crowns does not improve bond strength and degrades fitness accuracy because additional post-heat treatments induce thermal distortion. These findings are expected to facilitate the direct application of As-built SLM single crowns in dentistry to minimize post-manufacturing costs and time.

Effect of Fabrication Method and Heat Treatment on the Properties of Co-Cr Bio Alloy

Co-Cr alloys are widely used in dental and medical equipment since the development of the first cast Co-Cr-Mo alloy. This is due to its high mechanical properties and high resistance to wear and corrosion. This research aims to study the effect of the fabrication method (Investment Casting and Selective Laser Melting SLM by 3D printing) and heat treatments on the mechanical and tribological properties of Co-Cr-Mo alloy. It was found that the Selective Laser Melting method in general increases the ultimate tensile strength, strain and hardness compared to the Investment Casting method. Also, solution treatment and aging reduce the strength and strain values of the SLM samples and have no obvious effect on the casting samples. The wear test shows that wear rate of casting samples is lower than that of SLM samples.

An investigation on nitrogen uptake and microstructure of equimolar quaternary FeCoNiCr high entropy alloy after active-screen plasma nitriding

Under nitrogen diffusion treatments, N-expanded austenite (γN) can form at the surface of self-passivating Fe-Cr, Ni-Cr, and Co-Cr alloys at low temperatures, which provides beneficial hardening and enhancements in wear resistance without reducing corrosion resistance. Given the wide research interests in multicomponent equimolar alloys, an equimolar quaternary FeCoNiCr high entropy alloy (HEA) was investigated after active-screen plasma nitriding at 430–480 °C in this study. Firstly, the formation of γN-FeCoNiCr case at 430 °C was demonstrated with the bright case appearance after metallographic etching, the lattice expansion under XRD, the FCC electron diffraction patterns and the shear bands under TEM. Secondly, the thick treatment cases at ∼9–16 μm first indicated that N interstitial diffusion was not sluggish in the FeCoNiCr surface. Thirdly, analogous to stainless steels, the onset of dark regions in the etched γN-FeCoNiCr case was owing to the formation of a cellular mixture of CrN + γ-(Fe, Co, Ni) nano-lamellae at elevated treatment temperatures. The residual bright regions in γN-FeCoNiCr at 480 °C showed ∼1–3 nm CrN nanoprecipitates with no substantial Cr segregation. Additionally, a significant nanocrystalline layer was seen at the topmost surface at 480 °C, which is most likely associated with the high substrate Cr content.

Fit Accuracy of Cobalt–Chromium and Polyether Ether Ketone Prosthetic Frameworks Produced Using Digital Techniques: In Vitro Pilot Study

This pilot study aimed to compare the fit accuracy of cobalt–chromium (Co-Cr) and polyether ether ketone (PEEK) removable partial denture frameworks, produced by digital technologies. Two study models of previously prepared Kennedy’s Class I and Class III mandibular dental arches were scanned. For each model, two frameworks were digitally designed and manufactured using a Co-Cr alloy via the selective laser melting (SLM) technique, and using PEEK via the milling technique. A qualitative assessment of the framework’s fit accuracy to the corresponding study models was carried out using calibrated endodontic instruments and image amplification. Best-fit superimpositions between the reference design and the scanned frameworks were performed using the Geomagic Control X version 2018, 3D Systems software, allowing the expression of trueness by calculating the root mean square (RMS) value. Higher fit accuracy was observed for the milled frameworks, with the Class I PEEK framework showing the best fit accuracy to the corresponding model. RMS values were Class I—148.3 μm for Co-Cr and 69.2 μm for PEEK; Class III—107.2 μm for Co-Cr and 59.7 μm for PEEK. In the experimental conditions used, the milled PEEK frameworks showed better fit accuracy and higher trueness than the SLM-printed Co-Cr ones in both Kennedy classes.

Pit initiation on biomedical alloys-A review.

Biomedical alloys, like many engineering alloys, have chemical or physical heterogeneities at the surface, and such heterogeneities can potentially act as sites for pit initiation. Alloys of particular interest are 316/316L (and 316LVM) stainless steel, nitinol, and CoCr alloys. This review focuses on the sites-generally inclusions-that have been associated with pitting in various studies of biomedical alloys in simulated physiological solutions. The effect of these sites is discussed in relation to factors such as type and size. For both 316/316L stainless steel and nitinol, pitting has been found to initiate at two different types of inclusions: sulfide and oxide inclusions in stainless steel, and carbide and oxide inclusions in nitinol. Sulfide inclusions tend to be the predominant sites for pitting on 316/316L stainless steel, while there is some evidence to suggest that carbide inclusions may be more effective than oxide inclusions for pitting on nitinol. CoCrMo alloys differ from the other two alloys in that, although particles can be present in the form of carbides, the carbides typically do not provide sites for pit initiation except possibly for alloys with a high-C content, certain heat treatments, and when anodically polarized to high potentials. CoNiCrMo differs further in that TiN inclusions can be present in the vicinity of pits and might be associated with them, but irrespective of the initiation site, any pits are unlikely to grow because of repassivation.

Prioritizing biomaterials for spinal disc implants by a fuzzy AHP and TOPSIS decision making method

Considerable research has been focused on identifying the optimum biomaterial for spine implants. New technologies and materials have allowed surgeons to better grasp the biomechanical principles underpinning implant stability and function. An optimal biomaterial for total disc replacement (TDR) should include essential characteristics such as biocompatibility, long-term durability, the capacity to withstand mechanical stresses, and economic viability. Our research has focused on six biomaterials for TDR, including Ti–6Al–4V, CoCr alloy, stainless steel 316L, zirconia toughened alumina (ZTA), polyether ether ketone (PEEK) and ultra-high-molecular weight polyethylene (UHMWPE). Ten common properties, i.e., the Young’s modulus, density, tensile strength, the expense of the manufacturing process, the cost of raw material, wear rate, corrosion resistance, thermal conductivity, fracture toughness and compressive strength were utilized to assess these six different materials. The purpose of this study was to evaluate and rank the six alternative biomaterials proposed for use in the endplates and articulating surface of a spinal TDR. To accomplish this, a multi-criteria decision-making approach, namely the fuzzy analytic hierarchy process (fuzzy AHP) and the Technique of Order Preference by Similarity to Ideal Solution (TOPSIS) was adopted to solve the model. For validation and robustness of the proposed method, sensitivity analysis was performed, and comparison was performed with fuzzy-VIKOR and fuzzy-MOORA methods. In light of the study’s results, ZTA and Ti–6Al–4V were identified as the best suited materials for the articulating surface and endplates, respectively, in a spinal disc implant.

Comparison of tensile properties and porcelain bond strength in metal frameworks fabricated by selective laser melting using three different Co-Cr alloy powders

Statement of problemThe selective laser melting (SLM) manufacturing technique has been widely employed to produce Co-Cr dental metal frameworks. The selection of Co-Cr alloy powders has the potential to influence the microstructure and tensile properties, consequently impacting the bond strength of the metal-porcelain. However, limited information is available regarding the effect of Co-Cr alloy powder on these properties when all other factors remain consistent. PurposeThe purpose of this in vitro study was to assess how the choice of Co-Cr alloys during SLM manufacturing influences the microstructure, tensile properties, and bond strength of metal-ceramic combinations. Material and methodsThree different Co-Cr alloy powders, Co-Cr-Mo, Co-Cr-Mo-W, and Co-Cr-W were selected in this study. The powder characteristics and chemical compositions were analyzed using a scanning electron microscope (SEM) and energy dispersive X-ray (EDX) analysis, respectively. Subsequently, 12×12×15-mm cube specimens, cylindrical tensile test specimens, and 25×3×0.5-mm metal strips were fabricated using the SLM technique. Microstructural investigations of the cube specimens were conducted after metallographic preparation using SEM. The cylindrical tensile specimens (n=8) from each composition were subjected to tensile tests at a deformation rate of 0.5 mm/min. Following the application of ceramic to the metal specimens (n=10) in each group, the strength of the metal-ceramic bond was evaluated through a 3-point bend test conducted at a crosshead speed of 1 mm/min. Mechanical properties obtained from the tensile tests and bond strength values were statistically analyzed using a one-way ANOVA and Tukey post hoc comparison tests (α=.05). ResultsMelt pool boundaries, columnar and equiaxed grains, and precipitates were observed in the microstructures of 3 different alloys produced by SLM. The Co-Cr-Mo-W alloy had more uniformly dispersed and finely distributed precipitates compared with other alloy compositions. The Co-Cr-Mo-W alloy had exhibited the highest yield strength (1068.0 ±41.2 MPa) and ultimate tensile strength (1263.4 ±10.7 MPa) while showing the lowest ductility under the tensile tests (6.1 ±0.9%) among all 3 alloys. Significant differences in the tensile mechanical properties were observed in the alloys except between the yield strength of the Co-Cr-Mo and Co-Cr-W alloys. The highest elongation (8.9 ±1.2%) was seen in the Co-Cr-Mo alloy. However, no significant differences were detected regarding the bond strength of all 3 groups (P>.05). The mean bond strength values were approximately 42 MPa for all the alloys. ConclusionsThe results indicate that the selection of different Co-Cr alloy powders used in SLM production may influence both microstructure and tensile properties. However, the strength of the metal-ceramic bond of Co-Cr alloys remained unaffected by this selection.

Accuracy of fit for cobaltchromium bar over two implants fabricated with different manufacturing techniques: an in-vitro study

ObjectiveThe purpose of the invitro research was to compare the fit of Cobalt Chromium customized bar fabricated with different manufacturing processes cast metal bar, milled bar and 3D printed bar using scanning electron microscope.Materials and methodsClear epoxy resin molds were prepared. In each mold two parallel implants with a 14 mm distance from each other were embedded. Thirty Co-Cr custom bars were constructed and were divided equally into three groups: Group (I) (Co-Cr conv), group (II) milled bar (Co-Cr milled), and group (III) printed bar (Co-Cr print). The marginal fit at implant-abutment interface was scanned using scanning electron microscope (SEM).ResultsThere was a significant difference between the three studied groups regarding marginal misfit the between implant and fabricated bars with p-value < 0.001. The highest value of micro-gap distance was found in Co-Cr conventional group (7.95 ± 2.21 μm) followed by Co-Cr 3D printed group (4.98 ± 1.73) and the lower value were found in Co-Cr milled (3.22 ± 0.75).ConclusionThe marginal fit of milled, 3D printed and conventional cast for Co-Cr alloy were within the clinically acceptable range of misfit. CAD/CAM milled Co-Cr bar revealed a superior internal fit at the implant-abutment interface. This was followed by selective laser melting (SLM) 3D printed bar and the least fit was shown for customized bar with the conventional lost wax technique.

TWIP-assisted Zr alloys for medical applications: Design strategy, mechanical properties and first biocompatibility assessment

This study proposes a novel strategy for the design of a new family of metastable Zr alloys. These alloys offer improved mechanical properties for implants, particularly in applications where conventional stainless steels and Co-Cr alloys are currently used but lack suitability. The design approach is based on the controlled twinning-induced plasticity (TWIP) effect, significantly enhancing the ductility and strain-hardenability of the Zr alloys. In order to draw a “blueprint” for the compositional design of biomedical TWIP (Bio-TWIP) Zr alloys—using only non-toxic elements, the study combines d-electron phase stability calculations (specifically bond order (Bo) and mean d-orbital energy (Md)) with a systematic experimental screening of active deformation mechanisms within the Zr-Nb-Sn alloy system. This research aids in accurately identifying the TWIP line, which signifies the mechanism shift between TWIP and classic slip as the primary deformation mechanism. To demonstrate the efficacy of the TWIP mechanism in enhancing mechanical properties, Zr-12Nb-2Sn, Zr-13Nb-1Sn, and Zr-14Nb-3Sn alloys are selected. Results indicate that the TWIP mechanism leads to a significant improvement of strain-hardening rate and a uniform elongation of ∼20% in Zr-12Nb-2Sn, which displays both {332}<113> mechanical twinning and dislocation slip as the primary deformation mechanisms. Conversely, Zr-14Nb-3Sn exhibits the typical mechanical properties found in stable body-centered cubic (BCC) alloys, characterized by the sole occurrence of dislocation slip. Cell viability tests confirm the superior biocompatibility of Zr-Nb-based alloys with deformation twins on the surface, in line with existing literature. Based on the whole set of results, a comprehensive design diagram is proposed.

Structural, electrochemical, biological, and mechanical assessment of functionally graded Cr-based multilayers for enhanced metal-ceramic bond strength in dental restorations

The failures of metal-ceramic dental restorations happen due to the initiation of a corrosive process that leads to the deterioration of restorations from a mechanical and aesthetic point of view, by releasing ions and corrosion products, causing patient hypersensitivity, as well as by detaching the ceramic from the metal support. The purpose of this study was to improve the metal-ceramic adhesion of dental prosthetic frameworks by covering their metallic components with biocompatible inorganic coatings, resistant to corrosion in the oral cavity environment. Different coating architectures based on chromium oxynitrides were obtained by cathodic arc method on CoCr alloy substrate. GDOES results confirmed the proposed configuration of the multilayers, and (O + N)/(Cr + Si) ratio calculated for each component layer (ranging from 0.7 to 2.7) emphasized the gradual transition from a metallic character towards a ceramic character of the CrSiON outer layer. XRD analysis proved the stability of the coating structure when a ceramic sintering treatment was applied, the Cr2O3 trigonal phases formed as a result of heat treatment, having a beneficial effect on the metal-ceramic bond strength. After 12h immersion in artificial saliva (pH = 5), an increased protection efficiency was observed for all the proposed multilayers. Among them, the best behaviour was exhibited by CrSiN/CrSiON coating, as pointed out by electrochemical impedance spectroscopy. Even after 72h of immersion, the mentioned design proved the highest pore resistance, result ascribed to a more defect free structure, which acted as a corrosion barrier to the electrolyte ingress. However, biological assessment revealed that the best proliferating and metabolic support for human gingival fibroblasts was showed by Cr/CrSi/CrSiN/CrSiON coating. Similar results were obtained by mechanical characterization of the new CoCr-multilayers-ceramic systems (tests performed based on the requirements specified in ISO 9693:2012 standard), indicating that the coating with the highest number of interfaces had also the highest surface roughness and lower contact angles, and therefore, the best bond strength value.

Technological Aspects and Performance of High Entropy Alloys with Potential Application in Dental Restorations and Reducing Implant Failure

Amidst the prevalence of aggressive bacterial infections that can impact both oral and systemic health following various dental and implant procedures, the search for alternative, high-performing and biocompatible materials has become a challenging pursuit. The need for such investigations is increasing owing to the fact that toxicological risks of cobalt–chromium (CoCr) alloys used in dentistry have become a part of the EU’s new Medical Devices Regulations establishing that cobalt metal has been classified as carcinogenic, genotoxic and detrimental to reproduction. Within this context, this review proposes high entropy alloys (HEA) as potential alternatives and presents their characteristics and in vitro biological performance when used as a substrate or coating. Anatomical details of the oral cavity in relationship with prosthodontics and implant dentistry support the paper’s motivation and presentation. The review highlights the innovative manufacturing procedures, microstructure and properties of both the bulk and coatings of BioHEA. It evaluates the performance of BioHEAs based on their complete characterization and assesses their suitability for novel applications in dentistry, serving as the primary objective of this manuscript.

Ceramic Bond Strength of Various Metal Substrate Using Traditional and Digital Methods

Purpose: The aim of this study was to investigate the bond strength of cobalt-chromium (Co-Cr) metal frameworks prepared with three different production techniques with dental porcelain. Methods: In this study, a total of thirty disc samples divided to Three groups (n = 10/group) of metal cylinders (10 mm diameter x 4mm thickness with ring base (12 mm diameter x 1mm thickness) were fabricated by casting (Co–Cr), CAD CAM milling blank(Co–Cr) and by selective laser sintering SLM (Co–Cr) and abraded with airborne-particles then feldespathic porcelain was applied for all discs (10mm diameter x 2mm thickness), before the shear bond strength (SBS) test, the Surface characteristics of the dental alloys were observed by scanning electron microscopy (SEM) to determine the thickness of the oxide layer then surface roughness tester using TR220 portable roughness tester The average surface roughness (Ra) was determined for each group. SBS test-values and failure modes were recorded. Data were analyzed using ANOVA, Tukey’s HSD (a = 0.05). Result: no statistically significant difference of the metal-ceramic bond strength of the test roughness used between casting, milling, and laser no statistically significant difference of the metal-ceramic bond strength of the SBS test between casting compare with milling, and laser groups SBS test statistically significant difference of the metal-ceramic bond strength of the test between milling, and laser technique. The mode of failure shows was mainly cohesive and mixed for all specimens. Conclusion: Within the scope of this research, the CAD/CAM milling Co-Cr alloy has a shear bond strength comparable to the castable alloy. For metal-ceramic restorations, the CAD/CAM milling Co-Cr alloy is an alternative to the castable alloy. Co-