Cobalt-chromium Alloy Research Articles

Which metal surface treatment improves the bond strength between metal alloys and acrylic resin in removable partial dentures? A systematic review.

The union of the metal removable partial denture framework to the heat polymerized acrylic resin is related to prosthesis longevity. However, methods to enhance this bond are not clear to clinicians and dental laboratory technicians. The purpose of this systematic review was to identify which metal surface treatments best increase the bond strength between heat polymerized acrylic resin and removable partial denture alloys. This review was carried out following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and registered in the International Prospective Registry of Systematic Reviews (PROSPERO) database (CRD42022384926). Electronic searches were carried out independently, by 3 examiners in Medline/PubMed, Scopus, and Web of Science databases, and in the nonpeer-reviewed literature via ProQuest. The electronic searches resulted in 4143 articles, with 4055 after removing duplicates. After reading the titles and abstracts, 37 articles were selected for reading in full-text version, from which 6 articles were included. All studies evaluated materials for conventional acrylic resin denture base (heat polymerized), processed by water bath, bonded to metal. For the metal framework alloys, cobalt chromium (Co-Cr) alloys were used in 2 studies, titanium (Ti) in 2 studies, and Co-Cr and Ti in the other 2 studies. Different metal surface treatments were used as airborne-particle abrasion with aluminum oxide (particle sizes of 50µm, 110µm, and 250µm) followed by the primer application and the isolated use of the primer, compared to the absence of isolated intervention or airborne-particle abrasion of the metal surface. Among the different primers used, those based on 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) showed the highest acrylic resin-to-metal bond strength values. Airborne-particle abrading the metal with Al2O3 followed by applying a 10-MDP-based primer, increased the bond strength between metal framework alloys and heat polymerized acrylic resin denture base material.

Optimization of processing parameters for LPBF-manufactured CoCr alloys based on laser volume energy density

In this paper, the finite element method (FEM) and experiments were adopted to optimize the processing parameters of laser powder bed fusion-manufactured cobalt-chromium (CoCr) alloys on the basis of laser volume energy density. According to simulation results, both the maximum temperature, heat-affected zone and cooling rate of molten pool increased with the enhancement of laser power and scanning speed even under the same laser volume energy density. By conducting relevant experiments, it is found that the phase transformation, microstructure and mechanical properties were also influenced by the variation of laser power and scanning speed, and the LPBF-processed CoCr alloys with excellent forming quality could be acquired when the laser power was 160 W, and the scanning speed was 750 mm/s. Therefore, it is impracticable to optimize the processing parameters only on the basis of laser volume energy density, various methods should be employed to complete the whole optimization procedure.

Fatigue strength estimation of net-shape L-PBF Co–Cr–Mo alloy via non-destructive surface measurements

One of the primary challenges in utilizing additive manufacturing for load-bearing metal components in the aerospace industry lies in the relatively low fatigue strength and significant variability stemming from the typically rough as-built surfaces. The goal of this research is to develop a model able to robustly correlate parameters obtained by non-destructive measurements to the fatigue strength of a generic surface state for a cobalt-chrome alloy manufactured via laser powder bed fusion (L-PBF). The results show that a relatively accurate estimation of fatigue strength of a generic surface quality can be performed via high-quality non-destructive roughness measurements coupled with statistical considerations and fracture mechanics-based assessments. This provides the capability of comparing different surface states and selecting the best option for fatigue strength with limited experimental effort and might prospectively set the basis for qualification of L-PBF components in the presence of rough surfaces.

Comparison of fatigue behaviour and fracture toughness of cobalt chromium alloy fabricated by casting and selective laser melting methods

Co-Cr alloys are most commonly used base metal alloy in dentistry for the fabrication of many types of metallic substructures. They gained popularity due to their good mechanical properties and low cost. There are different techniques for fabrication of Co-Cr alloys which includes casting and DMLS technique. However, change in the fabrication techniques showed variation in mechanical properties. Forty Co-Cr samples each were made from two different techniques, Casting and DMLS. Fracture toughness was done with charpy’s impact test machine and fatigue behaviour test was done with nano universal testing machine. The samples were later observed under stereo electron microscope to assess the kind of failure. Unpaired t test revealed that there was statistically significant difference between two different groups. The mean difference of fracture toughness in Casting group was higher when compared with DMLS group. The number of fatigue cycles were higher in DMLS group than the casting group. Within the limitations of this in vitro study, casting group showed higher fracture toughness when compared to DMLS group, whereas fatigue limit was higher in DMLS group than casting group.

Evaluation of the relationship between metallurgical properties and metal-ceramic bond characteristics of Co-Cr alloys manufactured by different techniques

Metal-ceramic restorations made from cobalt chromium (Co-Cr) alloy have been increasing, but studies on the effects of different manufacturing techniques on metal-ceramic interface characteristics and metal-ceramic bond strength are sparse. The purpose of this in vitro study was to examine the metal-ceramic interface and the metal-ceramic bond strength of a Co-Cr alloy produced by casting, milling, and selective laser melting (SLM) with or without thermal cycling. Co-Cr alloys were prepared by casting, milling, and SLM. Two different SLM devices were used. Ninety-six specimens (25×3×0.5mm) were manufactured. The structure of the oxidation surface of Co-Cr specimens was examined by scanning electron microscopy (SEM) and by X-ray fluorescence spectroscopy (XRFS). After porcelain application, selected specimens were thermal cycled, and the strength of the metal-ceramic bond was measured by the 3-point bend test. All specimens were analyzed for failure type with a stereomicroscope. The elemental composition and morphology of the metal-ceramic interface were examined by XRFS and SEM with energy-dispersive X-ray (EDX). The results of bond strength were analyzed using a 2-way analysis of variance (ANOVA) for manufacturing methods and testing conditions and the Tukey honest significant difference (HSD) test (α=.05). The main effect of the interactions of the testing condition and manufacturing method variables on the bond strength variable was not statistically significantly different. No significant differences were found among the testing conditions tested (P=.638). Significant differences were found among the manufacturing methods tested statistically (P<.001). Statistically significant differences were found in the CAD-CAM and CONSEPT LASER groups, the CAD-CAM and SLM LASER groups, the CAD-CAM and CAST groups, and the CAST-SLM LASER groups (P<.05). Differences were observed among the interface morphologies of casting, milling, and the two SLM groups. The bond strength between Co-Cr alloy and ceramic is affected by the manufacturing method. The metal-ceramic bond strength is independent of thermal cycling. The bond strength value in all groups was over 25MPa, which has been considered clinically acceptable. The interface metallurgical structures of Co-Cr alloys were affected by different manufacturing techniques.

The Past, Present and Future of Biomaterials

Biomaterials are substances that can be introduced into the body or tissue for a wide array of therapeutic or diagnostic purposes. Biomaterials can be of both natural or synthetic origin. The first examples describing the use of biomaterials includes the Neanderthals use of wood as dental implanting materials, and from 7th BC to the 4th AD, the ancient civilizations of Greece and Rome used various other naturally occurring substances and metals for treatment of wounds and other medical complications. In 16th century in Europe, silver and gold materials were used for dental repair and iron threads were used for bone repairs and various immobilization procedures.1 Significant advancement has been made in the field of biomaterials in the recent decades, and both natural and synthetic biomaterials have been effectively used to replace various human tissues such as teeth, ligaments, tendons, bones, and load-bearing implants. The biocompatibility, bioactivity, and mechanical properties of biomaterials plays a pivotal role in meeting the need for long-term implants and bone replacement. Biomaterials in use include but are not limited to metal-based biomaterials (titanium alloys, alumina, stainless steel, zirconia, cobalt-chromium alloys) and polymer-based biomaterials (polymethyl methacrylate and ultra-high molecular weight polyethylene). These are usually selected because they meet the required criteria of mechanical strength, biocompatibility, and desired physical and chemical properties. Considerable progress has been made in improving the effectiveness of artificial joints, reducing wear, and extending the life of implants or prostheses inserted into the human body.2,3 Until recently, the focus had been on biomaterials as replacement materials. However, the main issue is immune rejection of the introduced material. Therefore, the focus has changed to using biomaterials for tissue regeneration. A viable cellular construct in a controlled laboratory environment for the purpose of transplantation can be achieved by using bioactive scaffolds that provide a structured environment to support cell growth and their function. Another strategy has been to trigger tissue regeneration within the body itself by using porous meshes or degradable bioactive materials which can facilitate the process.2 These techniques pose a risk of infection. Extensive research is currently underway to address these problems. In a recent study, scientists have successfully fabricated a composite scaffold of cellulose and silver nanoparticles.4 This innovative scaffold showed promising properties in preventing microbial infections and has the potential to prevent infections at wound sites.However, while it is important to acknowledge the above-mentioned beneficial properties of biomaterials; there is still a long way to go to achieve the desired goals. Immunomodulating biomaterials have been developed with the potential to effectively overcome common chronic diseases such as type 1 diabetes in non-obese diabetic mice. Supramolecular biomaterials, formed by non-covalent interactions between molecular components are being fabricated which can be activated or deactivated in response to physiological signals or which can mimic the signaling mechanisms seen in real biological systems. In addition, injectable biomaterials for delivering therapeutic drugs, proteins and genetic material are being developed, for treating a wide range of diseases via targeted delivery by bypassing immune system recognition. The use of synthetic and naturally produced injectable biomaterials in ongoing research has the potential for future applications in the treatment of bone deformities, detection and treatment of cancer, and heart related diseases.&#x0D; In Pakistan, researchers have diverted their attention towards biomaterials sciences and its potential role in biomedical devices since last two decade, evident from the increasing number of publications and patents. However, there is still a scarcity of good quality applied research in the field. In addition, the lack of capacity for conducting clinical trials of biomedical devices developed in Pakistan is also a hindrance to the commercialization of these products. For these products to reach the market, high quality clinical trials according to international best practices have to be conducted. It is imperative for Pakistan to develop centers where phase I and II clinical trials can be conducted that comply with the required international methodological, ethical and regulatory guidelines. This will only be possible where the triple helix model of Government-Academia-Industry collaboration is implemented in its true spirit.&#x0D; Editor-in-ChiefHow to cite this: Alamgir W, Haider A. The Past, Present and Future of Biomaterials. Life and Science. 2023; 4(4): 363-364 . doi: http://doi.org/10.37185/LnS.1.1.500&#x0D; &#x0D; &#x0D;

Interface Analysis between Inconel 625 and Cobalt-Chromium Alloy Fabricated by Powder Bed Fusion Using Pulsed Wave Laser.

A few components used in the aerospace and petrochemical industries serve in corrosive environments at high temperatures. Corrosion-resistant metals or unique processes, such as coating and fusion welding, are required to improve the performance of the parts. We have used laser powder bed fusion (LPBF) technology to deposit a 5 mm thick corrosion-resistant CoCrMo layer on a high-strength IN625 substrate to improve the corrosion resistance of the core parts of a valve. This study found that when the laser volumetric energy density (EV) ≤ 20, the tensile strength increases linearly with the increase in EV, and the slope of the curve is approximately 85°. The larger the slope, the greater the impact of EV on the intensity. When EV > 20, the sample strength reaches the maximum tensile strength. When the EV increases from 0 to 20, the fracture position of the sample shifts from CoCrMo to IN625. When EV ≤ 38, the strain increases linearly with the increase in EV, and the slope of the curve is approximately 67.5°. The sample strain rate reaches the maximum when EV > 38. Therefore, for an optimal sample strength and strain, EV should be greater than 38. This study provides theoretical and technical support for the manufacturing of corrosion-resistant dissimilar metal parts using LPBF technology.

Characterising Hydroxyapatite Deposited from Solution onto Novel Substrates: Growth Mechanism and Physical Properties.

Whilst titanium, stainless steel, and cobalt-chrome alloys are the most common materials for use in orthopaedic implant devices, there are significant advantages in moving to alternative non-metallic substrates. Substrates such as polymers may have advantageous mechanical biological properties whilst other substrates may bring unique capability. A key challenge in the use of non-metal products is producing substrates which can be modified to allow the formation of well-adhered hydroxyapatite films which promote osteointegration and have other beneficial properties. In this work, we aim to develop methodology for the growth of hydroxyapatite films on surfaces other than bulk metallic parts using a wet chemical coating process, and we provide a detailed characterisation of the coatings. In this study, hydroxyapatite is grown from saturated solutions onto thin titanium films and silicon substrates and compared to results from titanium alloy substrates. The coating process efficacy is shown to be dependent on substrate roughness, hydrophilicity, and activation. The mechanism of the hydroxyapatite growth is investigated in terms of initial attachment and morphological development using SEM and XPS analysis. XPS analysis reveals the exact chemical state of the hydroxyapatite compositional elements of Ca, P, and O. The characterisation of grown hydroxyapatite layers by XRD reveals that the hydroxyapatite forms from amorphous phases, displaying preferential crystal growth along the [002] direction, with TEM imagery confirming polycrystalline pockets amid an amorphous matrix. SEM-EDX and FTIR confirmed the presence of hydroxyapatite phases through elemental atomic weight percentages and bond assignment. All data are collated and reviewed for the different substrates. The results demonstrate that once hydroxyapatite seeds, it crystallises in the same manner as bulk titanium whether that be on a titanium or silicon substrate. These data suggest that a range of substrates may be coated using this facile hydroxyapatite deposition technique, just broadening the choice of substrate for a particular function.

Comparison of the Retention and Fit of Polyether Ether Ketone Clasps during Fatigue Circulation Tests

PurposeThe purpose of this study was to evaluate the fit and retention of clasps made of polyether ether ketone (PEEK) or cobalt–chromium alloy (Co–Cr) at different tooth positions in experimental simulations of in vitro wear and removal for 5 years. MethodsStandard crowns of the right mandibular first premolar (44) and first molar (46) were selected, and a circular three-arm clasp was designed, scanned and fabricated. Ten PEEK clasps were used as the experimental group, and 10 Co–Cr clasps were used as the control group. The seating channel was parallel to the side of the abutment base in both groups. The oral environment was simulated, and each clasp was tested in artificial saliva for 7200 cycles while the change in clasp retention force was recorded. The fit before and after the fatigue cycles was measured by the silicone rubber film copying method. Data were statistically analyzed using the independent samples t-test (α = 0.05). ResultsBefore circulation, the retention forces of the clasps at position 44 were 4.61 ± 0.91 N (PEEK) and 47.50 ± 10.59 N (Co–Cr), and the forces at position 46 were 3.38 ± 0.49 N (PEEK) and 28.79 ± 10.99 N (Co–Cr). After circulation, the retention forces of the clasps at position 44 were 4.15 ± 0.91 N (PEEK) and 13.90 ± 6.59 N (Co–Cr), and the forces at position 46 were 2.93 ± 0.25 N (PEEK) and 11.56 ± 3.93 N (Co–Cr). Before circulation, the fit of each clasp at the reference points (clasp tip, clasp arm, and occlusal rest) was between 41.70 μm and 170.29 μm, and after circulation, they were between 64.05 μm and 182.59 μm. The retention force and fit of the PEEK clasps did not undergo statistically significant changes from before to after circulation (P > 0.05). However, there were statistically significant (P < 0.05) decreases in the retention force of the Co–Cr clasps and the fit of the clasp tip during circulation. In addition, there was a sudden and large change in the retention force of the Co–Cr clasps after approximately 360 cycles. ConclusionsThe retention force and suitability of the PEEK clasps met the requirements for clinical use during testing that simulated the in vitro wear and removal procedure for 5 years. Compared with the Co–Cr clasp, the PEEK clasp underwent less fatigue deformation, which makes it feasible for clinical applications.

Device trueness in passivity and misfit of CAD-CAM frameworks: Conventional versus printed casts

Statement of problemObtaining a passive and well-adapted framework is challenging when intraoral scanning edentulous arches with multiple implants. The trueness of the printed casts is unclear. PurposeThe purpose of this clinical study was to evaluate the trueness of frameworks made from conventional and printed casts regarding clinical passivity and misfit. Material and methodsTen participants with complete mandibular fixed implant-supported interim prostheses retained by 4 implants were included. Each participant had a conventional impression and a digital scan made. The digital scan was made using an innovative device. Both conventional and digital casts were made, and the virtual images were used for milling the digital framework in cobalt chromium alloy. All frameworks were evaluated for passivity and marginal vertical misfit with the single screw test, with 4 attempts consisting of the tightened screw position, a test with all screws tightened, and an interspersed tightening test. The Kruskal-Wallis test was used to evaluate the trueness of the tested device for framework construction through the single screw test on vertical marginal misfit in the conventional and printed groups (α=.008). The Friedman test was used to assess the effect of test type (α=.05), and the Wilcoxon test was used to identify group-to-group differences (α=.017). ResultsThe absence of space between the framework and the abutments and interferences during its placement, as well as good stability, were observed clinically. In laboratory analysis, greater framework misfits were observed in the printed group compared with the conventional group when the single screw test was applied. Comparing the 3 tests used, the greatest misfits were observed when the framework was screwed onto the printed cast. ConclusionsThe innovative device tested for the intraoral scanning of multiple implants had clinically acceptable accuracy for the construction of passive and adapted frameworks. The conventional cast was more accurate than the printed cast, with lower misfit values, in all tests.

Wear Mechanisms of Cold-Sprayed Stellite-6 During Reciprocated Dry Sliding Under Different Sliding Speeds

Cobalt–chromium alloys are often employed in those environments that require reliable wear and friction properties. Cold Gas Dynamic Spray offers the opportunity to obtain good quality deposits of Stellite-6, that can be successfully used in harsh environments, where good surface performance, in terms of wear resistance, is required. It is also well-known that Stellite-6 is subjected to several physical changes at the interface during dry sliding, that are often related to the loading conditions. As a consequence, wear behavior of this alloy can undergo some variations that linear models are not able to capture, since micro-structural modifications occur during operation. To better understand the wear mechanisms of cold-sprayed Stellite-6 coatings together with the occurring physical phenomena, a systematic experimental study was performed, in fact, to date, no such in-depth tribological studies have been performed. Tests were conducted under combinations of two sliding speeds (0.1 and 0.5 m/s) and four contact pressure in the range of 2-5 MPa. In low-speed tests, abrasive wear is evident, where detachment and pull-out phenomena mainly affect the worn surface of coatings. On the other hand, subsurface cracking was observed in high-speed tests, as well as evidence of plastic deformation on the wear surface. These results suggest that observed wear mechanisms are more likely a consequence of adhesive wear. Unique to this study, the cross-sectional nano-indentation tests showed how the stiffness of the coating, near to wear interface, increases significantly in the case of the lowest value of sliding speed (i.e., v = 0.1 m/s), whereas tends to decrease at high speeds, i.e., v = 0.5 m/s, as a consequence of the formation of subsurface cracks into the coating.

Surface Corrosion from Implant–Abutment Couplings with Different Connection Designs Influences Osteoblasts’ Function: A Novel Technique

The improved peri-implant bone response demonstrated when utilizing the platform-switching concept may result from the reduced levels of metal ions released from implant–abutment surfaces to the surrounding tissues. These corrosion products may play a major role in crestal bone remodeling around dental implants. This study evaluated the effect of different implant–abutment couplings (platform-matched vs. platform-switched) on osteoblasts’ function. Titanium alloy and cobalt–chrome alloy abutments were coupled with titanium cylinders, forming either platform-switched or platform-matched groups, and were incubated in human osteoblast cultures utilizing a novel direct-exposure technique. Viability was evaluated over 21 days using Alamar Blue assay. Apoptosis was measured after 24 h using flow cytometry. The expression of genes related to bone resorption was analysed over 21 days using a real-time quantitative polymerase chain reaction assay. Cell viability was reduced from day 4 to day 21 (p &lt; 0.05), with higher rates of early apoptosis (p &lt; 0.05) compared to the controls. Apoptosis was higher in the platform-matched groups (p &lt; 0.05). The tested genes’ expression was up-regulated after 1 and 3 days of exposure to implant–abutment couplings (p &lt; 0.05). The upregulation was more pronounced in platform-matched groups (p &lt; 0.05). Exposure of osteoblasts to implant–abutment couplings induced adverse biological responses, which were more pronounced with platform-matched couplings. These reactions might be related to the increased amounts of metal ions released from the platform-matched couplings, highlighting the possible role of corrosion products in the mediation of crestal bone loss around dental implants.

Static, dynamic, and fatigue life investigation of a hip prosthesis for walking gait using finite element analysis

ABSTRACT Total hip arthroplasty (THA) is a common procedure that is performed for elderly people who suffer from hip pain and other hip-related problems. THA is an operation where an artificial joint is implanted in the femur and acts as the hip joint. THA has seen advancement to a greater extent in the 20th century. In this work, a novel hip implant design is proposed based on the existing literature data. The hip implants were provided with radial clearance between the head and stem junction. This implant design is analyzed by applying a walking gait that has been clinically prerecorded. Linear and volumetric wear rates are estimated at the head-stem junction, head-liner, and liner to acetabulum using Archard’s wear law. Total deformation, von Mises stress, contact stress, linear and volumetric wear rates were reported. The volumetric wear rate was found to be less than the existing literature, achieving the goal of increasing the life expectancy of the total hip prosthesis. The maximum wear rate is found at the head-stem junction for press-fit. It is observed that when the acetabular cup and femoral head are made of CoCr (Cobalt-Chromium) alloy, the liner with Ultra high molecular weight polyethylene (UHMWPE) and the stem with titanium alloy have a lesser wear rate when compared to other material combinations. Further, it is also found that the fatigue life of Ti (Titanium) alloy is higher than that of CoCr alloy and Ti alloy material combinations have the maximum factor of safety.

Investigation of Laser-Welded Co-Cr Dental Alloys by Microscopy and Mechanical Testing

In order to improve the hold and function of dentures for the patient, various prostheses made of metal, mostly metal alloys, are used every day in dental practise. Cobalt-chromium alloys are usually the first choice because they have very good mechanical properties and satisfactory clinical conditions. Nowadays, laser welding is increasingly used in dental practise due to its numerous advantages over other technologies. In this work, therefore, six commercially available Co-Cr alloys were investigated. Three of them are used for metal-ceramic work, two for denture frameworks and one is suitable for both applications. They were joined by laser welding and subsequently analysed microscopically. Their mechanical properties were determined and statistically evaluated. The microhardness of the laser-welded alloys is in the range of 282–465 MPa in the weld zone and between 283 and 435 MPa in the heat-affected zone. The flexural strength of the laser-welded alloys is lower than the control group, but an alloy for the metal-ceramic work (I-BOND NF) shows very similar value. Furthermore, this alloy, together with two other metal-ceramic alloys, survived a maximum of cycles in dynamic tests. It was found that the laser method can be used for joining Co-Cr alloys while ensuring appropriate parameters that guarantee the quality of the dental work.

In vitro biological responses of plasma nanocoatings for coronary stent applications.

In-stent restenosis and thrombosis remain to be long-term challenges in coronary stenting procedures. The objective of this study was to evaluate the in vitro biological responses of trimethylsilane (TMS) plasma nanocoatings modified with NH3 /O2 (2:1 molar ratio) plasma post-treatment (TMS + NH3 /O2 nanocoatings) on cobalt chromium (CoCr) alloy L605 coupons, L605 stents, and 316L stainless steel (SS) stents. Surface properties of the plasma nanocoatings with up to 2-year aging time were characterized by wettability assessment and x-ray photoelectron spectroscopy (XPS). It was found that TMS + NH3 /O2 nanocoatings had a surface composition of 41.21 ± 1.06 at% oxygen, 31.90 ± 1.08 at% silicon, and 24.12 ± 1.7 at% carbon, and very small but essential amount of 2.77 ± 0.18 at% nitrogen. Surface chemical stability of the plasma coatings was noted with persistent O/Si atomic ratio of 1.292-1.413 and N/Si atomic ratio of ~0.087 through 2 years. The in vitro biological responses of plasma nanocoatings were studied by evaluating the cell proliferation and migration of porcine coronary artery endothelial cells (PCAECs) and smooth muscle cells (PCASMCs). 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium (MTT) assay results revealed that, after 7-day incubation, TMS + NH3 /O2 nanocoatings maintained a similar level of PCAEC proliferation while showing a decrease in the viability of PCASMCs by 73 ± 19% as compared with uncoated L605 surfaces. Cell co-culture of PCAECs and PCASMCs results showed that, the cell ratio of PCAEC/PCASMC on TMS + NH3 /O2 nanocoating surfaces was 1.5-fold higher than that on uncoated L605 surfaces, indicating enhanced selectivity for promoting PCAEC growth. Migration test showed comparable PCAEC migration distance for uncoated L605 and TMS + NH3 /O2 nanocoatings. In contrast, PCASMC migration distance was reduced nearly 8.5-fold on TMS + NH3 /O2 nanocoating surfaces as compared to the uncoated L605 surfaces. Platelet adhesion test using porcine whole blood showed lower adhered platelets distribution (by 70 ± 16%), reduced clotting attachment (by 54 ± 12%), and less platelet activation on TMS + NH3 /O2 nanocoating surfaces as compared with the uncoated L605 controls. It was further found that, under shear stress conditions of simulated blood flow, TMS + NH3 /O2 nanocoating significantly inhibited platelet adhesion compared to the uncoated 316L SS stents and TMS nanocoated 316L SS stents. These results indicate that TMS + NH3 /O2 nanocoatings are very promising in preventing both restenosis and thrombosis for coronary stent applications.

Evaluation of the Retentive Forces from Removable Partial Denture Clasps Manufactured by the Digital Method

The purpose of this study was to evaluate the retentive forces over time of removable partial denture clasps fabricated by the digital method. Occlusal rest seats were fabricated on three premolar teeth fixed in acrylic blocks (9 × 20 × 40 mm). Digitization of the teeth was performed using a laboratory scanner (Zirkonzahn Scanner S600 GmbH, Gais, Italy). After the analysis and determination of the insertion axis, two types of clasps with mesial occlusal rests were designed per tooth: the back-action and the reverse back-action clasps, using the Partial Planner Zirkonzahn program. The file was sent for fabrication of six metal clasps from a cobalt-chromium SP2 alloy in the EOSINT M270 system by a direct laser sintering process. The Instron 5544 universal testing machine was used to perform 20,000 cycles of clasp insertion and removal in the corresponding tooth with a load cell of 100 N and a speed of 2.5 mm/s. The retentive force was recorded for each of the 1000 cycles, and the change in retention over time was calculated. Statistical analysis was performed using the nonparametric Mann–Whitney test and a significance level of 5%. At 16,000 cycles, a maximum change in retention of 3.74 N was recorded for the back-action clasps and a minimum of −24.28 N at 1000 cycles for the reverse back-action clasps. The reverse back-action clasps exhibited statistically significant lower change in retention than the reverse-action clasps at 4000 and 5000 cycles. No differences were observed in the remaining cycles. During the 20,000 cycles, the change in retention was low regardless of the type of clasp. For most cycles, there were no differences in the change in retention between the two types of clasps.

Biomechanical comparison of different framework materials in mandibular overdenture prosthesis supported with implants of different sizes: a finite element analysis

BackgroundThe aim of this study is to evaluate the stresses on the supporting bone, implants, and framework materials under masticatory forces in mandibular overdenture prostheses modeled with different framework materials and different implant types, using the Finite Element Analysis (FEA).MethodsFor the finite element modeling, two identical mandibular jaw models were created; one with two standard (diameter:4.1 mm/12 mm length) and the other with two mini-implants (diameter:2.4 mm/12 mm length) were placed in the canine teeth area. The polymethylmethacrylate (PMMA) denture was modeled upon them, supported by Cobalt Chromium alloy (CoCr), Poly-ether ether ketone (PEEK), and Zantex materials with framework. No framework was added as a control model; only PMMA overdenture prosthesis was modeled.ResultsRegardless of the framework materials of the overdenture prostheses, the stress values ​​on mini-implants in all models yielded approximately two times higher results comparing to standard implants. More stress transmission was observed in the supporting bone and implants in the control prostheses and overdenture prostheses supported with respectively PEEK, Zantex, CoCr alloy frameworks, respectively. In the framework materials, more stress occurred on CoCr, Zantex and PEEK in that order.ConclusionIn the light of this study, the use of mini-implants as an alternative to standard implants is not promising in terms of distribution and transmission of chewing stresses. As a framework material, standard rigid metal alloys were found to be more advantageous than polymer materials in terms of stress distribution.

Additive manufacturing of metallic biomaterials: sustainability aspect, opportunity, and challenges

ABSTRACT The use of cutting-edge techniques is beneficial for the research and development of biomaterials and the production of new sustainable biomaterials. Eco-friendly biomaterials should be promoted. As prospective substitutes for conventional materials, a variety of biomaterials have been conceived and produced to date and successfully used in various biomedical disciplines. The sustainability component in the additive manufacturing of biomaterials is the main goal of this article. There is discussion of various metallic biomaterials, including titanium, stainless steel, magnesium, cobalt-chromium alloy, zinc, tantalum etc. The effects of several additive manufacturing techniques on sustainability are examined. Also, the properties of additive manufactured biomaterials and sustainability aspect of biomaterials are discussed in detail. By reducing material waste and using time and energy efficiently, additive manufacturing can assist to lower costs and having less harmful effects on the environment. This article discussed sustainability aspects of different additive manufacturing techniques used for manufacturing of biomaterials.

Establishing the Durability and Reliability of a Dental Bur Based on the Wear.

This paper analyzes the phenomenon that conditions the durability and reliability of a type of dental bur based on the wear of the active part and with effect on its quality. For the experimental study, a conical-cylindrical dental bur and a sample dental material in cobalt-chromium alloy, cylindrical shape, tested on a specially made experimental installation were used. In this paper, the most significant parameter was considered (loss of mass, mw, through the wear of the active part of a tested dental bur), which highlights the studied wear phenomenon. This is useful for the establishment of the durability and reliability of the dental bur by the extension of the lifetime or even optimization of its operation. The wear phenomenon of the active part of dental bur is studied based on the results and experimental data obtained in the work process that was validated by interpolation and led to polynomial functions which approximate very well the dependent parameter, mw, considered in the experimental program. The results of the interpolation showed that in the first 11 h of work, the dental bur works with high efficiency (allow optimizing operation or offering new ideas for constructive solutions), after which it can be easily decommissioned; i.e., it should be replaced with a new one (establishing some possible criteria for replacing the used dental bur).

Ionic release of dental cobalt-chromium based alloys

Background: Since the 1980s, as the cost of noble metals has increased, more base metal alloys have been used in fixed and removable prostheses. Cobalt-chromium (Co-Cr) alloys are one of the most widely used base metal alloys in the prosthetic dental department and have several clinical uses. Co-Cr alloys are frequently used as having excellent biocompatibility, great strength, good resistance to tarnish, corrosion, and wear, as well as being heat-resistant and non-magnetic.&#x0D; Materials and Methods: For the ion release test, seventy specimens of a cobalt-chrome alloy disc with dimensions of 5 mm in diameter and 3 mm in thickness were created. They were divided into five groups, each of which had 14 specimens, based on the manufacturing method as follows: new cast alloy group; selective laser melting group (3D printer specimens); once recast alloy + old selective laser melting group; new cast + once recast alloy group; once recast alloy group.&#x0D; Result: The outcomes showed that there were no&#x0D; statistically significant differences in ion release in any of the groups examined (P&gt;0.05).&#x0D; Conclusion: The production technique and alloy composition have a slight influence on ion release. A positive clinical response is anticipated, since it was found that every group met the ionic release criteria of the international standards.