Cobalt Chromium Research Articles

Recent Developments of Bioactive Glass Electrophoretically Coated Cobalt-Chromium Metallic Implants

Coating surfaces with bioactive glass can be defined as depositing fine bioactive glasses on biomaterial substrates. Cobalt-chromium is a viable alternative to stainless steel for long-term applications with superior ductility. The mechanical properties of cobalt-chromium alloys are high strength with elastic modulus of 220–2300 GPa, more significant than the 30 GPa of bones. Combining metals and bioactive glass results in high biocompatibility and improved bioactivity of implant surfaces. In addition, it triggers new bone tissue to regenerate through osteogenesis and mineralisation. However, implantation failure still occurs and requires surgery revision due to a lack of adequate bone bonding and delamination at the coating surface of the implant. The current review summarises the adhesion between bioactive glass coatings and cobalt-chromium substrates applied through electrophoretic deposition (EPD).

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.

Study on the Fatigue Properties of Polyether Ether Ketone and Cobalt Chromium Alloy as Removable Partial Denture Clasp Materials

Study on the Fatigue Properties of Polyether Ether Ketone and Cobalt Chromium Alloy as Removable Partial Denture Clasp Materials

First-in-Human Evaluation of a Polymer-Free Everolimus-Eluting Stent Using a Titanium Dioxide Film.

In patients with coronary artery disease treated with permanent polymer-coated drug-eluting stents (DES), the persistent presence of a less biocompatible polymer might delay arterial healing. Thin strut polymer-free DES have the potential to improve clinical outcomes and reduce the duration of dual antiplatelet therapy (DAPT). The purpose of this first-in-human study was to assess the safety and effectiveness of a novel polymer-free DES in patients with de novo coronary lesions. The TIGERevolutioN® stent (CG Bio Co., Ltd., Seoul, Korea) consists of a cobalt chromium platform with a strut thickness of 70 μm and a surface treated with titanium dioxide onto which everolimus-eluting stent (EES) is applied abluminally (6 µg/mm of stent length) without utilization of a polymer. A total of 20 patients were enrolled, with de novo coronary lesions (stable or unstable angina) and > 50% diameter stenosis in a vessel 2.25 to 4.00 mm in diameter and ≤ 40 mm in length for angiographic, optical coherence tomography (OCT), and clinical assessment at 8 months. All patients received DAPT after stent implantation. The primary endpoint was angiographic in-stent late lumen loss (LLL) at 8 months. Twenty patients with 20 lesions were treated with TIGERevolutioN®. At 8 months, in-stent LLL was 0.7 ± 0.4 mm. On OCT, percent area stenosis was 29.2 ± 9.4% and stent strut coverage was complete in all lesions. No adverse cardiovascular event occurred at 8 months. The new polymer-free EES was safe and effective with low LLL and excellent strut coverage at 8 months of follow-up. Trial Registration: Clinical Research Information Service Identifier: KCT0005699.

Effect of Metal Surface Treatment on Bonding of Porcelain to Recycled Cobalt Chromium and Nickel Chromium

Effect of Metal Surface Treatment on Bonding of Porcelain to Recycled Cobalt Chromium and Nickel Chromium

Effect of vitamin E–enhanced highly cross-linked polyethylene on wear rate and particle debris in anatomic total shoulder arthroplasty: a biomechanical comparison to ultrahigh-molecular-weight polyethylene

Particle-induced osteolysis resulting from polyethylene wear remains a source of implant failure in anatomic total shoulder designs. Modern polyethylene components are irradiated in an oxygen-free environment to induce cross-linking, but reducing the resulting free radicals with melting or heat annealing can compromise the component's mechanical properties. Vitamin E has been introduced as an adjuvant to thermal treatments. Anatomic shoulder arthroplasty models with a ceramic head component have demonstrated that vitamin E-enhanced polyethylene show improved wear compared with highly cross-linked polyethylene (HXLPE). This study aimed to assess the biomechanical wear properties and particle size characteristics of a novel vitamin E-enhanced highly cross-linked polyethylene (VEXPE) glenoid compared to a conventional ultrahigh-molecular-weight polyethylene (UHMWPE) glenoid against a cobalt chromium molybdenum (CoCrMo) head component. Biomechanical wear testing was performed to compare the VEXPE glenoid to UHMWPE glenoid with regard to pristine polyethylene wear and abrasive endurance against a polished CoCrMo alloy humeral head in an anatomic shoulder wear-simulation model. Cumulative mass loss (milligrams) was recorded, and wear rate calculated (milligrams per megacycle [Mc]). Under pristine wear conditions, particle analysis was performed, and functional biologic activity (FBA) was calculated to estimate particle debris osteolytic potential. In addition, 95% confidence intervals for all testing conditions were calculated. The average pristine wear rate was statistically significantly lower for the VEXPE glenoid compared with the HXLPE glenoid (0.81 ± 0.64 mg/Mc vs. 7.00 ± 0.45 mg/Mc) (P<.05). Under abrasive wear conditions, the VEXPE glenoid had a statistically significant lower average wear rate compared with the UHMWPE glenoid comparator device (18.93 ± 5.80 mg/Mc vs. 40.47 ± 2.63 mg/Mc) (P<.05). The VEXPE glenoid demonstrated a statistically significant improvement in FBA compared with the HXLPE glenoid (0.21 ± 0.21 vs. 1.54 ± 0.49 (P<.05). A newanatomic glenoid component with VEXPE demonstrated significantly improved pristine and abrasive wear properties with lower osteolytic particle debris potential compared with a conventional UHMWPE glenoid component. Vitamin E-enhanced polyethylene shows early promise in shoulder arthroplasty components. Long-term clinical and radiographic investigation needs to be performed to verify if these biomechanical wear properties translate to diminished long-term wear, osteolysis, and loosening.

Enhanced corrosion resistance of CoCrMo by laser-based surface modification

Biomedical grade cobalt–chromium–molybdenum (CoCrMo) alloys are extensively used for load-bearing biomedical applications such as hip and knee implants due to their exceptional biocompatible and biomechanical properties. However, the strain-induced martensite ε-phase development during contact loading results in thin oxide layers that are prone to fracture leading to corrosion. The formation of thin oxide layers is undesirable for long-term deployment. We employed laser-texturing to enhance the corrosion resistance of the material in simulated body fluid by the formation of hcp ε-phase martensite and via the formation of oxide layers. However, partial formation of hcp ε-phase martensite was observed. By means of central composite design-based response surface methodology, three laser parameters such as average laser power, texture density and the number of passes were optimised for maximal open circuit potential, an indicator for minimal corrosion. The textured surfaces were found to assist in the cellular proliferation of fibroblasts and inhibit bacterial growth.

Impact of Milled Peek versus Conventional Chrome Cobalt Framework on Retention of Definitive Obturators for Unilateral Total Maxillectomy Patients

Impact of Milled Peek versus Conventional Chrome Cobalt Framework on Retention of Definitive Obturators for Unilateral Total Maxillectomy Patients

Evaluation of environmental pollution by heavy metals in the waters of Al-Ezz River north of Basra

This study was conducted on the Al-Ezz River in the Al-Qurna district, north of Basra city, seasonally from Autumn 2022 to summer 2023 at five stations along the river. The purpose of the study was to assess the river's pollution and determine the highest concentrations of certain heavy elements in its water (Cobalt Co, Cadmium Cd, Manganese Mn, Zinc Zn, Iron Fe, Chrome Cr, Lead Pb, and Copper Cu). The highest concentrations of these elements were (0.095, 0.238, 0.323, 1.461, 1.592, 2.801, 8.015, 695.423) mg/l respectively, while the lowest concentrations of heavy elements were (Co=Not Detected, Fe= Not Detected, Mn= Not Detected, Cd=0.010, Zn= 0.033,Pb= 0.062, Cr= 0.129) mg/l. The strongest correlation is between lead and iron (r=0.99). Cadmium shows a positive correlation (r=0.97) with chrome, while copper has a positive correlation (r=0.97) with cobalt. There is a strong positive correlation between iron (r=0.99) and manganese, as well as between manganese (r=0.99) and iron. Zinc also exhibits a positive correlation (r=0.99) with cobalt, and chrome (r=0.98) shows a positive correlation with cadmium and cobalt (r=0.99) with zinc.

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.

A risk-based decision making framework to analyze the properties of cobalt–chromium alloys

In this study, the properties of cobalt–chromium alloys are systematically prioritized to aid in the minimization of orthopedic implant failures and risks in biomedical applications. Within the model, six main groups (including a total of 31 properties) are defined: economic aspects, design and production properties, mechanical properties, physical properties, chemical properties and biological properties. A risk-based fuzzy decision making framework is proposed for prioritization. First, a risk-management decision matrix is created by employing interval type-2 fuzzy failure modes and effects analysis. Afterward, the properties of cobalt–chromium alloys are analyzed by utilizing interval type-2 fuzzy measurement of alternatives and ranking according to compromise solution. In the last phase, a prediction model is devised with an adaptive network fuzzy inference system to save computational time and effort and to enable the incorporation of new scientific results into the biomaterial evaluation process. The results of the current study demonstrate that compatibility, osseointegration, corrosion resistance, fatigue resistance and time-dependent deformation are the top five properties contributing to potential orthopedic implant failures and risks. Furthermore, the developed model produces very satisfactory results with acceptable deviations. Consequently, this study presents a new and reliable guide for the unbiased evaluation of cobalt–chromium alloys.

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.

Patient Satisfaction and Oral Health–Related Quality of Life for Single - Implant Mandibular Overdentures reinforced by Cobalt Chromium or PEEK Framework versus Conventional Complete Denture: A Crossover Trial.

Patient Satisfaction and Oral Health–Related Quality of Life for Single - Implant Mandibular Overdentures reinforced by Cobalt Chromium or PEEK Framework versus Conventional Complete Denture: A Crossover Trial.

Oxygen-Bridged Cobalt-Chromium Atomic Pair in MOF-Derived Cobalt Phosphide Networks as Efficient Active Sites Enabling Synergistic Electrocatalytic Water Splitting in Alkaline Media.

Electrochemical water splitting offers a most promising pathway for "green hydrogen" generation. Even so, it remains a struggle to improve the electrocatalytic performance of non-noble metal catalysts, especially bifunctional electrocatalysts. Herein, aiming to accelerate the hydrogen and oxygen evolution reactions, an oxygen-bridged cobalt-chromium (Co-O-Cr) dual-sites catalyst anchored on cobalt phosphide synthesized through MOF-mediation are proposed. By utilizing the filling characteristics of 3d orbitals and modulated local electronic structure of the catalytic active site, the well-designed catalyst requires only an external voltage of 1.53V to deliver the current density of 20mAcm-2 during the process of water splitting apart from the superb HER and OER activity with a low overpotential of 87 and 203mV at a current density of 10mAcm-2 , respectively. Moreover, density functional theory (DFT) calculations are utilized to unravel mechanistic investigations, including the accelerated adsorption and dissociation process of H2 O on the Co-O-Cr moiety surface, the down-shifted d-band center, a lowered energy barrier for the OER and so on. This work offers a design direction for optimizing catalytic activity toward energy conversion.

AN INVESTIGATION ON MICROSTRUCTURES, MECHANICAL AND WEAR BEHAVIOR OF LASER-CLADDED INCONEL 625 AND NIMONIC 90 OVER NIMONIC 90 SUBSTRATE

The wrought nickel–chromium–cobalt Nimonic 90 alloy is widely used in turbine blades, piston rings and forged tools due to their high stress-rupture strength and creep resistance up to 920∘C. The application components showed unavoidable wear behaviors at high loads due to the reduced resistance of the components. Hence, in order to increase the wear resistance of this alloy, Inconel 625 and Nimonic 90 particle depositions have been carried out on Nimonic 90 substrate through the laser-cladding techniques to study the microstructure, mechanical and tribological behaviors of alloys. The phases, microstructure and microhardness of the claddings were investigated by X-ray diffractometry (XRD), Transmission electron microscopy (TEM), Scanning electron microscope (SEM), Energy-dispersive X-ray spectroscopy (EDS) and hardness test, respectively. Results showed that the mean thickness of the interfacial layer of Inconel 625 and Nimonic 90 was 18.51 ± 4 [Formula: see text]m and 90.68 ± 7 [Formula: see text]m, respectively. The microstructure of the cladding surfaces resulted in dendritic and interdendritic structures. An overall analysis found that the gamma-Ni and hard laves phases were presented in Inconel 625 and Nimonic 90 clad surfaces, respectively. Nimonic 90 clad surface had a high hardness and wear resistance compared with Inconel 625 clad surface and substrate due to the present hard laves phase. Besides, the roughness of the Nimonic 90 clad surface was lower compared with the Inconel 625 clad surface and substrate.

Treatment of Distal Extension Edentulous Arches with Attachment Retained Cobalt Chromium Partial Dentures-A Case Report

Background: The awareness and demand for quality of dental treatment is relatively increasing in recent generation and more so, as far as aesthetics are concerned, along with other functions of the prosthesis. In treating partially edentulous mouth, it requires more attention, principally for esthetics, in design. While achieving the goal, the components which are incorporated in removable partial denture may result in unsightly appearance. Case Description: A 77 year old patient reported to the replacement of his missing teeth for which a conventional maxillary complete denture and cast removable partial denture with precision attachments were planned to construct. Extra coronal resilient attachment was planned to re-claim support and thereby regain of lost esthetics in the mandibular arch. Conclusion: Use of precision attachment has amplified the aspects of retention and particularly, esthetics when compared to conventional removable partial dentures.

Large head metal-on-metal bearing surface with a TMZF titanium alloy femoral stem with high rates of revision and trunnion failure

BackgroundMechanically assisted crevice corrosion at the head-neck interface puts implants at risk of trunnionosis, femoral head dissociation, implant failure and the development of metallosis. Metal-on-Metal bearings have very low wear rates, significantly lower than metal-on-polytethylene, but their wear results in cobalt and chromium ion systemic distribution. This is a study of the MITCH metal-on-metal bearing surface coupled with an Accolade TMZF stem. MethodsThis was a retrospective review of 24 total hip replacements 21 patients in that underwent MITCH TRH/Accolade TMZF implantation at a minimum of 12 years post operatively. The primary outcome of this study was all-cause revision with particular attention to revision due to trunnion failure and/or cobalt and chromium ion level. ResultsThere was a revision rate of 66.7 % (n = 16) at a minimum of twelve years post operatively. Most notably there were six revisions for a gross trunnion failure. Two cases were revised for impending trunnion failure. There were seven cases revised for elevated serum cobalt and chromium levels and one was revised for unexplained pain. DiscussionPatients in our study that underwent TMZF alloy cementless stems coupled with large cobalt chromium alloy heads are at high risk of catastrophic trunnion failure. The high rate of trunnnionosis in this implant combination is thought to be related to a significantly different Young's modulus due to a material mismatch coupled with galvanic corrosion.

Abstract 17002: Platelet-Derived Purified Exosome Product to Treat In-Stent Restenosis Porcine Model

Introduction: Patients with coronary artery disease (CAD) not amenable to revascularization are reported to have a 3-year mortality &gt;14%. Advances in treatment modalities including medical management, rotational atherectomy, balloon lithotripsy, and drug-eluting stents work for focal disease but poorly treat diffuse CAD. In a porcine model of in-stent restenosis, we here evaluated whether a pro-angiogenic platelet-derived exosome product (PEP) could be delivered into the perivascular space to foster collateral vessel formation. Methods/Results: Cobalt chromium stents were placed and were oversized by 1 mm in the left anterior descending (LAD) and posterior descending arteries (PDA) of sus scrofa domesticus pigs. In-stent restenosis was angiographically visualized at the 2-month timepoint, with hemodynamic significance documented with fractional flow reserve (FFR) of &lt;0.8. To document feasibility of PEP delivery into the perivascular space, exosomes were labeled with a far-red fluorescent tag and delivered into the perivascular bed. Here, the Bullfrog® micro-infusion catheter was positioned either in the great cardiac vein or the middle cardiac vein and PEP was delivered with the microneedle pointed towards the LAD or the PDA. Biodistribution demonstrated exosome retention and uptake around cardiac veins. Using the Bullfrog® technique, PEP was delivered in the perivascular space adjacent to areas of significant coronary stenosis. Initial results 1-month post-treatment demonstrated improved FFR of treated stenotic vessels (from 0.68 to 0.85), while untreated vessels demonstrate no change from previous FFR measurement (from 0.79 to 0.78). Conclusions: Here, exosome-mediated angiogenesis in the perivascular space improved coronary blood flow, distal to areas of stenosis. In patients with diffuse CAD, delivery of biotherapy in cardiac veins running anatomically parallel to stenosed epicardial arteries provides a novel therapeutic opportunity to supplement the existing armamentarium of therapies available for in-stent restenosis.

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.

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.