Nickel-chromium Dental Alloys Research Articles

Electrochemical behavior of TiN, CrN and TiN/CrN nanostructured coatings on the nickel-chromium alloy used in dental fixed prosthesis

ABSTRACT The aim of this research is the evaluation of the influence of TiN, CrN and TiN/CrN nanostructured coatings on corrosion resistance of nickel-chromium dental alloy in artificial saliva environment with two pH levels (3.0 and 6.5). Nickel-chromium alloy tested in this study were more resistant to corrosion in artificial saliva conditioning media when coated with different types of coating materials, as compared to uncoated alloy. The electrochemical measurements propose that the alloy with CrN coating has shown a high corrosion resistance in different pH levels. The superior passivation of CrN monolayer coating in modified Fusayama artificial saliva solution may be concluded from two essential factors, passive range, and corrosion current density. The passive range is well-developed, while the corrosion current density is much lower if compared to the other groups. Also, the Nyquist and polarization plots reveal that TiN, CrN and TiN/CrN nanostructured coatings have an excellent corrosion resistance which is considered much higher if compared to the substrate. The values of corrosion current density for CrN nanostructured coating in artificial saliva environment with two pH levels of 3.0 and 6.5 were 1.373 × 10−8 and 5.416 × 10−8 A.cm−2, respectively that were the lowest corrosion current density values among the other samples.

Tribological properties of different types of coating materials deposited by cathodic arc-evaporation method on Ni-Cr dental alloy

Wear can be regarded as one of the most essential factors in determining as well as controlling the long-term clinical performance of a metallic biomaterial, also nano-indentation is one of the most precise ways of comparing and determining the mechanical properties of restorative materials. This paper is simply considered as a report of how the tribological wear properties and nano-indention of uncoated and coated nickel chromium dental alloy are examined. Tests were undertaken in the study on the following coating materials: TiN/CrN multilayer, and TiN, CrN monolayer. The tribological tests were performed in artificial saliva so that wear factor and the friction coefficient can be determined. After that, scanning electron microscope (SEM) can help ascertaining the traces of wear. The results show that wear rate and friction coefficient of coated samples (TiN, CrN, and TiN/CrN) were lower than those of uncoated dental alloy (0.448, 0.339, 0.43, and 0.705) respectively, while hardness values for TiN-monolayer (25.378 GPa), CrN-monolayer (22.138 GPa), and TiN/CrN-multilayer (28.54 GPa) of coated samples were higher than those of uncoated dental alloy (4.24 GPa) respectively.

EDX analyisis of metal-ceramic interfaces of recasted nickel-chromium dental alloys

This research was performed to establish recasting effects of nickel-chromium dental alloys on the composition of their metal-ceramic interface in making fixed partial dentures. The metal-ceramic interface determines denture functional integrity and prevents damages on ceramics during mastication. Recycling of nickel-chromium alloys is often a practice, without detailed knowledge about possible effects on the composition of the metal-ceramic interface. Investigation of metal-ceramic samples is intended to show if base metal alloys for metal-ceramics are successfully recycled without any composition change in the metal-ceramic interface. The research was performed as an experimental study in which six metal-ceramic samples of nickel-chromium alloy ?Wiron 99? (Bego, Germany) were made. Alloy residues were recycled through twelve casting generations with the addition of 50 wt% of the new alloy on the occasion of every recasting. EDX analysis was performed by using the ?Inca X Sight? apparatus (Oxford Instruments, UK) and a SEM device JSM 6460 LV (JEOL, Japan). This appliance was used in conjunction with the PC software for quantification of chemical elements in order to determine the composition of metal-ceramic interfaces. Results of this research revealed significant differences between compositions of metal-ceramic interfaces in every examined recycle generation. Recasting had a negative effect on alloy components, which concentration is decreasing in the metal-ceramic junction zone. The concentration of cerium in the intermediate phase decreased the most, followed by concentrations of niobium, molybdenum, nickel and chromium. Results showed a permanent reduction of metal components up to the 12th generation of recycling. Cerium concentration (wt%) decreased from 28 to 16.26 %, nickel concentration from 3.31 to 1.82 % and chromium concentration from 2.95 to 2.03 %. Similarly, the molybdenum content decreased from 8.71to 4.68 wt%, while that of niobium from 9.82 to 3.97 wt%. Therefore, recasting of nickel-chromium alloys is not recommended because of changed composition of the metal-ceramic interface of these alloys.

Assessment of corrosion resistance of cast cobalt- and nickel-chromium dental alloys in acidic environments

The aim of this study was to compare the degradation resistance of nickel-chromium (Ni-Cr) and cobalt-chromium (Co-Cr) alloys used as a base material for partial dentures in contact with saliva. Wiron® 99 and Wironit Extra-Hard® were selected as representative casting alloys for Ni-Cr and Co-Cr alloys, respectively. The alloys were tested in contact with deionized water, artificial saliva and acidified artificial saliva. Material characterization was performed by X-ray diffractometry (XRD) and microhardness and nanohardness testing. The corrosion properties of the materials were then analyzed using open circuit potential analysis and potentiodynamic analysis. Alloy leaching in solution was assessed by inductively coupled plasma mass spectrometry techniques. Co-Cr alloy was more stable than the Ni-Cr alloy in all solutions tested. Leaching of nickel and corrosion attack was higher in Ni-Cr alloy in artificial saliva compared with the acidified saliva. The corrosion resistance of the Co-Cr alloy was seen to be superior to that of the Ni-Cr alloy, with the former exhibiting a lower corrosion current in all test solutions. Microstructural topographical changes were observed for Ni-Cr alloy in contact with artificial saliva. The Ni-Cr alloy exhibited microstructural changes and lower corrosion resistance in artificial saliva. The acidic changes did not enhance the alloy degradation. Ni-Cr alloys are unstable in solution and leach nickel. Co-Cr alloys should be preferred for clinical use.

XPS and electrochemical impedance spectroscopy studies on effects of the porcelain firing process on surface and corrosion properties of two nickel–chromium dental alloys

The aim of this study was to evaluate the effects of a simulated porcelain firing process on the surface, corrosion behavior and cell culture response of two nickel-chromium (Ni-Cr) dental alloys. A Be-free alloy and a Be-containing alloy were tested. Before porcelain firing, as-cast specimens were examined for surface composition using X-ray photoelectron spectroscopy and metallurgical phases using X-ray diffraction. Corrosion behaviors were evaluated using electrochemical impedance spectroscopy. 3T3 fibroblasts were cultured and exposed indirectly to specimens. MTT assays were counted after 3 and 6 days. The cell culture mediums exposed to specimens were analyzed for metal ion release. After porcelain firing, similar specimens were examined for the same properties. In both as-cast and fired conditions, the Be-free Ni-Cr alloy showed significantly more resistance to corrosion than the Be-containing Ni-Cr alloy, which exhibited BeNi phase. After porcelain firing, the corrosion resistance of the Be-free Ni-Cr alloy decreased statistically, corresponding with evident decreases of Cr and Ni oxides on the alloy surface. Also, the alloy's MTT assay decreased significantly corresponding with an obvious increase of Ni-ion release after the firing. For the Be-containing Ni-Cr alloy, the firing process led to increases of surface oxides and metallic Be, while its corrosion resistance and cell culture response were not significantly changed after porcelain firing. The results suggested that the corrosion resistance and biocompatibility of the Be-free Ni-Cr alloy decreased after porcelain firing, whereas the firing process had little effect on the same properties of the Be-containing Ni-Cr alloy.

Influence of different power outputs of intraoral Nd:YAG laser on shear bond strength of a resin cement to nickel–chromium dental alloy

Up to now, there is no any experience about the application of dental lasers to bond resin composites to metal surfaces in dentistry. The aim of this preliminary study was to evaluate if the laser irradiation of ceramic-covered alloy surface would improve the bond strength of resin to metal, and if different parameters of laser output may influence the strength of this bond. Fifty three cylinders (thickness of 5 mm and diameter of 10 mm) were made up of a commercially available nickel-chromium alloy by lost-wax technique. Forty prepared specimens were divided into four groups. Five specimens in each group were covered by slurry of dental opaque porcelain and irradiated by Nd:YAG laser using different output parameters for each group. Other five specimens in each group were treated using the same laser parameters without porcelain covering. Five sandblasted specimen served as control group. Panavia F2.0 was bonded on the metal surfaces using polyethylene tubes. In ceramic-coated specimens, silane was applied to achieve chemical bond between silica particles and resin cement. All specimens were thermocycled and subjected to shear bond strength (SBS) test (50 kgf at 0.5 mm/min). Two specimens of each ceramic-coated laser-treated groups were studied using scanning electron microscopy and wavelength dispersive X-ray spectroscopy which showed stabilization of silica particles on the metal surface. ANOVA procedure showed that although shear bond strength was significantly higher in porcelain-covered laser treated samples, but the effect of power output of laser irradiation was not significant (P = 0.917). There were no statistically significant difference between SBS in control samples and laser treated specimens without porcelain covering. It can be concluded that Nd:YAG laser surface treatment may improve the silica coating of alloy surface to achieve better resin-metal bond.

In Vitro Evaluation of Shear Bond Strength and Mode of Failure of the Interface between an Indirect Composite Bonded to Fiber‐Reinforced Composite Substructures

Failures of fixed partial dentures (FPDs) fabricated with fiber-reinforced composites (FRCs) have been attributed to veneering fractures. The aim of the present study was to investigate the shear bond strength and mode of failure between an indirect composite and FRC substructures. SR Adoro indirect composite was bonded to the following substructures: (a) flat surface made of unidirectional glass fibers (group A), (b) retentive sticks made of unidirectional glass fibers (group B), (c) flat surface made of fiber net (group C), (d) retentive sticks made of fiber net (group D), (e) nickel-chromium dental alloy (control, group E). For every group, 13 specimens were fabricated. All specimens were hydrothermocycled (5000 cycles, 5°C/30 sec, and 55°C/30 sec). A bond test was performed in a testing machine at a 0.5 mm/min crosshead speed according to ISO 10477. The failure mode was determined by examination of the fractured surfaces under an optical microscope. Selected specimens were examined with scanning electron microscope and with energy dispersive spectroscopy for compositional determination. The morphology (flat-sticks) and the type (unidirectional-net) of fibers on the bond strength were estimated. The mean shear bond strength was significantly different between groups E and A (p= 0.044), and groups A and B (p= 0.010). All FRC specimens showed cohesive failure. Group E showed predominantly adhesive failure. The bond strength was higher when sticks or fiber nets were used. Fiber nets and retentive sticks increase the shear bond strength between FRCs and indirect composite. In FPDs, the morphology and type of FRC substructures might influence the shear bond strength between the FRC substructure and the indirect veneering composite. With the proper design of these substructures, the number of veneering fractures may be decreased.

Evaluation of mechanical properties and porcelain bonded strength of nickel–chromium dental alloy fabricated by laser rapid forming

The aim was to evaluate the mechanical properties and porcelain bonded strength of nickel-chromium (Ni-Cr) dental alloy fabricated by laser rapid forming (LRF). The tensile properties and porcelain bonded strengths of LRF Ni-Cr dental alloy were evaluated by tensile tests (five specimens per group) and three-point bending tests (ten specimens per group). The same tests for the cast Ni-Cr dental alloy were used as for the control. The microstructure and the bonding interface of the metal substrate to porcelain were analyzed by optical microscopy (OM), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The tensile strength of LRF Ni-Cr dental alloy (840 MPa) was superior to that of the cast Ni-Cr alloy (670 MPa), but the ductility had decreased. The porcelain bonded strength of LRF Ni-Cr dental alloy was 44.7 MPa, which was also superior to that of the cast Ni-Cr dental alloy (41.6 MPa). According to analysis by Student's t-test, the porcelain bonded strengths of the Ni-Cr dental alloy presented statistically significant differences between the groups of LRF and cast alloy (P < 0.05), but the porcelain bonded strengths were all above the acceptable value required by the International Organization for Standardization (ISO) standard 9693 (25 MPa). The coefficient of thermal expansion (CTE, mean value of five specimens) of LRF Ni-Cr dental alloy (14 x 10(-6) degrees C(-1)) was higher than that (13.7 x 10(-6) degrees C(-1)) of the cast Ni-Cr dental alloy. Both LRF and cast Ni-Cr dental alloy had positive Deltaalpha, not exceeding the maximum difference (1 x 10(-6) degrees C(-1)) in CTE. SEM and EDS results showed that all the specimens measured for porcelain bonded strength and prepared from the LRF and cast Ni-Cr alloy exhibited a mixed mode of cohesive and adhesive failure. Evaluation of the mechanical properties and porcelain bonded strengths of LRF Ni-Cr alloy revealed that both superior tensile and porcelain bonded properties can be obtained. With improvement of the technique, it is hoped that the LRF Ni-Cr dental alloy could be a good alternative to the conventional cast Ni-Cr dental alloy in the future.

Effects of metallic ion toxicity on human gingival fibroblasts morphology.

Alloys used as implant materials release metal ions to surrounding tissues. Cytotoxic substances attack at the molecular level, and these effects are reflected in the structure of the cells and organelles. The objective of this study was to evaluate the cellular morphology and ultrastructural changes of cultured human gingival fibroblasts to salt solutions of ions (beryllium (Be+2), chromium (Cr+6 and Cr+3), nickel (Ni+2), molybdenum (Mo+6)) which may be released from nickel-chromium dental alloys. The concentrations chosen were based on previously conducted cell culture studies. Fibroblasts were exposed to the different ion concentrations for 24 or 72 h. Cellular morphology and ultrastructural features were examined using scanning electron microscopy and transmission electron microscopy. Ultrastructural alterations observed included irregular shaped nuclei for cells exposed to hexavalent chromium and nickel, pseudopodia for cells exposed to beryllium and molybdenum, and lipid droplet formation in cells exposed to nickel.

Raman investigation of crevice corrosion in nickel-chromium dental alloys containing beryllium

The presence of the small amounts of Be which are often added to the Inconel-type NiCrMo dental alloys to improve their castability leads to a dramatic increase of the corrosion processes in the presence of chlorides, with the formation of deep pits full of corrosion products. In this kind of alloys, crevice formation is normally unexpected and it is important to check whether Be is also able to promote crevice development. We showed that the metallurgical heterogeneities of these alloys, which are industrially used as-cast, are responsible for the tremendous increase of localized corrosion. We have proposed a simple configuration to simulate a crevice and to identify by Raman spectroscopy (RS) the corrosion products which are liable to appear, in order to characterize their differences with the products found in pits. This analysis is completed by results obtained using X-rays energy dispersive analysis (XEDS). A growth of spinels to the prejudice of the salts (molybdates, chromates) which are usually found in the pits is observed.

Cellular Response to Metallic Ions Released from Nickel-Chromium Dental Alloys

Concerns exist over the potential release of elevated levels of metal ions such as Ni and Be from Ni-Cr dental casting alloys, due to their susceptibility to accelerated corrosion. In this investigation, we evaluated the release of metal ions from four commercial Ni-Cr alloys, representing a range of compositions, in three-day cell culture tests. Metal ion release, as measured by atomic absorption spectroscopy, was correlated to changes in cellular morphology, viability, and proliferation. The results showed that the test alloys and their corrosion products did not affect cellular morphology or viabilities, but did decrease cellular proliferation. The types and amounts of metal ions released, which corresponded to the alloys' reported surface and corrosion properties, also correlated to observed decreases in cellular proliferation after 72 h. Neptune, which caused the smallest decrease in cellular proliferation as compared with control cells, released the lowest amount of corrosion products, due to its corrosion-resistant, high-Cr-Mo-containing, homogeneous surface oxide. The other test alloys, which were susceptible to accelerated corrosion processes, released higher levels of metal ions that correlated to larger decreases in thymidine incorporation. Metal ion levels increased with test time for all alloys but were not proportional to bulk alloy compositions. Ni ions were released at slightly higher than bulk alloy compositions, while Be was released at from four to six times that of bulk alloy compositions. The elevated release of Be ions was associated with reduced cellular proliferation.(ABSTRACT TRUNCATED AT 250 WORDS)

Surface analysis of nickel-chromium dental alloys

In this study, the surface compositions of four commercially available nickel-chromium alloys, Neptune, Rexalloy, Regalloy T, and Vera Bond, were compared and corelated to the alloys' corrosion behavior. The alloys were chosen to be representative of alloys with acceptable and unacceptable Cr levels, with and without Be additions. The results showed that the non-Be-containing alloys exhibited a homogeneous CrMo oxide surface which resulted in more corrosion resistant alloys. The Be-containing alloys were shown to have non-uniform oxide surfaces. Areas on the surfaces of these alloys were low in Cr and O and enriched in Be. The oxide surfaces of these alloys were more easily disrupted and provided little resistance to accelerated corrosion processes. Thus, it was found that not only were the Cr and Mo content of the alloys important for corrosion resistance, but the composition of the surface oxide as well.

The effect of beryllium on the corrosion resistance of nickel-chromium dental alloys

Base-metal alloys of the nickel-chromium system are widely applied in fixed prosthodontics. The principal purpose of the addition of beryllium is to increase the fluidity of the Ni-Cr alloy during melting and increase the castability. In this study the effects of beryllium addition, by weight percentages of 0.5, 1.0 and 2.0, respectively, on the microstructure and corrosion resistance of seven Ni-Cr-based and NP2-based dental alloys were examined in Ringer's solution at 37°C. The experimental results indicate that addition of beryllium has a very significant effect on lowering the pitting potentials, open-circuit potentials, passive-film resistances and, on the contrary, increasing the passive-film capacitances. The presence of beryllium greatly reduces the thickness of the passive film and makes the corrosion resistance worse. This effect is more pronounced for NP2-based dental alloys. Examination of the corroded surfaces reveals that it is the Ni-Be eutectic phase being preferentially attacked.