Non-precious Dental Alloys Research Articles

An innovative method for in-situ composition analysis of fixed metallic dental restorations

Dental restorations made from alloys corrode during their service time. In cases of suspected toxic or allergic reactions to the corrosion products, the composition of the intraoral dental restorations has to be determined. The sample materials can be obtained intra-orally in a non-destructive manner using the chipping test. Metallic shavings are extracted with the aid of a dental stone and graphite carrier platelet, which is then transferred to an electron microscope for electro dispersive X-ray (EDX) analysis. The chipping test suffers from a rather complicated and error-prone procedure of obtaining and transferring the samples. ObjectiveThe objective of the present study was the validation of a simplified method for non-destructive in-situ extraction of dental alloy samples, using a newly developed dental bur made from carbon fiber reinforced polyether ether ketone (PEEK), which at the same time serves as an electrically conductive sample carrier for EDX analysis. MethodsFifteen burs for dental hand pieces were manufactured from carbon fiber reinforced PEEK, using two formulations. The burs were passed over precious and non-precious dental alloys with different rotation speeds. The alloy samples embedded in the burs were analyzed using EDX and compared to a control. ResultsThe burs manufactured from PEEK containing 30% short carbon fibers proved sufficiently robust for sample extraction even from the harder non-precious metals. The results of EDX analysis were in accordance with the control,no statistical significant differences, free of contamination, and were not affected by rotation speed,higher as 20%. SignificanceThe proposed method is valid, practical and constitutes an improvement over the traditional chipping test.

The metallurgical characteristics of non-precious alloys using Nd:YAG laser welding.

BackgroundThis study aimed to determine the effect of hardness change according to penetration depth in the laser fusing zone and observed the correlation of the microstructure as an Nd:YAG laser was irradiated to Ni-Cr alloy for dental use by setting the spot diameter size with respect to defocusing distances. In all groups, the hardness depth profiles in the laser fusing zone and heat-affecteded zone (HAZ) had larger values than those of the base metal. In addition, the hardness values in places beyond the fusing zone and the HAZ were measured as being quantitatively lower.MethodsThe alloys used in this study were Verabond 2 V, Noritake Super, and Bellabond Plus, which are commercially used non-precious dental alloys. The specimens were cut to have a plate shape with a size of 0.5 × 3.0 × 2.5 mm. This was followed by setting the Nd:YAG laser output, pulse duration, and frequency to 60 W, 10 ms, and 5 Hz, respectively. The laser was then irradiated as the spot diameter condition varied between 0.5 mm and 1.4 mm in accordance with defocusing distance from 0.0 mm to 2.0 mm. After the laser irradiation, a cross-section of the fusing zone in the specimens was observed in terms of laser melted depth, hardness depth profile, and the microstructure of each alloy.ResultsThe observation result of the diffusion of the constituent elements and microstructure using field emission scanning electron microscopy, energy dispersive spectroscopy (EDS), and electron probe micro-analyzer showed that the fusing zone revealed a much finer dendritic form than the base metal due to the self-quenching effect after laser melting, while no change in constituent elements was found although some evaporation of the main elements was observed.ConclusionsThese results suggest that each Mo and Si combined inter-metallic compounds were formed on the interdendritic area. Through this study, the laser fusing zone had better hardenability due to the inter-metallic compound and grain refinement effect.

Mechanical Behaviour of CoCrMo Alloy with Si Content

. The paper present aspects about the obtaining of non-precious dental alloys (type CoCrMo and CoCrMoSi7), the determination of chemical composition by optical emission spectrometry and the experimental tests for determining the tensile strength, made on standard plate samples. The base material used in experiments was a commercial alloy, from CoCrMo system, which belongs to the class of dental non-precious alloys, intended to medical applications. The obtaining of studied alloy was made on arc re-melting installation, under vacuum, type MRF ABJ 900. The process followed to realize a rapid melting, with a maximum admissible current intensity. The samples for tests were obtained by casting in an electric arc furnace, under vacuum, in optimal conditions for melting and solidification and processing by electro-erosion, to eliminate all the disturbing factors which come by processing conditions for the samples. The determination of chemical composition for cobalt based alloys, by optical emission spectrometry, was made on SpectromaxX equipment with spark. The electrical discharge is made with the elimination of an energy quantity, fact which determine plasma forming and light issue. Tensile tests for standard samples, made from cobalt based alloy, was made on Instron 3382 testing machine, and assisted by computer. The obtained results are: elongation, elasticity modulus, tensile strength and offer complete information about the analyzed mechanical properties. For the certitude of obtained experimental results, the tests were made on samples with specific dimensions according ISO 6892-1:2009(E) standard, both for the tensile strength, and also machine operation.

The Effect of Mucine, IgA, Urea, and Lysozyme on the Corrosion Behavior of Various Non-precious Dental Alloys and Pure Titanium in Artificial Saliva

The corrosion of dental alloys has biological, functional, and aesthetic consequences. Various studies have shown that protein solutions can inhibit the corrosion of alloys. This study is planned to determine the relationship of organic constituents of saliva and the corrosion of dental alloys. The organic constituents are IgA, mucine, urea, and lysozyme which are encountered in the highest amounts in saliva and the dental materials are titanium (Ti), Co-Cr-Mo and Ni-Cr-Mo alloys, and dental amalgam, the most often used metallic components in dentistry. In particular, the interactions between the commonest salivary proteins, IgA, mucine, urea and lysozyme, and Ti, Co-Cr-Mo, Ni-Cr-Mo and dental amalgam were investigated. Each alloy was evaluated by cyclic polarization in each medium. The general anodic and cathodic behavior during forward and reverse cycles, the corrosion and passivation current densities (muA/cm2 ), and the corrosion and the pitting potentials (mV) were determined. The results have shown that Ni-Cr-Mo and dental amalgam alloys are highly susceptible to corrosion in all the investigated media. The Co-Cr-Mo alloy has shown high passive current densities in the solution of mucine and lysozyme in artificial saliva. Titanium instead, has shown a high resistance to corrosion and a stable passive behavior in all media, especially in a solution of mucine and IgA in synthetic saliva. Mucine and IgA, as well as urea and lysozyme, appeared to enhance the formation of a passive film layer on the Ti metal surface, thus inhibiting the corrosion. Based on the study findings, and especially considering the problem of nickel allergy and toxicity of mercury released from dental amalgam, the use of Co-Cr-Mo alloys and Ti to Ni-Cr-Mo alloys is recommended and alternatives to dental amalgam should be sought for patients with impaired salivary flow.

Hardness, Behavior and Metal Surface Evaluation of Recasting Non-Precious Dental Alloys

Recasting of economic alloys can change several properties. The number of recasting was found to have negligible effect on surface texture and on the amount of corrosion products released. The methods and equipments utilized in the casting of an alloy are important on the quality of casting. Carbon incorporated in a noble or economic alloy during casting is known to affect the mechanical values of the metal. In the present study we aimed to investigate the change in structure and metal hardness due to recasting. Materials and method: The effect of recasting, up to four times of a non precious “Finalloy” commercial dental alloy on their Rocwell C hardness behavior and their microstructures was inspected. Using “Kerr casting waxes” patterns were prepared similar to the samples from “Finalloy”. The investments were pre-heated to phase at temperatures between 900°C and 1000°C. The alloy was melted by an acetylene-oxygen flame in a silicate crucible and four groups were compared: New alloy and alloys casted two, three, and four times (n = 7). After casting, Brinell harnesses were recorded. Values of Rocwell C strength, for each specimen group were analyzed by one-way analysis of variance, followed by the Student- Newman-Keuls multiple range test. A metal microscope was used to evaluate the surface morphology of the samples before hardness tests. 1st Casting :30.65 ± 0.3 kgf, 2nd Casting: 31.33 ± 0.4 kgf, 3rd Casting:34.80 ± 0.3 kgf, 4th Casting: 35.5 ± 28 kgf represents the Rocwell hardness of the castings. The results showed that hardness, increased with repeated castings. The experimental data indicates that increasing the number of successive recasting of “Finalloy” enhances the Rocwell C hardness, thus, after remelting and recasting, the biological properties decreases. Microscope study: Increase of the carbon content on the gren bounders of a cobalt-chromium alloy causes a considerable change in its microstructure. The hardness and yield point for 0.05 %, 0.1 % and 0.2 % tensile strength and elongation were determined for these test-pieces. The results showed that hardness, yield points and tensile strength increased with increased carbon content, whereas the elongation lessened. We determined that carbon concentrated at gren bounders. The clinical importance of the study is that recasting affected the properties of the metal, for best biological results with dental alloys always new metals must be used.

Electrochemical behavior of non-precious dental alloys in bleaching agents

Corrosion behavior of dental alloys in artificial saliva containing different concentrations of hydrogen peroxide, carbamide peroxide and fluoride ions was studied using electrochemical technique. The alloys have been arranged according to its corrosion resistance in the hydrogen peroxide and carbamide peroxide as follows: wiron99 > wirolloy > wironit. Alloys suffer less corrosion rates in presence of carbamide peroxide than hydrogen peroxide. The effect of CH 6N 2O 3 on the corrosion is less than the effect of H 2O 2 and this is due to the presence of centers rich by electrons such as nitrogen and oxygen in CH 6N 2O 3. Nitrogen and oxygen adsorbed on the alloy surface forming protective layer isolate it relatively from the corrosive medium. The order of increasing resistivity of the alloys in fluoride solution is as follows: wironit > wiron99 > wirolloy. SEM for the three alloys in artificial saliva containing 0.015 M F − shows that wironit has less corrosion compared to the two other alloys and this agrees with the results obtained from potentiodynamic polarization curves and Nyquist impedance diagrams.

Electrochemical behaviour of recasting Ni–Cr and Co–Cr non-precious dental alloys

Corrosion behaviour of dental alloys in artificial saliva was studied using different chemical and electrochemical techniques. The order of corrosion rate for the three alloys in artificial saliva is: wironit < wirolloy < wiron99. This order agrees with the results of chemical studies for determining the cumulative ion concentration using ICP/MS. The open-circuit potential of wirolloy is more positive than wiron99. The higher corrosion rate of wiron99 compared to wirolloy is due to presence of high concentration of Mo. Increasing casting number leads to decrease R ct value and increasing C dl.

Effect of hydrophobicity on in vitro streptococcal adhesion to dental alloys.

Non-specific interactions such as electrostatic interactions, and surface free energy are of importance in bacterial adhesion to dental surfaces as they determine whether or not bacteria are attracted to the surface. The relationship between adherence of Streptococcus mitis, S. mutans, S. oralis and S. sanguinis on precious and non-precious dental alloys, and the bacterial and alloy surface hydrophobicities (a measure of the surface free energy) was studied. The number of adhering bacteria was determined by fluorescence microscopy counts. The hydrophobicity of the bacteria and alloy surfaces were evaluated by adhesion to hexadecane and water contact angles, respectively. Our results showed that (i) the surfaces of the tested alloys were hydrophobic, (ii) S. sanguinis, S. mutans and S. oralis were hydrophobic, and (iii) S. mitis was hydrophilic. S. oralis, the more hydrophobic strain, demonstrated the highest adherence on the tested materials, whereas S. mitis adhered least on the hydrophobic surfaces. For the tested alloys, bacterial adherence was highest for the high gold content alloy, and lowest for the non-precious alloy. Our results showed that for the tested bacterial strains, there was a significant correlation between bacterial adhesion and substratum hydrophobicity: hydrophobic metal surfaces favor adhesion of hydrophobic bacteria.

Release and detection of dental corrosion products in vivo: Development of an experimental model in rabbits

An experimental animal model was developed to investigate the release of metal ions from nonprecious dental alloys. Cast specimens of five Ni-Cr-alloys and Co-Cr-alloys were implanted intramuscularly in rabbits for periods of 2, 4, 8, and 12 weeks. The concentrations of nickel, chromium, cobalt, and molybdenum in the implant-loaded muscles were determined by electrothermal atomic absorption spectrometry (AAS) and neutron activation analysis (NAA). Reference muscle samples of each animal were analyzed to determine the individual control values. Significant increases in the tissue concentrations of these metals occurred in the immediate vicinity of the implants. Concentration gradients of the corrosion products were found between the implant contact tissue and the implant periphery (p less than 0.001). Tissue concentrations of nickel and chromium correlated (r less than 0.7). Microprobe analysis before and after implantation of the alloy specimens indicated an even corrosive loss of the alloy surfaces and changes in the surface element distributions. Advantages and limitations of this animal model are discussed, as well as its application in future studies.

Corrosion rate studies: measurements of corrosion rates of some non-precious dental alloys in artificial saliva.

Abstract The corrosion rates of dental alloys and of stainless steel have been quantitatively measured in aerated artificial saliva by the linear polarization method at room temperature (≈ 20°C), and at 37°C and 50°C.

Dental implications of nickel hypersensitivity

T he rising cost of gold and precious metals has been instrumental in the development of nonprecious alloys in dentistry, including many nonprecious alloys that contain nickel. In recent years, nickel hypersensitivity in humans has been of growing concern among dentists. Contact with nickel by susceptible individuals may produce a spectrum of hypersensitive reactions. Dermatitis and urticaria, the primary manifestations of nickel hypersensitivity, may be found in the area of contact as well as distant from the nickel source.‘s2 Urticaria and dermatitis of the hands, neck, and eyelids are commonly reported hypersensitive reactions to nickel.’ Nickel is a known carcinogen and nickel ions are released from nickel-containing alloys in the oral environment.3a4 It is not known, however, whether the release of nickel ions from dental alloys is high enough to be clinically significant. If so, as a result of the potential alteration in endocrine functions, changes in vital functions such as blood pressure, pulse, and temperature might be expected. Nickel-containing alloys have been linked to a decrease in the number of T-lymphocytes in humans.4 Normal immune function depends on a balance of T4 helper lymphocytes that label foreign cells and microorganisms and T8 suppressor lymphocytes that prevent white blood cells from affecting normal cells.4B 5-8 Indeed, metal allergies from dental alloys have been implicated as a possible cause of the oral lesions of lichen planus.” Nickel contact dermatitis is commonly observed, with some references claiming as high as a 28% positivity in nickel sulfate patch tests among the general population.” The incidence of nickel allergy is higher in women (31.9%), presumably because of sensitization from nickel-containing jewelry. lo With increased use of nickel in nonprecious dental alloys, it would be logical to expect

Microstructures in Non-precious Alloys Near the Porcelain-Metal Interaction Zone

The chemistry of microstructures near the interfacial reaction zones of four non-precious alloys and two different brands of dental porcelain has been analyzed. It was found that most non-precious dental alloys contain second phases which can alter elemental concentration profiles. Recommendations for assessing interfacial reaction zone chemistry in dental non-precious alloys are offered.