Solidification of Be-free Ni-based dental alloy

A novel, Nb- and Si-rich and Be-free Ni-based alloy was cast by two methods of investment casting and continuouscasting to study the microstructure evolution during solidification and its mechanical properties. The solidification of the alloy startedwith the primary crystallization of FCC-γ, followed by a binary eutectic reaction, with the formation of a heterogeneous constituent：FCC-γ＋G-phase, which replaced the low-melting eutectic （FCC-γ＋NiBe） in the Be-bearing alloys. AlNi6Si3 and γ′ formed during theterminal stages of solidification by investment casting, while the formation of AlNi6Si3 was suppressed by continuous casting. TheScheil solidification model agreed very well with the experimental results.

Electron Probe Microanalysis of Exogenous Pigmentation of Oral Mucosa Originating from Dental Alloy: Two Case Reports

Pigmentation of the oral mucosa is relatively common and has a wide variety of etiologies. Although most pigmented lesions of the oral mucosa are associated with deposition of melanin and accidental displacement of a dental alloy, accurate differential diagnosis of a pigmented lesion is important, especially in the case of malignant melanoma. We report two cases of oral mucosal pigmentation associated with accidental displacement of a dental alloy in which malignant melanoma was suspected. Excisional biopsy was carried out in these cases with the incision line set at approximately 5 mm from the lesions. Histopathologically, brownish foreign substances were observed in the lamina propria. Metal quantitative analyses of the extracted specimens were carried out by electron probe microanalysis (EPMA). The metal components and the mass concentration revealed that the metals were derived from a dental casting silver alloy in Case 1 and from a gold-silver palladium alloy in Case 2. Although exogenous pigmentation originating from a dental alloy is not rare, differential diagnosis of oral pigmented lesions is sometimes very difficult. In such cases, histopathological examination may be necessary for the diagnosis to exclude melanocytic lesions and EPMA may be effective to identify the causative dental alloy.

Preliminary Study on Some Properties of Co-Cr Dental Alloy Formed by Selective Laser Melting Technique

The surface condition, some properties and ion releasing behavior of cobalt-chromium （Co-Cr） dental alloy formed by selective laser melting （SLM） technique were investigated. Before porcelain fused firing, the surface condition of the Co-Cr alloy was observed using a scanning electron microscope （SEM）, and then the density and hardness were examined. After porcelain fused firing, the interface of porcelain and alloy was observed, and then the metal-ion release of the samples was tested. SLM technique provides Co-Cr alloy higher hardness than casting method. After degassing-oxidation procedure and porcelain fused firing, the interface of the alloy and porcelain showed excellent combination. Co ion was more than Cr ion released from SLM Co-Cr alloy, the amounts of Co and Cr ions were safe according to ISO security criterion. Considering the properties before and after porcelain fused sintering process, SLM technique is suitable for dental Co-Cr alloy restoration.

An analytical method for quantitative estimation of the cytotoxicity of dental alloys

An analytical method for quantitative estimation of the cytotoxicity of dental alloys is introduced. After the TC50 values of 9 metal cations of various dental casting alloys were established using the MTT assay and the concentrations of the corosively dissolved metal cations in the alloy extracts were measured by means of an ICP method. The cytotoxicity of dental alloys is induced as a function of the TC50 values and concentrations. The validity of the method is testified, by comparing the effective cytotoxicity of 19 dental alloys with those obtained directly by using MTT assay.

An analytical method for quantitative estimation of the cytotoxicity of dental alloys using MTT assay,ICP analysis and effective cytotoxicity calculation

The two most important criteria for dental materials are their biofunctional and biocompatible endurance within the anticipated life-span of the dental restoration in the mouth. Biocompatibility relates mainly to the allergenicity and the toxicity of the material. To test the non-specific toxicity of dental materials, in vitro cell culture assays have been developed. For in vitro screening, such tests are recommended to check the cytotoxicity of dental materials (ISO 10993 5). Various studies have already been performed to quantitatively determine the cytotoxicity level of dental alloys. However, as long as only dental alloys and the cell culture technique are applied, it is not possible to determine which of the alloying elements cause the cytotoxicity. Therefore, an analytical method is needed. Wataha et al determined in 1991 the TC50 values of 9 metal cations of various dental casting alloys, using cell culture methods. Kapert et al reported in 1994 a complex in vitro test concept, where the ICP analysis (inductively coupled plasma emission spectroscopy) was introduced to measure the trace elements extracted from various alloys. Experimentelle Zahnheilkunde, Universitts ZMK Klinik Freiburg, Germany (Lü XY and Kappert HF) The aim of the present study was to find a relation between the ICP results, the TC50 value of metal cations, and the cytotoxicity of dental alloys. The cytotoxicity levels of various dental alloys and the TC50 values of 10 metal cations were established using the MTT assay, an effective cell culture of method. Then, the concentrations of the corrosively soluted metal cations in the extracts of the alloys were measured using the ICP method. From all these experimental results it was found that the relation between the effective cytotoxicity Z eff of an alloy, the concentrations C i of i th trace element and the TC50 values T Ci of the i th metal cation can approximately be expressed by Z eff =∑iC i2·T Ci . Two significant applications of this expression are a) The cytotoxicity of an alloy can be estimated by ICP analysis of the extract if the TC50 values of the trace elements are know. b) The cytotoxicity of a new-developed-alloy can be estimated in advance, according to the alloying components.

Urinary levels of nickel and chromium associated with dental restoration by nickel-chromium based alloys

This paper aims to investigate if the dental restoration of nickel-chromium based alloy(Ni-Cr) leads to the enhanced excretions of Ni and Cr in urine.Seven hundred and ninety-five patients in a dental hospital had single or multiple Ni-Cr alloy restoration recently and 198 controls were recruited to collect information on dental restoration by questionnaire and clinical examination.Urinary concentrations of Ni and Cr from each subject were measure by graphite furnace atomic absorption spectrometry.Compared to the control group,the urinary level of Ni was significantly higher in the patient group of < 1 month of the restoration duration,among which higher Ni excretions were found in those with either a higher number of teeth replaced by dental alloys or a higher index of metal crown not covered with the porcelain.Urinary levels of Cr were significantly higher in the three patient groups of <1,1 to <3 and 3 to <6 months,especially in those with a higher metal crown exposure index.Linear curve estimations showed better relationships between urinary Ni and Cr in patients within 6-month groups.Our data suggested significant increased excretions of urinary Ni and Cr after dental restoration.Potential short- and long-term effects of Ni-Cr alloy restoration need to be investigated.

Microstructure and dry wear properties of Ti-Nb alloys for dental prostheses

The microstructure and properties of a series of binary Ti-Nb alloys for dental prostheses with niobium contents ranging from 5% to 20% were investigated. The experimental results indicate that the crystal structure and morphology of Ti-Nb alloys are sensitive to their niobium contents. When Nb content is 5%, the acicular α crystal grain is observed. When Nb content is 10%, the coarse equiaxed crystal grain and the fine, acicular α crystal grain are observed. When Nb content is 15%, only the α equiaxed crystal grain is observed. When the alloy contains 20%Nb, the equiaxed and dendritic α crystal grain are observed. For Ti-Nb alloys, the increase of Nb content modifies the microstructure of Ti-Nb alloys significantly and decreases their compression elastic modulus, in which Ti-20Nb alloy shows the largest compression strength and Ti-5Nb alloy shows the best plasticity. The dry wear resistance of Ti-Nb alloys against Gr15 ball was investigated on CJS111A ball-disk wear instrument. For Ti-Nb alloys, Ti-10Nb alloy shows a smallest steady friction coefficient, Ti-5Nb alloy shows the smallest wear depth and best wear resistance, and Ti-15Nb alloy shows the largest wear depth and worst wear resistance. The phenomenon of furrow cut happens and furrows form during wear tests.

Electrochemical behavior of Co-Cr and Ni-Cr dental cast alloys

The cast structures influencing the electrochemical corrosion behavior of Co-Cr and Ni-Cr dental alloys were studied using potentiodynamic polarization and AC impedance in 0.9% (mass fraction) NaCl solution at (37±1) ℃. The phase and microstructure of the alloys that were fabricated using two different casting methods viz. centrifugal casting and high frequency induction casting, were examined using X-ray diffraction analysis, scanning electron microscopy and energy dispersive spectroscopy. The roles of alloying elements and the passive film homogeneity on the corrosion resistance of Co-Cr-Mo and Ni-Cr-Mo dental cast alloys were reviewed. The results of electrochemical study show that the dependence of corrosion resistance on the microstructure associated with the casting methods is marginal. The Co-Cr alloy exhibits more desirable corrosion resistance properties than the Ni-Cr alloy. There is severe preferential dissolution of Ni-rich, Cr and Mo depleted zones in the Ni-Cr alloy.

Corrosion behaviours of the dental magnetic keeper complexes made by different alloys and methods

The keeper and cast dowel-coping, as a primary component for a magnetic attachment, is easily subjected to corrosion in a wet environment, such as the oral cavity, which contains electrolyte-rich saliva, complex microflora and chewing behaviour and so on. The objective of this in vitro study was to examine the corrosion resistance of a dowel and coping-keeper complex fabricated by finish keeper and three alloys （cobalt-chromium, CoCr; silver-palladium-gold, PdAu; gold-platinum, AuPt） using a laser- welding process and a casting technique. The surface morphology characteristics and microstructures of the samples were examined by means of metallographic microscope and scanning electron microscope （SEM）. Energy-dispersive spectroscopy （EDS） with SEM provided elements analysis information for the test samples after 10% oxalic acid solution etching test. Tafel polarization curve recordings demonstrated parameter values indicating corrosion of the samples when subjected to electrochemical testing. This study has suggested that massive oxides are attached to the surface of the CoCr-keeper complex but not to the AuPt-keeper complex. Only the keeper area of cast CoCr-keeper complex displayed obvious intergranular corrosion and changes in the Fe and Co elements, Both cast and laser-welded AuPt-keeper complexes had the highest free corrosion potential, followed by the PdAu-keeper complex. We concluded that although the corrosion resistance of the CoCr-keeper complex was worst, the keeper surface passive film was actually preserved to its maximum extent. The laser-welded CoCr- and PdAu-keeper complexes possessed superior corrosion resistance as compared with their cast specimens, but no significant difference was found between the cast and laser-welded AuPt-keeper complexes. The Fe-poor and Cr-rich band, appearing on the edge of the keeper when casting, has been proven to be a corrosion-prone area.

Surface and Subsurface Defects Studies of Dental Alloys Exposed to Sandblasting

The defects created in commercial dental alloys during blasting with alumina particles propelled in compressed air under pressure 0.1 and 0.4 MPa have been studied using positron annihilation spectroscopy, scanning electron microscopy and X-ray diffraction. It was observed that higher pressure causes the increase in roughness and damaged zone range. The type of defects was determined as vacancies on dislocations. The defect concentration decreases with the depth and depends on alloys' type and applied pressure. The Rutherford backscattering spectroscopy and variable energy positron beam studies indicate shallow alumina deposition in material and show that small pressure of 0.1 MPa is not enough to remove metal surface oxides completely in 60 s in all studied dental alloys.

Influence of Ni and Cr Content on Corrosion Resistance of Ni-Cr-Mo Alloys for Fixed Dental Prostheses in 0.05% NaF Aqueous Solution

The Ni-Cr-Mo alloys have been used as dental prostheses because they own a good mechanical strength, high corrosion resistance and even to be economically viable. These alloys corrosion protection against in salt solutions typical of physiological media is due to passivation phenomenon with an oxide surface layer formation, mainly chromium oxides. This protective film, subjected to a mechanical stress in a corrosive environment, can partially dissolve by releasing ions, which have deleterious effects in a human body. Fluoride ions, existing in hygiene products, change the buccal environment and their presence may enable a localized corrosion process initiation. The aim of this work has been to investigate the chemical composition influence of three alloys in corrosion resistance to: A (Ni-73% Cr-14% Mo-8.5% Be-1.8% Al-1.8%), B (Ni-61% Cr-25% Mo-10.5% Si-1.5%) and C (Ni-65% Cr-22.5% Mo-9.5%) in media containing fluorides that simulate mouthwashes solution. The study has been done in a 0.05% NaF solution, pH 6, at 37°C using electrochemical techniques. The alloy with the highest nickel and the lowest chromium content is not passive in the middle studied, showing a continuous increase in current density with the potential increasing, while the other alloys show passivation range of 600 mV and passive current density of about 10-6 A/cm2.

Study on the Effect of Dental Metal Alloys on the Histamine Liberation of Blood Basophiles in Vitro

Biomaterials for restoration or replacement of diseased tissues may have any origin.The major characteristic for biomaterials is biocompatibility.All biomaterials,used in medicine (dentistry,in particular),interreact with the organism tissues.And the changes occur both in the materials and the organism tissues.It is considered that there are no "inert biomaterials." The number of allergic diseases and complications is constantly growing all over the world,taking an important place in the structure of infectious and noninfectious pathology[1].Pollen,household,epidermal,and food-borne allergens,and haptens are the most frequent sources of sensibilization.

Estimation of the Patients'Adaptation to Noble Alloy Dentures Relying on the Parameters of Biological Fluids in Oral Cavities

For the study of the effect of Plagodent and Palladent noble alloy dentures (OJSC "SIC 'Supermetal'", Russia), the elemental compositions of the fluids obtained from gingival sulcus of abutment teeth of metal ceramic dentures with frames made of the above-stated dental alloys, have been investigated. Response of white blood cells and fibroblasts in the gingival fluid and the mixed saliva of the patients a long time after prosthetic repair, relying on the content of proinflammatory interleukins IL-1 β and IL-6, anti-inflammatory interleukins IL-4 and IL-10, the factor of tumor necrosis TNF-α and lactoferrin, has been investigated. The results obtained have convincingly proved the biosafety of the Plagodent and Palladent noble alloys.

Effect of hydrogen peroxide concentration on surface properties of Ni-Cr alloys

The effect of concentration of hydrogen peroxide （H2O2） on the surface properties of Ni-Cr alloys was studied. Surface roughness and surface morphology of Ni-Cr alloys were evaluated by surface profiler and scanning electron microscopy after being immersed in different concentrations of H2O2 for 112 h. Surface corrosion products of Ni-Cr alloys were analyzed by photoelectron spectrograph after being immersed in 0% and 30% H2O2. The order of increasing surface roughness of Ni-Cr alloys after being immersed in different concentrations of H2O2 was 0〈3.6%〈10%〈30%. As the concentration of hydrogen peroxide increased, the surface roughness of Ni-Cr alloys increased and the surface morphology showed different degrees of corrosion. According to the XPS results, the corrosion products formed on the outmost surface layer of the studied samples are Ni（OH）2 and BeO.

Nanostructure and corrosion behaviors of nanotube formed Ti-Zr alloy

In order to investigate the nanostructures and corrosion behaviors of Ti-Zr alloys,nanotube formed Ti-Zr(10%,20%,30% and 40% in mass fraction) alloys were prepared by arc melting and the condition of controlling nanostructure was at 1 000 ℃ for 24 h in argon atmosphere;formation of nanotubes was conducted by anodizing a Ti-Zr alloy in H3PO4 electrolyte with a small amount of fluoride ions at room temperature.The corrosion properties of specimens were examined through potentiodynamic test(potential range of -1 500-2 000 mV) in 0.9% NaCl solution by using potentiostat.Microstructures of the alloys were observed by optical microscope(OM),field emission scanning electron microscope(FE-SEM) and X-ray diffractometer(XRD).Diameter of nanotube does not depend on Zr content,but interspace of nanotube predominantly depends on Zr content,which confirms that ZrO2 oxides play a role to increase the interspace of nanotube formed on the surface.

Analysis of Deformation in Ni-Cr Structures with New and Recast Alloys

The present study analyzed new and recast Ni-Cr alloys, regarding the relationship between the applied force and the deformation in cantilevered bar segments, with dimensions of 4.0 mm, 3.5 mm, 3.0 mm in thickness, 4.5 mm width and 15 mm length, on a universal testing machine “EMIC”. The bars in the tests were initially obtained acrylic resin by 4.8 mm wide × 4.3 mm thick × 4 cm long. We obtained 30 bars divided into two groups, with 15 to test new alloys and 15 with alloys recast. The alloy used was Tilite. For the application of the load, the bars were attached to “EMIC” where the active tip of 200 kgf load cell was at a specific point of the bar (15 mm) with a speed of 0.5 mm per minute. The data showed statistically significant differences in relation to alloys and thickness among the bars, and all thicknesses evaluated were different. Thus, it was concluded that there was statistically significant difference between the groups and their variables, and that the alloys recast could be reused at least 1 time, without loss of properties.

含稀土氧化物的WC-TiC-TaC-Co/CuZnNi复合耐磨堆焊材料

以WC-TiC-TaC-Co硬质合金、CuZnNi及氧化物La2O3为原料,研制出一种具有高耐磨性和良好抗冲击性能的堆焊材料,利用SEM、TEM、摩擦磨损试验分析了堆焊材料的组织及耐磨性,探讨了稀土氧化物对堆焊材料组织性能的影响.研究结果表明:硬质合金与Cu基合金通过元素扩散形成连接界面;堆焊层耐磨性随硬质合金含量的增加而增加,随载荷的增加而降低;加入La2O3后,基体组织细化,硬质合金与基体的界面上形成微晶过渡区,改善了界面结合强度,堆焊层耐磨性得到提高.

Osteoblast integration of dental implant materials after challenge by sub-gingival pathogens: a co-culture study in vitro

Sub-gingival anaerobic pathogens can colonize an implant surface to compromise osseointegration of dental implants once the soft tissue seal around the neck of an implant is broken. In vitro evaluations of implant materials are usually done in monoculture studies involving either tissue integration or bacterial colonization. Co-culture models, in which tissue cells and bacteria battle simultaneously for estate on an implant surface, have been demonstrated to provide a better in vitro mimic of the clinical situation. Here we aim to compare the surface coverage by U2OS osteoblasts cells prior to and after challenge by two anaerobic sub-gingival pathogens in a co-culture model on differently modified titanium （Ti）, titanium-zirconium （TiZr） alloys and zirconia surfaces. Monoculture studies with either U2OS osteoblasts or bacteria were also carried out and indicated significant differences in biofilm formation between the implant materials, but interactions with U2OS osteoblasts were favourable on all materials. Adhering U2OS osteoblasts cells, however, were significantly more displaced from differently modified Ti surfaces by challenging sub-gingival pathogens than from TiZr alloys and zirconia variants. Combined with previous work employing a co-culture model consisting of human gingival fibroblasts and supra-gingival oral bacteria, results point to a different material selection to stimulate the formation of a soft tissue seal as compared to preservation of osseointegration under the unsterile conditions of the oral cavity.

Microstructure and wear properties of YT758/CuZnNi hardfacing materials

Hardfacing materials containing YT758 hardmetal particles cemented by Cu-based alloy was deposited on the substrate to produce milling tools by oxy-acetylene flame process. Microstructure and wear properties of the hardfacing layers were analyzed by scanning electron microscopy(SEM) and electron dispersion X-ray spectroscopy(EDXS) and wear test. The results show that inter-diffusion zone is found at the interface of YT758/CuZnNi, which promises to improve the bonding strength of YT758/CuZnNi. The wear resistance of YT758/CuZnNi hardfacing layers is higher than that of YG8/CuZnNi hardfacing layers. The working efficiency of the milling tools strengthened by YT758/CuZnNi is approximately 23 times higher than that strengthened by YG8/CuZnNi.

Synthesis of Co-Cr-Mo Fluorapatite Nano-Composite Coatings by Pulsed Laser Deposition for Dental Applications

Aim: The study was to fabricate FA nanopowder/Co-Cr-Mo dental alloy nanocomposite using pulsed laser deposition (PLD), and to evaluate bioactivity properties on simulated body fluid. Methods: In this work, the FA nanopowder was prepared by mixing calcium hydroxide (Ca(OH)2), phosphorouspent oxide (P2O5) and calcium fluoride (CaF2) in a planetary high energy ball mill using zirconium vial. Fluorapatite (FA) nanopowder was processed in the form of pellet for pulsed laser deposition process. The Co-Cr-Mo alloy was coated with FA nanopowder which was approximately 35 - 65 nm at various laser energy, pressure and time. The X-ray diffraction (XRD) was used to analyze phase, crystallinity and size distribution of Co-Cr-Mo/FA nanocomposite. The surface analysis was by scanning electron microscopy (SEM), Atomic Force microscopy (AFM) and Energy dispersive spectroscopy (EDS). Results: From the results obtained, It was shown that FA nanopowder deposited on Co-Cr-Mo alloy was stable during 14 days of incubation on simulated body fluid. It was also observed that the FA nanopowder coated on the surface of the alloy was still intact after the deposition process, which indicated the bioactivity and biocompatibility of the material. Conclusions: The fabrication of FA nanocomposite based dental alloys (Co-Cr-Mo) using PLD was done successfully. This was confirmed by various characterization techniques, which included XRD, AFM, SEM and EDS.