The effects of recasting on the cytotoxicity of base metal alloys

Limitations of reuse for silver-palladium alloys -Evaluating post-recasting heat treatment impact on corrosion resistance

The aim of this study was to investigate the effect of repeated casting and heat treatment on the corrosion resistance of a commercial Ag-Pd-Cu-Au alloy as evaluated by electrochemical techniques. After repeated casting, the fifth cast of the Ag-Pd-Cu-Au alloy exhibited dramatic degradation of properties, although upon heat treatment, this corrosion resistance did improve. Despite the improvement by heat treatment, after five castings, this alloy may not have satisfactory hardness for clinical use. These results of this study demonstrate that, up to the fourth cast and heat treatment, the Ag-Pd-Cu-Au alloy has acceptable corrosion resistance and hardness.

Investigation of optical and biocompatible properties of polyethylene glycol-aspirin loaded commercial pure titanium for cardiovascular device applications

This research investigates the optical and biocompatible properties of alkali-treated cpTi immersed in aspirin and different molecular weights of polyethylene (PEG). Instrumental characterizations were performed using scanning electron microscopy (SEM), Raman spectroscopy, and ultraviolet–visible spectroscopy. Additionally, drug release, antithrombotic, and cell adhesion studies were conducted in in-vitro conditions. The SEM micrographs showed that heat treatment of NaOH modified cpTi substrates increased the average surface pore size by 217%. Raman spectra’s active modes confirmed the presence of titanate groups which intensified the semiconductive nature of alkali-treated cpTi substrates. Further, the semiconductive nature was confirmed through the shift of the energy bandgap from 2.69 to 2.9 eV. The continuous redshift of the absorbance edge with an increase in the molecular weight of PEG indicates improved optical property. Following the Rigter–Peppas dynamic model, the drug release kinetics showed a non-Fickian dispersion (n < 1) and super case II transport (n = 2.21) for PEG-coated cpTi substrates. The alkali-treated cpTi-aspirin-PEG surface exhibits suitable antithrombotic property and interstitial cell adhesion with PEG coating. The modified surface on cpTi demonstrated a promising technique to improve the optical, antithrombotic, and biocompatibility performances, which are the prime requirement for the blood-interacted cardiovascular devices such as stents.

A Comparative Electrochemical and Morphological Investigation on the Behavior of NiCr and CoCr Dental Alloys at Various Temperatures

The purpose of our study is to compare the behavior of two reprocessed dental alloys (NiCr and CoCr) at different temperatures considering the idea that food and drinks in the oral cavity create various compositions at different pH levels; the novelty is the investigation of temperature effect on corrosion parameters and ion release of dental alloys. Electrochemical stability was studied together with morphology, elemental composition and ions release determination. The results obtained are in good concordance: electrochemistry studies reveal that the corrosion rate is increasing by increasing the temperature. From SEM coupled with EDS, the oxide film formed on the surface of the alloys is stable at low temperatures and a trend to break after 310K. ICP-MS results evidence that in accordance with increasing temperature, the quantities of ions released from the alloys immersed in artificial saliva also increase, though they still remain small, less than 20 ppm.

The effects of recasting on the cytotoxicity of dental base metal casting alloys

Aim and Objectives

In dentistry, base metal casting alloys are extensively used for the fabrication of inlays, onlays, crowns, bridges, partial dentures, etc. During the casting of these alloys, excess amount of material used than needed will be collected as sprue buttons at the end, which is either added to the fresh alloy during casting and reused or disposed of.

Materials and Methods

The aim of the present in vitro experimental study was to investigate the effect of the complete recasting of four commercially available cobalt-chromium (Co-Cr) and nickel-chromium (Ni-Cr) base metal casting alloys on their cytotoxicity. During the study, four groups of alloys were subjected to complete recasting up to twenty times without the addition of new alloy. The cytotoxicity assessment of the selected alloys after recasting (Co-Cr and Ni-Cr alloys) was carried out using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay.

Results

The results indicated that Co-Cr alloys exhibit superior cell viability compared to Ni-Cr alloys, and cytotoxic potential of the alloys increased with repeated casting and led to increased cell death. The recasting of alloys in the present study did not show high cytotoxicity even after the 20^th recasting.

Conclusion

From the results of the present study, it can be concluded that the alloys generated as a waste in the dental laboratory can be safely reused up to five times or at least once before they can be disposed, which reduces the cost of the treatment and also helps in conserving the natural resources.

Effect of Shot Peening on the Mechanical Properties and Cytotoxicity Behaviour of Titanium Implants Produced by 3D Printing Technology

Structural discontinuities characterize the implants produced directly from metal powders in 3D printing technology. Mainly, the surface defects should be subjected to procedures associated with surface layer modification (likewise shot peening) resulting in the increase of the implant service life maintaining optimal biocompatibility. Therefore, the purpose of the present study was to investigate the effect of type of shot used for the peening process on the Ti-6Al-4V implants functional properties as well as the biological properties. The components were produced by DMLS (direct metal laser sintering) additive technology. The surfaces of titanium specimens have been subjected to the shot peening process by means of three different shots, i.e., CrNi steel shot, crushed nut shells, and ceramic balls shot. Then, the specimens have been subjected to profilometric analysis, microhardness tests, and static strength testing as well as to the assessment of biocompatibility in respect of cytotoxicity using human BJ fibroblasts. The shot peening process causes the strengthening of surface layer and the increase of strength parameters. Furthermore, the test results indicate good biocompatibility of surfaces being tested, and the effect of shot peening process on the titanium alloy cytotoxicity is acceptable. At the same time, most favourable behaviour in respect of cytotoxicity has been found in the case of surfaces modified by means of ceramic balls > nut shells > CrNi steel shot correspondingly.

Effect of addition of recast materials on characteristics of Ni-Cr-Mo alloys

The purpose of this study was to assess the effect on selected mechanical properties, of adding recast materials to the NiCrMo alloy of newly produced castings.

Three groups of dental alloy NiCrMo (trade named Remanium CS+) were prepared by mixing 50% new alloy to alloy remnants from previous castings. The specimens in the first casting group used 100% new alloy and served as control (C1). The second group consisted of equal amounts of new alloy and alloy remnants cast only once (C2). The third group contained 50% of new alloy and alloy cast twice (C3). Microstructural analysis was performed and the chemical composition, hardness and the metal-ceramic bond strength were assessed. In addition, EDS analysis (mapping) was undertaken. Hardness and bond strength results were also statistically analysed.

In spite of the fact that recasting brought about small changes in hardness and chemical composition (C, Cr and Mo), these effects were found to not affect their functional properties in the oral cavity. Still, significant differences between new alloy and the recasted groups (p < 0.05) were demonstrated in the course of statistical analysis of Vickers hardness test (for α = 0.05). All analysed research groups have a similar average adhesion at 48.51÷49.24 MPa (p > 0.05).

The recasting procedure described in the paper can be done safely in dentistry. If previously casted material is used, it should be mixed with new material. The use of the material prepared in this way can lower the costs of NiCrMo castings.

Effect of Recasting on Physical Properties of Base Metal Alloys: An In Vitro Study

Aims and Objectives

This study aims to establish the outcome of recasting on tensile strength, modulus of elasticity, and hardness of Nickel-chromium alloys.

Materials and Methods

Fifty wax patterns were fabricated, using the lost wax technique, the measurements of which were standardized. They were categorized into five groups of ten each. Group I included samples casted with new alloy alone. Group II samples consisted of 75% new alloy and 25% once casted alloy. Group III was casted with 50% of each. Group IV with 25% new metal and 75% previous alloy and samples of Group V samples were casted with once casted alloy alone. Modulus of elasticity and tensile strength were measured by universal testing machine, whereas hardness using microhardness tester. The values were statistically analysed. IBM Corp. Released 2011. IBM SPSS Statistics for Windows, Version 20.0. IBM Corp, Armonk, NY, USA. for Windows software was used for analysis.

Results

We found a slight variation in mean tensile strength and modulus of elasticity, which was statistically insignificant variation among the groups. However, there was a significant difference in mean hardness between Groups III, IV, and V.

Conclusion

It is prudent to use pure alloy alone for casting. However, in view of environment and economical factors, addition of <50% reused alloy to pure alloy is satisfactory clinically.

Corrosion behavior and cytocompatibility of a Co–Cr and two Ni–Cr dental alloys before and after the pretreatment with a biological saline solution

Objectives. The aim of this study was to evaluate the corrosion behavior and cytocompatibility of a Co–Cr and two Ni–Cr dental alloys before and after the pretreatment with a biological saline solution.

Technological features of metal-ceramic prosthesis frameworks manufactured from domestic alloys of precious and base metals

The aim of the study was to examine changes in physical and mechanical properties of dental alloys depending of the initial composition at re-casting. Russianc precious alloys: Plagodent (AuPtPd) and Palladent (PdAu) and base alloys: Vitiriy-N (NiCrMo) and Vitiriy-C (CoCrMo) were used as study samples, which were divided in three groups: a primary casting from the granules; 50% of re-casting; 100% of re-casting. We investigated the yield strength in bending, coefficient of thermal expansion and hardness. Changing in the composition of the alloys has led to changes of all physical and mechanical properties.

In vitro cytotoxicity of metallic ions released from dental alloys

The cytotoxicity of a dental alloy depends on, but is not limited to, the extent of its corrosion behavior. Individual ions may have effects on cell viability that are different from metals interacting within the alloy structure. We aimed to investigate the cytotoxicity of individual metal ions in concentrations similar to those reported to be released from Pd-based dental alloys on mouse fibroblast cells. Metal salts were used to prepare seven solutions (concentration range 100 ppm-1 ppb) of the transition metals, such as Ni(II), Pd(II), Cu(II), and Ag(I), and the metals, such as Ga(III), In(III), and Sn(II). Cytotoxicity on mouse fibroblasts L929 was evaluated using the MTT assay. Ni, Cu, and Ag are cytotoxic at 10 ppm, Pd and Ga at 100 ppm. Sn and In were not able to induce cytotoxicity at the tested concentrations. Transition metals were able to induce cytotoxic effects in concentrations similar to those reported to be released from Pd-based dental alloys. Ni, Cu, and Ag were the most cytotoxic followed by Pd and Ga; Sn and In were not cytotoxic. Cytotoxic reactions might be considered in the etiopathogenesis of clinically observed local adverse reactions.

Treatment of multiple ceramic alloys before recasting

STATEMENT OF PROBLEM

Dental laboratories often reuse dental casting alloys by recasting them, but the processing methods before recasting require further research.

PURPOSE

The purpose of the study was to determine the treatment methods to remove the surface contamination of the previously melted alloys before recasting.

MATERIAL AND METHODS

Cobalt-chromium (Co-Cr), commercially pure titanium (CP Ti), palladium-copper-gallium (Pd-Cu-Ga), and gold-platinum (Au-Pt) ceramic alloys were investigated in the present study. Field emission scanning electron microscopy, energy-dispersive x-ray spectroscopy (EDAX), and x-ray photoelectron spectroscopy (XPS) were used to evaluate the changes in the surface structures and compositions of Co-Cr, CP Ti, Pd-Cu-Ga, and Au-Pt ceramic alloys after airborne-particle abrasion and immersion in various chemical solutions for different time periods. The data obtained by EDAX and XPS were statistically analyzed by Kruskal-Wallis and Nemenyi tests (α=.05).

RESULTS

By using appropriate mechanical and chemical treatment procedures, the contamination content of previously cast ceramic alloys was found to be below the detection limits of EDAX and XPS. The statistical results showed that, compared to the control group (new alloys after polishing), the impurity element was not detected after being treated with these methods, which was not statistically different to control group.

CONCLUSIONS

The surface contamination of ceramic alloys was effectively removed by using certain mechanical and/or chemical treatment methods. Within the limitations of the present study, the most appropriate ways to treat ceramic alloys before recasting were as follows: (1) for Co-Cr ceramic alloys: Al2O3 airborne-particle abrasion and immersion in aqua regia for 15 min; (2) for CP Ti ceramic alloys: Al2O3 airborne-particle abrasion and immersion in 65% HNO3 and 40% HF 1:7 (V/V) for 60 min; (3) for Pd-Cu-Ga ceramic alloys: glass bead airborne-particle abrasion and immersion in 40% HF solution for 30 min; and (4) for Au-Pt ceramic alloys: glass bead airborne-particle abrasion.

Effect of alloy recasting on the color of opaque porcelain applied on different dental alloy systems

STATEMENT OF PROBLEM

The effect of different proportions of recast dental alloys on the color of overlying opaque porcelain (OP) is unknown.

PURPOSE

The purpose of this study was to compare the color of OP applied on 2 different proportions (50% and 100%) of recast alloys with the color of commercially available shade tabs of OP.

MATERIAL AND METHODS

Six different metal alloy systems (2 base: Metalloy CC, Cr-Co [B-MCC]; Heraenium NA, Ni-Cr [B-HNA]; 3 noble: Cerapall 2, Pd-Au [N-CP2]; Triumph, Pd-Ag [N-T]; V-Deltaloy, Au-Pd [N-VD]; and 1 high-noble: V-Gnathos Plus, Au-Pt [HN-GP]) were selected for the fabrication of disk-shaped specimens (10 mm in diameter, 1 mm in thickness). Each alloy was divided into 2 subgroups: 50% new alloy with 50% recast alloy (n=3) and 100% recast alloy (n=3). OP (B1) was applied (0.1 mm) to all specimens. The color coordinates (L*, a*, b*) of each specimen and the corresponding commercially available OP shade tab (control) were measured with a spectroradiometer, and color differences between specimens and control group were calculated. Data were statistically analyzed (2-way ANOVA, Ryan-Einot-Gabriel-Welsch multiple range test, α=.05).

RESULTS

For each alloy, ΔL*(L(control)(-)L(recastalloy)) values for the 2 subgroups were not statistically different from each other. The Δa* and Δb* of different proportions of N-CP2, B-HNA, N-VD, and HN-GP were not statistically different within the alloys. However, the a* values of 100% recast N-T and B-MCC were significantly closer to the a* values of the control group, and the b* values of 50% recast B-MCC were significantly closer to the b* values of the control group (P<.05). Delta E(control-recast) alloy values for different proportions of alloys were not statistically different. However, color differences did not meet the criterion of clinical acceptability (ΔE=3.46).

CONCLUSIONS

According to the results of this study, the different proportions (50% and 100%) of recast alloys used have similar effects on the color of OP. Differences between the final color of OP on the recast alloys used and the color of OP shade guide tabs did not meet the criterion of clinical acceptability considered in this study.

An invitro analysis of elemental release and cytotoxicity of recast nickel-chromium dental casting alloys

Recasting of the casting alloys affects the composition and elemental release which may have cytotoxic effect different from the pure alloy in the surrounding tissues. An Invitro study was conducted to investigate the elemental release and their cytotoxic effects from commercially available Ni-Cr dental casting alloys, commonly used for fabricating fixed partial dentures. Three Ni-Cr alloys [Wiron 99(A), Ceramet (B), and Hi Nickel CB (C)] were tested. Alloy specimens (disks 3 × 5 mm) were casted and grouped as follows: Group I (A(1)/B(1)/C(1)): 100% pure alloy; Group II (A(2)/B(2)/C(2)): 50% new with 50% recast; and Group III (A(3)/B(3)/C(3)): 100% recast. Disks of each alloy type from each group were transferred to Dulbecco's modified eagle medium and left for 3 days at 37°C in an atmosphere of 5% CO(2). Ni, Cr, Co, Cu and Mo elemental release from metal alloys into culture medium was investigated using Inductively Coupled Plasma Mass Spectrometry. Cytotoxicity was tested using mouse fibroblast cells and MTT Assay. Controls consisted of 6 wells containing cells with no alloy specimens. Data were analyzed by two-way analysis of variance followed by t-test. The total amount of elements released in parts per billion for various casting groups were Group I, A(1)-6.572, B(1)-6.732, C(1)-8.407; Group II, A(2)-22.046, B(2)-26.450, C(2)-29.189; Group III, A(3)-84.554, B(3)-88.359, C(3)-92.264. More amounts of elements were released in Hi Nickel CB than Ceramet and Wiron 99 in all the three test groups. Percentage of viable cells from MTT analysis were Group I, A(1)-62.342, B(1)-61.322 C(1)-60.593, Group II, A(2)-58.699, B(2)-56.494, C(2)-52.688, Group III, A(3)-53.101, B(3)-52.195, C(3)-47.586. The viable cells present in the culture media were more in Wiron 99 than Ceramet and Hi Nickel CB. Elemental release increased with amount of recast alloy. Amongst the three alloys tested Hi Nickel CB had significantly higher elements released compared to Ceramet and Wiron 99 in 100% pure alloys, 50% recast and 100% recast alloys. Wiron 99 showed least element release in 100% pure alloy, 50% recast and 100% recast specimens. 100% pure alloys of all three alloys are less cytotoxic, but their cytotoxicity is more on 50% and 100% re-casted alloys. Out of all three variations of casting Wiron 99 was least cytotoxic, followed by Ceramet and Hi Nickel CB. Recasting of alloys significantly increased the elements released and their cytotoxicity.

A clinical evaluation of cobalt-chromium metal-ceramic fixed partial dentures and crowns: A three- to seven-year retrospective study

STATEMENT OF PROBLEM

In severely compromised dentition, loading of long-span and cantilever metal-ceramic fixed partial dentures (FPDs) could result in framework deformation and porcelain fractures. The use of cobalt-chromium (Co-Cr) alloys may be advantageous, but there is little information on the longevity of, and complications with, prostheses made with these alloys.

PURPOSE

The aim of this retrospective study was to report the survival and complication rates of Co-Cr metal-ceramic FPDs and crowns followed over a 3- to 7-year period.

MATERIAL AND METHODS

The study included 42 patients with a total of 51 FPDs and 12 single crowns assigned to 1 of 3 groups. The 3 groups comprised patients with abutment teeth with a questionable prognosis (n=10), advanced chronic periodontitis (n=19), or abutment teeth with a positive prognosis (n=13). The FPDs had a mean of 9.7 units (range of 3-14). Of the FPDs, 32 were provided with a cantilever on 1 side (n=24) or both sides (n=8). The mean observation time was 51 months (range of 28-82). All patients were examined by 2 independent prosthodontists using the California Dental Association (CDA) assessment system for evaluation. One-way ANOVA with Fisher's LSD post hoc test and the Mann-Whitney U test were used for statistical analyses (alpha=.05).

RESULTS

Seventeen (34%) of the FPDs had biological and/or technical complications. Six (12%) FPDs were completely or partially removed during the observation period, 1 framework fractured, and 9 (17.6%) FPDs had ceramic fractures. Fifteen of the 21 fractured FPD units were related to FPDs that were placed in 3 patients with bruxing habits. The CDA rating for marginal integrity was "excellent" for more than 98% of the abutments. No patients reported adverse reactions to the material.

CONCLUSIONS

Metal-ceramic FPDs made of cobalt-chromium alloy performed acceptably in the questionable prognosis and advanced chronic periodontitis groups.