Thermal expansion and corrosion resistance of cobalt-chromium alloys fabricated by contemporary manufacturing processes: an in vitro study / Expansión térmica y resistencia a la corrosión de aleaciones de cobalto-cromo fabricadas mediante procesos de abricación contemporáneos: un estudio in vitro

In Purpose: The fabrication technique can influence the mechanical properties of Cobalt-Chromium (Co-Cr) dental alloys. Hence, the present study aims to determine the corrosion resistance and thermal expansion of alloys manufactured using three contemporary techniques. Material and Methods: A total of nine specimens of Co-Cr alloy were prepared according to ISO 22674 by each one of the three manufacturing processes (three in each process); conventional casting, direct metal laser sintering (DMLS) and milling (MIL). All these specimens were tested for coefficient of thermal expansion and corrosion resistance. The data was tabulated and analyzed statistically. Results: The difference in the thermal expansion of alloys fabricated using three techniques was non-significant at almost all the temperatures from 50 ºC to 950 ºC (p>0.05), except 450 ºC and 600 °C. The polarization resistance of specimens manufactured using the conventional method was more compared to DMLS and MIL at pH 5 (Conventional>MIL>DMLS) (p<0.001). Conclusion: The thermal expansion behavior of alloys manufactured using the three selected techniques were similar, whereas, at acidic pH, the corrosion resistance of conventional and MIL were better than the DMLS.

Antecedentes: La técnica de fabricación puede influir en las propiedades mecánicas de las aleaciones dentales de cobalto-cromo (Co-Cr). Por lo tanto, el presente estudio tiene como objetivo determinar la resistencia a la corrosión y la expansión térmica de aleaciones fabricadas con tres técnicas contemporáneas. Material y Métodos: Se prepararon un total de nueve probetas de aleación de Co-Cr según ISO 22674 por cada uno de los tres procesos de fabricación (tres en cada proceso); fundición convencional, sinterización directa de metal por láser (DMLS) y fresado (MIL). Todos estos especímenes fueron probados para determinar el coeficiente de expansión térmica y la resistencia a la corrosión. Los datos fueron tabulados y analizados estadísticamente. Resultados: La diferencia en la dilatación térmica de las aleaciones fabricadas con las tres técnicas no fue significativa en casi todas las temperaturas desde 50ºC hasta 950ºC (p>0,05), excepto 450ºC y 600ºC. La resistencia a la polarización de las muestras fabricadas con el método convencional fue mayor en comparación con DMLS y MIL a pH 5 (Convencional>MIL>DMLS) (p<0, 0 01). Conclusión: El comportamiento de expansión térmica de las aleaciones fabricadas con las tres técnicas seleccionadas fue similar, mientras que, a pH ácido, la resistencia a la corrosión de la convencional y la MIL fue mejor que la de la DMLS.

Effect of Metal Primers on Bond Strength of a Composite Resin to Nickel-Chrome Metal Alloy

Abstract This study evaluated the effects of three metal primers and one multi-mode adhesive system on the shear bond strength (SBS) of a flowable composite resin to nickel-chrome metal alloy (Ni-Cr). Ninety plates were cast from Ni-Cr and divided in nine groups (n=10). The surfaces were sandblasted with Al2O3 and primed with three adhesive primers: Alloy Primer (AP), Universal Primer (TP) and RelyX Ceramic Primer (CP), and a multi-mode adhesive (Scotchbond Universal, SU). The Adper Single Bond Plus (SB) and SU adhesives were also combined with adhesive primers. Control group did not have any surface treatment. The groups were: AP, AP+SB, AP+SU, TP+SB, TP+SU, CP+SB, CP+SU and SU. Composite cylinders were built on alloy surface. After 24 h, half the specimens were subjected to SBS and the other half to thermal cycling before testing. Data were analyzed by two-way ANOVA and Tukey’s test (a=0.05). Failure modes were assessed by SEM observation. Higher SBS were obtained with AP and TP combined with adhesives at 24 h and the lowest one for control group. Thermocycling reduced SBS for AP, CP+SU and SU. Combination between TP and SU resulted in the highest SBS after the thermocycling. TP groups showed all types of failures and high incidence of mixed failures. The use of AP and UP metal primers before application of SU and SB adhesive systems increased the SBS of composite to Ni-Cr. These combinations between metal primers and adhesives had the highest SBS after thermocycling.

Resumo Este estudo avaliou os efeitos de três primers para metais e um sistema adesivo multi-mode na resistência da união por cisalhamento (SBS) de um compósito resinoso de baixa viscosidade a uma liga niquel-cromo (Ni-Cr). Noventa placas Ni-Cr foram divididas em 9 grupos (n=10). As superfícies foram jateadas com Al2O3 e condicionadas com três primers adesivos: Alloy Primer (AP), Universal Primer (TP) e Rely X Ceramic Primer (CP) e um adesivo multi-mode (Scotchbond Universal, SU). Os adesivos Adper Single Bond Plus (SB) e SU foram combinados com os primers para metais. O grupo controle não recebeu nenhum tipo de tratamento superficial. Os grupos foram: AP, AP+SB, AP+SU, TP+SB, TP+SU, CP+SB, CP+SU e SU. Cilindros de resina foram construídos na superfície da liga. Após 24 h, metade dos espécimes foi submetido ao SBS, a outra metade foi termociclada previamente. Os dados foram analisados pelos testes ANOVA dois fatores e Tukey (a=0.05). Os tipos de fraturas foram determinados utilizando microscopia eletrônica de varredura (MEV). Os maiores valores de SBS foram obtidos com AP e TP combinados com adesivos após 24 h e o menor valor foi obtido no grupo controle. A ciclagem térmica reduziu a SBS para AP, CP+SU e SU. Combinação entre TP e SU resultou em altos valores de SBS após termociclagem. Os grupos TP apresentaram todos os modos de fratura e alta incidência de fraturas mistas. O uso dos primers AP e UP para metais antes da aplicação dos sistemas adesivos SU e SB aumentou a SBS entre o Ni-Cr e a resina composta. Essa combinação entre primers e adesivos mostrou os maiores valores de SBS após a termociclagem.

Corrosion behavior of self-ligating and conventional metal brackets

Objective: To test the null hypothesis that the aging process in self-ligating brackets is not higher than in conventional brackets. Methods: Twenty-five conventional (GN-3M/Unitek; GE-GAC; VE-Aditek) and 25 self-ligating (SCs-3M/Unitek; INs-GAC; ECs-Aditek) metal brackets from three manufacturers (n = 150) were submitted to aging process in 0.9% NaCl solution at a constant temperature of 37 ± 1ºC for 21 days. The content of nickel, chromium and iron ions in the solution collected at intervals of 7, 14 and 21 days was quantified by atomic absorption spectrophotometry. After the aging process, the brackets were analyzed by scanning electron microscopy (SEM) under 22X and 1,000X magnifications. Results: Comparison of metal release in self-ligating and conventional brackets from the same manufacturer proved that the SCs group released more nickel (p < 0.05) than the GN group after 7 and 14 days, but less chromium (p < 0.05) after 14 days and less iron (p < 0.05) at the three experimental time intervals. The INs group released less iron (p < 0.05) than the GE group after 7 days and less nickel, chromium and iron (p < 0.05) after 14 and 21 days. The ECs group released more nickel, chromium and iron (p < 0.05) than the VE group after 14 days, but released less nickel and chromium (p < 0.05) after 7 days and less chromium and iron (p < 0.05) after 21 days. The SEM analysis revealed alterations on surface topography of conventional and self-ligating brackets. Conclusions: The aging process in self-ligating brackets was not greater than in conventional brackets from the same manufacturer. The null hypothesis was accepted. .

Objetivo: testar a hipótese nula de que o processo de envelhecimento em braquetes autoligáveis não é superior ao de braquetes convencionais. Métodos: Vinte e cinco braquetes metálicos convencionais (GN, 3M/Unitek; GE, GAC; VE, Aditek) e 25 autoligáveis (SCs, 3M/Unitek; INs, GAC; ECs, Aditek) de três fabricantes (n = 150) foram submetidos ao envelhecimento em solução de NaCl à temperatura constante de 37 ± 1ºC, durante 21 dias. O conteúdo de íons níquel, cromo e ferro na solução coletada com 7, 14 e 21 dias foi quantificado por meio de espectrofotometria de absorção atômica. Depois de completado o processo de envelhecimento, os braquetes foram analisados com microscópio eletrônico de varredura (MEV), em magnificações de 22x e de 1.000x. Resultados: comparando-se a liberação de metais por braquetes autoligáveis e convencionais do mesmo fabricante, observou-se que o grupo SCs liberou mais níquel (p < 0,05) que o grupo GN após 7 e 14 dias, mas menos cromo (p < 0,05) após 14 dias e menos ferro (p < 0,05) nos três períodos experimentais. O grupo INs liberou menos ferro (p < 0,05) que o grupo GE após 7 dias, e menos níquel, cromo e ferro (p < 0,05) após 14 e 21 dias. O grupo ECs liberou mais níquel, cromo e ferro (p < 0,05) que o grupo VE após 14 dias; entretanto, liberou menos níquel e cromo (p < 0,05) após 7 dias e menos cromo e ferro (p < 0,05) após 21 dias. A análise no MEV demonstrou alterações na topografia da superfície de braquetes convencionais e autoligáveis. Conclusões: o processo de envelhecimento em braquetes autoligáveis não foi superior ao de braquetes convencionais do mesmo fabricante. A hipótese nula está aceita. .

An in vitro comparison of nickel and chromium release from brackets

This study aimed at comparing amounts of nickel (Ni) and chromium (Cr) released from brackets from different manufacturers in simulated oral environments. 280 brackets were equally divided into 7 groups according to manufacturer. 6 groups of brackets were stainless steel, and 1 group of brackets was made of a cobalt-chromium alloy with low Ni content (0.5 percent). International standard ISO 10271/2001 was applied to provide test methods. Each bracket was immersed in 0.5 ml of synthetic saliva (SS) or artificial plaque fluid (PF) over a period of 28 days at 37ºC. Solutions were replaced every 7 days, and were analyzed by spectrometry. The Kruskal-Wallis test was applied. Amounts of Ni release in SS (µg L-1 per week) varied between groups from "bellow detection limits" to 694, and from 49 to 5,948.5 in PF. The group of brackets made of cobalt-chromium alloy, with the least nickel content, did not release the least amounts of Ni. Amounts of Cr detected in SS and in PF (µg L-1 per week) were from 1 to 10.4 and from 50.5 to 8,225, respectively. It was therefore concluded that brackets from different manufacturers present different corrosion behavior. Further studies are necessary to determine clinical implications of the findings.

Stress analysis on the free-end distal extension of an implant-supported mandibular complete denture

A comparative and qualitative analysis of the tensions generated in the cantilever region of an implant-supported mandibular complete denture was conducted using the three-dimensional finite element method. The mechanical properties of the components were input in the model and a load of 15 N was applied in pre-determined points. In the first simulation, the load was applied on the occlusal surface of the first premolar. In the second simulation, it was applied on the first and second premolars. In the third simulation, it was applied on the first and second premolars and on the first molar. The different occlusion patterns produced similar tension distributions in the cantilever region, which followed a similar pattern in the three simulations. In all of the cases, the highest levels of tension were located in the region of the first implant. However, as the loads were dislocated distally, the tensions increased considerably. The more extensive the cantilever, the more compromised will be the infrastructure, the prosthetic components and the implants. Regardless of the length of the cantilever, the highest tensions will always be located in the region of the implant next to the load application point.

[Physiochemical influence of soil minerals on the organic reduction of soil chromium]

The physiochemical influence of soil minerals [Bentonite, Kaolinite, Diatomite, Rutile and Ferrihydrite] on the organic reduction of chromium [VI] has been investigated with Oxalic acid as the organic reductant. The effect of pH and particle sizes of the soil minerals were also investigated. Results showed that with 0.1mol/dm[3] concentration of Oxalic acid, the concentration of chromium[VI] remaining was 0.28, 0.34, 0.38, 0.46 and 0.52mg/kg for Bentonite, Rutile, Diatomite, Kaolinite and Ferrihydrite respectively whereas at 0.5 mol/dm[3] of oxalic acid, the concentration of chromium reduced to 0.20, 0.26, 0.30, 0.38, and 0.44mg/kg for Bentonite, Rutile, Diatomite, Kaolinite and Ferrihydrite. Increased concentration of oxalic acid increased the reduction of chromium[VI] to chromium[III]. At pH 5.0, the concentration of chromium [VI] left was 0.28, 0.34, 0.38, 0.46 and 0.52mg/kg for Bentonite, Rutile, Diatomite, Kaolinite and Ferrihydrite while at pH 2.5, concentration was 0.16, 0.22, 0.26, 0.34 and 0.43mg/kg respectively. At particle size of 47-42 microns, concentration of chromium[VI] was 0.28, 0.34, 0.38, 0.46, 0.52mg/kg for the same order of the soil minerals. At micron sizes of 33-29 and 28-25 ranges the concentration of chromium[VI] left was 0.23, 0.29, 0.33, 0.41 and 0.47mg/kg for both micron sizes and corresponding minerals as well. These results showed that above 33-29 micron sizes, the influence of particle size was negligible

Biosorption of Cr (VI) ions from electroplating industrial effluent using immobilized Aspergillus niger biomass.

A fungus, Aspergillus niger was chemically treated with 0.1 M H2SO4 and 0.1 N NaOH to form biosorbent and it was immobilized in calcium alginate beads. The biosorption capacity of immobilized biosorbents for Cr (VI) was found to depend on pH, contact time, biosorbent dose and initial concentration of Cr (VI). The maximum uptake of Cr (VI) was 92.5, 95.9 and 98.4 mg respectively at a pH of 1.5 and with an increase in pH up to 10.5 the metal uptake decreased gradually up to 38.75, 50.19 and 65.28 mg respectively for acid treated, untreated and base treated fungal biosorbents. Increase in biosorbent dose up to 1 g of biomass and contact time up to 60 min resulted in an increase in biosorption from 19.6, 15.6 and 26.1 mg at a biosorbent dose of 0.1 g 100 ml(-1) to 92.45, 95.7 and 98.52 mg at a biosorbent dose of 1.0 g 100 ml(-1) and then further increase in adsorbent dose and contact time did not resulted in more Cr (VI) adsorption by per unit weight of biosorbent. The value of Kad (adsorption rate constant) revealed the pseudo-first order nature of biosorption. The percentage metal uptake by the biosorbent was found to decrease upto 62.33, 52.67 and 83.5 percent respectively for acid treated, untreated and base treated fungal biosorbents at the 300 mgl(-1) Cr (VI) ion concentration. The resulted data was found to fit well in Langmuir model of adsorption isotherm with a high value of correlation coefficient. The value of Qmax, b (Langmuir constants), R(L) (separation factor) and delta G (Gibb's free energy) revealed the favourable nature of adsorption. The biosorbed metal was eluted from the biosorbent by using 0.1 M H2SO4 as elutant. Immobilized biosorbent can be reused for five consecutive biosorption/desorption cycles without apparent loss of efficiency after its reconditioning. The biosorbent was found to perform well in the electroplating industrial effluent.

Estudio del pH y presencia de metales pesados de un trióxido mineral / Study of the pH and the presence of heavy metals from a mineral trioxide

El propósito del presente trabajo fue comparar in vitro la capacidad de alcalinización por inmersión en agua destilada de dos trióxidos minerales y analizar su polvo para determinar la presencia de metales pesados como arsénico y cromo en su composición. Se prepararon tres muestras para cada grupo. Se registró el pH del agua destilada, se sumergió cada muestra y se volvió a realizar la medición inmediatamente a la hora, a las tres horas y a los 7 días, mateniéndolñas en una estufa a 37ºC. Se determinó la presencia de arsénico por espectrometría de absorción atómica con generación de hidruros y de cromo por espectrometría de absorción atómica con horno de grafito. Los resultados del pH fueron evaluados en función del tiempo. El pH inicial de CPM fue 10,14 y a los 7 días 10,94, en tanto que para ProRoot MTA fue 8,98 y 11,87 respectivamente, determinando que el incremento del pH de CPM y MTA fue diferente en cuanto a tiempo y valores de pH. El análisis estadístico mostró el efecto significativo de los factores material, tiempo y su interacción (p<0,01). Los resultados del análisis químico determinaron la presencia de arsénico y cromo en ambos materiales; CPM: As (2,1mg/kg), Cr (3,2mg/kg); ProRoot-MTA As (2,0mg/kg), Cr (3,5mg/kg).

Biosorption of Cr (VI) with Trichoderma viride immobilized fungal biomass and cell free Ca-alginate beads.

Ability of Cr (VI) biosorption with immobilized Trichoderma viride biomass and cell free Ca-alginate beads was studied in the present study. Biosorption efficiency in the powdered fungal biomass entrapped in polymeric matric of calcium alginate compared with cell free calcium alginate beads. Effect of pH, initial metal ion concentration, time and biomass dose on the Cr (VI) removal by immobilized and cell free Ca-alginate beads were also determined. Biosorption of Cr (VI) was pH dependent and the maximum adsorption was observed at pH 2.0. The adsorption equilibrium was reached in 90 min. The maximum adsorption capacity of 16.075 mgg(-1) was observed at dose 0.2 mg in 100 ml of Cr (VI) solution. The high value of kinetics rate constant Kad (3.73 x 10(-2)) with immobilized fungal biomass and (3.75 x 10(-2)) with cell free Ca- alginate beads showed that the sorption of Cr (VI) ions on immobilized biomass and cell free Ca-alginate beads followed pseudo first order kinetics. The experimental results were fitted satisfactory to the Langmuir and Freundlich isotherm models. The hydroxyl (-OH) and amino (-NH) functional groups were responsible in biosorption of Cr (VI) with fungal biomass spp. Trichoderma viride analysed using Fourier Transform Infrared (FTIR) Spectrometer.

Biosorption of chromium (VI) from aqueous solutions by the husk of Bengal gram (Cicer arientinum)

The potential to remove Cr (VI) from aqueous solutions through biosorption using the husk of Bengal gram (Cicer arientinum), was investigated in batch experiments. The results showed removal of 99.9 percent of chromium in the 10 mgl-1 chromium solution, the biomass required at saturation was 1 g mg-1. Kinetic experiments revealed that the dilute chromium solutions reached equilibrium within 180 min. The biosorptive capacity of the (bgh) was dependent on the pH of the chromium solution, with pH 2 being optimal. The adsorption data fit well with the Langmuir and Freundlich isotherm models. The adsorption capacity calculated from the Langmuir isotherm was 91.64 mg Cr (VI)/g at pH 2. The adsorption capacity increased with increase in agitation speed and an optimum was achieved at 120 rpm. The biosorption of Cr (VI) was studied by Fourier transform infrared spectroscopy (FTIR), which suggested that the presence of Cr (VI) ions in the biomass affects the bands corresponding to hydroxyl and carboxyl groups. Comprehensive characterisation of parameters indicates bgh to be an excellent material for biosorption of Cr (VI) to treat wastewaters containing low concentration of the metal.

Prevention of chromate induced oxidative stress by alpha-lipoic acid.

The parenteral administration of alpha-lipoic acid (LA) protected against chromate induced oxidative stress in mouse liver. A shift in Cr induced pro-oxidant state to antioxidant-state by LA was noteworthy. The degree of protection was significant and similar in different LA administration regimens (prior-, co- and post- parenteral Cr exposure) explored. An improved status of the tissue antioxidants by LA appeared to be the mechanism of mitigation. The results are of chemopreventive value and suggest a possible alternative to ascorbic acid for abrogation of Cr toxicity.

Removal of heavy metal from industrial wastewater using chitosan coated oil palm shell charcoal

This research focuses on understanding biosorption process and developing a cost effective technology for treatment of heavy metals-contaminated industrial wastewater. A new composite biosorbent has been prepared by coating chitosan onto acid treated oil palm shell charcoal (AOPSC). Chitosan loading on the AOPSC support is about 21 percent by weight. The shape of the adsorbent is nearly spherical with particle diameter ranging 100~150 µm. The adsorption capacity of the composite biosorbent was evaluated by measuring the extent of adsorption of chromium metal ions from water under equilibrium conditions at 25ºC. Using Langmuir isotherm model, the equilibrium data yielded the following ultimate capacity values for the coated biosorbent on a per gram basis of chitosan: 154 mg Cr/g. Bioconversion of Cr (VI) to Cr (III) by chitosan was also observed and had been shown previously in other studies using plant tissues and mineral surfaces. After the biosorbent was saturated with the metal ions, the adsorbent was regenerated with 0.1 M sodium hydroxide. Maximum desorption of the metal takes place within 5 bed volumes while complete desorption occurs within 10 bed volumes. Details of preparation of the biosorbent, characterization, and adsorption studies are presented. Dominant sorption mechanisms are ionic interactions and complexation.

Removal of toxic Cr(VI) by the adsorption of activated carbons prepared from Simarouba shells.

Removal of toxic Cr(VI) in aqueous medium was investigated using activated carbon adsorbents prepared from Simarouba glauca seed shells. The pH effect, Cr(VI) concentration, adsorbent dosage and contact time period were studied in batch experiment. The removal of Cr(VI) was in general most effective at pH range 2.0-4.0 and high Cr(VI) concentrations. Activated carbons are prepared at 80050 degrees C temperature. One is non-impregnated and the remaining three are impregnated with zinc chloride in 1:1,1:2,1:3 ratio. Important characteristics of activated carbons are also investigated. The data for all the adsorbents fit well to the Freundlich adsorption isotherm. The removal of Cr(VI) is around 97% was observed with 1:2 impregnated activated carbon at pH 3.0 where as other adsorbents showed much lower activities.

Biosorption and elution of chromium from immobilized Bacillus coagulans biomass.

Bacillus coagulans, a tannery wastewater isolate, previously shown to bind dissolved Cr(VI), retained its ability to biosorb Cr(VI) in different matrices. Polymeric materials like agar, agarose, calcium alginate and polyacrylamide were screened. Agarose emerged as the suitable candidate for biomass immobilization mainly due to its higher stability and integrity in acidic pH. Aptness of agarose as the matrix for B. coagulans biomass was revealed during Cr(VI) biosorption from natural wastewater.

Bioremediation of chromium contaminated environments.

Bioremediation is the most promising and cost effective technology widely used nowadays to clean up both soils and wastewaters containing organic or inorganic contaminants. Discharge of chromium containing wastes has led to destruction of many agricultural lands and water bodies. Utilisation of chromium(Cr) reducing microbes and their products has enhanced the efficiency of the process of detoxification of Cr(VI) to Cr(III). This review focuses mainly on the current technologies prevalent for remediation like natural attenuation, anaerobic packed bed bioreactors (using live cells, Cr(VI) reductases or their byproducts) and use of engineered microorganisms. Treatment of wastewaters by biosorption or using biofilms and immobilized microbial cells are also discussed.

Influence of chromium on the corrosion behaviour of stainless steels in sulphuric acid containing halide ions

The passivation of iron in aqueous media has been investigated over a number of years [1-4.] Bartlett and Stephenson [5] and Froment et al. [6] pointed out that, the anodic deposition of FeSO[4] on iron in sulphuric acid solutions. Krstulonic et al. [7] reported the anodic passivation of Armco iron I in a wide range of sulphuric acid concentration