ABSTRACT
In this paper, the influence of a nickel binder metal and molybdenum carbide as an additional alloying element on the microstructure and corrosion behavior of WC-based cemented carbides, processed by conventional powder metallurgy, was studied, and a comparison with conventional cemented carbide (WC-Co) was carried out. The sintered alloys were characterized, before and after corrosive tests, by analyses using optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction. The corrosion resistance of the cemented carbides was investigated by open circuit potential, potentiodynamic polarization, and electrochemical impedance spectroscopy in a 3.5 wt.% NaCl solution. The WC-NiMo cemented carbides showed microstructures similar to those of WC-Co; however, pores and binder islands were observed in the microstructures. The corrosion tests showed promising results, the WC-NiMo cemented carbide showed superior corrosion resistance and higher passivation capacity than the WC-Co cemented carbide. The WC-NiMo alloy showed a higher EOC ≈-0.18 V vs. Ag|AgCl|KCl3mol/L than the WC-Co (EOC≈-0.45 V vs. Ag|AgCl|KCl3mol/L). The potentiodynamic polarization curves showed lower current density values throughout the potential range for the WC-NiMo alloy, and it was observed that Ecorr was less negative (≈-0.416 V vs. Ag|AgCl|KCl3mol/L) than for WC-Co (≈-0.543 V vs. V vs. Ag|AgCl|KCl3mol/L). The EIS analysis confirmed low rate corrosion of WC-NiMo associated with the formation of a passive thin layer. This alloy showed a higher Rct (1970.70 Ω).
ABSTRACT
OBJECTIVES: Controversy exists about whether the elastic modulus (E) mismatch between the loading indenter and ceramic materials influences fatigue testing results. The research hypotheses were that for porcelain veneered Y-TZP crowns 1) A low modulus Steatite indenter (SB) leads to higher fatigue reliability compared to a high modulus tungsten carbide indenter (WC); 2) Different surface damage patterns are expected between low and high modulus indenters after sliding contact fatigue testing. All ceramic crowns will exhibit similar step-stress accelerated life testing (SSALT) contact fatigue reliability (hypothesis 1) and failure characteristics (hypothesis 2) when using high stiffness tungsten carbide (WC, E = 600 GPa) vs. enamel like steatite (SB, E = 90 GPa) indenters. METHODS: Manufacturer (3M Oral Care) prepared Y-TZP-veneered all-ceramic molar crowns were bonded to aged resin composite reproductions of a standard tooth preparation and subjected to mouth-motion SSALT fatigue (n = 18 per indenter type). Failure was defined either as initial inner cone crack (IC), or final fracture (FF) when porcelain fractured (chipping). Selected IC specimens that did not progress to FF were embedded in epoxy resin and sectioned for fractographic analysis. RESULTS: The distribution of failures across the load and cycle profiles lead to similar calculated Weibull Use Level Probability Plots with overlap of the 2-sided 90% confidence bounds. The calculated reliability for IC and FF was equivalent at a mission of 300 N or 700 N load and 50,000 cycles, although the WC indenter had a trend for lower reliability for IC at 700 N. Both indenters produced similar patterns of wear and cracking on crown surfaces. Fractographic landmarks showed competing failure modes, but sliding contact partial inner cone cracks were the most dominant for both groups. SIGNIFICANCE: The more compliant Steatite indenter had similar veneered crown fatigue reliability and failure modes to those found with use of a high stiffness tungsten carbide indenter (hypotheses 1 and 2 rejected).
Subject(s)
Ceramics , Crowns , Composite Resins , Dental Porcelain , Dental Restoration Failure , Dental Stress Analysis , Materials Testing , Reproducibility of ResultsABSTRACT
Introdução: Atualmente, existem muitas dúvidas em relação aos métodos de limpeza de fresas, o que estimula o estudo desses métodos visando maior eficiência e menor prejuízo desses instrumentos rotatórios. Objetivo: Avaliar a influência de métodos de limpeza sobre a eficiência de corte e sobre as características morfológicas de fresas de açoinoxidável de carbeto de tungstênio (carbide). Material e método: Trinta fresas foram divididas em cinco grupos (n = 6), de acordo com o método de limpeza: L1- escova de aço; L2- escova de nylon; L3- ultrassom + água destilada; L4- ultrassom + solução desincrustante; L5- nenhum método de limpeza (controle). As fresas foram utilizadas para o corte de esmalte dental bovino durante seis períodos de 12 minutos cada. Após cada período, as fresas eram limpas (exceto L5) seguindo o protocolo estabelecido para cada grupo. A eficiência de corte foi determinada pelo método da perda de massa e as características morfológicas, por meio de análise fotomicrográfica. Resultado: As médias da quantidade de desgaste após 72 minutos de uso foram: L1 = 0,3558 g; L2 = 0,4275 g; L3 = 0,4652 g; L4 = 0,4396 g, e L5 = 0,4854 g. Houve diferença significante para o tempo de uso (p < 0,001) e o método de limpeza (p < 0,001). O grupo L1 apresentou pior desempenho. Independentemente do grupo experimental, a análise morfológica revelou alterações nas lâminas de corte a partir de 12 minutos, sendo o grupo L1 o mais afetado. Conclusão: O método mais prejudicial à eficiência de corte e que mais alterou as características morfológicas das fresas carbide foi a limpeza com escova de aço.
Introduction: Currently, there are many questions regarding the cleaning methods seeking greater efficiency and less loss of burs. Aim: the aim of this study was to evaluate the influence of cleaning methods on the cutting efficiency and morphological characteristics of stainless steel burs tungsten carbide (carbide). Materials and method: Thirty burs were divided into five groups (n = 5) according with the cleaning method: L1- steel brush, L2- nylon brush, L3- ultrasound + distilled water, L4- ultrasound + descaling solution and L5- no cleaning method (control). Theburs were used for the cutting of bovine enamel during six periods of 12 minutes each. After each period, the burs were cleaned (except L5) following the protocol established for each group. The cutting efficiency was determined by mass loss and morphological characteristics. Result: The average amount of wear after 72 minutes of use were L1 = 0.3558 g; L2 = 0.4275 g; L3 = 0.4652 g; L4 = 0.4396 g e L5 = 0.4854 g; significant differences in the time of use (p < 0.001) and cleaning method (p < 0.001). The L1 group showed the worst performance. Regardless of theexperimental group, morphological analysis revealed alterations in the cutting blades soon after the first 12 minutes, being L1 the most affected group. Conclusion: The cleaning with wire brush was the most damaging method to the cutting efficiency and to the morphology of carbide burs.