Corrosion Resistance of Cr–Co Alloys Subjected to Porcelain Firing Heat Treatment—In Vitro Study

Dorota Rylska,Jerzy Sokołowski,Bartłomiej Januszewicz,Grzegorz Sokołowski

doi:10.3390/pr9040636

Dorota Rylska, Jerzy Sokołowski + Show 2 more

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https://doi.org/10.3390/pr9040636

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Abstract

The procedure of ceramics fusion to cobalt–chromium (Co–Cr) base dental crowns affects their corrosion behavior and biological tolerance. This study’s purpose was to comparatively evaluate the effect of heat treatment (HT) applicable for dental ceramics firing on the corrosion properties among Co–Cr base alloys fabricated via different methods: casting (CST), milling soft metal and post sintering (MSM), and selective laser melting (SLM). All specimens were subjected to a heat treatment corresponding to a full firing schedule. The microstructure and elemental composition of oxidized surfaces were investigated by scanning electron microscopy and energy dispersive spectroscopy. Corrosion properties were examined by electrochemical potentiodynamic polarization tests. The values of jcorr, Ecorr, Rp, and breakdown potential Ebr were estimated. The oxide layers formed during the HT process corresponded to the composition of the original alloys’ structure. Among the thermal treated alloys, SLM showed the highest corrosion resistance, followed by the MSM and CST. This may be attributed to uniform distribution of alloying elements in homogenous structure and to the reduced porosity, which enhances corrosion resistance and decreases the risk of crevice corrosion. The overall corrosion behavior was strongly influenced by the segregation of alloying elements in the microstructure, thus, is directly determined by the manufacturing method.

Highlights

Despite the growing popularity of all-ceramic restorations, a significant number of prosthetic works are made using the method of ceramics fusion on metal
The corrosion resistance after heat treatment (HT) simulating porcelain firing was affected by the microstructure of the oxides covering surface of alloys
The highest resistance to corrosion after the HT was observed in selective laser melting (SLM) alloys due to the microstructural homogeneity of the oxide layers

Summary

Introduction

Despite the growing popularity of all-ceramic restorations, a significant number of prosthetic works are made using the method of ceramics fusion on metal. Due to the high cost of noble metal alloys, base metal alloys, such as cobalt–chromium (Co–Cr), are more extensively used for the metal–ceramic restorations’. The low density, high hardness, and tensile strength [1] make base metal alloys superior to noble metals. The most popular technique is lost-wax casting, there are several dental technologies for manufacturing a final product from cobalt–. Chrome base alloys as alternatives to traditional casting techniques. These alternative methods include the milling of solid metal, milling in soft material, and sintering in a protective atmosphere (MSM) and selective laser melting (SLM) [2,3,4]. The milling alloys (1) are not likely to indicate procedural errors, such as impurities and shape deformations as a result of thermal tension and (2) show lower corrosion susceptibility than alloys manufactured by casting (CST) [5]

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