Does Simulated Porcelain Firing Influence Corrosion Properties of Casted and Sintered CoCr Alloys?

The aim of the study was to evaluate how heat processing used for dental porcelain firing influences the surface properties of sintered and casted CoCr alloy. Two CoCr alloys, Soft Metal LHK (milling in soft material and sintering) and MoguCera C (casting), were used for the study. The samples were examined using SEM–EDS before and after heat treatment. Next, corrosion examinations (Ecorr, jcorr, polarization curve, Ebr) were performed. Finally, the samples were evaluated under SEM. Based on the results, the following conclusions might be drawn: 1. Thermal treatment (porcelain firing) did not cause chemical impurities formation on the surface of CoCr alloy; 2. The sintered metal exhibited significantly higher corrosion resistance than the casted one due to its homogeneity of structure and chemical composition; 3. Heat treatment (porcelain firing) decreased the resistance of casted and sintered CoCr alloy to electrochemical corrosion. The reduction in corrosion resistance was significantly higher for the casted alloy than for the sintered alloy; 4. The corrosion resistance decrease might be due to an increased thickness and heterogeneity of oxide layers on the surface (especially for the casted alloy). The development of corrosion process started in the low-density areas of the oxide layers; 5. The sintered metal seems to be a favourable framework material for porcelain fused to metal crowns.

Microwave vs conventional porcelain firing: Greenware to biscuit crystallochemical transformations

This work reports and compares the structural crystallochemical transformations occurring during the microwave and conventional porcelain manufacture. Batches of greenware (just dried) porcelain pieces are microwave and electrically fired at increasing temperatures, from 420 °C up to 1100 °C. Crystallochemical transformations are identified by XRD analysis, and compared the results from samples microwave and conventionally fired. Microwave fired samples show the full and rapid collapse of kaolinite structure for firing temperatures just above 500 °C, whereas the collapse of kaolinite structure of the electrically fired samples is progressive, from about 500 °C up to 950 °C. Muscovite structure totally collapses at about 950 °C for microwave fired greenware samples, whereas muscovite structure total collapse only occurs at about 1050 °C for electrically fired greenware samples. Microwave and electric firing lead to appreciable differences in the sanidine – orthoclase – microcline structural transformations. Mullite formation could be identified in the microwave fired samples at temperatures 50 °C lower than in the electrically fired ones, especially for the conventional firing temperatures above 1050 °C, the same temperature reported in the literature.

Evaluation of Color Tone and Exfoliation Resistance of Porcelain-Firing Ti with White Oxide Coating as an Opaque Layer

One of the applications of titanium in the dental field is a porcelain-fired-metal crown. It is made by firing porcelain multiple times with different composition of ceramics on a metallic abutment tooth. Regarding firing process to metallic abutment, a primer is generally required to be applied in advance of a porcelain firing and the opaque porcelain is applied to cover the metallic color of the abutment. By the way, our recent research shows that white oxide films formed on the Ti substrate have a color tone similar to opaque porcelain. Therefore, porcelain-fired-Ti samples replacing primer and opaque porcelain firing with the TiO2 oxide layer were fabricated and evaluated in this study. Color tone and peel strength were evaluated, and cross-sectional observation was observed by SEM and EPMA.