Sinterização de cerâmicas feldspáticas odontológicas utilizando energia de micro-ondas.

Abstract

Dental porcelains are known in dentistry due to high hardness, biocompatibility and excellent optical properties, which make them able to artificially reproduce the natural teeth. These materials are sintered in the conventional fast firing furnace at high temperatures and faster heating rates. The possibility of the microwave processing for heating these materials is something new, and proven lack of research in the literature. The purpose of this study was to evaluate and compare microstructure, mechanical and physical properties obtained by dental porcelains sintering in a conventional furnace versus microwave furnace. Five coverage dental porcelains were selected: EX-3 (Noritake), Starlight Ceram (Dentsply), VMK 95, VM 7, and VM 13 (Vita) that were characterized for X-ray diffraction (XRD), fluorescence spectrometry, granulometry and scanning electron microscopy (SEM). Thirty specimens of each material were prepared, according to ISO 6872 and directions of the manufacturer. Ten specimens were sintered in a conventional furnace and 20 sintered using microwave energy, which 10 sintered at a time established as optimal for each material, and the remaining 10 subdivided into two groups which five were sintered with variation less than one minute and one more minute. The specimens were submitted to physical and mechanical tests of determining water absorption, apparent density and porosity, flexural strength and Vickers microhardness. The phase composition was examined by using X-ray diffraction and microstructure characteristics were studied with scanning electron microscopy. Data were statistically analyzed using ANOVA, Tukey's test (α=0.05) and independent t test (α=0.05). The results of water absorption and apparent porosity showed similar values between conventional and optimal microwave sintering for the groups: EX-3, VMK 95 and VM7, however significant differences for the groups: Starlight ceram and VM 13. No significant differences for microhardness and flexural strength were found, except for EX-3 group flexural strength which was higher for conventional sintering. Microstructural differences between the types of microwave sintering were examined with scanning electron microscopy and XRD. The results showed that microwave sintering produced specimens with mechanical properties similar to those obtained by conventional sintering.