Efeito da condensação e queima na formação de defeitos microestruturais em cerâmicas feldspáticas dentárias

Feldspar-based dental ceramics joined to metallic substructures are frequently used for unitary or extensive dental prosthetic restorations. As the manufacturing technique significantly affects the performance of dental ceramic restorations, the aim of this study was to evaluate the effect of multiple firing cycles and compaction method on the formation af microstructural defects in feldspar-based dental ceramics. Commercial powders of two dentin feldspar-based ceramics (A and B) were characterized by XRD and particle size distributions. After that, ceramic samples were produced by compaction without ultrasonic vibration and fired once, compaction with ultrasonic vibration and fired once, and finally, compaction with ultrasonic vibration and fired four times. The fired materials were ground and polished, characterized by SEM-EDS and optical microscopy. A hot-pressed feldspar-based ceramic (C) was used for comparison purpose. The XRD analysis showed the presence of leucite as the only crystalline phase. The particle size distributions of both ceramics tested were trimodal with the presence of larger particles in B ceramic. The microstructural analysis revealed the presence of pores in the fired ceramics. The volume of pores was larger in the compacted samples without ultrasonic vibration. The samples submitted to four firing cycles had a smaller number of pores, however, with the presence of cracks generated during cooling because of differences in thermal expansion coefficients. Therefore, the results showed that the adequate compaction and firing procedure involved ultrasonic vibration followed by firing once, which provides microstructural characteristics similar to hot-pressed ceramics.