Dental zirconia microwave-sintering followed by rapid cooling protocol.

OBJECTIVES: This study aimed to evaluate the effect of microwave sintering temperature and cooling rate (MS) on 3Y-TZP ceramics and its influence on the ceramic microstructure and mechanical properties. Specifically, to optimize the sintering process, reducing the total sintering time compared to conventional sintering. MATERIALS AND METHODS: Eighty-four pre-sintered Y-TZP discs (Vipi block Zirconn, VIPI) (ISO 6872) were divided into seven groups (n = 12) according to the sintering conditions: conventional sintering (CS) at 1530 °C for 120 min and microwave sintering at 1400 °C (MS1400) and 1450 °C (MS1450) for 15 min followed by different cooling conditions: rapid cooling (RC), cooling at 400 °C (C400) and 25 °C (C25). The specimens were submitted to apparent density measurements, X-ray diffraction analysis (XRD), scanning electron microscopy, and biaxial flexural strength test. Data was statistically analyzed through two-way ANOVA, Tukey, Sidak, Dunnett and Weibull (α = 0.05). RESULTS: All MS1400 groups presented lower density values than the CS and MS1450 groups. Two-way ANOVA revealed that the MS temperature and cooling rate affected the biaxial flexural strength of the Y-TZP (p < 0.01). Group MS1400RC presented lower biaxial flexural strength values (681.9 MPa) than MS1450RC (824.7 MPa). The cooling rate did not statistically decrease the biaxial strength among the groups submitted to microwave sintering at 1450 °C. XRD analysis showed that the sintering and cooling temperature did not induce tetragonal to monoclinic phase transformation. CONCLUSIONS: Microwave sintering at 1450 °C for 15 min followed by rapid cooling can be a viable fast alternative protocol for Y-TZP sintering, compared with the conventional sintering, reducing the total sintering time by 75% and reducing the energy used for the sintering process without affecting the Y-TZP biaxial flexural strength and relative density compared to the conventional sintering. Moreover, the microwave technique promoted smaller grains and did not induce monoclinic phase formation.

A aplicação de um glaze na superfície de cimentação melhora a adesão da zircônia ao cimento resinoso? / Does the application of a glaze layer in the intaglio surface improve the adhesion between zirconia and resin cement?

Este trabalho teve como objetivo avaliar o efeito de diferentes tratamentos de superfície na resistência adesiva entre a interface zircônia/cimento resinoso. Blocos de zircônia (12 x 11,6 x 1,2 mm) foram divididos em cinco grupos (n=10) e classificados conforme o tratamento de superfície. Nas amostras em que a superfície não foi jateada, os filmes de glaze foram avaliados em função do condicionamento ou não das amostras com ácido fluorídrico (HF). No jateamento das superfícies das cerâmicas foram utilizadas microesferas de alumina, com e sem revestimento de sílica, e avaliada a influência dos tratamentos na resistência adesiva entre a superfície da cerâmica e o cimento resinoso. No teste de resistência de união, as amostras com glaze condicionado e com jateamento (alumina + sílica) apresentaram resultados superiores em relação às amostras não jateadas. As falhas foram classificadas em adesiva, mista e coesiva com a ajuda de um estereomicroscópio. A caracterização das superfícies foi avaliada por microscopia eletrônica de varredura e espectroscopia de energia dispersiva. A espessura dos filmes glaze, obtida pela micrografi a da secção transversal das amostras, apresentou espessuras semelhantes independentemente do tratamento. Os tratamentos de superfície da zircônia com glaze condicionado (com e sem secagem) e jateamento (alumina + sílica) obtiveram os melhores resultados de resistência de união.

This work aimed to evaluate the effect of different surface treatments on bond strength at the zirconia/resin cement interface. Zirconia blocks (12 x 11.6 x 1.2 mm) were divided into five groups (n=10) and classified according to the surface treatment. In the samples wherein the surface glaze has not been sandblasted the films were assessed for conditioning or not the samples with hydrofluoric acid (HF). Alumina microespheres with and without silica coating were used to blast the surfaces, and also to study the effect of treatments on bond strength between the ceramic surface and the resin cement. In the bond strength test samples with conditioning glaze and sandblasting (alumina + silica) showed higher scores than the non-blasted samples. The flaws were classified as adhesive, cohesive and mixed with the aid of a stereomicroscope. Surface characterization was evaluated by scanning electron microscopy and energy dispersive spectroscopy. The thickness of the glaze film obtained by the micrograph of the cross section of the samples showed similar thicknesses regardless of treatment applied. The zirconia surface treatments with conditioning glaze (with and without drying) and sandblasting (alumina + silica) generated the best bond strength results.