Effect of conventional and microwave glazing on surface roughness of metal ceramics: An atomic force microscopy analysis

This study investigated and compared the surface roughness achieved by glazing porcelain samples in a conventional and a microwave oven. Materials and Methods: Two commercial brands of metal ceramics were used, VITA VMK MASTER and IPS CLASSIC. Sixty samples were fabricated, 30 for each type of ceramic. The samples were sintered in the conventional oven and hand-polished to remove any irregularities. Samples (n = 10) from each type of ceramic were further divided into three groups as follows: hand-polished (Group A), conventional oven glazed (Group B), and microwave glazed (Group C). Each specimen was evaluated for surface roughness by atomic force microscope. Data were statistically analyzed using two-way analysis of variance (ANOVA) and Tukey's post hoc test (a = 0.05). Results: Two-way ANOVA indicated a highly significant difference in surface roughness based on the type of glazing (P < 0.001), there was a significant difference based on the metal ceramics (P = 0.002). There was also a significant interaction between the type of glazing and metal ceramics (P = 0.009). The images obtained from the atomic force microscope corroborated the measured values. Conclusions: All the results indicate that microwave glazing can be a feasible option for glazing porcelain specimens. It was concluded that surface topography is influenced by surface treatment and microwave glazed ceramic is superior to conventional oven glazed ceramic and hand-polishing showed greater surface roughness when compared to glazing. IPS CLASSIC ceramic showed relatively smooth surface when compared to VITA VMK MASTER irrespective of the surface treatment.

Influence of the microwave sintering period on the 3 point flexural strength and shade of zirconia restoration / 대한치과재료학회지

In this study, we tried to confirm clinically applicable applicability by comparing the difference in 3 point flexural strength and shade of the prosthesis depending on microwave sintering time of dental CAD / CAM zirconia. 3 Point flexural strength specimens (n=30) and shade measurement specimens (n=28) were prepared and sintered at different sintering times. 3 point flexural strength and shade were measured and analyzed by independent t-test (α=0.05). Measurement result of 3 point flexural strength the average of short-term sintering (STS) was 245.47±29.89 MPa, the average of long-term sintering (LTS) was 284.27±31.56 MPa, and there was a statistically significant difference (p 0.05). The 3 point flexural strength of the zirconia restorations fabricated by short time and long time was high in long time sintering. However, other conditions may be required for clinical applications. Since the shade test did not show any significant color difference according to sintering time, it is considered to be sufficient for clinical application.

Crystal Modification on Lithium Disilicate Glass Ceramics Sintered Using Microwaves / Modificación de Cristales de Cerémicas de Vidrio de Disilicato de Litio Sinterizadas con Microondas

ABSTRACT: Microwaves are an interesting alternative to process dental ceramics. It is well documented that Microwave Hybrid Sintering (MHS) allows important savings in time and energy consumption. However, little is known about its effect on lithium disilicate glass ceramics, a popular material in dentistry today. We analyzed the microstructure of lithium disilicate glass ceramics sintered with MHS compared with conventional sintering. We sintered lithium disilicate glass ceramics using MHS and conventional furnaces, and we analyzed the samples using X-Ray diffraction and SEM. Samples sintered with MHS showed an increased crystalline phase, with an increased number of crystals. These crystals have larger perimeters compared with samples sintered in conventional furnaces. MHS produced a different crystallization pattern and crystal/ matrix ration in lithium disilicate glass ceramics when compared to conventional sintering. This can be associated with the improved mechanical properties of these materials reported previously.

RESUMEN: Las microondas son una interesante alternativa para procesar cerámicas dentales. Está bien documentado que el Sinterizado Híbrido por Microondas (MHS) permite ahorros importantes de tiempo y energía. Sin embargo, poco se ha publicado respecto a sus efectos en cerámicas de disilicato de litio, un material bastante popular en odontología en estos días. En este artículo analizamos la micro estructura de cerámicas de disilicato de litio sinterizada con MHS comparada con el sinterizado convencional. Sinterizamos muestras de cerámicas de disilicato de litio usando MHS y hornos convencionales, y analizamos las muestras usando difracción de rayos X y SEM. Las muestras sintetizadas usando MHS tienen una mayor fase cristalina, con mayor número de cristales. Estos cristales tienen además perímetros mayores, comparados con las muestras sinterizadas en hornos convencionales. MHS produce patrones de cristalización y proporción de cristal/matrix diferentes a las producidos por sinterizado convencional. Esto puede asociarse a las mejoras en propiedades mecánicas reportadas previamente.

Study on friction and wear properties of dental zirconia ceramics processed by microwave and conventional sintering methods / 华西口腔医学杂志

<p><b>OBJECTIVE</b>This study evaluated the wear of an antagonist and friction and wear properties of dental zirconia ceramic that was subjected to microwave and conventional sintering methods.</p><p><b>METHODS</b>Ten specimens were fabricated from Lava brand zirconia and randomly assigned to microwave and conventional sintering groups. A profile tester for surface roughness was used to measure roughness of the specimens. Wear test was performed, and steatite ceramic was used as antagonist. Friction coefficient curves were recorded, and wear volume were calculated. Finally, optical microscope was used to observe the surface morphology of zirconia and steatite ceramics. Field emission scanning electron microscopy was used to observe the microstructure of zirconia.</p><p><b>RESULTS</b>Wear volumes of microwave and conventionally sintered zirconia were (6.940±1.382)×10⁻², (7.952±1.815) ×10⁻² mm³, respectively. Moreover, wear volumes of antagonist after sintering by the considered methods were (14.189±4.745)×10⁻², (15.813±3.481)×10⁻² mm³, correspondingly. Statistically significant difference was not observed in the wear resistance of zirconia and wear volume of steatite ceramic upon exposure to two kinds of sintering methods. Optical microscopy showed that ploughed surfaces were apparent in zirconia. The wear surface of steatite ceramic against had craze, accompanied by plough. Scanning electron microscopy showed that zirconia was sintered compactly when subjected to both conventional sintering and microwave methods, whereas grains of zirconia sintered by microwave alone were smaller and more uniform.</p><p><b>CONCLUSIONS</b>Two kinds of sintering methods are successfully used to produce dental zirconia ceramics with similar friction and wear properties.
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Surface roughness and volumetric contraction of a Y-TZP ceramic sintered by microwave energy and by resistive heating / Rugosidade da superfície e contração volumétrica de uma cerâmica Y-TZP sinterizada por energia de microondas e por aquecimento resistivo

Objectives: The aim of this study was to evaluate a Y-TZP ceramic sintered by a microwave protocol on volume shrinkage and surface roughness. Material and Methods: Twenty four (N=24) Y-TZP discs were fabricated by milling in CAD/ CAM for size standardization. The mean final dimensions of the specimens were 15 mm X 1.6 mm. Samples were divided into 2 groups (n=12): conventional resistive heating sintering protocol (C - Control) and microwave sintering protocol (MO - experimental). For the characterization of the specimens, surface roughness (Ra and Rz parameters) was evaluated with a roughness tester, and volume shrinkage was measured with a hand micrometer. Data were statistically evaluated by Student's t and Mann-Whitney U tests (α=0.05). Results: The roughness results were: 0.25 µm ± 0.02 (Ra) and 2.68 µm ± 0.666 (Rz) for the MO samples; 0.26 µm ± 0.04 (Ra) and 2.73 µm ± 0.461 (Rz) for the C group (Ra: p = 0.19; Rz: p = 0.81). The shrinkage results was: MO (21.02% ± 2.70) and C (20.10% ± 0.52) (p = 0.274). Conclusion: The conventional and microwave sintering methods were similar regarding surface roughness and volume shrinkage of Y-TZP dental ceramic (AU)

Objetivo: avaliar uma cerâmica de zircônia estabilizada com óxido de ítrio (Y-TZP) sinterizada por um protocolo em micro-ondas quanto à contração volumétrica e a rugosidade superficial. Material e Métodos: Vinte e quatro discos (n = 24) de Y-TZP foram fresados em CAD / CAM para padronização do tamanho. A dimensões finais médias dos corpos de prova foram de 15 mm X 1,6 mm. As amostras foram divididas em 2 grupos (n = 12): protocolo de sinterização convencional por aquecimento resistivo (C - Controle) e protocolo de sinterização por microondas (MO - experimental). A caracterização das amostras foi realizada pela avaliação da rugosidade superficial, com um rugosímetro (parâmetros Ra e Rz) e da contração volumétrica, medida com um micrômetro manual. Os dados foram estatisticamente avaliados pelos testes de t-Studant e U-Mann-Whitney (α=0,05). Resultados: Os resultados de rugosidade foram: 0,25 µm ± 0,02 (Ra) e 2,68 µm ± 0,666 (Rz) para o MO; e 0,26 µm ± 0,04 (Ra) e 2,73 µm ± 0,461 (Rz) para o grupo C (Ra: p = 0,19; Rz: p = 0,81). A contração volumétrica foi de: MO (21,02% ± 2,70) e C (20,10% ± 0,52) (p = 0,274). Conclusão: os métodos de sinterização convencionais e de microondas são semelhantes, no que diz respeito à rugosidade superficial e retração de volume da cerâmica dental Y-TZP. (AU)