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Objetivo: Este estudo avaliou o efeito do glazeamento e da ciclagem térmica na resistência à flexão biaxial e na dureza Vicker’s de diferentes materiais à base de zircônia. Material e Métodos: Espécimes de disco (15 mm x 1,15 mm) de zircônia foram confeccionados usando 3 sistemas (ZirkonZahn, Cercon, Ceramill) de acordo com a recomendação de cada fabricante. Os espécimes de cada sistema cerâmico foram randomicamente divididos em 2 grupos. Enquanto metade dos espécimes foram glazeados, a outra metade permaneceu não glazeado. Adicionalmente, cada grupo foi divido em 4 subgrupos submetidos a diferentes ciclagens térmicas (0-control, 1000, 3000, 5000 ciclos, 5-55 ºC). A resistência à flexão biaxial foi realizada em uma máquina de teste universal (1 mm/min). As amostras não glazeadas foram submetidas a microdureza Vicker’s antes e após a ciclagem térmica (0-control, 1000, 3000, 5000 cycles, 5-55 ºC). Os dados foram estatisticamente analisados usando ANOVA 1-fator, ANOVA 2-fatores e teste de Tukey’s (p < 0,05). Resultados: Nas amostras não cicladas (1104-1388 MPa), o glazeamento reduziu significativamente a resistência à flexão biaxial de todos os sistemas cerâmicos (845.65-897.35 MPa) (p = 0,000). Enquanto nos grupos não glazeados todas as modalidades de ciclagem térmica reduziram significantemente a resistência à flexão biaxial (864- 1156 MPa) (p = 0,000), nos grupos glazeados a ciclagem térmica não afetou os resultados (829.4- 854.9 MPa) (p = 0,405). Comparados aos grupos não envelhecidos (1414.1 VHN), a ciclagem térmica reduziu significantemente a dureza Vickers apenas para o Cercon (1365.9 VHN) (p = 0,005). Conclusão: O glazeamento reduz a resistência à flexão biaxial dos sistemas à base de zircônia testados. As amostras não glazeadas foram mais afetadas pela ciclagem que as amostras glazeadas. Estas informações podem ter relevância clínica na durabilidade de reconstruções em zircônia monolítica.

Objective: This study evaluated the effect of glazing and thermal cycling on biaxial flexural strength and Vickers hardness of different zirconia framework materials. Material and Methods: Disc shaped zirconia specimens (15 mm x 1.15 mm) were fabricated using three systems (ZirkonZahn, Cercon, Ceramill) according to each manufacturer`s instructions. The specimens of each system were randomly divided into 2 groups. While half of the specimens were glazed, the other half was left unglazed. Each group was further divided into 4 subgroups to be subjected to thermal cycling (0-control, 1000, 3000, 5000 cycles, 5-55 ºC). Biaxial flexural strength was tested in a universal testing machine (1 mm/min). Unglazed zirconia specimens were subjected to Vickers microhardness with and without thermal cycling (0-control, 1000, 3000, 5000 cycles, 5-55 ºC). Data were statistically analyzed using one-way ANOVA, twoway ANOVA and Tukey’s test (p < 0.05). Results: In non-aged conditions (1104-1388 MPa), glazing significantly decreased the biaxial flexural strength of all zirconia ceramics (845.65-897.35 MPa) (p = 0.000). While in the non-glazed groups, all thermal cycling regimens significantly decreased the biaxial flexural strength (864 -1156 MPa) (p = 0.000), in glazed groups thermal cycling did not affect the results (829.4-854.9 MPa) (p = 0.405). Compared to the non-aged group (1414.1 VHN), thermal cycling decreased the Vickers hardness significantly only for Cercon (1365.9 VHN) (p = 0.005). Conclusion: Glazing decreased the biaxial flexural strength of the zirconia ceramics tested. Unglazed zirconia ceramics were weaker against thermal cycling compared to glazed ones. For the long-term durability of monolithic zirconia reconstructions, this information may have clinical significance.

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The aim of this study was to evaluate the effect of glazing on biaxial flexural strength of different zirconia core materials. Disc-shaped zirconia (ZirkonZahn, Cercon, Ceramill) specimens (15 mm x 1.15+/-0.02 mm) were prepared according to manufacturers' instructions. The specimens from each system were divided into 2 groups (N= 10): unglazed and glazed. Glaze liquid was applied on the entire surface of the specimens of the glazed group and fired according to manufacturers' instructions. Flexural strength test was performed in a universal testing machine (crosshead speed: 1 mm/min). Data were statistically analyzed using two-way ANOVA and Tukey's test (p= 0.05). The mean flexural strength values for unglazed ZirkonZahn specimens (1388+132 MPa) were significantly higher than those of unglazed Cercon (1104+124 MPa) and unglazed Ceramill (1172+127 MPa) specimens. The mean flexural strength of glazed specimens did not show any statistically significant difference. Glazing decreased the flexural strength results significantly for all systems (p< 0.05). Glazing decreased the flexural strength values for ZirkonZahn, Cercon and Ceramill specimens. Unglazed ZirkonZahn specimens revealed significantly higher mean flexural strength values than that ofunglazed and glazed zirconia materials tested in this study.

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El objetivo de este estudio fue evaluar el efecto del glaseado sobre la resistencia flexural biaxial de diferentes tipos de materiales para núcleo a base de circonia. Se confeccionaron especímenes de circonia en forma de disco (15 mm x 1.15±0.02 mm) de acuerdo con las instrucciones delfabricante. Los especímenes de cada sistema fueron divididos en dos grupos (n=10): glaseados y sin glasear. El líquido glaseador fue aplicado sobre toda la superficie de los especímenes del grupo glaseado y fue cocido de acuerdo con las instrucciones del fabricante. Se llevó a cabo el ensayo de resistencia flexural en una máquina universal (velocidad de desplazamiento del cabezal: 1mm/min). Los datos fueron analizados estadísticamente pormedio de ANOVA de dos vías y prueba de Tukey (p=0.05). El valor medio de resistencia flexural para los especímenes sin glasear ZirkonZahn (1388±132 MPa) fue significativamentemás elevado que los especimenes sin glasear Cercon (1104±124 MPa) y Ceramill (1172±127 MPa). El valor medio de resistencia flexural para los especimenes glaseados no mostródiferencias significativas. El glaseado disminuyó significativamente la resistencia flexural de todos los sistemas (p<0.05). El glaseado disminuye los valores de resistencia flexural de los especímenes de ZirkonZahn, Cercon y Ceramill. Los especimenes sin glasear ZirkonZahn revelaron valores significativamente máselevados que aquellos materiales glaseados y sin glasear a basede circonia empleados en este estudio.

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The surface of zirconia may be damaged during grinding, influencing the mechanical properties of the material. The purpose of this study was to compare the flexural strength of zirconia after different grinding procedures. Twenty bar-type zirconia specimens (21 x 5 x 2 mm) were divided into 4 groups and ground using a high-speed handpiece or a low-speed straight handpiece until the bars were reduced 1 mm using two different grinding times: continuous grinding and short-time grinding (n=5). Control specimens (n=5) were analyzed without grinding. The flexural strengths of the bars were determined by using 3-point bending test in a universal testing machine at a crosshead speed of 0.5 mm/min. The fracture load (N) was recorded, and the data were analyzed statistically by the Kruskal Wallis test at a significance level of 0.05. In the test groups, high-speed handpiece grinding for a short time had produced the highest mean flexural strength (878.5 ± 194.8 MPa), while micromotor continuous grinding produced the lowest mean flexural strength (733.8 ± 94.2 MPa). The control group was the strongest group (928.4 ± 186.5 MPa). However, there was no statistically significant differences among the groups (p>0.05). Within the limitations of the study, there was no difference in flexural strength of zirconia specimens ground with different procedures.

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