Efeito do desgaste e ciclo térmico de regeneração sobre o limite de fadiga de uma Y-TZP e sobre a resistência flexural e de união de corpos-de-prova bicamada Y-TZP/cerâmica feldspática
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2018-08-03
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Universidade Estadual Paulista (Unesp)
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O objetivo deste estudo foi avaliar o efeito do desgaste e do ciclo térmico de regeneração (R) no limite de fadiga flexural e na caracterização superficial da cerâmica LavaTM Y-TZP e avaliar a influência de métodos de desgaste e do R sobre a resistência à flexão e de união da cerâmica LavaTM Y-TZP recoberta por cerâmica de cobertura. Foram obtidos espécimes em forma de barra (20 x 4,0 x 1,2 mm, n=40; 20 x 4,0 x 1,5 mm, N=80). Metade das barras de 1,2 mm constituíram o grupo controle (C), enquanto as de 1,5 mm foram desgastadas sob irrigação (DI) ou não (D). A outra metade dos espécimes de 1,2 mm e das desgastadas foram submetidas ao R (1000 ºC, 30 min), gerando os grupos CR, DIR e DR. O limite de fadiga (500.000 ciclos, 10 Hz) foi avaliado pelo método de escada. A topografia da superfície (n=3) e a área da fratura (n=3) foram avaliadas por MEV. Transformação de fase foi avaliada por difração de raios-X. Os dados de limite de fadiga foram submetidos ao teste ANOVA dois fatores e Tukey (α=0,05). Além disso, barras (N=72) de Y-TZP nas dimensões 20 x 4,0 x 1,20 mm (Controle (C); n=24) e 20 x 4,0 x 1,50 mm (n=48) foram obtidas. Os espécimes com 1,50 mm de altura foram desgastadas, com fresa diamantada (DF) ou pedra específica para zircônia (DP). Metade dos espécimes do grupo Controle e metade das desgastadas foram submetidas ao R (CR, DFR e DPR). Em seguida, a cerâmica de cobertura IPS e.max Ceram foi aplicada sobre todos os espécimes, sendo a dimensão final dos espécimes de 20 x 4,0 x 2,4 mm. Foi realizado o ensaio monotônico de resistência à flexão. Os dados foram analisados pelo teste ANOVA dois fatores e Tukey (α=0,05). Para o teste de união por iniciação de trinca entre os espécimes bicamada Y-TZP/cerâmica de cobertura foram confeccionadas 10 barras de zircônia para cada condição experimental (N=60), nas dimensões de 25 x 3,0 x 0,5 mm, aplicada, na região central, a cerâmica de cobertura nas dimensões de 8,0 x 3,0 x 1,0 mm. O teste de resistência de união foi conduzido em máquina de ensaios EMIC DL-2000. Os dados foram analisados por Anova dois fatores (α=0,05). Nos grupos não submetidos ao R, a média do limite de fadiga do DI foi maior (P<0,05) do que nos grupos D e C, sem diferença entre si (P>0,05). Quando submetidos à R, foi observada que DI>C>D (P<0,05). O R aumentou o limite de fadiga do grupo C e diminuiu o dos grupos D e DI (P<0,05). Os desgastes criaram ranhuras evidentes na superfície de zircônia. Falhas iniciaram no lado de tração de todos os espécimes. As porcentagens de fase monoclínica foram diferentes antes e depois da carga cíclica. Nos espécimes bicamada, previamente à aplicação do R, houve aumento significativo da resistência à flexão dos grupos desgastados em relação ao controle. Após aplicação do R não houve diferença estatisticamente significativa entre os grupos desgastados e controle. O R não produziu efeito sobre a resistência à flexão dos espécimes bicamada submetidos ou não aos desgastes. Não houve diferença entre os grupos para o teste de resistência de união.
The aim of this study was to evaluate the effect of grinding and regeneration cycle (R) on the flexural fatigue limit and on the surface characterization of LavaTM Y-TZP ceramics and evaluate the influence of grinding methods and of R on the flexural strength and bonding strength between LavaTM Y-TZP and veneering porcelain specimens. Bar-shaped specimens (20 x 4.0 x 1.2 mm, n = 40; 20 x 4.0 x 1.5 mm, N=80) were obtained. Half of the 1.2 mm specimens was the control group (C), while the 1.5 mm specimens were ground under irrigation (DI) or not (D). Half of ground specimens and half of the 1.2 mm specimens were submitted to R (1000 ° C, 30 min), forming the groups CR, DIR and DR. The fatigue limit (500,000 cycles, 10 Hz) was evaluated by the staircase method. Surface topography (n=3) and fracture area (n=3) were evaluated by SEM. Phase transformation was evaluated by X-ray diffraction. Fatigue limit data were analyzed by two-way ANOVA and Tukey tests (α=.05). Moreover, Y-TZP bars (N=72) in the dimensions of 20 x 4.0 x 1.20 mm (Control (C); n=24) and 20 x 4.0 x 1.50 mm (n=48) were obtained. The specimens with 1.50 mm in height were ground, with diamond burs (DF) or zirconia stone (DP). Half of the specimens of the Control group and half of ground ones were submitted to R (CR, DFR and DPR). Then, veneering porcelain (IPS e.max Ceramic) was applied over all specimens, acquiring the final dimension of 20 x 5.0 x 2.4 mm. The monotonic flexural strength test was performed. Data were analyzed by two-way ANOVA and Tukey tests (α=.05). For de-bonding/crack initiation strength between Y-TZP and veneering porcelain, 10 bars of zirconia were used for each experiment (N=60), with dimensions of 25 x 3.0 x 0.5 mm, applied on center region, the veneering porcelain in the dimensions of 8.0 x 3.0 x 1.0 mm. The bond strength was measured on EMIC DL-2000 testing machine. Data were analyzed by two-way ANOVA (α=.05). In groups not submitted to R, the mean flexural fatigue limit of DI was higher (P<.05) than that D and C groups, similar between them (P>.05). When R was present, it was observed that DI>C>D (P<.05). The C increased the fatigue limit of C group and decreased that of D and DI groups (P<.05). Grinding created evident grooves on the zirconia surface. Failures started on the tension side of all specimens. The amount of monoclinic phase was different before and after cyclic loading. On bilayered specimens, previous to R, it was observed a significant increase of flexural strength on ground groups compared to control. After R, there was not significant difference among ground and control groups. The R was not capable to produce effects on the flexural strength of the bilayered specimens submitted or not to grinding. There was no statistical difference among groups for the bond strength test.
The aim of this study was to evaluate the effect of grinding and regeneration cycle (R) on the flexural fatigue limit and on the surface characterization of LavaTM Y-TZP ceramics and evaluate the influence of grinding methods and of R on the flexural strength and bonding strength between LavaTM Y-TZP and veneering porcelain specimens. Bar-shaped specimens (20 x 4.0 x 1.2 mm, n = 40; 20 x 4.0 x 1.5 mm, N=80) were obtained. Half of the 1.2 mm specimens was the control group (C), while the 1.5 mm specimens were ground under irrigation (DI) or not (D). Half of ground specimens and half of the 1.2 mm specimens were submitted to R (1000 ° C, 30 min), forming the groups CR, DIR and DR. The fatigue limit (500,000 cycles, 10 Hz) was evaluated by the staircase method. Surface topography (n=3) and fracture area (n=3) were evaluated by SEM. Phase transformation was evaluated by X-ray diffraction. Fatigue limit data were analyzed by two-way ANOVA and Tukey tests (α=.05). Moreover, Y-TZP bars (N=72) in the dimensions of 20 x 4.0 x 1.20 mm (Control (C); n=24) and 20 x 4.0 x 1.50 mm (n=48) were obtained. The specimens with 1.50 mm in height were ground, with diamond burs (DF) or zirconia stone (DP). Half of the specimens of the Control group and half of ground ones were submitted to R (CR, DFR and DPR). Then, veneering porcelain (IPS e.max Ceramic) was applied over all specimens, acquiring the final dimension of 20 x 5.0 x 2.4 mm. The monotonic flexural strength test was performed. Data were analyzed by two-way ANOVA and Tukey tests (α=.05). For de-bonding/crack initiation strength between Y-TZP and veneering porcelain, 10 bars of zirconia were used for each experiment (N=60), with dimensions of 25 x 3.0 x 0.5 mm, applied on center region, the veneering porcelain in the dimensions of 8.0 x 3.0 x 1.0 mm. The bond strength was measured on EMIC DL-2000 testing machine. Data were analyzed by two-way ANOVA (α=.05). In groups not submitted to R, the mean flexural fatigue limit of DI was higher (P<.05) than that D and C groups, similar between them (P>.05). When R was present, it was observed that DI>C>D (P<.05). The C increased the fatigue limit of C group and decreased that of D and DI groups (P<.05). Grinding created evident grooves on the zirconia surface. Failures started on the tension side of all specimens. The amount of monoclinic phase was different before and after cyclic loading. On bilayered specimens, previous to R, it was observed a significant increase of flexural strength on ground groups compared to control. After R, there was not significant difference among ground and control groups. The R was not capable to produce effects on the flexural strength of the bilayered specimens submitted or not to grinding. There was no statistical difference among groups for the bond strength test.
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Cerâmica, Resistência de materiais, Microscopia Eletrônica, Ceramics, Material Resistance, Microscopy, Electron