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OBJECTIVE: The aim of this study was to evaluate the effect of four different finishing procedures on the fatigue strength of a fully stabilized zirconia (5Y-FSZ) material. MATERIALS AND METHODS: Disc-shaped specimens of a 5Y-FSZ (Katana UTML, Kuraray Noritake) were made (ISO 6872-2015), grinded with 600- and 1200-grit silicon carbide paper, sintered as recommended, and randomly assigned into four groups according to the finishing technique: C (control, as-sintered), P (polished with polishing rubbers), G (glaze application - powder/liquid technique), and PG (polished with polishing rubbers + glaze application - powder/liquid). Then fatigue strength (staircase method), X-ray diffraction (XRD), and scanning electron microscopy (SEM) analyses were performed. RESULTS: The C group presented the lowest fatigue strength, while the PG group presented the highest. The P and G groups presented intermediate behavior, presenting similar statistical results. XRD showed similar crystalline phase patterns for all groups. SEM images revealed some changes in the zirconia surface, with the P group presenting some scratches on the surface, while the scratches in the PG group were filled with the glaze material. CONCLUSION: None of the techniques analyzed in this study impaired the fatigue strength of fully stabilized zirconia. Importantly, the polishing rubbers combined with glaze application (PG group) improved its fatigue strength. CLINICAL RELEVANCE: The polishing rubbers followed by glaze application improve the fatigue strength in ultra-translucent zirconia.

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OBJECTIVE: To evaluate the composition, flexural strength and fatigue behaviour of lithium disilicate ceramic (LD) after repeated firings and different staining techniques. METHODS: LD discs were fabricated and divided according to number of firing cycles and staining technique: CO - control, discs were crystallized (850°C/10min); SC - single-step characterization - crystallization and staining (applied with a thin brush) were performed in a single step with one firing cycle (850°C/10min); and DC - double-step characterization - crystallization firing cycle was performed first (850°C/10min), followed by staining firing cycle (770°C/90s). Specimens were fired two, four or six times (one crystallization firing cycle and one, three or five staining firing cycles), resulting into 9 groups (n=30): COII, COIV, COVI, SCII, SCIV, SCVI, DCII, DCIV and DCVI. The composition of the specimens was investigated (EDS, XRD, Raman spectroscopy), and the biaxial flexural strength (n=10) and staircase tests (n=20, 5×104 cycles, 5Hz) were performed. Data were subjected to one-way ANOVA and Tukey's test (α=0.05). RESULTS: EDS and XRD revealed amorphous content for stained groups. Biaxial flexural strength was not affected by repeated firings in any group, but stained groups presented lower flexural strength than control groups (p=0.001). The fatigue limit results decreased in all groups compared to flexural strength. SC groups showed similar (SCII and SCIV) or even higher fatigue limits (SCVI) than the control groups, and DC showed the lowest fatigue limit values. SEM and Raman suggested that the interfaces between staining and the LD showed only an overlap for the DC groups, whereas for the SC it was suggested an interaction between the stain and the LD. SIGNIFICANCE: Repeated firings did not result in decreased lithium disilicate flexural strength.Staining affected flexural strength and also resulted in increased amorphous content in the characterized specimens. Single-step staining resulted in the highest fatigue limit.

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This study evaluated the effect of grinding and regeneration firing on the flexural fatigue limit and surface characterization of Lava™ Y-TZP ceramic. Forty bar-shaped specimens with 20 × 4.0 × 1.2 mm constituted the as-sintered group (AS = control group), and 80 specimens with 20 × 4.0 × 1.5 mm were ground with cylindrical laboratory stone under water-cooling (WG) or in a dry condition (G) to reach 1.2 mm in thickness. Half of specimens were submitted to regeneration firing (1000 °C, 30 min), forming the groups AS/R, WG/R and G/R. Fatigue limit (500,000 cycles, 10 Hz) was determined by staircase method in a 4-point flexural fixture. Data were analyzed by 2-way ANOVA and Tukey HSD tests (α = 0.05). The surface topography (n = 3) and fracture area (n = 3) were evaluated by SEM. Samples were also analyzed by Rietveld refinement from X-ray diffraction data. ANOVA revealed significant differences (P < .001) for grinding protocol, regeneration firing and their interaction. In the groups not submitted to regeneration firing, the mean flexural fatigue limit of WG was higher (P < .05) than that of G and AS, with no statistical difference between each other (P > .05). After regeneration firing the inequality WG>AS>G (P < .05) was observed. The regeneration firing increased the fatigue limit of AS group and decreased those of G and WG groups (P < .05). Grinding protocols created evident grooves on zirconia surface. Failures initiated on tensile side of all specimens. The percentages (wt%) of monoclinic phase before cyclic loading were: AS (7.4), AS/R (6.5), G (2.8), G/R (0.0), WG (4.4), WG/R (0.0); and after cyclic loading: AS (8.6), AS/R (1.2), G (2.4), G/R (5.7), WG (6.3), WG/R (0.0). Wet grinding did not compromise the fatigue limit of zirconia, increasing its mechanical strength. Regeneration firing reduced the fatigue limit of ground samples, despite reducing the amount of monoclinic phase in all experimental conditions.

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This study investigated the effect of etching with distinct hydrofluoric (HF) acid concentrations on the cyclic load-to-failure (CLf) of simplified lithium disilicate glass-ceramic restorations adhesively cemented to a dentin analogue (n = 20): non-etched/control (CTRL), or etched for 20 s with HF acid at 3% (HF3), 5% (HF5), or 10% (HF10). A silane coating was then applied onto the ceramic surfaces. Fatigue tests followed the staircase approach (initial load= 720 N; step-size= 70 N; 500,000 cycles per sample; 20 Hz) using a hemispheric stainless-steel piston (Ø= 40 mm) under water. The CLf data were analyzed using Dixon and Mood method. Topographic and fractographic analyses were conducted. CLf (in N) of HF3 (1355 ±â€¯32.0) and HF5 (1335 ±â€¯58.8) groups were the highest and statistically similar; HF10 presented intermediate CLf (1175 ±â€¯132.9), while the non-etched group had the lowest one (965 ±â€¯145.0). Topographical analysis showed that the higher the HF acid concentration, the more pronounced the topographical changes. All failures (radial cracks) started from the inner surface of the ceramic discs. Topographical changes promoted by intermediate HF acid concentrations (3% and 5%) may improve fatigue performance for adhesively-cemented lithium disilicate restorations.

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OBJECTIVE: To investigate the effect of intaglio surface adjustment of simplified lithium disilicate ceramic restorations adhesively cemented to a dentin-like material on its fatigue behavior. METHODS: Ceramic discs (IPS e.max CAD) were prepared and an in-Lab simulation of machining roughness was performed by grinding with SiC paper (#60). Ceramic discs were divided into 4 groups according to the internal adjustment of the cementation surface: no adjustments (CTRL); adjustment with a medium (M), fine (F), or extra fine (FF) diamond bur. Dentin-like material discs were also produced. Ceramic disc intaglio surfaces were etched (5% hydrofluoric acid; 20s) and received a silane coating. Dentin-like material discs were etched (10% hydrofluoric acid; 1min) and received a primer coating. Pairs of ceramic/dentin-like material were adhesively cemented (Multilink Automix), and fatigue failure load tests were performed using the Staircase approach (250,000 cycles; 20Hz). Roughness, topographic and fractographic analyses were performed. Statistical analyses were carried out through ANOVA tests. RESULTS: All ground groups (M=521.3 N; F=536.9 N; FF=676.2 N) presented lower fatigue failure load values than the control (1241.6 N). M diamond bur created a rougher surface than F (Ra and Rz parameters). However, FF was similar to F and M for Ra, and similar to F for Rz. SIGNIFICANCE: Bur adjustments on the intaglio surface of simplified lithium disilicate ceramic restorations greatly decreased the fatigue failure load even using an extra-fine diamond bur. Care should be taken when internal adjustments are needed.

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The force-frequency relationship (FFR) is an important intrinsic regulatory mechanism of cardiac contractility. However, a decrease (negative FFR) or no effect (flat FFR) on contractile force in response to an elevation of heart rate is present in the normal rat or in human heart failure. Reactive oxygen species (ROS) can act as intracellular signaling molecules activating diverse kinases as calcium-calmodulin-dependent protein kinase II (CaMKII) and p-38 MAP kinase (p-38K). Our aim was to elucidate the intracellular molecules implicated in the FFR of isolated rat ventricular myocytes. The myocytes were field-stimulated via two-platinum electrodes. Sarcomere length was recorded with a video camera. Ca2+ transients and intracellular pHi were recorded by epifluorescence. Increasing frequency from 0.5 to 3 Hz decreased cell shortening without changes in pHi. This negative FFR was changed to positive FFR when the myocytes were pre-incubated with the ROS scavenger MPG, the NADPH oxidase blocker apocynin, or by inhibiting mitochondrial ROS production with 5-HD. Similar results were obtained when the cells were pre-incubated with the CaMKII blocker, KN-93, or the p-38K inhibitor, SB-202190. Consistently, the levels of phosphorylation of p-38K and the oxidation of CaMKII were significantly higher at 2 Hz than at 0.5 Hz. Despite the presence of positive inotropic effect during stimulation frequency enhancement, Ca2+ transient amplitudes were reduced in MPG- and SB-202190-treated myocytes. In conclusion, our results indicate that the activation of the intracellular pathway involving ROS-CaMKII-p-38K contributes to the negative FFR of rat cardiomyocytes, likely by desensitizing the response of contractile myofilaments to Ca2+.

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Abstract This study evaluated the effect of grinding protocols and resintering on flexural fatigue limit and surface characterization of LavaTM Y-TZP. Bar-shaped specimens (20×4.0×1.2 mm, n=40; 20×4.0×1.5 mm, n=80) were obtained. Half of the thinner specimens (1.2 mm) constituted the as-sintered group (AS), while the thicker ones (1.5 mm) were ground with diamond burs under irrigation (WG) or not (G). The other half of thinner and half of ground specimens were resintered (1000 ºC, 30 min), forming the groups ASR, WGR and GR. Fatigue limit (500,000 cycles, 10 Hz) was evaluated by staircase method in a 4-point flexural fixture. Data were analyzed by 2-way ANOVA and Tukey's test (α=0.05). Surface topography (n=3) and fracture area (n=3) were evaluated by SEM. X-ray diffraction data (n=1) was analyzed by Rietveld refinement. ANOVA revealed significant differences (p<0.001) for the grinding protocol, resintering and their interaction. Grinding increased the fatigue limit of non-resintered groups. There was no significant difference among the resintered groups. Resintering significantly increased the fatigue limit of the AS group only. Both protocols created evident grooves on zirconia surface. The failures initiated at the tensile side of all specimens. The percentages (wt%) of monoclinic phase were AS (8.6), ASR (1.2), G (1.8), GR (0.0), WG (8.2), WGR (0.0) before, and AS (7.4), ASR (6.5), G (3.2), GR (0.2), WG (4.6), WGR (1.1) after cyclic loading. Grinding increased the fatigue limit of non-resintered Y-TZP and formed evident grooves on its surface. Resintering provided significant increase in the fatigue limit of as-sintered specimens. In general, grinding and resintering decreased or zeroed the monoclinic phase.

Resumo Este estudo avaliou o efeito de protocolos de desgaste e ressinterização no limite de fadiga flexural e na caracterização da superfície da zircônia LavaTM. Corpos-de-prova em forma de barra (20×4,0×1,2 mm, n=40; 20×4,0×1,5 mm, n=80) foram obtidos. Metade das barras com menor altura (1,2 mm) constituiu o grupo controle (AS), enquanto as de maior altura (1,5 mm) foram desgastadas com fresas diamantadas com (WG) ou sem (G) irrigação. A outra metade dos corpos-de-prova de menor altura e metade dos desgastados foram ressinterizadas (1000 °C, 30 min), obtendo-se os grupos ASR, WGR e GR. O limite de fadiga (500.000 ciclos, 10 Hz) foi avaliado pelo método de escada em dispositivo de flexão em 4 pontos. Os dados foram analisados pelos testes ANOVA a dois fatores e Tukey (α=0,05). A topografia de superfície (n=3) e área de fratura (n=3) foram avaliadas por MEV. Os dados de difração de raios-X (n=1) foram analisados pelo refinamento de Rietveld. ANOVA revelou diferenças significantes (p<0,001) para desgaste, ressinterização e interação entre os fatores. O desgaste aumentou o limite de fadiga para os grupos não ressinterizados. Não houve diferença significante entre os grupos ressinterizados. A ressinterização aumentou o limite de fadiga somente para o grupo AS. Ambos os protocolos criaram riscos evidentes na superfície da zircônia. As falhas iniciaram sempre no lado de tração. A porcentagem de fase monoclínica foi: AS (8.6), ASR (1.2), G (1.8), GR (0.0), WG (8.2), WGR (0.0) antes e AS (7.4), ASR (6.5), G (3.2), GR (0.2), WG (4.6), WGR (1.1) após a ciclagem. O desgaste aumentou o limite de fadiga da zircônia não ressinterizada e formou ranhuras evidentes na sua superfície. A ressinterização promoveu aumento significativo no limite de fadiga somente para o grupo controle. Em geral, o desgaste e a ressinterização diminuíram ou anularam o conteúdo de fase monoclínica.

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O objetivo deste trabalho foi mensurar a função de sensibilidade ao contraste de padrões circulares concêntricos (FSCr) com freqüências radiais de 0,25; 0,5; 1,0 e 2,0 cpg em crianças (8-9, 10-11 e 12-13 anos) e adultos jovens. Foram estimados limiares de contraste para 40 participantes (30 crianças e 10 adultos jovens) utilizando o método psicofísico da escolha forçada e nível baixo de luminância. Todos os participantes apresentavam acuidade visual normal e se encontravam livres de doenças oculares identificáveis. Os resultados mostraram que as curvas de FSCr de crianças de 8-9, 10-11 e 12-13 anos melhoram de forma significativa com a idade. Os resultados mostraram ainda que a FSCr de crianças de 12-13 anos é mais baixa do que a de adultos jovens. Estes resultados sugerem que o desenvolvimento da percepção visual de estímulos circulares concêntricos ocorre gradualmente se prolongando além dos 12-13 anos.

The aim of this study was to measure the function of contrast sensitivity to concentric circular patterns (rCSF) with radial frequencies of 0.25, 0.5, 1.0 and 2.0 cpd in children (8-9, 10-11 and 12-13 years of age) and young adults. Contrast thresholds were measured in 40 participants (thirty children and ten young adults) using the psychophysical forced-choice method and low luminance level. All participants were free from identifiable ocular diseases and had normal acuity. The results showed that curves for rCSFs of 8-9, 10-11 and 12-13 years old improved significantly with age. The rCSFs for the 12-13 years old was lower than those of adults. It is suggested that the development of visual perception in concentric circular stimuli increases gradually beyond 12-13 years of age.

El objetivo de este trabajo fue mensurar la función de sensibilidad al contraste de padrones circulares concéntricos (FSCr) con frecuencias radiales de 0,25; 0,5; 1,0 y 2,0 cpg en niños (8-9, 10-11 y 12-13 años) y adultos jóvenes. Fueron estimados umbrales de contraste para 40 participantes (30 niños y 10 adultos jóvenes) utilizando el método psicofísico de la elección forzada y nivel bajo de luminancia. Todos los participantes presentaban acuidad visual normal y estaban libres de enfermedades oculares identificables. Los resultados mostraron que las curvas de la FSCr de niños de 8-9, 10-11 y 12-13 años mejoran de forma significativa con la edad. Los resultados mostraron aún que la FSCr de niños de 12-13 años es más baja que la de adultos jóvenes. Estos resultados sugieren que el desarrollo de la percepción visual de estímulos circulares concéntricos ocurrí gradualmente prolongándose después de los 12-13 años.

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Em termos gerais, a FSC tem sido usada para caracterizar o desenvolvimento da percepção visual da forma de crianças. O objetivo do presente estudo foi mensurar e comparar curvas de sensibilidade ao contraste para estímulos radiais (FSCr) e grades senoidais (FSC) em crianças pré-escolares com o método psicofísico da escolha forçada- senoidais de 0,25; 0,5; 1 e 2 cpg em crianças pré-escolares (4 e 5 anos) e adultos jovens com o método psicofísico da escolha forçada. Participaram 15 voluntários com a acuidade visual normal ou corrigida distribuídos igualmente nas três faixas etárias. Os resultados mostraram que a sensibilidade melhora com o desenvolvimento e que a sensibilidade de todos os participantes foi maior para as grades senoidais do que para as freqüências radiais. Estes resultados sugerem que os estímulos radiais e as grades senoidais são processados por áreas visuais diferentes.

In general the FSC is used to characterise the development of the visual perception of material by children. The aim of the present work was to mensure and compare contrast the sensitivity curves to differ then of the radical stimuly (FSCr) and sine-wave gratings (FSC) in pré-school children, usind the psychophysical method of choice-forced for radial and sine-wave gratings stimuli of 0.25; 0.5; 1 and 2 cpd in 4-5 yearold preschool children and young adults using the psychophysical forced-choice staircase method. Fifteen volunteers with corrected-to-normal visual acuity, five in each age range, participated in the experiments. The results showed that the sensitivity improves with the development and that in for all participants the sensitivity was higher for sine-wave gratings than the radial frequencies. These results suggest that the radial and the sine-wave gratings stimuli are processed by different visual areas.

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