Caracterização microestrutural e resistência à fadiga de zircônias de alta, super e extra translucidez / Microstructural characterization and fatigue strength of high, super and extra translucent zirconia ceramics

O objetivo deste estudo foi caracterizar a microestrutura de cerâmicas de zircônia parcialmente estabilizada com ítria com diferentes níveis de translucidez e avaliar o efeito na dureza, tenacidade à fratura e resistência à flexão biaxial (ensaio com carga monotônica e resistência à fadiga). Amostras em forma de disco foram obtidas de cerâmica de zircônia de alta translucidez (Vita YZ HT), super translucidez (Vita YZ ST) e extra translucidez (Vita YZ XT), seguindo as diretrizes da ISO 6872/2015 para testes de resistência à flexão biaxial, e também na menor espessura de utilização indicada pelo fabricante (dimensões finais de 12 mm de diâmetro, 0,7 e 1,2 ± 0,1 mm de espessura). Para a caracterização, foram realizadas análises de difração de raios-X (DRX), microscopia eletrônica de varredura (MEV) e espectroscopia de dispersão de energia (EDS), para análise das propriedades mecânicas, dureza Vickers, tenacidade à fratura e resistência à flexão biaxial (ensaio com carga monotônica) e ensaio de resistência à fadiga em flexão biaxial (ensaio acelerado step-stress). A zircônia ST e XT apresentaram defeitos superficiais na análise de MEV, enquanto a zircônia HT apresentou maior uniformidade dos grãos na superfície. Todas as cerâmicas apresentaram composições químicas semelhantes, diferindo principalmente na quantidade de ítria, que foi maior com o aumento da translucidez do material; nos resultados de DRX, a quantidade de fase cúbica também foi maior com o aumento da translucidez (XT> ST> HT). XT e HT apresentaram os maiores valores de dureza e quanto à tenacidade à fratura, HT difere de ST e XT, que foram semelhantes. Em relação à resistência à fadiga e probabilidade de sobrevivência, XT (0,7 mm e 1,2 mm) apresentou o pior desempenho mecânico (resistência à flexão biaxial à fadiga e ciclos até a falha), enquanto HT e ST apresentaram valores estatisticamente semelhantes e superiores à XT, mesmo em espessuras finas (0,7 mm) e espessura convencional (1,2 mm). A zircônia super translúcida (ST) apresenta comportamento de fadiga semelhante à zircônia altamente translúcida HT, que já possui um excelente reconhecimento na literatura. Cerâmicas de extra translucidez (XT) ainda precisam evoluir no processamento. Mudanças na microestrutura das cerâmicas de zircônia translúcida e na quantidade de ítria disminuiram as propriedades mecânicas(AU)

The aim of this study was to characterize the microstructure of Yttria partially stabilized zirconia ceramics with different levels of translucency and to evaluate the effect on the hardness, fracture toughness and biaxial flexural strength (monotonic and fatigue). Disc-shaped specimens were obtained from high translucency (Vita YZ HT), super translucency (Vita YZ ST) and extra translucency zirconia ceramics (Vita YZ XT), following ISO 6872/2015 guidelines for biaxial flexural strength testing (final dimensions of 12 mm in diameter, 0.7 and 1.2 ± 0.1 mm in thickness). For characterization, X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and energy dispersion spectroscopy (EDS) analyzes were performed and for mechanical properties, Vickers hardness, fracture toughness and biaxial flexural strength (monotonic and fatigue). The ST and XT zirconia showed surface defects under SEM analysis, while HT zirconia exhibited greater grain uniformity on the surface. All ceramics showed similar chemical compositions, differing mainly in the amount of yttria, which was higher as the translucency of the material increased; and in XRD the amount of cubic phase was also greater with the increased translucency (XT > ST > HT). XT and HT present the highest hardness values and about the fracture toughness, HT differs from ST and XT, which were similar. Regarding the fatigue strength and survival probability, XT (0.7 mm and 1.2 mm) showed the worst mechanical performance (fatigue biaxial flexural strength and cycles until failure), while HT and ST presented statistically similar values and higher than XT, even between thin (0.7 mm) and conventional thickness (1.2 mm). Super translucent zirconia (ST) has similar fatigue behavior than high-translucent zirconia HT, which already has an excellent recognition in the literature. Extra (XT) translucency ceramics still need to evolve in processing. Changes in the microstructure of translucent zirconia ceramics and the amount of yttria have reduced the mechanical properties(AU)

Risk communication in the context of clinical research

Abstract Physicians and dentists usually make clinical decisions and recommendations without a clear understanding of the meaning of the numbers regarding the accuracy of diagnostic tests and the efficacy of treatments. This critical review aimed to identify problems in the communication of diagnostic test accuracy and treatment benefits and to suggest strategies to improve risk communication in these contexts. Most clinical decisions are taken under uncertainty. Health professionals cannot predict the outcome in one individual patient. This uncertainty invites these professionals to make decisions based on heuristics, which gives rise to several cognitive biases. Cognitive biases are automatic and unconscious, so how is it possible to mitigate their undesirable effects on risk interpretation in the context of clinical practice? Some forms of risk communication reinforce cognitive bias, while others weaken them. Maybe one of the most difficult obstacles to overcome is the difficulty to think with numbers. This difficulty probably arises from a mismatch of ancestral adaptations of the brain having to deal with modern environments, which are quite different from the ancestral ones. There are two quite common, but bad, forms of risk communication: the conditional probability and the relative risk reduction or efficacy. People, including physicians and dentists, are confused with this kind of information. The main methods discovered so far to facilitate a clearer understanding are to emphasize the base rates of the events and to use absolute numbers, that is to use natural frequencies, instead of percentages and conditional probabilities.

Reliability, failure probability, and strength of resin-based materials for CAD/CAM restorations

ABSTRACT Objective: This study investigated the Weibull parameters and 5% fracture probability of direct, indirect composites, and CAD/CAM composites. Material and Methods: Discshaped (12 mm diameter x 1 mm thick) specimens were prepared for a direct composite [Z100 (ZO), 3M-ESPE], an indirect laboratory composite [Ceramage (CM), Shofu], and two CAD/CAM composites [Lava Ultimate (LU), 3M ESPE; Vita Enamic (VE), Vita Zahnfabrik] restorations (n=30 for each group). The specimens were polished, stored in distilled water for 24 hours at 37°C. Weibull parameters (m= modulus of Weibull, σ0= characteristic strength) and flexural strength for 5% fracture probability (σ5%) were determined using a piston-on-three-balls device at 1 MPa/s in distilled water. Statistical analysis for biaxial flexural strength analysis were performed either by both one-way ANOVA and Tukey's post hoc (α=0.05) or by Pearson's correlation test. Results: Ranking of m was: VE (19.5), LU (14.5), CM (11.7), and ZO (9.6). Ranking of σ0 (MPa) was: LU (218.1), ZO (210.4), CM (209.0), and VE (126.5). σ5% (MPa) was 177.9 for LU, 163.2 for CM, 154.7 for Z0, and 108.7 for VE. There was no significant difference in the m for ZO, CM, and LU. VE presented the highest m value and significantly higher than ZO. For σ0 and σ5%, ZO, CM, and LU were similar but higher than VE. Conclusion: The strength characteristics of CAD/ CAM composites vary according to their composition and microstructure. VE presented the lowest strength and highest Weibull modulus among the materials.

Avaliaçäo da erupçäo de dentes decíduos entre crianças nascidas com baixo peso e com peso normal / Evaluation of the deciduos tooth eruption in children born with normal weight and with low weight

O objetivo deste trabalho foi verificar a cronologia e frequência de erupçäo dos dentes decíduos em crianças com peso normal(>2.500 gramas) e com baixo peso (