Static and cyclic loading effects on fracture toughness of contemporary CAD/CAM restorative materials

OBJECTIVES: To test and compare the effects of static and cyclic loading on fracture toughness (K1C) and microhardness of dental restorative CAD/CAM materials. MATERIAL AND METHODS: Five commercially available CAD/CAM restorative materials were included in this study: Lava™ Ultimate Restorative (3M ESPE), IPS Empress® CAD (Ivoclar Vivadent), Enamic® (VITA), IPS e.max® CAD (Ivoclar Vivadent), and CERASMART™ (GC Dental). Polished rectangular bars 4×2×14 mm (n=30) were prepared from mill blocks for each material. Single notch of 0.5-1 mm in depth was made on the center of one length edge. Ten specimens per group for each material were randomly selected for 1) static mode, 2) after 100k cyclic loads, and 3) after 200k cyclic loads. The survival bars after the fatigue test were then subjected to a three-point flexural test. K1C values were determined on ‘single-edge-pre-crack-beams’ (SEPB) method. In addition, random specimens after the flexural test were selected for Vickers microhardness test from each group. Additionally indentation fracture method (IF) was used to determine surface fracture toughness for e.max CAD and Empress CAD. All the results were analyzed via ANOVA with Tukey’s HSD test or least square regression model using JMP Pro 12.0. RESULTS: The mean fracture toughness (K1C) of the material tested in static mode (3.2 MPa.m1/2 for e.max CAD, 2 MPa.m1/2 for Lava Ult, 1.95 MPa.m1/2 for Empress CAD, 1.92 MPa.m1/2 for Enamic, and 1.65 MPa.m1/2 for Cerasmart). The 100k fatigue group (4.02 MPa.m1/2 for e.max CAD, 3.06 MPa.m1/2 for Cerasmart, 2.55 MPa.m1/2 for Lava Ult, 2.01 MPa.m1/2 for Enamic, 1.94 MPa.m1/2 for Empress CAD) The 200k fatigue group (3.14 MPa.m1/2 for Cerasmart, 2.83 MPa.m1/2 for Lava Ult, 2.68 MPa.m1/2 for e.max CAD, 2.01 MPa.m1/2 for Enamic, 1.72 MPa.m1/2 for Empress CAD). While there was a significant difference in the mean fracture toughness (K1C) and (VHN) after fatigue of material tested (p<0.05). CONCLUSION: The CAD/CAM materials tested exhibited a higher K1C values after cyclic loading, along with lower K1C compared to the static group. In addition, K1C values by IF method exhibit lower K1C values after fatigue that was not a good way to test the fracture toughness value.2018-09-28T00:00:00

Assessment of the Dentin Bond Strength Values of Resin Modified Glass Ionomer Restorative Material using Different In Vitro Test Methods

Objective: To assess whether the in vitro dentin bond strength values of a resin-modified glass ionomer restorative material (RMGI) are affected by different in vitro test methods. Methods: Mid-depth occlusal dentin of 36-extracted human third molars free of defects was exposed and finished with wet 600-grit silicon carbide paper for 10s. A commercially-available RMGI (Fuji II LC, GC America) was applied to all specimens according to manufacturer’s instructions, after which specimens were stored in 100% humidity at 37 °C for 24 h. Specimens were then randomly divided into three different test groups (n=12): shear bond strength (SBS), microtensile bond strength (µTBS), and four-point bending bond strength (4PBBS). Specimens were loaded to failure using universal testing machines and test-specific parameters: Instron for SBS and 4PBBS tests, EZ-Test for the µTBS test. The mode of bond failure (adhesive, cohesive or mixed) was qualitatively assessed with optical stereomicroscopy. Data were analyzed using one-way ANOVA and descriptive statistics. Results: There was a statistically significant difference between bond strength values for the different test methods (p<0.05). The mean bond strength values (± SD, in MPa) were 15.7 (±7.1) for SBS, 9.7 (±5.3) for µTBS and 37.3 (±12.8) for 4PBBS. With respect to the mode of failure, most SBS failures were adhesive in nature (83%), while the majority of µTBS and 4PBBS failures were mixed (69% and 47% respectively). Several µTBS and 4PBBS specimens failed during processing (before testing). Conclusion: The in vitro dentin bond strength values of a resin-modified glass ionomer material are greatly affected by the test method. The mode of bond failure is also affected by test method. The SBS test method demonstrated the highest percentage of adhesive failure and proved to be less technique sensitive. The majority of µTBS and 4PBBS failures were mixed. Use of the µTBS and 4PBBS may not be optimal laboratory test methods for comparison of the relative bond strength of RMGI materials to dentin. Use of the SBS test may allow more controlled comparison of the adhesive dentin bond among various RMGI formulations, whether already commercially available or under development.Master of Scienc

Corticotropin-releasing hormone as the homeostatic rheostat of feto-maternal symbiosis and developmental programming In utero and neonatal life

A balanced interaction between the homeostatic mechanisms of mother and the devel- oping organism during pregnancy and in early neonatal life is essential in order to ensure optimal fetal development, ability to respond to various external and internal challenges, protection from adverse programming, and safeguard maternal care availability after parturition. In the majority of pregnancies, this relationship is highly effective resulting in successful outcomes. However, in a number of pathological settings, perturbations of the maternal homeostasis disrupt this symbiosis and initiate adaptive responses with unpre- dictable outcomes for the fetus or even the neonate. This may lead to development of pathological phenotypes arising from developmental reprogramming involving interaction of genetic, epigenetic, and environmental-driven pathways, sometimes with acute conse- quences (e.g., growth impairment) and sometimes delayed (e.g., enhanced susceptibility to disease) that last well into adulthood. Most of these adaptive mechanisms are activated and controlled by hormones of the hypothalamo-pituitary adrenal axis under the influ- ence of placental steroid and peptide hormones. In particular, the hypothalamic peptide corticotropin-releasing hormone (CRH) plays a key role in feto-maternal communication by orchestrating and integrating a series of neuroendocrine, immune, metabolic, and behavioral responses. CRH also regulates neural networks involved in maternal behavior and this determines efficiency of maternal care and neonate interactions. This review will summarize our current understanding of CRH actions during the perinatal period, focusing on the physiological roles for both mother and offspring and also how external challenges can alter CRH actions and potentially impact on fetus/neonate health

Early nutrition and adult health: Perspectives for international and community nutrition programs and policies

Recent economic changes throughout the world, either development or crises and recessions, have prompted a host of nutrition related problems, including a decreased prevalence of undernutrition, an increase in the prevalence of diet related diseases, widespread food insecurity as crop prices increase, and so on. In addition, evidence is mounting that suggests that exposure to poor nutrition early in life is a predisposing factor for chronic diseases in adulthood. Thus, the role of international or community nutrition professionals is vital to not only studying and understanding the interplay between economics, food policy, and health, but also to improving the ability to intervene and prevent many problems related to food insecurity in developed and developing countries. The purpose of this review is to outline and describe these issues as a means to open discussion on how to best alleviate major nutrition problems in the world