Comparative Study of the Shear Bond Strength of Flowable Composite in Permanent Teeth Treated with Conventional Bur and Contact or Non-Contact Er:YAG Laser

Introduction:The aim of this study was to evaluate and compare the in vitro effect of the Erbium-Doped Yttrium Aluminum Garnet (Er:YAG) laser with different radiation distances and high-speed rotary treatment on the shear bond strength of flowable composite to enamel of human permanent posterior teeth .Methods : freshly extracted human molar teeth with no caries or other surface defects were used in this study (n=45). The teeth were randomly divided into 3 groups. Group 1: treated with non-contact Er:YAG Laser and etched with Er:YAG laser, Group 2: treated with contact Er:YAG Laser and etched with Er:YAG laser, Group 3 (control): treated with diamond fissure bur and etched with acid phosphoric 37 % . Then the adhesive was applied on the surafces of the teeth and polymerized using a curing light appliance. Resin cylinders were fabricated from flowable composite. Shear bond strength was tested at a crosshead speed of 0.5 mm/min.Results: The amount of Shear Bond Strength (SBS) in the 3 treatment groups was not the same (P<0.05).The group in which enamel surfaces were treated with diamond fissure bur and etched with acid (conrtol group) had the highest mean shear bond strength (19.92±4.76) and the group in which the enamel surfaces were treated with contact Er:YAG laser and etched with Er:YAG laser had the lowest mean shear bond strength (10.89±2.89). Mann-whitney test with adjusted P-value detected significant difference in shear bond strength between the control group and the other 2 groups (P < 0.05).Conclusion: It was concluded that both contact and non-contact Er:YAG laser treatment reduced shear bond strength of flowable resin composite to enamel in comparison with conventional treatment with high speed rotary. Different Er:YAG laser distance irradiations did not influence the shear bond strength of flowable composite to enamel

Isolation and characterization of homoisoflavonoids from Scilla persica HAUSSKN

Plantas medicinais apresentam muitas atribuições tradicionais, incluindo o tratamento de doenças de origem infecciosa. A pesquisa científica é extremamente importante na avaliação dos usos tradicionais. Neste estudo, cinco homoisoflavonóides: 3-(4'-hidroxibenzilideno)-5,7-diidroxi-6-metoxicroman-4-ona(autumnalina), 3-(4'-hidroxibenzil)-5,7-diidroxi-6- metoxicroman-4-ona (3,9-diidro-autumnalina), 3-(3',4'-diidroxibenzil)-5,8-diidroxi-7- metoxicroman-4-ona, 3-(3',4'-diidroxibenzilideno)-5,8-diidroxi-7- metoxicroman-4-ona e 3-(3',4'-diidroxibenzilideno)-5,7-diidroxi-6- metoxicroman-4-ona foram isolados dos bulbos da planta Scilla persica HAUSSKN. Suas estruturas foram estabelecidas com base na extensa análise espectroscópica, como RMN, EM, IV e UV.Medicinal plants have many traditional claims including the treatment of ailments of infectious origin. In the evaluation of traditional claims, scientific research is extremely important. In this study, five homoisoflavonoids named 3-(4'-hydroxybenzylidene)-5,7-dihydroxy-6-methoxychroman-4-one(Autumnalin),3-(4'-hydroxybenzyl)-5,7-dihydroxy-6-methoxychroman-4-one (3,9-dihydro-autumnalin), 3-(3',4'-dihydroxybenzyl)-5,8-dihydroxy-7-methoxychroman-4-one,3-(3',4'-dihydroxybenzylidene)-5,8-dihydroxy-7-methoxychroman-4-one and 3-(3',4'-dihydroxybenzylidene)-5,7-dihydroxy-6-methoxychroman-4-one, were isolated from the bulbs of the plant Scilla persica HAUSSKN. Their structures were established on the basis of extensive spectroscopic analyses such as NMR, MS, IR and UV

Vortex formation and dissolution in sheared sands

Using digital image correlation, we track the displacement fluctuations within a persistent shear band in a dense sand specimen bounded by glass walls undergoing plane strain compression. The data evidences a clear, systematic, temporally recurring pattern of vortex formation, dissolution, and reformation throughout macroscopic softening and critical state regimes. During softening, locally affine deformation zones are observed at various locations along the shear band, which we argue to be kinematic signatures of semi-stable force chains. Force chain collapse then occurs, inducing vortex formation. Local jamming at the conflux of opposing displacements between adjacent vortices arrests the vortices, providing an avenue for potential new force chains to form amidst these jammed regions. The process repeats itself temporally throughout the critical state. The pattern further correlates with fluctuations in macroscopic shear stress. We characterize the nature of the observed vortices, as they are different in our sands comprised of irregular shaped particles, as compared to previous observations from experiments and numerical simulations which involved circular or rounded particles. The results provide an interesting benchmark for behavior of non-circular/non-spherical particles undergoing shear.National Science Foundation (U.S.) (grant CMMI-0748284)University of Southern CaliforniaUniversity of Southern California Women in Science and Engineering (WiSE) Progra

Synthesis and identification of the novel urazolediamine with phthalimide group

366-369A diamine, 4-(4-phthalimidophenyl)-1,2,4-triazolidyne-3,5-diamine or urazolediamine (UD) has been synthesized in 8 steps from 4-nitrobenzoic acid. The diamine has been characterized by FTIR, 1H NMR and melting point and can be used as a monomer for the preparation of polyesters, polyamides and polyimides

Some rock mechanics problems with application for hydraulic fracturing

Thesis: Ph. D. in Geophysics, Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2019Cataloged from PDF version of thesis.Includes bibliographical references (pages 185-205).Hydraulic fracturing is an essential tool used to enhance connectivity in shale gas reservoirs by maximizing the intersection between the hydraulic fracture (HF) and pre-existing natural fractures (NF) or faults. The technique is most effective when the hydraulic fracture crosses natural fractures rather than arresting on them. Experiments conducted to examine the interaction between HF and artificial pre-existing faults suggest that the coupling of diffusivity and fault slip is an important element of the HF-fault interaction problem. Fault slip, once activated is associated with an apparent increase in diffusivity. Whether the hydrofracture crosses or arrests on the pre-existing fault is also affected by surface roughness, differential stresses, and fault slip mode (i.e., stable or stick-slip sliding). Calibrated piezoelectric transducers were used to measure acoustic emissions (AE) generated during HF and fault slip.Moment tensor analysis of these events was used to distinguish pure tensile, shear, and possibly closure events during the experiments. Seismic moment magnitudes were approximately -7 for events during the initiation of the HF and about -5 for events during fault slip. Such a low ratio of seismic moments for tensile and slip events may explain the small numbers of tensile events recorded during reservoir stimulations. I also studied the time-dependent behavior in shales to gain insight into the post-stimulation efficiency of exploitations. Shale experiences strain hardening and compaction during loading by both isostatic (pressure-driven) and differential stress (shear-driven). Transient creep strain increased linearly with log(time), possibly transitioning to constant rate in timescale of several days. Motivated by the multi-scale nature of heterogeneities in shales, I examined the micromechanics of deformation using the nano-indentation technique.Elastic and creep moduli found in nano-indentation and triaxial tests agreed within a factor of 2, but within that factor, the creep strength may depend on spatial scale.by Saied Mighani.Ph. D. in GeophysicsPh.D.inGeophysics Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Science