The stepwise self-assembly of europium sesquioxide nanocrystals into larger, anisotropic europium hydroxychloride nanostructures is observed. This involves the thermally assisted growth of 4.0 nm nanocrystals into elongated structures, called nanoneedles, and the subsequent assembly of those nanoneedles into larger, oriented bundles, called nanospindles. High-resolution transmission electron microscopy provides the size distribution, shape and atomic spacing of the nanostructures, whereas selective area electron diffraction and x-ray diffraction measurements identify their crystallinity. The optical properties, attributed to the environment of the host lattice for the europium ions, are investigated through photoluminescence measurements.
Optical spectroscopy stands as a powerful tool to gather information on the physical phenomena involved in the laser ablation process. This work reports on the time-resolved measurement of the ablation plume generated by a Q-switched Nd:YAG laser. Chicken heart tissue was used as sample. A helium-neon laser, aligned perpendicularly to the Nd:YAG laser beam and parallel to the ablated surface, was used as a probe beam. The probe light is collected by an optical fiber and sent to a spectrophotometer for analysis. A CCD detector was connected to the spectrometer. The technique reveals the differences in the plume behavior. Our results show that the plume is formed with some delay time with respect to the high energy laser pulse. The data show the constitution of the plume for different moments in time allowing the identification of the sodium emission lines in the chicken myocardium. For times lower than 40 μs just light components are ejected from the tissue while the heavier components of the plume takes much more time to be ejected and later to dissipate from the path of the probe beam.
In this work we employ a novel probe-beam technique to access the plume dynamics in the laser ablation process. A helium-neon laser in the scattered-beam mode was used to probe the plume. The sample used was a chicken myocardium tissue. The scattered probe light was collected by a 600 mm optical fiber and sent to a ¼ m spectrometer. After finding an adequate acquisition time window, the scattered He-Ne laser light was analyzed for several delay times. The plume luminescence was also collected. While no defined spectral lines could be observed for a 100 μs acquisition time window, a large number of emission lines could be analyzed for the 5 ms gate, the optimum gate window. Our results also show that the ejected material starts to be registered by the spectrometer at about 40 μs after the ablation pulse has been fired. The measurement of the relative atomic composition by means of the laser ablation and the analysis of the ablation plume dynamics were performed. The results pointed out the presence of many elements including sodium, hydrogen and others. Understanding the mechanisms involved in tissue ablation allows reduced damage and better results depending on the application goals.
The aim of the present work is to analyze the histological changes on hamster buccal mucosa caused by the topical use of 7,12-dimethylbenzanthracene (DMBA) and exposition to a 220 µJ/pulse nitrogen laser light (@ 337 nm) at an average power of 2,3 mW. Twenty-one hamsters divided into two experimental groups were treated six times with DMBA. One hamster was kept as control. Group I was composed by ten hamsters and was submitted only to DMBA. Group II, also with ten hamsters, received the same treatment as group I and was exposed to the laser radiation. The time duration of each irradiation section was 10 seconds. All the treatment happened in alternated days. The histological analysis took place twice, after the end of the treatment and after sixty days. Both experimental groups presented dilatation of vessels, thickening of the epithelial tissue and the presence of inflammatory infiltrates. The preliminary results indicates that in group II the number of dilated vessels and its new area are much more significant than in group I.
In the past years, lasers have become a special tool in dentistry. To study the effects of laser apicoectomy compared to the conventional surgical treatment, freshly-extracted single-root teeth were used, submitted to traditional endodontic treatment and divided into four groups: Group I, conventional apicoectomy using diamond burs; Group II, the same treatment as Group I, however, with a 15 second orthophosphoric acid application; Group III Er:YAG laser cut (10 Hz - 400 mJ); and finally, Group IV Er:YAG laser cut (10 Hz - 400 mJ) and surface treatment with Nd:YAG laser (10 Hz - 2 W). The samples were submitted to 2,5 % blue methylene dye solution, at 25 degree(s)C and 37 degree(s)C for 36 h and 18 h, respectively, and analyzed under optical microscope. The results show that Group II had the higher permeability of all the groups and Group IV had the lower one, due to the successful Nd:YAG laser surface treatment.
The effects of laser exposure on mineralized tissues like enamel have been explored for years as a technique to remove caries and for dental hard-tissue preparation. However the efficiency of this technique has been questioned. In this work, six freshly-extracted third molars were irradiated by a superpulse of CO<SUB>2</SUB> laser, generally used in Transmyocardio Revascularization, and submitted to Scanning Electron Microscopy (SEM) analyzes. The cavities caused by laser irradiation on the dental tissues were analyzed considering its shape and depth. The CO<SUB>2</SUB> superpulse presented a high efficiency in the removal of dental mass and no sign of carbonized tissue was found on the ablated surface. All cavities generated by laser irradiation presented a conic shape with average depth depending on energy density applied.
Fifteen human embedded third molars were used in this in vitro study to evaluate the effects of two bleaching products associated or not with Argon laser application. The samples received a cervical-apical cut and were longitudinally cut into 4 parts resulting in 75 specimens. These parts were divided at random into 5 groups and submitted to the traditional power bleaching procedure for enamel. Group 1 was separated as a control group. Group 2 was exposed to 37 % carbamide peroxide bleaching solution and developed with an Argon laser application. The same solution was used in Group 3 but the bleaching was developed with an halogen lamp irradiation. 35 % carbamide peroxide were used in Groups 4 and 5. One was developed as Group 2 and the other as Group 3. The samples were analyzed under a photoreflectance experiment. We observed that Group 2 presented more white spectra than Group 3. However, Groups 4 and 5 showed the same results independent of the use of the laser or the halogen lamp for the light curing. Comparing both bleaching products, the 35 % carbamide peroxide was more efficient on its purposes than the other one.
Ten human third molars were used in this in vitro study to analyze the depth of dentin modification induced by a Nd:YAG laser. This technique has been used as a procedure to treat dentin hypersensitivity to air and to mechanics stimulation. Five techniques of sample preparation were used in this work but just one of them preserves the area under study for observation. The samples were irradiated with 170mJ of energy per pulse and an average depth of 100 micrometers of modification of the dentin was observed under scanning electron microscopy (SEM).
The effects of laser or acid exposure on dentin have been explored for a number of years. Many researchers quite the recrystallization process, therefore there has been no scientific-oriented analysis regarding this issue. The first use of the word 'recrystallization' in laser treated dentin, was done by Dederich et al. They referred to needle-like crystals observed under Scanning Electron Microscopy (SEM) with high magnification. Further researchers continued quoting the recrystallization process in their works even though no evidence of crystals could be seen in their SEM pictures. In this work, four specimens of third human molars were prepared: one specimen was conditioned with 37 percent phosphoric acid, another was irradiated with a 10 Hz Nd:YAG laser at 1,5 W, after receiving the Er:YAG laser treatment. We maintained a control sample with no treatment. The samples were submitted to x-ray diffraction measurements and SEM, performed with the JSM-5900LV microscope of the LME/LNLS.