SUMMARY
The purpose of this study was to determine the reliability of the data acquisition and modeling process of laser and white light scanners by evaluating the reproducibility of digitized simulated crowns with different convergences. A secondary purpose was to analyze the influence of die preparation by testing this hypothesis with a set of dies without ditching compared with a set with well-defined margins. Ditching or trimming the die defines the position of the margin and acts as a guide to gingival contour when the restoration is being waxed. Two light scanners (a white light optical scanner [Steinbichler Gmbh, Neubeuern, Germany] and red laser light scanner [TurboDent System, Taichung, Taiwan]) were evaluated. Two sets of simulated crowns were fabricated as cone frustrum models with a total occlusal convergence (TOC) of 0°, 5°, 10°, 15°, 20°, and 25° and a 9-mm base and 3-mm height using a precision milling machine and computer-aided design/computer-aided manufacturing (CAD/CAM) technique. One set of the dies was ditched immediately below the finish line to enhance marginal definition. Each die was optically digitized five times directly with the two different measuring systems. The area of each triangle in the scan that is occlusal to the margin line was calculated and summed to produce the final surface area measurement provided. The digitizing error was compared with the computed surface area of the original master die sets and compared with a paired t-test (df=4; 95% CI). There was no difference in accuracy of the untrimmed dies between the two systems evaluated. We also did not find any difference in the 0° (p=0.12) and 5° degree (p=0.21) groups among the ditched dies. However, when the TOC exceeded 5°, there was a significant difference between the two groups, with the laser groups having a smaller error percentage. Three-dimensional light scanning was not affected by the convergence angle except in the 0°-5° range. Trimming the dies greatly affected the accuracy of scanning.
Basal plane stacking faults (BSFs) with density of ∼1 × 106 cm−1 are identified as the dominant defect in the annealed ZnO thin films grown on c-plane sapphire by atomic layer deposition. The dominant peak centered at 3.321 eV in low-temperature photoluminescence measurements is attributed to the emission from the BSFs. The emission mechanism is considered to be the confined indirect excitons in the region of quantum-well-like structure formed by the BSFs. The observed energy shift of 19 meV with respect to the BSF-bounded exciton at low temperature may be caused by the localization effect associated with the coupling between BSF quantum wells.
A novel process of surface modification for multiwalled carbon nanotubes (MWCNTs) by using electron cyclotron resonance plasma is proposed. The process uses a H 2 /O 2 gas mixture as etching gas and applies a bias voltage of -250 DCV to the process stage to extract and accelerate hydrogen and oxygen cations. The generated high density and high incident energy cations are employed to create defects on the surface of nanotubes through ion bombardment. The oxygen cations with high reduction potential are simultaneously applied, oxidizing the surface of the nanotubes so as to form functional groups on the side walls most effectively. Additionally, being far from the plasma sheath, the MWCNTs can be maintained at a lower temperature to prevent from being decomposed under the high energy plasma. The efficiency of this method was systematically analyzed using X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and thermogravimetric analysis. The experimental results have shown that the proposed method is a highly effective way to functionalize MWCNTs, resulting in the nanotubes with high concentration of oxygen-containing functional groups and minimal structural damage within very short process time.
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