Large-area electron beam irradiation for surface polishing of cast titanium.
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Cast titanium is a known hard-to-polish material, and its final polishing step is a perpetual challenge. The best way to tackle this challenge lies in automatic and non-mechanical polishing methods. Against this background, the suitability of large-area electron beam (EB) irradiation was examined in this study. In parallel, the optimum condition for efficient surface polishing was investigated. Cast titanium specimens were prepared, whereby their surface glossiness, surface roughness, and corrosion resistance were measured before and after EB irradiation. After EB irradiation, favorable results were observed: the cast titanium surface became smooth, the glossiness increased, and corrosion resistance was enhanced. These results were attributed to the low heat conductivity of titanium. With mechanical polishing, this property results in temperature rise and burnout reaction of the titanium surface with oxygen and the abrasives. However, during EB irradiation, the low heat conductivity of titanium was an advantage in raising the surface temperature to the melting point, such that a smooth surface was yielded after solidification. Based on the results obtained, automatic polishing by EB seemed to be a suitable polishing method for metal frameworks of removable dentures, and an efficient one too by saving time and effort. (+info)
Grindability of alpha-case formed on cast titanium.
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The hardened alpha-case (alpha-case) layer inevitably forms on the surface of titanium castings when prepared by investment casting. Because the hardness of the alpha-case is incomparable to that of the interior structure, the perception exists that the alpha-case is difficult to remove during cutting, grinding and polishing. Grindability (ease of grinding) of cast cpTi and cast Ti-6Al-4V was evaluated by grinding cast specimens incrementally using a SiC abrasive wheel. The present study revealed that the presence of the brittle alpha-case with lower fracture toughness is beneficial in grinding titanium. The alpha-case on the ductile cpTi can be ground much easier than its bulk interior structure. In less ductile Ti-6Al-4V, the grinding rate is much higher than that of cpTi, and the alpha-case and its interior structure are at similar levels since the fracture toughness of its alpha-case and the bulk material is not large enough. (+info)
Effect of temperature variation on the cytotoxicity of cast dental alloys and commercially pure titanium.
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Ultrastructural modifications at the level of marginal periodontium in the case of incorrect dental reconstruction.
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Our study focused on the evolution of the marginal periodontium inflammatory process caused by an incorrect dental reconstruction. Our research studied a control group and a group of patients having traumatic and inflammatory lesions in different stages of evolution. A pronounced rarefaction of the junction desmosome structures as well as an inflammatory process pointed out by the presence of macrophages, neutrophils, Langerhans' cells, and mastocytes. The presence of altered fibroblasts and collagen fibers in the electron microscopic sections of vascular lesions represents microscopic signs of the inflammation and support the theory of local immunoglobulin synthesis. (+info)
Concerns of hydrothermal degradation in CAD/CAM zirconia.
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Effects of sonic scaling on the surface roughness of restorative materials.
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The surface roughness of dental restorative materials has a crucial effect on the health of dental and periodontal tissues as well as for the longevity of restorations. In this study we tested a glass ionomer restorative cement, two nanohybrid resin composites, a flowable resin composite and a silorane-based composite. Twenty cylindrical specimens of each material were prepared, cured, polished and instrumented with a sonic scaler (Alegra ST ZE-55 RM W&H, Austria). The mean surface roughness was recorded using a profilometer (SJ-201, Mitutoyo, Japan) at three stages: before scaling, after scaling and after re-polishing. Additional specimens were analyzed by scanning electron microscopy and back-scattered imaging. Data were examined statistically by analysis of variance (ANOVA) and post-hoc tests at a level of significance of P < 0.05. The profilometric measurements and the SEM evaluation showed that, in most of the materials tested, the surface roughness was significantly increased after sonic instrumentation. After re-polishing the specimens, the roughness values were decreased. Periodontal scaling should include polishing of restorations in order to overcome alterations in surface roughness. (+info)