The effect of commercially pure titanium and alternative dental alloys on the marginal fit of one-piece cast implant frameworks

OBJECTIVES: The purpose of this study was to measure and compare the passive fit and vertical fit of one-piece cast frameworks fabricated with three different materials: commercially pure titanium (CP Ti), cobalt-chromium alloy (Co-Cr) and nickel-chromium-titanium alloy (Ni-Cr-Ti). METHODS: Fifteen frameworks simulating bars for fixed prosthesis in a model with five implants were fabricated and arranged into three different groups according to the material used. The fit of the framework abutment interface was measured using an optical microscope, when only one screw was manually tightened at a terminal abutment (passive fit) or when all framework screws were tightened to 10 N cm torque (vertical fit). Data were statistically analyzed using Kruskal-Wallis and Mann-Whitney tests (alpha=0.05). RESULTS: Mean and standard deviation values of passive fit and vertical fit are presented, respectively: CP Ti [88 (74) microm and 22 (9) microm], Co-Cr [229 (184) microm and 66 (35) microm], Ni-Cr-Ti [200 (175) microm and 32 (24) microm]. There were no significant differences between passive fit of Co-Cr and Ni-Cr-Ti frameworks (p=0.313), but both alloys were statistically different from CP Ti (p<0.001 and 0.035, respectively), which showed the best results. As for vertical fit, CP Ti and Ni-Cr-Ti alloy were statistically similar (p=0.162) and they presented a better vertical fit than Co-Cr alloy (p<0.001). CONCLUSIONS: Within the limitations of this study, it was possible to conclude that one-piece cast frameworks resulted in unacceptable passive fit and vertical fit, no matter which material had been used to fabricate them. However, the best results were obtained using CP Ti followed by Ni-Cr-Ti and Co-Cr alloys, respectively.     

溶剂处理对钛-瓷结合强度的影响

目的 考察丙酮,乙酸乙酯,９５％乙醇及１５氢氟酸对钛－瓷结合产生的影响。方法 采用剪切实验法。结果 纯钛经丙酮、乙酸乙脂,９５％乙醇及１％氢氟酸处理后再烤瓷,太－瓷剪切强度分别为５３．２９ＭＰａ,５２．５４Ｍｐａ,５０．６９ＭＰａ,及２１．１８ＭＰａ,而未经任何清洗处理的对照组剪切强度值为２６．７５ＭＰａ。Ｔｉ－７５合金烤瓷前经丙酮,乙酸乙酯,９５％乙醇及１％氢氟酸处理后其钛－瓷剪切强度分别为５７     

钛种植术后早期放疗高压氧对种植体与骨结合的影响

目的探讨高压氧（ＨＢＯ）对钛种植术后早期放疗种植体与骨结合的影响。方法将纯钛种植体植入兔双腿胫骨干骺端,术后放疗,并在不同时期辅以ＨＢＯ治疗。对标本进行Ｘ线检查、组织学、扫描电镜及Ｘ线能谱分析。结果种植术后２周放疗,可使种植体的直接骨性结合率（ｄｉｒｅｃｔｃｏｎｔａｃｔｌｅｎｇｔｈｆｒａｃｔｉｏｎ,ＤＣＬＦ）降低４０％,新生骨的成熟明显推延,辅助ＨＢＯ治疗可提高种植体的ＤＣＬＦ,但仍低于未做放疗组。结论辅助ＨＢＯ只能从一定程度上促进种植体与骨的结合,不随治疗时间延长而有进一步改善。应用ＨＢＯ时机的不同对骨结合影响不大。     

The Formation of 14H-LPSO in Mg–9Gd–2Y–2Zn–0.5Zr Alloy during Heat Treatment

There is a new long-period stacking ordered structure in Mg–RE–Zn magnesium alloys, namely the LPSO phase, which can effectively improve the yield strength, elongation, and corrosion resistance of Mg alloys. According to different types of Mg–RE–Zn alloy systems, two transformation modes are involved in the heat treatment transformation process. The first is the alloy without LPSO phase in the as-cast alloy, and the Mg_xRE phase changes to 14H-LPSO phase. The second is the alloy containing LPSO phase in the as-cast state, and the 14H-LPSO phase is obtained by the transformations of 6H, 18R, and 24R. The effects of different solution parameters on the second phase of Mg–9Gd–2Y–2Zn–0.5Zr alloy were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The precipitation mechanism of 14H-LPSO phase during solution treatment was further clarified. At a solution time of 13 h, the grain size increased rapidly initially and then decreased slightly with increasing solution temperature. The analysis of the volume fraction of the second phase and lattice constant showed that Gd and Y elements in the alloy precipitated from the matrix and formed 14H-LPSO phase after solution treatment at 490 °C for 13 h. At this time, the hardness of the alloy reached the maximum of 74.6 HV. After solution treatment at 500 °C for 13 h, the solid solution degree of the alloy increases, and the grain size and hardness of the alloy remain basically unchanged.     

Electrochemical Production of Bismuth in the KCl–PbCl2 Melt

An anode dissolution of binary metallic lead–bismuth alloys with different concentrations of components has been studied in the KCl–PbCl₂ molten eutectic. The dissolution of lead is found to be a basic process for the alloys of Pb–Bi (59.3–40.7), Pb–Bi (32.5–67.5), Pb–Bi (7.0–93.0) compositions in the whole interval of studied anode current densities. A limiting diffusion current of lead dissolution was observed at 2 A/cm² and 0.1 A/cm² for the alloys of Pb–Bi (5.0–95.0) and Pb–Bi (3.0–97.0) compositions, respectively. The dissolution of bismuth takes place at the anode current densities exceeding the mentioned values. The number of electrons participating in the electrode reactions is detected for each mechanism. Based on the theoretical analysis, the experimental electrolysis of bismuth was performed in the laboratory-scale electrolytic cell with a porous ceramic diaphragm. The final product contained pure bismuth with a lead concentration of 3.5 wt.%.     

Stability of Weld Pool and Elimination of Weld Defects in Aluminum Alloy Plasma Arc Keyhole Welding at Continuously Varying Positions

Mathematical statistics were used to study the stability of weld pool and the elimination of weld defects in aluminum alloy plasma arc keyhole welding at continuously varying positions. In the mathematical model, the mass transfer position and spatial welding position were taken as the input, and the shape of the welded joints (symmetry/deviation) was taken as the output. The results showed that the fitted curves of the front, back, and average deviations of the weld seam were all similar to the actual curves. According to the optimum results obtained in the experiment and the mathematical models, the mass transfer position only needs to be adjusted once (near to 30°) during the continuously varying positions, from vertical-up to horizontal welding. A breakthrough from fixed environmental variables to dynamic environmental variables in the process control of the keyhole weld pool was realized, which enabled the Al-alloy keyhole weld pool to resist the disturbance caused by gravity during variable position welding. The deviation of the welded joints of the whole plate was smaller than 0.5 mm, and the mechanical properties of the weld reached at least 85% compared to those of the base material, thus meeting the requirements of Al-alloy welding.     

Enhanced Elevated-Temperature Strength and Creep Resistance of Dispersion-Strengthened Al-Mg-Si-Mn AA6082 Alloys through Modified Processing Route

In the present work, we investigated the possibility of introducing fine and densely distributed α-Al(MnFe)Si dispersoids into the microstructure of extruded Al-Mg-Si-Mn AA6082 alloys containing 0.5 and 1 wt % Mn through tailoring the processing route as well as their effects on room- and elevated-temperature strength and creep resistance. The results show that the fine dispersoids formed during low-temperature homogenization experienced less coarsening when subsequently extruded at 350 °C than when subjected to a more typical high-temperature extrusion at 500 °C. After aging, a significant strengthening effect was produced by β″ precipitates in all conditions studied. Fine dispersoids offered complimentary strengthening, further enhancing the room-temperature compressive yield strength by up to 72–77 MPa (≈28%) relative to the alloy with coarse dispersoids. During thermal exposure at 300 °C for 100 h, β″ precipitates transformed into undesirable β-Mg₂Si, while thermally stable dispersoids provided the predominant elevated-temperature strengthening effect. Compared to the base case with coarse dispersoids, fine and densely distributed dispersoids with the new processing route more than doubled the yield strength at 300 °C. In addition, finer dispersoids obtained by extrusion at 350 °C improved the yield strength at 300 °C by 17% compared to that at 500 °C. The creep resistance at 300 °C was greatly improved by an order of magnitude from the coarse dispersoid condition to one containing fine and densely distributed dispersoids, highlighting the high efficacy of the new processing route in enhancing the elevated-temperature properties of extruded Al-Mg-Si-Mn alloys.     

Effects of palladium addition on emission of mercury vapor from dental amalgam

OBJECTIVES: The purpose of this investigation was to test the hypothesis that palladium causes a reduction in mercury emission when added to dental amalgam during condensation. METHODS: Mercury vapor release was measured in a closed bottle system and an Intraoral Flow device(IOF). Conventional amalgam restorations were modified by addition of various palladium pellets. 1.57 mm diameter palladium pellets with different porosities were fabricated. These pellets were then placed in amalgam restoration using typical condensation and carving procedures. The samples were stored in a closed bottle and mercury measurements were taken from the bottles at 30 min, 1, 3, 5, 24 and 48 h and 7 days after trituration using a Jerome 411 Mercury Vapor Analyzer (Arizona Instrument Corp., Jerome, AZ). The palladium pellets identified as the most effective in mercury vapor reduction were further tested in an IOF device. Data were analyzed by two-way ANOVA followed by Tukey HSD pairwise analysis for significant findings (alpha = 0.05). RESULTS: The palladium containing amalgams when tested in the closed bottle system yielded significantly lower (p < 0.05) mercury vapor release than the controls. Pellets fabricated with the highest porosity yielded the greatest reduction in overall mercury vapor release. In the IOF device the overall amount of mercury vapor released from the palladium containing amalgams was also significantly less than the control (p < 0.05). SIGNIFICANCE: Mercury vapor emission from dental amalgam was greatly reduced by adding palladium pellets to amalgam during condensation. These techniques require only slight modifications of the standard operative procedures.     

烤瓷用镍-铬合金金属氧化膜的研究

目的 分析国产Ｎｉ－Ｃｒ合金在烤瓷烧结条件下所生成的金属氧化膜的性能,探讨颈部灰线的成因。方法 应用Ｘ线衍射法与电子扫描法对国产Ｎｉ－Ｃｒ合金铸年经烤瓷烧结后,表现氧化膜的物相以及氧化膜与基体合金的成分进行分析;同时,应用俄歇电子能谱对经烤瓷烧结后与未经烤瓷烧结的铸件表现氧化膜的厚度、各元素变化趋势进行了分析研究。结果经烧结后的铸件表现氧化膜中主要有Ｃｒ２Ｏ３、ＮｉＣｒ２Ｏ４、ＳｉＯ２等氧化物及合