Studies on gallium alloys for dental restorations. 2. Electron probe microanalysis for hardened gallium alloys

Hardened gallium alloys were analyzed by scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). The cores, matrix and white irregular shape phases were visible with SEM. The round or irregular shape cores contained Ag, Pd, Cu and Zn but did not contain Ga and In. The dark irregular shape matrix, which surrounded the core, consisted of Ga-Ag, Ga-Pd, Ga-Cu and Ga-Sn phases. However, the amount of Ga-Sn phase was very low. The white phase in the matrix was Ag-In phase.     

Liquid gallium alloys for metallic plastic fillings

Ga-In-Sn alloys that are liquid at room temperature have been developed to replace mercury in metal plastic fillings. These liquid alloys were mixed with Ag-Pd-Sn-Cu-Zn to form powder alloys, 'a plasto-metallic body'. Various physical properties of these materials were evaluated. Strength increased markedly immediately after mixing, and polishing was possible on the same day. A good marginal seal could be expected as these materials expand on setting. The technique for filling is simpler and more rapid than is the case with amalgam materials. These materials also seem to be useful in paediatric dentistry for the handicapped, where extensive treatments are frequently performed under general anaesthesia.     

Fatigue and tensile strength of dental gallium alloys after artificial saliva immersion

Fatigue strength using the stair-case method and tensile strength of dental gallium alloys after artificial saliva immersion were measured for evaluating the effects of corrosive environment storage on the mechanical properties of the gallium alloys. The fatigue and the tensile strengths of both gallium alloys stored in artificial saliva were significantly decreased after 12-month storage, while those stored in air increased with storage period. The fracture surfaces of the specimens in artificial saliva showed not only metallic luster but also dark areas. In the dark area, the matrix might have dissolved during immersion. These results suggested that the concern over corrosion resistance of gallium alloys still remained.     

Galvanic corrosion and cytotoxic effects of amalgam and gallium alloys coupled to titanium

The aim of this study was to examine and compare the galvanic corrosion of a conventional, a dispersed high-copper, and a palladium-enriched spherical high-copper amalgam and a gallium alloy coupled to titanium in saline and cell culture solutions, and to evaluate the effects of the couples on cultured cells. The potentials and charge transfers between amalgams and titanium were measured by electrochemical corrosion methods. Cytotoxicity of the couples, as indicated by the uptake of neutral red vital stain, was determined in 24-h direct contact human gingival libroblast cell cultures. Results of this study indicated that before connecting the high-copper amalgams to titanium, the amalgams exhibited more positive potentials which resulted in initial negative charge transfers, i.e. corrosion of titanium. However, this initial corrosion appeared to cause titanium to passivate, and a shift in galvanic currents to positive charge transfers, i.e. corrosion of the amalgam samples. Lower galvanic currents were measured for the amalgam-titanium couples as compared to the gallium alloy-titanium couple. Coupling the conventional or the palladium-enriched high-copper amalgams to titanium did not significantly affect the uptake of neutral red as compared to cells not exposed to any test alloy. However, significant cytotoxic effects were observed when the dispersed-type high-copper amalgam and the gallium alloy were coupled to titanium. Even though the corrosion currents measured for these couples were less than gold alloys coupled to amalgam, these results suggest there is the potential for released galvanic corrosion products to become cytotoxic. These data warrant further investigations into the effects of coupling amalgam and gallium alloys to titanium in the oral environment.     

Photoelastic assessment of the expansion of direct-placement gallium restorative alloys.

OBJECTIVE: The purpose of this study was to assess, via a photoelastic resin, the expansion of gallium restorative alloys under conditions similar to those found in the clinical situation. METHOD AND MATERIALS: Two gallium alloys, Galloy and Gallium GF II, were tested, along with a high-copper amalgam, Dispersalloy, and a low-copper alloy, New True Dentalloy. The gallium alloys were tested as (1) uncontaminated, (2) contaminated with water, Ringer's solution, or a cell culture medium, and (3) immersed in these fluids at times ranging from 5 minutes to 3 days. The gallium and amalgam alloys were condensed in a hole drilled in a block of photoelastic resin and observed for 3 months. The amount of stress was recorded on color slides taken through polarized light at regular intervals. The photographs of the color bifringen stress patterns at 1 and 3 months were ranked by two independent evaluators for least to greatest observed stress. RESULTS: Dispersalloy had the least expansion, followed by uncontaminated Galloy and Galloy contaminated with water. Next came Galloy contaminated with cell culture medium, Galloy contaminated with Ringer's solution, contaminated New True Dentalloy, and Gallium GF II. The last group was Gallium GF II contaminated with any of the three solutions. Both gallium alloys immersed in the three fluids showed a strong edge effect, and by 6 weeks many of the gallium alloys had extruded from the mold. CONCLUSION: These results corroborate the findings of some clinical studies that have shown that these gallium alloys can potentially cause catastrophic failures.     

Comparative evaluation of clinical efficacy of gallium and amalgam alloys in primary molars

The present study was conducted to compare the clinical efficacy (marginal integrity and bulk fracture) of two alloys--Galloy (gallium based) and Aristaloy (amalgam based) in primary molars. 90 primary molars with initial caries formation were selected. 45 were restored with Galloy and 45 with Aristaloy in Class I and II preparations. They were evaluated at two-month intervals for 6 months. The results showed that Galloy performed at par with Aristaloy with regards to marginal integrity and bulk fracture. Hence Galloy can be considered as an interesting substitute in Pedodontic practice.     

Cytotoxicity of corroded gallium and dental amalgam alloys. An in vitro study.

The cytotoxicity of one gallium and three different dental amalgam alloys was assessed in a cell culture system. Two evaluation methods were used, the filter method and an extraction method. Before being tested, set specimens of the alloys were stored in 0.9% NaCl solution for 1 and 10 weeks, to corrode. The alloys showed various degrees of cytotoxicity, ranging from mild to marked. Differences were found between the two testing methods, but in most cases no major differences in cytotoxicity were found between the Ga alloy and the amalgams. The results encourage further study and development of the Ga alloy, which is mercury-free.     

Strength and microstructure of IPS Empress 2 glass-ceramic after different treatments

PURPOSE: This investigation was designed to determine whether heat pressing and/or simulated heat treatments affect the flexure strength and microstructure of the lithium disilicate glass-ceramic of the IPS Empress 2 system. MATERIALS AND METHODS: Four groups of the lithium disilicate glass-ceramic were prepared as follows: group 1 = as-received material; group 2 = heat-pressed material; group 3 = heat-pressed and stimulated initial heat-treated material; and group 4 = heat-pressed and simulated heat-treated material with full firings for a final restoration. Three-point bending tests and scanning electron microscopy (SEM) analysis were conducted. RESULTS: The flexure strength of group 2 was significantly higher than that of group 1. However, there were no significant differences in strength among groups 2, 3, and 4, or between groups 1 and 4. The SEM micrographs of the lithium disilicate glass-ceramic showed a closely packed, multidirectionally interlocking microstructure of numerous lithium disilicate crystals protruding from the glass matrix. The crystals in the glass matrix of the heat-pressed materials (groups 2, 3, and 4) were a little more homogeneous and about 2 times bigger than those of the as-received material (group 1). These changes of the microstructure were greatest between groups 1 and 2. However, there were no marked differences among groups 2, 3, and 4. CONCLUSION: Although there were significant increases in the strength and some changes of the microstructure after the heat-pressing operation, the combination of heat pressing and simulated subsequent heat treatments did not produce an increase of strength of IPS Empress 2 glass-ceramic.     

反复熔铸对牙科烤瓷合金显微结构的影响

目的: 探讨反复熔铸对钴铬、纯钛、钯铜镓、金铂烤瓷合金显微结构的影响。方法: 在真空加氩气保护环境下,将4种烤瓷合金单纯反复熔铸1~3次。每次再熔铸前,烤瓷合金均经过课题组前期研究所得“烤瓷合金再熔铸前最佳处理方法”处理,根据金属显微组织检验方法（GB/T13298-2015）,分别对熔铸前、熔铸1~3次后的烤瓷合金进行研磨、抛光、浸蚀,采用金相显微镜或扫描电镜检测金相显微结构。结果: 随着熔铸次数增加,钴铬烤瓷合金晶粒粗化、晶粒间基质和晶界间化合物增多。纯钛烤瓷合金随熔铸次数增加,晶粒粗化明显。2次熔铸后,晶粒有等轴化倾向,3次熔铸则出现针刺状β相。钯铜镓烤瓷合金在2、3次熔铸后,晶粒结构略有长大。金铂烤瓷合金晶粒结构未随熔铸次数发生明显改变。结论: 反复熔铸显著改变钴铬、纯钛、钯铜镓烤瓷合金的显微结构,建议由厂家回收再利用烤瓷合金废旧料。     

Strength of bond with Comspan Opaque to three silicoated alloys and titanium

In Sweden high-gold alloys or cobalt-chromium alloys are used for resin-bonded prostheses. The bond strength between a resin cement and different sandblasted or silicoated metals were measured before and after thermocycling; in connection with this some rapid thermocycling methods were studied. The effect of different storage times and different protection coatings on bond strength were tested. Finally, the influence of rubbing and contamination with saliva on bond strength were investigated. Silicoating increased the bond strength significantly. The highest bond strengths were these of silicoated Wirobond and titanium, unsusceptible to thermal stress; the bond strengths of the sandblasted metals were the weakest, and sensitive to thermocycling as well. The influence on bond strength for silicoated gold alloys, protected with an unpolymerized composite resin coating, stored in sealed plastic bags up to 7 days, was negligible. Rubbing and contamination with saliva did not influence bond strength. Preferably, silicoated Wirobond and titanium should be used for resin-bonded prostheses, but gold alloys may still be adequate for clinical use. The experimental method described for storing, sealing, and cleaning the silicoated metal surfaces in this article can be recommended for laboratory and clinical use.     

Strength of bond with Comspan Opaque to three silicoated alloys and titanium

Abstract – In Sweden high-gold alloys or cobalt-chromium alloys are used for resin-bonded prostheses. The bond strength between a resin cement and different sandblasted or silicoated metals were measured before and after thermocycling; in connection with this some rapid thermocycling methods were studied. The effect of different storage times and different protection coatings on bond strength were tested. Finally, the influence of rubbing and contamination with saliva on bond strength were investigated. Silicoating increased the bond strength significantly. The highest bond strengths were these of silicoated Wirobond and titanium, unsusceptible to thermal stress; the bond strengths of the sandblasted metals were the weakest, and sensitive to thermocycling as well. The influence on bond strength for silicoated gold alloys, protected with an unpolymerized composite resin coating, stored in sealed plastic bags up lo 7 days, was negligible. Rubbing and contamination with saliva did not influence bond strength. Preferably, silicoated Wirobond and titanium should be used for resin-bonded prostheses, but gold alloys may still be adequate for clinical use. The experimental method described for storing, sealing, and cleaning the silicoated metal surfaces in this article can be recommended for laboratory and clinical use.     

两种热处理方式对激光焊接钴铬-镍铬异种合金力学性能和组织结构的影响

探讨常规热处理和烤瓷对激光焊接钴铬-镍铬异种合金力学性能和组织结构的影响,以期为异种合金的临床应用提供参考.方法将0.5 mm厚的钴铬合金和镍铬合金试件各15个从中间断开,进行激光焊接,制成30个钴铬-镍铬异种合金焊件.焊后用随机数字表将焊件随机分为3组,每组10个.对照组不做处理,热处理组焊件进行常规热处理,烤瓷组焊件进行烤瓷处理.测试3组焊件的拉伸强度和延伸率,扫描电镜观察拉伸断口,能谱分析测试3组焊件熔焊区、钴铬焊接交界区和镍铬焊接交界区元素.结果经热处理和烤瓷处理后,焊件拉伸强度分别为(537.15±43.91)MPa和(534.58±48.47)MPa,延伸率分别为(7.65±0.73)%和(7.40±0.45)%.烤瓷组拉伸断口出现明显的韧窝结构,热处理组拉伸断口表现为深而大的韧窝;钴铬侧合金成分向熔焊区和镍铬侧有一定程度的扩散,热处理组比烤瓷组扩散更明显.结论热处理和烤瓷过程均可在一定程度上改善激光焊接钴铬-镍铬异种合金焊接接头的性能,热处理对焊接接头性能的改善比烤瓷更明显.     

pH值对烤瓷工艺处理后的合金耐腐蚀性能的影响

目的研究不同pH值对经过烤瓷处理过的烤瓷合金的耐腐蚀性能的影响。方法制作金合金、纯钛、钴铬合金、镍铬合金试件,常规临床烤瓷,分别置于不同的pH值溶液中,应用电化学综合测试系统和腐蚀分析软件对受试合金行动电位极化扫描,绘制合金在人工唾液中的极化曲线,获得并分析材料的自腐蚀电位(Ecorr)和腐蚀电流密度(Icorr)。结果4种合金临床烤瓷加工后在同一pH值人工唾液中自腐蚀电位负值增加的排序为金合金、纯钛、钴铬合金、镍铬合金;4种合金在pH为5.6±0.04、pH=为.6±0.04人工唾液中均比pH为6.8±0.04中自腐蚀电流密度增大,自腐蚀电位负值增大。结论纯钛与金合金耐腐蚀性能好于钴铬合金,镍铬合金,随pH值下降,非贵金属耐腐蚀性能下降明显。     

Effects of recasting on the chemical composition, microstructure, microhardness, and ion release of 3 dental casting alloys and titanium

This study evaluated the effects of recasting on high noble, noble, and nickel-based alloys, as well as on titanium. Four specimens of each material were cast and recast 7 times. Chemical composition, microstructure, microhardness, and ion release were determined before and after the first cast and following each recast. Zinc and tin concentrations in the high noble alloy decreased significantly with recasting; consequently, the release of these ions decreased as well. A significant increase in Vickers hardness appeared in the fifth recast in both the high noble alloy and titanium. The noble alloy and the nickel-based alloy demonstrated great stability after 7 recasts. The results suggest not recasting titanium.