Magfit磁性附着体铸接式和焊接式衔铁口外磁性固位力的测定

目的　比较铸接和焊接对衔铁口外磁性固位力的影响,为临床应用提供实验依据。方法　制作Mag- fitMD800磁性附着体铸接式衔铁试件5个和焊接式衔铁试件6个,对照组为未经处理的成品衔铁,在万能测试机上对3组试件垂直向磁性固位力进行测定。结果　焊接式衔铁组和铸接式衔铁组的口外垂直向磁性固位力分别为 (4·223 3±0·217 0)N、(3·792 9±0·296 4)N。焊接式衔铁组口外垂直向磁性固位力明显大于铸接式衔铁组(P< 0·05)。结论　焊接对磁性附着体磁性固位力的影响较铸接小。     

激光焊接式衔铁与铸接式衔铁的性能比较

目的 :比较不同处理方式对衔铁性能的影响 ,为临床应用磁性附着体提供参考。方法 :Z 3型磁性附着体 18只随机分为 3组。以钴铬合金作为覆盖牙根的支撑板根帽合金高温铸接衔铁 1组 ,Nd :YAG激光焊接衔铁 1组 ,另 1组衔铁不作处理。利用万能拉伸试验机测试 3组磁性附着体的固位力 ,采用粗糙度仪测量 3组衔铁表面光洁度 ,并分别进行比较。结果 :应用激光焊接式衔铁与应用铸接式衔铁的磁性附着体固位力无差别 ,但比衔铁未作处理的磁性附着体的固位力略小。铸接式衔铁表面在粗糙度仪下可见点状缺陷 ,表面光洁度低于激光焊接式衔铁表面光洁度。结论 :采用激光焊接与铸接方式制作钉帽衔铁能够满足临床应用磁性附着体要求     

磁性覆盖义齿根面结构常用制作方法及比较

衔铁与根面结构的选择及制作直接关系到磁性附着体义齿的修复效果。该文总结了目前衔铁根面结构的类型,包括预成桩核型、铸接式、激光焊接式及铸造式衔铁等,并比较了各类衔铁的制作方法和特点。     

铸接式衔铁吸附面性状的实验研究

目的:用铸接法制作磁性覆盖义齿根面结构,分别采用不同合金行常规铸造,观察不同合金铸造温度对衔铁吸附面性状的影响。方法:采用金合金、镍铬合金、纯钛,分别与Magdisc500成品衔铁包埋铸造,制作根面结构。用扫描电镜和电子探针对打磨抛光前衔铁表面附着物进行形貌观察和成分分析。结果:金合金组及镍铬合金组衔铁表面无氧化物生成,纯钛组衔铁表面有氧化物生成,3组试件衔铁表面的附着物均有包埋料残余。结论:不同铸造温度的合金会对衔铁吸附面产生不同的影响,提示临床上应采用金合金或镍铬合金铸接衔铁。     

磁性附着体焊接式衔铁在下颌全口覆盖义齿中的应用

目的 以铸接式衔铁为对照,探讨焊接式衔铁对下颌全口覆盖义齿口内磁性固位力的影响。方法 以Magfit磁性附着体作为固位装置,对9名采用焊接式衔铁和铸接式衔铁的患者分别进行下颌磁性附着体全口覆盖义齿修复。测定同一患者粘固磁体前、后义齿前部垂直向固位力。结果 两组在粘固磁体后义齿固位力均有明显增加。两组在义齿前部固位力增加值分别为414.7±218.09 g,322.2±318.30 g。结论 在下颌全口覆盖义齿中焊接式衔铁对于提高义齿的固位力具有重要的应用前景。     

衔铁与不同金属铸接前后金相结构的比较

目的:用铸接法制作磁性覆盖义齿根面结构,分别采用不同合金进行常规铸造,观察不同合金铸造温度对衔铁金属显微结构的影响。方法:分别采用金合金、镍铬合金、纯钛与Magdisc500成品衔铁包埋铸造、抛光、平整、清洁并制作金相试件。用金相显微镜对铸接前后的衔铁进行金相分析,以成品衔铁作为对照。结果:与铸造前相比,金合金组衔铁晶粒无明显变化。镍铬合金组、纯钛组衔铁晶粒变大、变粗,纯钛组更为粗大。结论:用不同合金铸接衔铁,会对衔铁的金相产生影响;合金铸造温度越高,晶粒越粗大。金合金组影响最小。     

激光焊接技术改进对衔铁焊接质量影响的实验研究

目的:探讨激光焊接技术的改进对磁性附着体衔铁与基桩焊接质量的影响,为临床应用提供实验依据.方法:采用Nd:YAC激光点焊机,以牙科高熔钴铬合金为基体金属对W600型磁性附着体成品衔铁进行焊接.试件分3组,分别作焊接面坡口和无坡口的设计以及不同焊接参数的设置.对焊接后3组试件的表面、显微结构、纵剖面等进行观察,比较焊接质量.结果:坡口组焊接深达全层,焊接缺陷较少;无坡口组焊接深度较浅.3组试件均未发现明显的热影响区以及过高显微硬度的淬硬组织.结论:焊接面的坡口设计,增加了焊接深度,提高了焊接质量.本实验条件下所增加的激光强度有利于焊接质量的提高.     

两种铸造温度对铸接式衔铁性能的影响

目的　观察两种铸造温度对铸接式衔铁性能的影响 ,探讨应用高温铸造方法制作衔铁钉帽的可行性。方法　取同类成品衔铁分别经中温和高温铸造得到 2组衔铁钉帽 ,对衔铁表面的氧化膜形态与厚度、衔铁与铸造合金结合情况以及衔铁与磁体的磁吸力大小等指标进行比较。结果　 2组衔铁表面氧化膜的形态明显不同 ,高温组衔铁各表面氧化膜厚度 (表面 :7 5 9μm ,合金铸接面 :6 17μm)均厚于中温组 (表面 :4 6 5 μm ,合金铸接面 :3 95 μm) ;2组衔铁金属的金相形态及衔铁与磁体磁引力大小 (中温组 :433 6g ,高温组 :433 8g)均无明显差异 ;衔铁与各自合金铸接的质量均较好。结论两种铸造温度对衔铁结构和其主要性能的影响无明显差异 ,临床可以考虑采用高温铸造制作衔铁钉帽     

3种不同金属铸接式衔铁磁力差异的比较

目的:分别对金合金、镍铬合金及纯钛3种金属铸接式衔铁,进行磁力测试,比较3种金属衔铁磁力的差异。方法:采用金合金、镍铬合金、纯钛3种金属为材料,分为3组,每组4件样本,与Magdisc500成品衔铁包埋铸造,制作根面结构。通过拉伸实验测试附着体磁引力大小并进行方差分析。结果:金合金组磁引力均值为4.84N,镍铬合金组均值为4.61N,纯钛组均值为4.12N。方差分析显示:3组两两间均存在显著差异(P<0.01)。结论:采用3种金属,通过铸接法制作的衔铁,其磁力均有一定程度下降,金合金组磁力下降最小。     

衔铁可卸式磁性附着体的研制及对MRI影响的对比研究

目的：解决磁性附着体应用对MRI的影响。方法：开发衔铁可卸式磁性附着体，比较几种形式衔铁对MRI的影响程度及不同MRI扫描地钛片所造成的伪影大小。结果：（1）几种表式衔铁对MRI的影响由大到小依次为：预成钉帽状衔铁、钴铬合金铸接的衔铁，贵金属合金铸接的衔铁，钛 桩可卸式衔铁，钛桩（拆卸盘状衔铁及中心螺丝后）。（2）可卸式衔铁拆下盘状衔铁及中心螺丝后，钛桩对MRI影像几乎没有影响。（3）标准SE序列拍摄钛片时所造伪影最小。结论：衔铁可卸式磁性附着体解决了MRI的伪影问题。尤其适用于头颅及颜面部肿瘤切除后需要长期追踪观察的患者。     

Comparative study of the surface characteristics, microstructure, and magnetic retentive forces of laser-welded dowel-keepers and cast dowel-keepers for use with magnetic attachments

STATEMENT OF PROBLEM: Information regarding the merits and problems associated with connecting a keeper to a dowel and coping using a laser welding technique has not been explored extensively in the dental literature. PURPOSE: This in vitro study compared the surface characteristics, microstructure, and magnetic retentive forces for a dowel and coping-keeper mechanism fabricated using a laser welding process and a cast-to casting technique. MATERIAL AND METHODS: Five cast-to and 6 laser-welded dowel and coping-keeper specimens were tested. Using 5 freestanding keepers as the control group, the surface characteristics and microstructures of the specimens were examined by means of stereomicroscopy, metallographic microscopy, and scanning electron microscopy (SEM). Energy-dispersive spectroscopic (EDS) microanalysis with SEM provided elemental concentration information for the test specimens. The vertical magnetic retentive forces (N) of the 3 groups were measured using a universal testing machine. The results were statistically compared using 1-way analysis of variance and the Newman-Keuls multiple range test (alpha =.05). RESULTS: The laser-welded dowel-keeper generally maintained its original surface smoothness as well as the original microstructure. Elements diffused readily through the fusion zone. The surface of the cast dowel-keeper became rough with the formation of an oxide layer, the microstructure changed, and there was only limited elemental diffusion in the fusion zone. The average vertical magnetic retentive force of the laser-welded group, the cast group, and the control group were 4.2 +/- 0.2 N, 3.8 +/- 0.3 N, and 5.6 +/- 0.3 N, respectively. Statistically significant differences in vertical magnetic retentive force were found between the control group and both the laser-welded and cast groups (P <.01). Compared with the cast dowel-keepers, the average vertical magnetic retentive force of the laser-welded dowel-keepers was significantly higher (P <.05). CONCLUSION: The laser welding technique had less influence on the surface characteristics, the microstructure, and the magnetic retentive forces of keepers relative to techniques that incorporate a keeper at the time of cast dowel and coping fabrication.     

Tensile properties and hardness of cast Fe-Pt magnetic alloys

STATEMENT OF PROBLEM: There is little information about the mechanical properties of castable magnetic attachments made of iron-platinum (Fe-Pt) alloys after heat treatment. MATERIAL AND METHODS: Dumbbell-shaped tensile specimens were cast with 5 alloys: 2 types of Fe-Pt alloys for magnets and keepers, pure Ti, Ti-6Al-7Nb, and Co-Cr alloy. The tensile specimens of the Fe-Pt magnets and keepers underwent different heat treatments to obtain the appropriate properties for a magnet and a keeper. Vickers hardness was measured prior to testing. Tensile testing was conducted in a universal testing machine at a crosshead speed of 2 mm/min until failure. Ultimate tensile strength, yield strength, elongation, and modulus of elasticity were recorded. The data were analyzed using 1-way analysis of variance and the Tukey test (alpha=.05), fractured surfaces were examined using a scanning electron microscope (SEM). RESULTS: The highest tensile and yield strengths were found for Ti-6Al-7Nb, followed by Co-Cr, CP Ti, and the Fe-Pt keeper. There was no significant difference in ultimate tensile strength between the CP Ti and the Fe-Pt keeper. The lowest elongation was found for the Fe-Pt magnet (2.8%), whereas the Fe-Pt keeper had the highest elongation (14.0%). The Fe-Pt magnet and keeper had similar modulus of elasticity values. The hardness of the cast Fe-Pt magnets was the highest among the metals tested. SEM micrographs of the Fe-Pt keepers showed a microstructure with ductile dimple fractures, whereas the Fe-Pt magnets were characterized by brittle fractures at the grain boundaries. CONCLUSIONS: The mechanical properties of the cast Fe-Pt keepers were similar to those of the cast pure Ti. The Fe-Pt magnets were extremely hard and brittle.     

A Quality Assessment of the Casting Process on Magnetic Keepers

PURPOSE: The objective of this study was to qualitatively investigate the effect of the burn-out (mold) temperature, investment material, and casting alloy on the surface integrity of the Magfit EX keeper. MATERIALS AND METHODS: Forty-two Magfit EX keepers were waxed-up, invested in five investment materials (Beauty-Cast, Cristobalite, CM-10, Cera-Fina, Castorit-super), and subjected to burn-out temperatures ranging from 450 to 700 degrees C at intervals of 50 degrees C. The keeper samples were then cast into copings with three alloys (Castwell, Protor 3, Optimum) under standard conditions. The keeper surfaces were then examined under a microscope, and the compositions were assessed by an X-ray micro-analyzer in a scanning electron microscope (SEM). A new keeper served as control. RESULTS: At a burn-out temperature of 550 degrees C, the keeper surface started to disintegrate. X-ray micro-analysis showed an increase in oxygen content with increasing temperature. At 700 degrees C, the keeper surface disintegrated, and the composition differed markedly from that of the new keeper. The keeper surfaces were intact with all investments except those with Beauty-Cast. The keeper surfaces were found to be damaged when the casting alloy was Optimum. CONCLUSIONS: Beauty-Cast investment with a burn-out temperature of 700 degrees C is unsuitable for casting the Magfit EX keeper-coping unit. Also, high fusing alloys are not recommended for casting Magfit EX keepers.     

The laser welding technique applied to the non precious dental alloys procedure and results

AIM: The laser welding technique was chosen for its versatility in the repair of dental metal prosthesis. The aim of this research is to assess the accuracy, quality and reproducibility of this technique as applied to Ni-Cr-Mo and Cr-Co-Mo alloys often used to make prosthesis METHOD: The alloy's ability to weld was evaluated with a pulsed Nd-Yag Laser equipment. In order to evaluate the joining, various cast wires with different diameters were used. The efficiency of the joining was measured with tensile tests. In order to understand this difference, metallographic examinations and X-Ray microprobe analysis were performed through the welded area and compared with the cast part. RESULTS: It was found that a very slight change in the chemistry of the Ni-Cr alloys had a strong influence on the quality of the joining. The Co-Cr alloy presented an excellent weldability. A very important change in the microstructure due to the effect of the laser was pointed out in the welding zone, increasing its micro-hardness. CONCLUSION: The higher level of carbon and boron in one of the two Ni-Cr was found to be responsible for its poor welding ability. However for the others, the maximum depth of welding was found to be around 2mm which is one of the usual thicknesses of the components which have to be repaired.     

等离子弧焊、钨极气体保护焊、激光焊焊接牙科纯钛显微结构比较

目的研究等离子弧焊、钨极气体保护焊(TIG焊)、激光焊接牙科纯钛试件的表面成型及金相结构。方法制备金相试件,对3种焊接试件的金相情况进行比较12件试件经过3种焊接方法焊接后,观察表面成型情况。结果激光焊接热影响区最小,表面成型良好,等离子焊接热影响区较大,TIG焊表面污染严重,热影响区大。激光焊接晶粒细小、均一、规则,等离子焊晶粒稍增大,TIG焊试件晶粒粗大、变形。结论等离子焊接与激光焊接是比较理想的牙科钛材焊接方法。