压差式铸钛机的熔铸条件对纯钛铸件组织结构的影响

目的：分析进口压差式铸钛机铸造的纯钛铸件内部组织结构和缺陷原因，探讨提高纯钛铸造修复体组织结构致密度，减少杂质，避免内部缺陷的方法。方法：应用X－线金属探伤仪定位，数字式金相显微镜分析纯钛铸件内部的组织结构。并应用痕量气体分析仪对气泡内残留成分进行分析，同时对气泡内壁的组织结构进行金相学分析。结果：纯钛铸件内部的气泡主要来自于熔铸室的氩气保护和铸道直径过细，过长所致。结论：短、粗铸道和改进熔铸室的氩气保护方式是减少铸件内部缺陷的关键。     

牙科精密铸钛技术的研究进展

钛制冠桥，可摘义齿支架已应用于临床，但钛的铸造技术尚待改进。本文回顾了国内外对牙科铸钛技术的研究；介绍国外对牙科铸钛机，包埋料，铸造工艺等方面的研究；对各种牙科铸钛机的可铸性能，包埋料的理化性能对钛铸件质量的影响，铸模温度对钛铸伯质量的影响，以及铸道的设计对钛铸件质量的影响等进行了综述。     

改进蜡型制作工艺提高钛支架的铸造完整性

目的：研究不同蜡型制作工艺对钛支架铸造完整性的影响。方法：统计1626件钛支架铸件,按蜡型制作工艺不同分为4组,检测出有铸造缺陷的钛铸件,计算每组铸造缺陷率。结果：常规组、设置排气道组、安置水平铸道组、设置水平铸道与排气道组的铸造缺陷率分别是26%、8%、13%、2%,组间比较有显著性差异。结论：在蜡型制作时,设置水平铸道与排气道可明显提高钛支架铸件的完整性。     

包埋料和铸道参数对Ti-24Nb-4Zr-7.9Sn合金铸流率的影响

目的:优选适合Ti-24Nb-4Zr-7.9Sn合金铸造的包埋料、铸道直径和长度, 以便提高该合金的铸流率.方法:采用网状试样法,计算 Ti-24Nb-4Zr-7.9Sn合金在3 种包埋料、3 种铸道直径和长度条件下的铸流率,做析因设计的统计学分析.结果:包埋料、铸道直径和长度对Ti-24Nb-4Zr-7.9Sn合金的铸流率均有显著影响(P<0.05),但不认为包埋料、铸道直径和长度两两之间及三者相互之间存在交互作用(P>0.05).结论:使用氧化镁系铸钛专用包埋料,选择直径5 mm、长度5 mm的铸道包埋铸造,可取得铸流率高达(94.90±4.67)%.     

隐形义齿684例临床分析

隐形义齿是一种新型可摘式义齿修复方法 ,作者对 6 84例临床应用进行总结一、材料与方法1.牙列缺损患者 6 84例 ,男 2 5 4例 ,女 4 30例 ;年龄 13～70岁。缺牙 15 10颗 ,共制作隐形义齿修复体 76 6件。牙位 :切牙 5 6 4颗 ,占 37.35 % ;尖牙 6 0颗占 3.97% ;双尖牙 2 93颗 ,占 19.4 0 % ;磨牙 5 93颗 ,占 39.2 9%。方法 :适用于前后牙单个牙缺失、间隔缺失、游离和非游离缺失。要求基牙健康 ,有适当的牙合龈高度和牙间隙及倒凹。用硬质石膏模型。主铸道和分铸道互相联通 ,避免形成锐角 ,以利顺利铸入。采用特制型盒包埋 ,不能形成倒凹。铸压…     

高熔合金铸造不全的原因分析

笔者对我科临床高熔合金铸造836个有圈离模铸造中35个铸圈,51个铸件铸造不全的原因进行回顾分析。其中因合金量不足的15件,蜡模太薄的9件、铸道设计不当的10件,铸圈烘烤温度不够的5件,铸造时机不适当的10件,铸道口不符合要求的6件。现逐一分析如下:一、合金量不足1.多数是由于估算材料的用量未掌握好,致投料不足。实践证明,估算材料的用量必须将铸道包括在内。足够的合金,产生足够的铸造压力,才     

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钛铸件质量与包埋材料关系已成为口腔材料学研究热点之一。进口铸钛包埋材料虽好但价格昂贵。本研究使用我科自配ZrP99铸钛包埋材料包埋铸造钛件,通过检测不同铸模温度时钛铸件的金属表面性状、内部气孔含量和     

钴-铬合金铸造可摘局部义齿折断临床分析

目的：分析临床Co-Cr合金铸造可摘局部义齿(RPD)折断原因，以提高义齿质量。方法：对289件Co-Cr合金铸造RPD进行回顾总结，并对其发生铸造缺陷、折断进行统计分析。结果：本文289件铸件中，肉眼检查有铸造缺陷者93件，占31．3％，其余196件行X线探测检查有缺陷者36件，占18．6％。义齿各部位出现铸造缺陷机率：卡环小连接体处较高，下颌高于上颌。戴牙2年后折断32件，其中原铸造有缺陷者28件，占87．5％。结论：①铸造缺陷是造成铸造RPD折断的主要原因。②应用X线探测仪进行铸造义齿检测，是提高修复质量的有效方法。     

高熔合金铸造支架的铸道设计

局部义齿采用钴铬合金等高熔合金铸造支架时,合理地设计高熔合金铸造支架的铸道,不仅能使铸造获得成功,而且能提高铸件的质量和工作效率。近来,我们使用天津医院设备厂制造的高频离心式铸造机,采用单铸道进行浇铸,获得了成功。在制作的50件金属支架中,仅1例失败。     

铸道设计对贵金属烤瓷合金铸态组织影响的实验研究

目的 研究不同的铸道设计形式对贵金属烤瓷合金铸态组织的影响，为该类合金的临床规范化应用提供理论依据。方法 应用倒置式金相显微镜观察BioHeradorN金烤合金不同铸道设计形式下的铸态组织，通过观察铸件中缩孔缩松产生的数量和分布比较铸道设计形式（树型、环型、环型）对铸件的影响程度。结果 铸道设计形式对合金铸态组织有明显影响，随铸道设计形式不同缩孔缩松产生的数量及分布有异。除环型铸道设计外，其它形式的铸道设计会使铸件中产生明显的铸造缺陷，即缩孔缩松的数量分布增多增广。结论 BioHeradorN金烤瓷合金铸态组织以环型铸道设计组织最为致密，常见缩孔缩松缺陷不易产生。     

Internal porosity of cast titanium removable partial dentures: Influence of sprue direction on porosity in circumferential clasps of a clinical framework design

STATEMENT OF PROBLEM: Although internal porosity is a potential risk factor for clasp fracture, little is known about its frequency in the clasps of titanium removable partial dentures. PURPOSE: This study investigated the influence of the direction of auxiliary sprues on porosity in the circumferential clasps of a pressure-cast titanium removable partial denture. MATERIAL AND METHODS: Wax patterns of a removable partial denture framework were made on 10 identical refractory casts of a Kennedy class II, modification 1, mandibular partially edentulous arch. For the auxiliary sprues directed to the circumferential clasps, 2 designs were used: straight and curved. Casting was performed in a 1-chamber pressure casting machine. Pore number and size were assessed on radiographs of the castings. The data were analyzed with the 2-tailed Student t test (P <.05). Randomly selected specimens were sectioned for morphologic observation of the internal surface of the pores. RESULTS: The number of pores >or=0.5 mm diameter and the total number of pores were significantly lower in the molar lingual arms of the curved sprue group than in the corresponding clasp arms of the straight sprue group (P =.03 and P =.009, respectively). No significant differences between the 2 groups were found for pores of any size in other locations. The pores had smooth internal surfaces. CONCLUSION: Within the limitations of this study, the curved sprue design produced significantly less porosity in the circumferential clasp arms of a cast titanium removable partial denture than the conventional straight design. The results suggest that internal porosity in titanium castings can be controlled through sprue design.     

Effect of sprue design on the castability and internal porosity in pure titanium castings.

OBJECTIVE: The aim of the study was to evaluate the pure titanium castability and internal porosity with 3 different sprue designs. METHOD AND MATERIALS: The sprue designs selected were the conventional cylindrical, funnel-shaped, and sheet-form sprue formers. To evaluate the castability, the mesh monitor was chosen. Eight mesh patterns (14 3 14 mm) of 49 squares were attached to each type of sprue design. They were invested in titanium investment material and cast in a semiautomatic titanium casting machine. The titanium castings were evaluated by 2 methods. One was the visual observation of the castings for completeness, and the second was the radiographic qualitative analysis for the location of the internal porosities. RESULTS: Data were analyzed with analysis of variance and Student t test for paired comparison among different sprue designs. According to analysis of variance, all sprue designs revealed a statistically significant difference at the 5% level of confidence (P <.05, F = 3.50). Mesh patterns attached to funnel-shaped sprue designs showed better percentage castability values. CONCLUSION: For titanium, casting using a funnel-shaped sprue design displayed better castability values and less internal porosities in the castings.     

Internal porosity of cast titanium removable partial dentures: influence of sprue direction and diameter on porosity in simplified circumferential clasps.

OBJECTIVE: The behavior of molten titanium in molds of complicated shape is still insufficiently understood; consequently, definite spruing criteria are not yet available for titanium RPD frameworks. This study investigated the influence of sprue design on porosity in pressure-cast titanium circumferential clasps. METHODS: The patterns of 90 circumferential clasps were sprued with three directions (0, 30 and 60 degrees , as measured between the sprue and the symmetry plane of the clasp assembly) and three sprue diameters (1.5, 2.0 and 2.5mm). CPTi was cast in a one-chamber pressure casting machine. Pore number and size were assessed on radiographs of the castings. Statistical analysis was done by two-way analysis of variance (ANOVA), followed by Fisher's PLSD post hoc test. RESULTS: The porosity in lingual arms increased significantly with increase of sprue diameter and sprue angle, while the porosity in minor connectors had an inversely proportional distribution. Very low porosity, uninfluenced by sprue design, was found in buccal arms. In conclusion, internal porosity in titanium circumferential clasp arms can be minimized through sprue design: the 0 degrees sprue direction produced the least porosity, while for the 30 and 60 degrees directions, 1.5mm diameter sprues produced lower porosity than 2.0 and 2.5mm diameter sprues. SIGNIFICANCE: In this study, the lowest porosity in titanium circumferential clasp arms was obtained with sprues attached perpendicularly to the minor connectors, regardless of sprue diameter. Conventional sprue directions produced significantly higher porosity in clasp lingual arms, the amount of porosity increasing with sprue diameter.     

Investigation of the effect of three sprue designs on the porosity and the completeness of titanium cast removable partial denture frameworks.

STATEMENT OF PROBLEM: Although titanium has been used to cast removable partial denture frameworks, the casting process is arduous and requires specialized equipment. PURPOSE: This study evaluated the ability of 3 sprue designs (tree, ball, and circular) to produce complete, void-free castings of removable partial denture frameworks made from commercially pure titanium. METHODS AND MATERIAL: A cast with a Kennedy class III, modification 1, partially edentulous arch was used. The blocked-out cast was modified to facilitate assessment of the completeness of the casting of the clasp arms. Thirty refractory casts were made, and 10 wax patterns for each sprue design were fabricated and invested with ethyl silicate investment. Castings were made with an arc-type automatic casting machine in an argon atmosphere. Castings were examined with radiographic equipment to detect the presence of voids in the castings, and the completeness to each casting was visually verified. Data on porosities were tabulated and statistically analyzed with 1-way ANOVA followed by Student Newman-Keuls test. Chi-square analysis was used to identify statistically significant differences in casting defects among the 3 sprue designs. RESULTS: No statistically significant differences in the total number of porosities were found between the 3 sprue designs (P =.51). Results of completeness of castings evaluated by using chi-square test revealed a statistically significant deference among the 3 sprue designs (P =.008). CONCLUSION: The ball-sprue design produced the most complete castings for the removable partial denture titanium frameworks.     

Numerical simulation of porosity-free titanium dental castings

The objective of this research was to analyse, predict and control the porosity in titanium dental castings by the use of numerical simulation. A commercial software package (MAGMASOFT) was used. In the first part of the study, a model casting (two simplified tooth crowns connected by a connector bar) was simulated to analyse shrinkage porosity. Secondly, gas pores were numerically examined by means of a ball specimen with a "snake" sprue. The numerical simulation results were compared with the experimental casting results, which were made on a centrifugal casting machine. The predicted shrinkage levels coincided well with the experimentally determined levels. Based on the above numerical analyses, an optimised running and gating system design for the crown model was proposed. The numerical filling and solidification results of the ball specimen showed that this simulation model could be helpful for the explanation of the experimentally indicated gas pores. It was concluded that shrinkage porosity in titanium dental casting was predictable, and it could be minimised by improving the running and gating system design. Entrapped gas pores can be explained from the simulation results of the mould filling and solidification.     

Comparison of the effects of three sprue designs on the internal porosity in crowns cast with a silver-free high-palladium alloy

This study tested the effect of bsprue design on internal porosity of a silver-frees high-palladium alloy. The designs evaluated consisted of: (1) a cylindrical sprue, (2) a cylindrical sprue with a reservoir, and (3) cylindrical sprue with a constriction at the point of attachment with the pattern. Ten identical complete crowns were made with each sprue design. The cast crowns were embedded in epoxy resin, sectioned, and polished. A total of six sites for each sample were analyzing computer. The mean amount of internal porosity from all analyzed sites for each sprue design was calculated as a percent site porosity per total site and differences between the experimental sites and groups tested. The analysis of variance found no significant differences among the sprues and no significant interaction, but determined a significant difference (p less than 0.05) among the sites analyzed. Tukey's studentized range test showed that the sprue contained a significantly greater percentage of porosity than any of the other sites analyzed.     

Application of laser measuring, numerical simulation and rapid prototyping to titanium dental castings.

OBJECTIVES: This paper describes a method of making titanium dental crowns by means of integrating laser measuring, numerical simulation and rapid prototype (RP) manufacture of wax patterns for the investment casting process. METHODS: Four real tooth crowns (FDI No. 24, 25, 26, 27) were measured by means of 3D laser scanning. The laser digitized geometry of the crowns was processed and converted into standard CAD models in STL format, which is used by RP systems and numerical simulation software. Commercial software (MAGMASOFT) was used to simulate the casting process and optimize the runner and gating system (sprue) design. RP crowns were 'printed' directly on a ModelMaker II 3D Plotting System. A silicone negative mold (soft tool) was made from the RP crowns, then more than hundreds wax crowns were duplicated. The duplicated crowns were joined to the optimized runner and gating system. By using the investment casting process 20-25 replicas of each crown were made on a centrifugal casting machine. All castings were examined for porosity by X-ray radiographs. RESULTS: By using the integrated scanning, simulation, RP pattern and casting procedure, cast crowns, free of porosity, with excellent functional contour and a smooth surface finish, were obtained from the first casting trial. SIGNIFICANCE: The coupling of laser digitizing and RP indicates a potential to replace the traditional 'impression taking and waxing' procedure in dental laboratory, with the quality of the cast titanium prostheses also being improved by using the numerically optimized runner and gating system design.     

The effect of sprue design on the marginal accuracy of titanium castings

The purpose of this study was to measure the effects of sprue number and position on cast titanium crown margins. Twenty‐four complete veneer crown wax patterns were fabricated on a stainless steel die with a 30° bevel finish line. Twelve wax patterns were sprued with one 8‐gauge wax sprue and the remaining 12‐gauge double sprued. All patterns were invested with a phosphate bonded investment. Castings were made with a titanium casting machine following the manufacturer's instructions and using commercially pure titanium (> 99·5%) ingots. The castings were than carefully cleansed and the margins were examined with indirect impression technique. Data were analysed with an ANOVA and the Student's t ‐test with confidence level at 95%. The results revealed that the marginal discrepancy for the double sprueing group (32·1 ± 12·8 μm) has significantly less discrepancy ( P < 0·001) than the single sprueing group (49·8 ± 16·4 μm). There was no statistically significant differences in marginal discrepancy between locations within the sprueing techniques ( P > 0·05). An improvement in the degree of casting accuracy of titanium crown was indicated by the double sprue design used in this investigation.     

Porosity and accuracy of multiple-unit titanium castings

The objective of this investigation was to determine whether titanium could be used to cast reproducible multiple-unit dental restorations. A metal analog was machined to simulate preparations for a three-unit fixed partial denture. Castings were made with four different sprue designs at three temperatures. Marginal accuracy and porosity were evaluated. A total of 70 titanium castings were made with an argon/electric arc/vacuum/pressure casting machine. Ten castings were made in the conventional manner by use of gold-palladium alloy as a control to compare the marginal gap. The results revealed that the porosity was less when a large individual sprue (6-gauge) was used. It was also noted that the lower pattern burnout temperatures of 910 degrees C and 920 degrees C exhibited significantly smaller marginal gaps than did the higher temperature of 930 degrees C.     

The effect of sprue attachment design on castability and porosity

Sprue attachment design is an important and controversial variable that can affect casting characteristics of castability and porosity. Four sprue attachment designs--straight, flared, abrupt constriction, and gradual constriction--were investigated. Standardized wax copings simulating complete veneer metal ceramic crowns with knife-edge margins were sculpted on refractory investment dies, sprued, invested, and cast with Olympia alloy. The specimens were embedded, sectioned, and polished. Castability was analyzed by measuring the width of the cast meniscus of the margins. The margin widths of the flared and the straight sprue attachment groups were significantly less than the abrupt or gradual constriction attachment group (p less than 0.05). Photomicrographs revealed discernible differences in the relative quantity and location of porosity in the sprue-coping junctions. The straight and flared sprue attachment groups were less porous than the abrupt or gradual constriction groups (p less than 0.01). Flared and straight sprue attachments optimized castability and minimized porosity.