Geetha, K R (2006) Effect of various sprue designs on the properties of base metal alloy castings. Masters thesis, Ragas Dental College & Hospital, Chennai.
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Abstract
INTRODUCTION : The casting of dental alloys is one of the procedures to prepare various types of metallic restorations in prosthodontics. William Taggart (1907) first described the lost wax casting process in dentistry. The procedure involves the preparation of the wax patterns, spruing the wax patterns, investing and wax burn out procedures followed by ingress of molten metal into the mold. The ability of the molten alloy to completely occupy the mold created by the elimination of a pattern is defined as castability. Incomplete castability may result in deficient castings. The structural faults in a dental casting can result from any combination of problems related to spruing, investing, wax elimination, alloy melting, casting, and solidification of the casting. The defects such as shrinkage porosity, porosity due to occluded gases, porosities due to back pressure of gases in the mold, porosities due to inclusion of investment, incomplete filling of the mold prior to solidification, incomplete filling of the margins due to surface tension effects, and suck back porosities can occur resulting in unacceptable casting. The objectives of this study were: 1. To compare the castability of the castings obtained from conical, cylindrical and bottle neck sprue designs. 2. To compare the mass of the castings obtained from conical, cylindrical and bottle neck sprue designs. 3. To compare the microhardness of the castings obtained from conical, cylindrical and bottle neck sprue designs. 4. To compare the porosity of the castings obtained from conical, cylindrical and bottle neck sprue designs. MATERIALS AND METHOD : This study was conducted to compare the efficacy of 3 sprue designs on the castability, mass, microhardness and porosity of base metal alloy castings. The following materials were used for the study: • Prefabricated, wax mesh pattern (BEGO, Germany). • Pattern Resin (GC Corporation, TOKYO, JAPAN). • Colloidal Silica. (Investment BS Liquid 1, Heraeus Kulzer GmbH, Germany). • Phosphate bonded investment (MOLDAVEST exact, Heraeus Kulzer, GmbH, Germany). • Base metal nickel chromium alloy (HERAENIUM-S, Heraus Kulzer, GmbH, Germany). The testing equipments used in the study included the following: • Physical balance (Mettler Tolledo Digital Weighing Machine, Co., OHIO, U.S.A.). • Microhardness tester (Reichert Microhardness tester, Reichert, AUSTRIA). • Quantimet Image Analyzer (Quantimet Corp., LONDON., ENGLAND). METHOD : The study included the following procedures: • Selection of test sample, design and specifications. • Specifications for the 3 test sprue designs and their fabrication. • Attachment design of the acrylic sprue patterns to the wax mesh pattern. • Casting and retrieval of the test samples. • Evaluation of the properties of the test samples obtained from the 3 different sprue designs. SUMMARY: This study was done to evaluate and compare the properties of castings obtained from three sprue designs, namely, bottleneck, conical, and cylindrical. A wax mesh pattern with a dimension of 16mm x 16mm that provided 6 x 6 square shaped spaces was used as a test pattern. A two-part stainless steel mold was used to prepare the reproducible test sprue designs. The acrylic pattern resin samples, 10 each, for the 3 sprue designs were obtained and attached to each of the wax mesh pattern. The cylindrical sprue design was connected to the mesh pattern with a straight attachment, the bottleneck sprue design with a constricted attachment and the conical sprue design with a flared attachment. The samples were cast with nickelchromium alloy. The castings were retrieved and evaluated for castability, mass, microhardness and porosity. The results obtained were statistically analyzed. The sprue design did not have any apparent influence on castability, mass and microhardness values of the base metal castings in this study. The bottle neck and conical sprue designs were superior when compared to the cylindrical sprue design in reducing the porosity of the base metal alloy castings. CONCLUSION : The results of this study yielded the following conclusions: 1. The bottle neck, conical and cylindrical sprue designs employed in this study exhibited complete castability. 2. The differences in the mean mass values between the bottle neck, conical, and cylindrical sprue designs were not statistically significant. The three test sprue designs did not exert any apparent influence on the mass (density) of the castings. 3. The differences in the mean microhardness values between the bottle neck, conical, and cylindrical sprue designs were not statistically significant. The three test sprue designs did not exert any apparent influence on the microhardness of the castings. 4. There was a significant reduction in the percentage porosity of castings obtained with the bottle neck and conical sprue designs as compared to the cylindrical sprue design. 5. There was no difference in the percentage porosity of castings obtained with the bottle neck and conical sprue designs. 6. Order of ranking of the three sprue designs that yielded castings with reduced porosity is as follows: a. Bottle neck sprue design, b. Conical sprue design, c. Cylindrical sprue design.
| Item Type: | Thesis (Masters) |
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| Uncontrolled Keywords: | sprue designs, base metal alloy castings. |
| Subjects: | DENTAL > Prosthodontics and Crown and Bridge |
| Depositing User: | Kambaraman B |
| Date Deposited: | 19 Jan 2018 01:27 |
| Last Modified: | 19 Jan 2018 01:27 |
| URI: | http://repository-tnmgrmu.ac.in/id/eprint/5494 |
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