The effect of casting machine and investment on the castability of titanium / 대한치과보철학회지

STATEMENT OF PROBLEM: Despite of the recent development of the titanium casting system methods, the casting defects such as imperfect casting and internal porosity were frequently observed. PURPOSE: The purposes of this study were to compare and measure the castability, microhardness, and surface reaction between Grade 2 pure titanium and Ti-6Al-4V by casting these alloys from the different sprue design conditions. MATERIAL AND METHODS: Depending on the sprue designs and titanium alloys, 42 ready-made wax patterns were used. By analyzing the remodeling of the cast, internal porosity, microhardness, and titanium surface layer of SEM, there were several results we observed. RESULTS: 1. The measured castability of titanium were categorized in the ascending order: individual sprue group, runner bar group, and single group. This data are based on the statistically signigicant differences. 2. The castability of titanium has not showed the statistically significant differences among the alloys. However, CP-Ti groups were superior to Ti-6Al-4V groups by showing the noticeable castability. 3. The surface layers of the castings of all groups have showed 5 micrometer titanium oxide layers irrespective of sprue designs and titanium alloys. CONCLUSION: From the above study results, by fabricating the restorations from the centrifugal casting machine direct sprue designs revealed better castability. As we increased the number of sprues in the wax pattern, it revealed better castability. The castability of pure titanium rather than that of Ti-6Al-4V was remarkable. To fabricate the complex forms of the restorations, further researches on the efficient sprue designs and titanium alloys must be made.

The effect of sprue design on the internal porosity of titanium castings / 대한치과보철학회지

STATEMENT OF PROBLEM: The high melting temperature and chemical reactivity of titanium necessitates casting machines different from those used in conventional casting. Despite the new developments in Ti casting systems, inadequate mold filling and internal porosity are frequently observed casting defects. Therefore, the study on the fabrication technique including sprue design to solve these casting defects is still necessary. PURPOSE: The purpose of this study was to evaluate the effect of sprue design and cross sectional area of sprue on the internal porosity. MATERIALS AND METHODS: 30 simulated cast three units titanium crowns were prepared. 5 cast crowns for each with different sprue design(sinlge sprue, double sprue and plate sprue) of two cross sectional areas(small and large cross sectional areas) were fabricated. The sections of titanium castings were photographed in a microscope at x100 magnification to record internal porosities. RESULTS AND CONCLUSION: Within the limits of this study, the following conclusions were drawn: 1. There was a significantly lower in internal porosity of titanium castings for large cross sectional area of sprue group than the small group(P>.05). 2. There was no significant difference in internal porosity among sprue designs in similar cross sectional area of sprue(P>.05).

Computer-aided casting design for implant titanium superstructures / 대한치과보철학회지

STATEMENT OF PROBLEM: It is difficult to obtain a good titanium casting body using the traditional sprue design because of high melting point of Ti, and the low fluidity and high reactivity of molten Ti. PURPOSE: A new sprue design for titanium casting bodies needs more trial and error. In order to decrease the number of trial and error, computer simulation(MAGMASOFT, Magmasoft Giessereitechnologie GmbH, Achen, Germany) was used to optimize sprue design in U-shaped implant superstructures. MATERIAL AND METHOD: Five kinds of sprue were examined for the design of the sprue former for titanium casting: Sprue design A(sprue length 4 mm, rectangular shape, 4 sprues), Sprue design B(sprue length 4 mm, round shape, radius 2 mm, 7 sprues), Sprue design C (sprue length 2 mm, round shape, radius 2 mm, 7 sprues), Sprue design D (sprue length 2 mm, cone shape, large radius 3mm, small radius 2mm, 7 sprues), and Sprue design E( sprue length 2 mm, one unit channel shape). Sprue design F(sprue length 2mm, one unit channel hape) was also examined for the design of the customized sprue former in the Biotan system(Schutz Dental Gmbh, Germany). The casting bodies were taken in Sprue design A, Sprue design D, Sprue design E, and Sprue design F in the Biotan casting system. The numerically predicted defects were compared with the experimental dental castings by the radiographic and sectional view observations. RESULTS: 1. According to the result of computer simulation, turbulence during mold filling was decreased in the sequence of Sprue design F, Sprue design E, Sprue design D, Sprue design C, Sprue design B, and Sprue design A. 2. The calculated solidification time contours indicate that hot spot was moved from the casting body to the sprue button in the sequence of Sprue design A, Sprue design B, Sprue design C, Sprue design D, and Sprue design E. The filling pattern of Sprue design F was similar to that of Sprue design E. 3. The predicted filling pattern shows that less turbulence was found in the customized sprue former than in the standard sprue former. 4. According to the results of the radiographic and cross sectional observations, casting defects less than 1mm were found at the center of a casting body with Sprue design E and Sprue design F. However, larger casting defects of 4mm were found in a casting with Sprue design A. 5. The predicted casting porosity was similar to that of the real casting. CONCLUSION: One unit channel-type and customized sprue former can be recommended. Further research and development of various sprue designs using computer simulation is necessary to optimize casting design, in order to reduce the formation of casting defects in implant titanium superstructures.