There has been a great interest in the use of titanium for fixed and removable prostheses in recent because of its excellent biocompatibility. However, the high melting temperature and chemical reactivity of titanium necessitates casting systems different from those used in conventional casting. The current titanium casting systems are based on an electricarc design for melting the metal in an argon atmosphere and its exclusive investment. 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. In this study, to evaluate the effect of sprue design on the castability of simulated cast titanium crowns, 10 cylindrical cast crowns for each group with four different sprue design(Single group, Double group, Runner bar group, Reservoir group) were fabricated. An impression of the entire casting margin was made and cut at 90°intervals, and the sections were photographed in a microscope at 100 X magnification to record marginal discrepancy. The internal porosities of the cast crowns were disclosed by radiographs. Within the limits of this study, the following conclusions were drawn: 1. The overall mean marginal discrepancies for each group were as follows: Double group, 43.65 ㎛; Reservoir group, 50.27㎛; Single group, 54.17㎛; Runner bar group,58.90㎛(p<0.05). 2. The mean of marginal discrepancies for wax patterns was 10.65㎛. 3. The numbers of internal porosity showed the most in Runner bar group followed by Single group, Reservoir group, and Double group.
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