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 a nd position on cast titanium crown margins. Twenty-four complete venee r crown wax patterns were fabricated on a stainless steel die with a 3 0 degrees bevel finish line. Twelve wax patterns were sprued with one 8-gauge wax sprue and the remaining 12-gauge double sprued. All patter ns were invested with a phosphate bonded investment. Castings were mad e with a titanium casting machine following the manufacturer's instruc tions and using commercially pure titanium (> 99.5%) ingots. The casti ngs were than carefully cleansed and the margins were examined with in direct impression technique. Data were analysed with an ANOVA and the Student's t-test with confidence level at 95%. The results revealed th at the marginal discrepancy for the double sprueing group (32.1 +/- 12 .8 mu m) has significantly less discrepancy (P < 0.001) than the singl e sprueing group (49.8 +/- 16.4 mu m). There was no statistically sign ificant differences in marginal discrepancy between locations within t he sprueing techniques (P > 0.05). An improvement in the degree of cas ting accuracy of titanium crown was indicated by the double sprue desi gn used in this investigation.