THE EFFECTS OF SPRUE DESIGN ON THE ROUGHNESS AND POROSITY OF TITANIUMCASTINGS

Purpose. This study measured the effects of the sprue number and posit ion on the roughness and porosity of cast titanium crowns. Material an d methods. Twenty-four complete veneer crown wax patterns were fabrica ted on a stainless steel die with a 30-degree bevel finish line. Twelv e wax patterns were sprued with one 8-gauge wax sprue and the remainin g 12 were double sprued. All patterns were invested with a phosphate b onded investment. Castings were made with a titanium casting, accordin g to the manufacturer's instructions, with commercially pure titanium (> 99.5%) ingots. The castings were carefully cleaned and the surface roughness was measured with a profilometer. The specimens were then em bedded and sectioned. Internal porosities were quantified with photogr aphs by computerized image analysis. Data were analyzed with an ANOVA and the Student's t test with a confidence level of 95%. Results. The roughness value of the occlusal third of the crowns for the single spr ue group (Ra = 3.0 +/- 0.9 mu m) was significantly higher than other m easurements (p < 0.05). There were statistically significant differenc es in values of porosity areas between the single sprue group (1.5 +/- 0.7 mm(2)) and the double sprue group (0.2 +/- 0.2 mm(2)) (p < 0.01). The double sprue design resulted in a relatively smoother casting sur face and less internal porosity than the single sprue design. Conclusi ons. Improvements in the degree of roughness and porosity of titanium crown castings were the result of the double sprue design.