The effects of sprue design on the roughness and porosity of titanium castings.

PURPOSE

This study measured the effects of the sprue number and position on the roughness and porosity of cast titanium crowns.

MATERIAL AND METHODS

Twenty-four complete veneer crown wax patterns were fabricated on a stainless steel die with a 30-degree bevel finish line. Twelve wax patterns were sprued with one 8-gauge wax sprue and the remaining 12 were double sprued. All patterns were invested with a phosphate bonded investment. Castings were made with a titanium casting, according 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 embedded and sectioned. Internal porosities were quantified with photographs 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 sprue group (Ra = 3.0 +/- 0.9 microns) was significantly higher than other measurements (p < 0.05). There were statistically significant differences in values of porosity areas between the single sprue group (1.5 +/- 0.7 mm2) and the double sprue group (0.2 +/- 0.2 mm2) (p < 0.01). The double sprue design resulted in a relatively smoother casting surface and less internal porosity than the single sprue design.

CONCLUSIONS

Improvements in the degree of roughness and porosity of titanium crown castings were the result of the double sprue design.