OBJECTIVETo investigate the method of enhancing the accuracy of titanium crowns by improving the casting method.

METHODSA self-assembled die was used to fabricate 48 standardized wax crowns. The dies were averagely divided into two groups. 21 crowns were successfully fabricated from one group according to the improved techniques. 18 crowns were fabricated by traditional method. A reference mark was scribed 90 degrees apart at four sites on the margin of each wax pattern and respective die. The distance between the margins of the wax pattern and the die was measured under a stereomicroscope. Similar method was also applied to measure the margin of castings. The castings were longitudinally split through midline. The distance between the 4 points(B',C',D',E') selected in the inner part of the crown and the die was respectively examined.

RESULTSCastings acquired by the improved method were more complete and had smoother surface. Marginal discrepancy value had significant difference between the two groups. Value in experimental group was smaller. Distance from B',E' to die between the two groups had no significant difference, but the distance from C',D' to the die was significantly different. The experimental group was smaller.

CONCLUSIONStandardized crowns fabricated by the improved titanium casting technique were more accurate, but special investment for titanium crowns and bridges should be developed to compensate the casting shrinkage of metal.