Abstract:

Objective To investigate expansion characteristics of two kinds of commercial investment（Cristo balite MicroⅡ and Cristo Quick）, and their effects on cast accuracy of a dental Ag-Pd casting alloy. Methods Two kinds of investment were mixed at the ratio of 1 ∶3. The setting and thermal expansion curves of the investment were recorded according to the requirements of ISO7490 and expansion rate calculated, respectively. Plate-like wax-patterns with pre-marked points were invested in casting rings（lined with ceramic fiber liners with thickness of 0.45 mm）. Castwell M.C dental alloy were melted with gas flame and cast with a centrifugal casting machine. The differences between the castings and the wax patterns at corresponding points were calculated to represent the dimensional changes of the investment. Results The setting, thermal and total expansion rates were 0.68, 1.18, 1.86 for Cristo balite MicroⅡ, and 0.94, 1.03, 1.97 for Cristo Quick. The setting and thermal expansion rates were statistically significant between two kinds of investment（P<0.05）, while not for the total expansion rates（P>0.05）. Effect of different investment on the precision of castings was not statistically significant（P>0.05）. Conclusion Within the scope of this study, gypsum-bonded investment with similar total expansion rates but different expansion characteristics has no effect on the casting precision of Ag-Pd dental alloys.

Key words: gypsum-bonded investment, dental casting alloy, linear expansion, cast precision