[Comparison of casting precision of two kinds of commercially available gypsum-bonded investment with different setting and thermal expansion characteristics].
OBJECTIVE
To investigate expansion characteristics of two kinds of commercial investment (Cristo balite Micro II 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 Micro II, 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).


CONCLUSIONS
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.
Tong
Xun
X
State Key Laboratory of Oral Diseases, Sichuan University, Chengdu 610041, China.
Zhao
Yao
Y
Meng
Yu-Kun
YK
D002133:Calcium Sulfate; D002516:Ceramics; D003722:Dental Alloys; D003734:Dental Casting Investment; D003735:Dental Casting Technique; D007449:Investments
D003722:Dental Alloys; D003734:Dental Casting Investment; D002133:Calcium Sulfate