Abstract: Objective To investigate the effect of difference between thermal and setting expansion rate of the investments on the deformation of resulted castings. Methods Plate -like wax patterns with pre -marked points were invested in two different gypsum -bonded investments of the same total expansion rate. One was higher in setting expansion rate, while the other was higher in thermal expansion rate. Casting rings were lined with a dry ceramic fiber liner by thickness of 0.7 mm. The difference between the castings and the wax patterns at corresponding points were calculated to represent the dimensional changes of the investments with different thermal and setting expansion rate in the rings at different directions. Results In the scope of this study, the casting expansions of the two investments on the axial direction were larger than the radial direction. The difference between the cast and the wax created by higher thermal expansion rate investment on each direction was statistically
significant（P<0.05）, while higher setting expansion rate investment was not statistically significant（P>0.05）. Effects of two investments on the precision of castings were statistically significant（P<0.01）. Conclusion The two gypsum-bonded investments with different thermal and setting expansion rate have effect on the casting precision. The investment with higher setting expansion rate should be applied when invested with liner in the casting rings.

Key words: gypsum-bonded investment, thermal expansion, setting expansion, casting precision