Abstract:

Objective To study the effects of different heating timings after mixing the materials and different heating methods on the expansion characters of a quick- heating gypsum- bonded investment. Methods The setting expansion rate of GC Cristoquick Ⅱ gypsum- bonded investment was measured with a setting expansion tester 30, 60, 120 min after mixing the material respectively. The thermal expansion rates of the material at different setting time（30, 60, 120 min after mixing） and under different heating treatment methods（quick and conventional heating techniques）were also determined using a thermal dilatometer for dental investments, the total linear expansion rate were calculated. The effects of heating time and heating methods on the expansion of the investments were statistically analyzed with SPSS 11.0 software, using ANOVA multiple comparison（α=0.05）. Results Statistical differences were found among the setting and thermal expansion rates of the investment at different heating timings after mixing the material（P <0.01）. Setting expansion, thermal expansion and total expansion rates increased with the setting time before heat treatment, while thermal expansion rates under different（quick and conventional） heating methods were not statistically significant（P >0.05）. Conclusion The expansion characters of the quick - heating gypsum- bonded investment are influenced by different heating timings after mixing the material. The heat treatment technique of this quick- heating investment recommended needs to be modified to ensure casting precision.

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