Effect of mixing methods on the physical properties of dental stones☆

Abstract 

Objectives

This in vitro comparative study evaluated the effect of different stone mixing methods on material properties of four dental stones. Two ADA type IV stones (Silky-Rock and Snap-Stone), one type V high expansion stone (Die Keen), and one recently introduced type V specialty stone (HandiMix) were chosen for this study.

Methods

Forty cylindrical specimens (25mm×12.5mm) were cast for each of the nine stone sub-groups and bench dried at 23±2°C for 1 and 24h. Specimens were then tested in an Instron in tensile and compression modes at crosshead speeds of 0.5 and 1.0mm/min, respectively. Four rectangular-shaped specimens (30mm×15mm×15mm) of each stone type were cast and bench dried for 48h. Knoop microhardness measurements were obtained from defined areas on each specimen for surface hardness testing using 200g load and 20s dwell time. A 12.6mm² area was then delimited in the center of two sides of each specimen and photographed under low power magnification (40×). The average pore number per area was then determined for each specimen for surface porosity testing. The setting time and setting expansion for each stone type was recorded as well.

Results

ANOVA (P<0.001) and Ryan–Einot–Gabriel–Welsh test (P<0.05) showed significant differences between diametral tensile strengths and pore numbers for both stone types and mixing methods.

Conclusion

Within the limitations of this study, the newly introduced mixing method did not appear to have an effect on the physical properties of HandiMix stone.

Keywords: HandiMix, Dental stone, Gypsum, Compressive strength, Diametral tensile strength, Setting time, Setting expansion, Surface porosity, Microhardness, Hand-mixing, Vacuum-mixing, Shake-mixing