IADR Abstract Archives
Water/Powder ratio and Hardness of Recycled Gypsum Products
Objective: To dehydrate gypsum-based dental stones using a ventilated radiant heat source to create a re-usable powder suitable for re-introduction to dentistry, construction, arts and crafts, or agriculture. The goal of this study was to determine the optimal water/powder ratio and the surface hardness of the dehydrated gypsum.
Methods: We collected used models from the graduating class and divided the materials into two main groups, stone and plaster. From preliminary studies, we optimized the controlled test environment that is adequate for regenerating plaster from gypsum. The parameters were dry heat of 130oC for16h and the active removal of steam. The dehydrated gypsum products were pulverized and went through a series of ASTM sieves down to particles sizes comparable to commercial products. Shore Durometer Hardness test was performed (Type "A-2" ASTM D2240). Differences among groups were identified using ANOVA with Tukey post-hoc analyses (n=10, α≤0.05).
Results: Groups with same letter were not significantly different.
Materials |
Manufacturers |
Water/Powder |
Surface Hardness Number |
ResinRock |
Whip Mix Corp |
14mL/70g |
93.7±1.9 |
Labstone Blue |
Heraeus Kulzer |
30mL/100g |
90.9±2.2 |
Model Plaster |
Heraeus Kulzer |
70mL/150g |
79.5±1.1 |
Microstone |
Whip Mix Corp |
40mL/140g |
88.3±2.4 A,B |
Snap-Stone |
Whip Mix Corp |
33mL/140g |
86.8±2.0 A |
Mounting Plaster |
Whip Mix Corp |
43mL/70g |
72.6±2.1 D |
Experimental Stone-1 |
NA |
45mL/80g |
87.5±1.6 B |
Experimental Stone-2 |
NA |
45mL/90g |
82.7±2.1 C |
Experimental Plaster-1 |
NA |
60mL/80g |
83.5±2.1 C |
Experimental Plaster-2 |
NA |
60mL/90g |
71.5±1.9 D |
Conclusions: We have been successful in dehydrating gypsum in our controlled test environment. The dehydrated gypsum can be remolded according to our optimized water/powder ratio. The surface hardness of the experimental stones and plasters are comparable to commercial products.