Crystal formations obtained from evaporating clear filtrates of dental stone mixed with various solutions were examined with an optical and scanning electron microscope. It was found that when K2SO4 was present in any concentration, a spherulitic structure dissimilar to that of CaSO4 2H2O and K2SO4 was dominant. It is concluded that syngenite (a complex compound of CaS04 and K2SO4) forms at the center of the nuclei of crystallization and is responsible for spherulitic formation. The use of K2SO4 solution and saturated CaSO 4 solution was also found to improve the strength both at one and 24 h.
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References
1.
Kuner, W. and Michman, S.: Setting Expansion of Plaster of Paris, J Dent Res46 :661-665,1967.
2.
Combe, E.C. and Smith, D.C.: Some Properties of Gypsum Plaster, Br Dent J117 :237-245, 1964.
3.
Earnshaw, R. and Marks, B.I.: The Measurement of Setting Time of Gypsum Products, Aust Dent J9:17-26, 1964.
4.
Water, E.H. and Lewis, K.W.: Measurement of the Time of Initial Set of Gypsum Plasters, Chem and Industry , pp. 1156-1164, 1960.
5.
Docking, A.R. : Gypsum Research-Australia: The Setting Process , L Dent J15:372-376. 6. Lautenschlager, E.P. and Corbin, F.: Investigation of Expansion of Dental Stone, J Dent Res48:206-210, 1969.
6.
Peyton, F.A. ; Leibold, J.P.; and Ridg-Ley , G.V.: Surface Hardness, Compressive Strength, and Abrasion Resistance of Indirect Die Stones , J Prosthet Dent2:381-389, 1952. 8. Mahler, D.B.: Hardness and Flow Properties of Gypsum Materials, J Prosthet Dent1:188-195,1960.
Earnshaw, R. and Smith, D.C.: The Tensile and Compressive Strength of Plaster and Stone, Aust Dent J11:415-422, 1966. 11. Earnshaw, R.: The Consistency of Dental Gypsum Products , Aust Dent J18:33-37, 1973.
9.
Phillips, R.W. : Skinner's Science of Dental Materials, 7th ed., W.B. Saunders Co., 1973, pp. 67-72.
10.
Greener, E.H. ; Harcourt, J.K.; and Lautenschlager , E.P.: Materials Science in Dentistry, 2nd ed., Baltimore. MD: The Williams and Wilkins Co., 1972, p. 267. 14. Guide to Dental Materials and Devices, 8th ed., 1976.
11.
Ridge, M.T. and Surkevicius, H.: Hydration of Calcium Sulfate Hemihydrate . II, J Appl Chem12:252-256, 1962.
12.
Ridge, M.T. and Surkevicius, H.: Hydration of Calcium Sulfate Hemihydrate . I, J Appl Chem12:246-252,1962.
13.
Schiller, K. : Mechanism of Re-crystallization in Calcium Sulfate Hemihydrate Plaster, J Appl Chem12:135-144, 1962.
