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Flexural Strength and Fracture Toughness of Dicor Glass-ceramic after Embedment Modification
I.L. Denry
The Ohio State University, College of Dentistry, 305 W. 12th Avenue, Columbus, Ohio 43210
S.F. Rosenstiel
The Ohio State University, College of Dentistry, 305 W. 12th Avenue, Columbus, Ohio 43210
Previous studies on the surface properties of Dicor castable glass-ceramic have shown the formation of a specific crystalline phase at the glass-ceramic/embedment interface. If this phase is not removed by grinding, it leads to an undesirable strength decrease. The aims of this study were: (1) to determine the nature of this surface layer, (2) to promote the formation of a different crystalline phase at the surface with the intention of improving the properties of the glass-ceramic, by modification of the composition of the Dicor ceramming embedment, and (3) to evaluate the fracture toughness and flexural strength of Dicor glass-ceramic after embedment modification.
Modifications were made to the embedment by incorporation of 2.5 wt% of lithium fluoride and ceramming at various temperatures. X-ray diffraction was used to determine the crystalline nature of the surface layer. Fracture toughness was investigated by the indentation technique. The maximum bi-axial stresses were calculated after the samples were fractured in water on a ball-on-ring fixture at 0.5 mm/min. With the recommended embedment and ceramming cycle, the crystalline phase constituting the ceram layer was a calcium magnesium silicate CaMg(SiO3)2 (diopside).
The crystalline composition of the ceram layer was successfully modified by addition of 2.5 wt% lithium fluoride to the embedment. This promoted the crystallization of mica in the ceram layer and increased the fracture toughness of the glass-ceramic when the ceramming temperature was 950 or 975°C. The flexural strength was significantly increased when the ceramming temperature was 1000°C.
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Journal of Dental Research, Vol. 72, No. 3,
572-576 (1993)
DOI: 10.1177/00220345930720030301
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I. L. Denry
Recent Advances in Ceramics for Dentistry
Critical Reviews in Oral Biology & Medicine,
January 1, 1996;
7(2):
134 - 143.
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