title: Flexural strength and fracture toughness of Dicor glass-ceramic after embedment modification.
abstract: 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 degrees C. The flexural strength was significantly increased when the ceramming temperature was 1000 degrees C.
authors.affiliation: Ohio State University, College of Dentistry, Columbus 43210.
authors.forename: I L
authors.initials: IL
authors.lastname: Denry
authors.forename: S F
authors.initials: SF
authors.lastname: Rosenstiel
mesh_terms: D000535:Aluminum / Q000032:analysis / Q000737:chemistry; D017607:Aluminum Compounds; D002118:Calcium / Q000032:analysis; D002516:Ceramics / Q000032:analysis / Q000737:chemistry*; D003461:Crystallography; D003776:Dental Porcelain / Q000032:analysis / Q000737:chemistry*; D004548:Elasticity; D004577:Electron Probe Microanalysis; D005459:Fluorides / Q000737:chemistry; D005898:Glass / Q000032:analysis / Q000737:chemistry*; D006244:Hardness; D008094:Lithium / Q000737:chemistry; D018020:Lithium Compounds; D008274:Magnesium / Q000032:analysis; D017633:Magnesium Silicates; D008422:Materials Testing; D011188:Potassium / Q000032:analysis; D012824:Silicic Acid / Q000737:chemistry; D012825:Silicon / Q000032:analysis; D013314:Stress, Mechanical; D013499:Surface Properties; D014961:X-Ray Diffraction; D015040:Zirconium / Q000032:analysis
chemical_list: D017607:Aluminum Compounds; C047475:Dicor ceramic; D018020:Lithium Compounds; D017633:Magnesium Silicates; D003776:Dental Porcelain; C005013:Florisil; D012824:Silicic Acid; C074224:diopside; C027651:lithium fluoride; C004832:hexafluorosilicate; D008094:Lithium; D015040:Zirconium; D000535:Aluminum; D008274:Magnesium; D005459:Fluorides; D011188:Potassium; D002118:Calcium; D012825:Silicon; C032311:aluminum fluoride