Alper Ozdogan1, Hatice Ozdemir2. 1. Assistant Professor, Department of Prosthodontics, Faculty of Dentistry, Atatürk University, Erzurum, Turkey. Electronic address: alprozdgn@gmail.com. 2. Associate Professor, Department of Prosthodontics, Faculty of Dentistry, Atatürk University, Erzurum, Turkey.
Abstract
STATEMENT OF PROBLEM: Repeated firings cause materials to be exposed to additional heat treatments. The effect of these additional heat treatments on the mechanical properties of lithium disilicate glass-ceramics is not fully known. PURPOSE: The purpose of this in vitro study was to determine the effects of repeated firing on the mechanical properties of lithium disilicate glass-ceramics produced by 2 different techniques, press and computer-aided design and computer-aided manufacturing (CAD-CAM). MATERIAL AND METHODS: Eighty rectangular (25×4×2 mm) lithium disilicate glass-ceramic specimens were used in this study, 40 produced by heat pressing and 40 by milling, and divided into 4 groups (n=10) with a different number of veneer porcelain firings (1 to 4). After firing, the Vickers hardness, flexural strength (3-point bend test), and fracture toughness were determined, and the specimens were analyzed with an environmental scanning electron micrograph. Data were analyzed with analysis of variance (ANOVA) (α=.05). RESULTS: The repeat firing processes did not affect the flexural strength of the specimens in either group (P>.05), while the surface hardness and fracture toughness were significantly changed (P<.05). CONCLUSIONS: Increasing the number of firings adversely affected the mechanical properties of lithium disilicate glass-ceramics.
STATEMENT OF PROBLEM: Repeated firings cause materials to be exposed to additional heat treatments. The effect of these additional heat treatments on the mechanical properties of lithium disilicate glass-ceramics is not fully known. PURPOSE: The purpose of this in vitro study was to determine the effects of repeated firing on the mechanical properties of lithium disilicate glass-ceramics produced by 2 different techniques, press and computer-aided design and computer-aided manufacturing (CAD-CAM). MATERIAL AND METHODS: Eighty rectangular (25×4×2 mm) lithium disilicate glass-ceramic specimens were used in this study, 40 produced by heat pressing and 40 by milling, and divided into 4 groups (n=10) with a different number of veneer porcelain firings (1 to 4). After firing, the Vickers hardness, flexural strength (3-point bend test), and fracture toughness were determined, and the specimens were analyzed with an environmental scanning electron micrograph. Data were analyzed with analysis of variance (ANOVA) (α=.05). RESULTS: The repeat firing processes did not affect the flexural strength of the specimens in either group (P>.05), while the surface hardness and fracture toughness were significantly changed (P<.05). CONCLUSIONS: Increasing the number of firings adversely affected the mechanical properties of lithium disilicate glass-ceramics.