Effect of heat pressing on the mechanical properties of a mica‐based glass‐ceramic

Abstract

Previous work has shown that heat pressing of mica-based glass-ceramics can lead to crystal alignment along the direction of pressing. The purpose of this study was to evaluate the effect of heat pressing on the fracture toughness of mica-based glass-ceramics. Glass rods (12 x 60 mm) were prepared by melting the glass composition at 1400 degrees C for 2 h. Ingots (12 x 12 mm; n = 5) and discs (12 x 1.5 mm; n = 10) were cut from the rods. The discs were heat treated to simulate heat pressing and served as controls. A machinable mica-based glass- ceramic (Dicor MGC) also served as control. Bar-shaped wax patterns (2 x 4 x 22 mm) were invested and heat pressed at 875 degrees C. The elastic constants were determined with the use of the pulsed ultrasonic velocity method. The fracture toughness was measured by the indentation strength technique. The degree of texture was assessed qualitatively by X-ray diffraction and quantitatively on digital SEM micrographs. The results showed that the mean fracture toughness of the heat-pressed specimens (1.96 +/- 0.19 MPa. m(0.5)) was significantly higher than that of the heat-treated controls (1.51 +/- 0.21 MPa. m(0.5)) or the proprietary mica glass-ceramic (Dicor MGC; 1.66 +/- 0.04 MPa. m(0.5)) (p <.001). It was concluded that heat pressing led to a significant increase in fracture toughness in mica glass-ceramics because of crystal alignment along the direction of pressing.

Bioactive and inert dental glass‐ceramics

“…Uno et al and Qin et al substituted K + or Na + with Ba 2+ or Ca 2+ as the interlayer ions of mica crystals, which resulted in the formation of high‐strength mica glass‐ceramics . Oriented mica glass‐ceramics fabricated by hot‐pressing or extrusion processes had higher strength and toughness than the conventional castable mica glass‐ceramics that contained randomly oriented mica crystals with a house‐of‐cards structure . In addition, these materials could be reinforced with ZrO 2 crystallized from the bulk glass .…”

“…55,56 Oriented mica glassceramics fabricated by hot-pressing or extrusion processes had higher strength and toughness than the conventional castable mica glass-ceramics that contained randomly oriented mica crystals with a house-of-cards structure. [57][58][59][60][61] In addition, these materials could be reinforced with ZrO 2 crystallized from the bulk glass. [62][63][64][65][66] It has been reported that a calcium mica-based nanocomposite containing nano-size (20-50 nm) tetragonal-ZrO 2 particles exhibits notably a high flexural strength (500 MPa) and fracture toughness ).…”

Transient and residual stresses induced during the sintering of two dentin ceramics

“…Sintering may result in the introduction of thermally induced residual stresses [22] which can result in the deformation of the ceramic body [24] and a modification of the measured BFS [24,26]. It has been suggested that heat-pressing fabrication routes for glass-ceramic materials are advantageous by reducing the likelihood of the formation of large flaws [27,28] and minimising thermally induced residual stresses [22]. A further important clinical influence on restoration fracture resistance is the impact of cementation protocols which may modify surface defect distributions [29][30][31] Therefore, the aim of the current study was to investigate the effect of heat-pressing and subsequent pre-cementation (acid-etching) and resin-cementation operative M a n u s c r i p t 3 techniques on the development and magnitude of the transient and residual stresses in different clinically relevant thicknesses of a lithium disilicate glass-ceramic characterised using a profilometric technique [23][24][25].…”

Transient and residual stresses in a pressable glass–ceramic before and after resin–cement coating determined using profilometry

“…Sintering may result in the introduction of thermally induced residual stresses 22 which can result in the deformation of the ceramic body 24 and a modification of the measured BFS. 24,26 It has been suggested that heat-pressing fabrication routes for glassceramic materials are advantageous by reducing the likelihood of the formation of large flaws 27,28 and minimising thermally induced residual stresses. 22 A further important clinical influence on restoration fracture resistance is the impact of cementation protocols which may modify surface defect distributions [29][30][31] and transient and residual stress states.…”