title: The effects of repeated heat-pressing on properties of pressable glass-ceramics.
abstract: The aim of this study was to evaluate the properties of four heat-pressed glass-ceramic materials after repeated heat-pressing. Two commercially available heat-pressed glass-ceramic systems [Optimal pressable glass-ceramics (OPC and 3G) and Empress pressable glass-ceramics (Empress and Empress2)] were selected. Disc samples (14 mm x 1.4 mm) of each tested material were heat-pressed and used as controls. Sprue and button parts of the pressed groups were retrieved and used for repeated heat-pressing to construct specimens of re-pressed group. All the heat-pressed casting procedures were performed according to the manufacturers' instructions. A biaxial flexural strength (BFS) test (ISO 6872) was performed to determine the strength of pressed and re-pressed glass-ceramic disc specimens (n = 10) at a crosshead speed of 0.5 mm min(-1). Ions eluted from etching procedure were collected and examined using inductively coupled plasma mass spectrometer. Surface characteristics were examined with electron probe microanalysis, X-ray diffraction and secondary electron imaging (SEI). The data were analysed statistically (ANOVA + Tukey's HSD post hoc test, P < 0.05). The BFS values obtained ranged from 123.5 +/- 18.5 to 365.9 +/- 35.5 MPa. The re-pressed Empress2 group had a statistically significant higher BFS mean than the pressed control group (P < 0.05). The SEI micrographs of the lithium disilicate-reinforced glass-ceramic material (Empress2) showed a densely packed, interlocking microstructure and an increase in size with preferred orientation of the lithium disilicate crystals after repeated heat-pressing. Repeated heat-pressing treatment produced a statistically significant increase in the flexural strength of Empress2 glass-ceramic material.
authors.affiliation: Department of Restorative Dentistry, School of Dentistry, University of Washington, Seattle, Washington 98195-7456, USA. akchung@u.washington.edu
authors.forename: K-H
authors.initials: KH
authors.lastname: Chung
authors.forename: J-H
authors.initials: JH
authors.lastname: Liao
authors.forename: J-G
authors.initials: JG
authors.lastname: Duh
authors.forename: D C-N
authors.initials: DC
authors.lastname: Chan
mesh_terms: D000538:Aluminum Silicates; D002516:Ceramics; D019245:Compressive Strength; D003764:Dental Materials; D003776:Dental Porcelain; D004577:Electron Probe Microanalysis; D006358:Hot Temperature; D018020:Lithium Compounds; D013058:Mass Spectrometry / Q000379:methods; D008422:Materials Testing / Q000379:methods; D013499:Surface Properties; D013718:Tensile Strength; D014961:X-Ray Diffraction
chemical_list: D000538:Aluminum Silicates; D003764:Dental Materials; C118557:Empress 2; D018020:Lithium Compounds; C105911:Optimal Pressed Ceramic; D003776:Dental Porcelain; C078519:leucite; C023506:Glass ceramics