title: The effect of spark plasma sintering on lithium disilicate glass-ceramics.
abstract: OBJECTIVE
  To evaluate the effects of spark plasma sintering (SPS) on the microstructure of lithium disilicate glass-ceramics.
  
  
  METHODS
  IPS e.max CAD glass-ceramic samples were processed using spark plasma sintering (SPS) and conventionally sintered (CS) as a comparison. Specimens were sintered at varying temperatures (T1: 840°C, T2: 820°C, T3: 800°C), heating rates (HR1: 150°C/min, HR2: 300°C/min, HR3: 500°C/min) and pressures (P1: 15MPa, P2: 50MPa, P3: 70MPa). IPS e.max Press glass powder samples were densified at 750 and 800°C (50 or 200MPa pressure). Samples were characterized using XRD, HTXRD, and SEM and quantitative image analysis.
  
  
  RESULTS
  There was a significant increase in median crystal size (MCS) between the CS and the SPS T1 groups. A statistical difference (p>0.05) in MCS between SPS T1 and SPS T2 groups was observed. The SPS HR3 sample produced a smaller MCS than the CS, SPS HR1 and HR2 groups (p<0.05). The SPS P3 sample had a reduction in MCS compared with the CS group (p<0.05). XRD of the SPS samples revealed major lithium disilicate/lithium metasilicate phases and minor lithium orthophosphate and cristobalite/quartz phases. Densified IPS e.max Press glass samples resulted in fine fibrils or graduated lithium disilicate crystals.
  
  
  CONCLUSIONS
  The effects of SPS were used to refine the microstructure of IPS e.max CAD lithium disilicate glass-ceramics. Densification by SPS of IPS e.max Press glass resulted in textured and fine nano-crystalline microstructures. SPS generated glass-ceramic microstructures may have unique properties and could be useful in the production of CAD/CAM materials for dentistry.
authors.affiliation: Centre for Adult Oral Health, Institute of Dentistry, Barts and the London School of Medicine and Dentistry, Queen Mary University of London, Turner Street, Whitechapel E1 2AD, UK.
authors.forename: Fatima
authors.initials: F
authors.lastname: Al Mansour
authors.affiliation: Dental Physical Sciences, Institute of Dentistry, Barts and The London School of Medicine and Dentistry, Queen Mary University of London, Mile End Road, E1 4NS, UK.
authors.forename: Natalia
authors.initials: N
authors.lastname: Karpukhina
authors.affiliation: School of Engineering and Materials Science, Queen Mary University of London, Mile End Road, E1 4NS, UK.
authors.forename: Salvatore
authors.initials: S
authors.lastname: Grasso
authors.affiliation: School of Engineering and Materials Science, Queen Mary University of London, Mile End Road, E1 4NS, UK.
authors.forename: Rory M
authors.initials: RM
authors.lastname: Wilson
authors.affiliation: School of Engineering and Materials Science, Queen Mary University of London, Mile End Road, E1 4NS, UK.
authors.forename: Mike J
authors.initials: MJ
authors.lastname: Reece
authors.affiliation: Centre for Adult Oral Health, Institute of Dentistry, Barts and the London School of Medicine and Dentistry, Queen Mary University of London, Turner Street, Whitechapel E1 2AD, UK. Electronic address: m.cattell@qmul.ac.uk.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Cattell
mesh_terms: D002516:Ceramics / Q000737:chemistry*; D017076:Computer-Aided Design; D003460:Crystallization; D003764:Dental Materials / Q000737:chemistry*; D003776:Dental Porcelain / Q000737:chemistry*; D003799:Dental Stress Analysis; D055119:Elastic Modulus; D006244:Hardness; D006358:Hot Temperature; D008422:Materials Testing; D013499:Surface Properties
chemical_list: D003764:Dental Materials; C493120:lithia disilicate; D003776:Dental Porcelain; C023506:Glass ceramics
keywords: Crystallization; Glass-ceramic; Lithium disilicate; Microstructure; Spark plasma sintering; X-ray diffraction