title: The effects of repeated heat-pressing on the mechanical properties and microstructure of IPS e.max Press.
abstract: OBJECTIVE
  We evaluated the effects of repeated heat-pressing on the mechanical properties and microstructure of IPS e.max Press.
  
  
  METHODS
  A total of 20 specimens were fabricated including 10 heat-pressed once and another 10 heat-pressed twice. The density, porosity, and surface roughness (Ra) were evaluated. Three-point flexural strength following the ISO 6872 and Vickers hardness were measured, and fracture toughness (KIC) was calculated. Specimens were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM).
  
  
  RESULTS
  Compared to a single heat-press treatment, the density decreased and porosity increased after two heat-pressing events. A significant difference in density was observed. The flexural strength, Vickers hardness and fracture toughness significantly decreased after two heat-pressing events. The XRD patterns show that the intensity of the crystalline phase better corresponds to lithium disilicate (Li2Si2O5) after two heat-presses than only one. The SEM images detailed the interlocking microstructure of rod-shaped Li2Si2O5 crystals after one heat-press. These became oriented after two heat-presses, and the crystal size became larger.
  
  
  CONCLUSIONS
  This study showed that repeated heat-pressing was detrimental to the density, porosity, strength, hardness, and toughness of IPS e.max Press.
authors.affiliation: Department of Stomatology, Jinling Hospital, Nanjing University School of Medicine, Nanjing 210002, China; Department of Fixed Prosthodontics, Osaka University Graduate School of Dentistry, Osaka 565-0871, Japan. Electronic address: t-xuehua2008@hotmail.com.
authors.forename: Xuehua
authors.initials: X
authors.lastname: Tang
authors.affiliation: Department of Stomatology, Jinling Hospital, Nanjing University School of Medicine, Nanjing 210002, China.
authors.forename: Chengzhong
authors.initials: C
authors.lastname: Tang
authors.affiliation: Department of Stomatology, Jinling Hospital, Nanjing University School of Medicine, Nanjing 210002, China.
authors.forename: Han
authors.initials: H
authors.lastname: Su
authors.affiliation: Department of Stomatology, Jinling Hospital, Nanjing University School of Medicine, Nanjing 210002, China.
authors.forename: Huinan
authors.initials: H
authors.lastname: Luo
authors.affiliation: Department of Fixed Prosthodontics, Osaka University Graduate School of Dentistry, Osaka 565-0871, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Nakamura
authors.affiliation: Department of Fixed Prosthodontics, Osaka University Graduate School of Dentistry, Osaka 565-0871, Japan.
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Yatani
mesh_terms: D003776:Dental Porcelain / Q000737:chemistry*; D006358:Hot Temperature; D008422:Materials Testing; D018583:Pliability; D011312:Pressure; D013499:Surface Properties; D013718:Tensile Strength
chemical_list: C508050:IPS e.max Press; D003776:Dental Porcelain
keywords: IPS e.max Press; Mechanical properties; Microstructure; Repeated heat-pressing