title: Hardness of resin cement cured under different thickness of lithium disilicate-based ceramic.
abstract: BACKGROUND
  The lithium disilicate-based ceramic is a newly developed all-ceramic material, which is lithium disilicate-based and could be used for fabricating almost all kinds of restorations. The extent of light attenuation by ceramic material was material-dependent. Ceramic materials with different crystal composition or crystalline content would exhibit distinct light-absorbing characteristics. The aim of this study was to analyze the influence of ceramic thickness and light-curing time on the polymerization of a dual-curing resin luting material with a lithium disilicate-based ceramic.
  
  
  METHODS
  A lithium disilicate-based ceramic was used in this study. The light attenuation caused by ceramic with different thickness was determined using a spectral radiometer. The commercial dual-cured resin cement was light-cured directly or through ceramic discs with different thickness (1, 2 and 3 mm, respectively) for different times (10, 20, 30, 40, 50 and 60 seconds, respectively). The polymerization efficiency of resin cement was expressed in terms as Vickers hardness (VHN) measured after 24 hours storage. Two-way analysis of variance (ANOVA) and Tukey's HSD tests were used to determine differences.
  
  
  RESULTS
  Intensity of polymerizing light transmitted through ceramic discs was reduced from 584 mW/cm(2) to about 216 mW/cm(2)2, 80 mW/cm(2) and 52 mW/cm(2) at thicknesses of 1 mm, 2 mm and 3 mm, respectively. Resin cement specimens self-cured alone showed significantly lower hardness values. When resin cement was light-cured through ceramic discs with a thickness of 1 mm, 2 mm and 3 mm, no further increasing in hardness values was observed when light-curing time was more than 30 seconds, 40 seconds and 60 seconds, respectively.
  
  
  CONCLUSIONS
  Within the limitation of the present study, ceramic thickness and light-curing time had remarkable influence on the polymerization of dual-cured resin cement. When resin cement is light-cured beneath a lithium disilicate ceramic with different thickness, prolonging light-curing time accordingly may still be necessary to insure complete polymerization.
authors.affiliation: Medical Office, Chinese People's Liberation Army General Hospital, Beijing 100853, China. zhang_xuan422@hotmail.com
authors.forename: Xuan
authors.initials: X
authors.lastname: Zhang
authors.forename: Fu
authors.initials: F
authors.lastname: Wang
mesh_terms: D002516:Ceramics / Q000737:chemistry*; D003776:Dental Porcelain / Q000737:chemistry*; D008027:Light; D019279:Resin Cements / Q000737:chemistry*
chemical_list: D019279:Resin Cements; C493120:lithia disilicate; D003776:Dental Porcelain