title: Influence of Light Irradiation Through Zirconia on the Degree of Conversion of Composite Cements.
abstract: OBJECTIVE
  To assess the light irradiance (LI) delivered by two light-curing units and to measure the degree of conversion (DC) of three composite cements and one flowable composite when cured through zirconia or ceramic-veneered zirconia plates with different thicknesses.
  
  
  METHODS
  Three dual-curing composite cements (Clearfil Esthetic Cement, Panavia F2.0, G-CEM LinkAce) and one light-curing flowable composite (G-aenial Universal Flo) were investigated. Nine different kinds of zirconia plates were prepared from three zirconia grades (YSZ: Aadva and KATANA; Ce-TZP/Al2O3: NANOZR) in three different thicknesses (0.5- and 1.5-mm-thick zirconia, and 0.5-mm-thick zirconia veneered with a 1.0-mm-thick veneering ceramic). Portions of the mixed composite cements and the flowable composite were placed on a light spectrometer to measure LI while being light cured through the zirconia plates for 40 s using two light-curing units (n = 5). After light curing, micro-Raman spectra of the composite films were acquired to determine DC at 5 and 10 min, 1 and 24 h, and at 1 week.
  
  
  RESULTS
  The zirconia grade and the thickness of the zirconia/veneered zirconia plates significantly decreased LI. Increased LI did not increase DC. Only the Ce-TZP/Al2O3 (NANOZR) zirconia was too opaque to allow sufficient light transmission and resulted in significantly lower DC.
  
  
  CONCLUSIONS
  Although zirconia-based restorations attenuate the LI of light-curing units, the composite cements and the flowable composite could be light cured through the YSZ zirconia. LI is too low through Ce-TZP/Al2O3 zirconia, necessitating the use of self-/dual-curing composite cements.
authors.forename: Masanao
authors.initials: M
authors.lastname: Inokoshi
authors.forename: Pong
authors.initials: P
authors.lastname: Pongprueksa
authors.forename: Jan
authors.initials: J
authors.lastname: De Munck
authors.forename: Fei
authors.initials: F
authors.lastname: Zhang
authors.forename: Kim
authors.initials: K
authors.lastname: Vanmeensel
authors.forename: Shunsuke
authors.initials: S
authors.lastname: Minakuchi
authors.forename: Jozef
authors.initials: J
authors.lastname: Vleugels
authors.forename: Ignace
authors.initials: I
authors.lastname: Naert
authors.forename: Bart
authors.initials: B
authors.lastname: Van Meerbeek
mesh_terms: D000537:Aluminum Oxide / Q000737:chemistry; D002516:Ceramics / Q000737:chemistry / Q000528:radiation effects; D002563:Cerium / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry / Q000528:radiation effects*; D055117:Curing Lights, Dental / Q000145:classification; D003764:Dental Materials / Q000737:chemistry / Q000528:radiation effects*; D003801:Dental Veneers; D006801:Humans; D008027:Light; D055115:Light-Curing of Dental Adhesives / Q000295:instrumentation; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry; D015591:Microspectrophotometry; D011092:Polyethylene Glycols / Q000737:chemistry; D058105:Polymerization; D011109:Polymethacrylic Acids / Q000737:chemistry; D011140:Polyurethanes / Q000737:chemistry; D011829:Radiation Dosage; D019279:Resin Cements / Q000737:chemistry / Q000528:radiation effects*; D012542:Scattering, Radiation; D013059:Spectrum Analysis, Raman; D013499:Surface Properties; D015019:Yttrium / Q000737:chemistry; D015040:Zirconium / Q000737:chemistry*
chemical_list: C475766:Ce-TZP-Al2O3; D003188:Composite Resins; D003764:Dental Materials; C528107:G-Cem resin cement; D008689:Methacrylates; C438843:Panavia-Fluoro; D011109:Polymethacrylic Acids; D011140:Polyurethanes; D019279:Resin Cements; C530542:clearfil esthetic cement; C499362:yttria stabilized tetragonal zirconia; C029824:urethane dimethacrylate luting resin; C020946:triethylene glycol dimethacrylate; D002563:Cerium; D011092:Polyethylene Glycols; D015019:Yttrium; D015040:Zirconium; D000537:Aluminum Oxide; C028541:zirconium oxide