title: Degree of conversion of dual-polymerizing cements light polymerized through monolithic zirconia of different thicknesses and types.
abstract: BACKGROUND
  Monolithic zirconia restorations are increasingly common. Dual-polymerizing cements have been advocated for cementation. The opacious nature of zirconia restoration can attenuate light, compromising optimal resin polymerization and eventually restoration debonding.
  
  
  OBJECTIVE
  The purpose of this in vitro study was to evaluate the influence of material thickness on light irradiance, radiant exposure, and the degree of monomer conversion (DC) of 2 dual-polymerizing resin cements light-polymerized through different brands of monolithic zirconia.
  
  
  METHODS
  Dual-polymerizing resin cements (RelyX Ultimate; 3M-ESPE, and Variolink II; Ivoclar, Vivadent) were mixed according to the manufacturers' instructions with a film thickness of 40 μm, placed under a 10 × 10 mm specimen of monolithic zirconia (Prettau Anterior by Zirkonzahn, Katana by Noritake, BruxZir by Glidewell, and Zenostar by Wieland) and a zirconia core control (ICE zirkon by Zirkonzahn) at various thicknesses (0.50, 1.00, 1.50, and 2.00 mm, n = 5 of each thickness). Each specimen was irradiated for 20 seconds (RelyX Ultimate) and 40 seconds (Variolink II) with Elipar S10 (3M-ESPE, 1200 mW/cm(2)). The amount of irradiance and radiant exposure was quantified for each specimen. Fourier transform infrared spectroscopy was used to measure the DC from the bottom surface of the resin. Statistical analysis was performed with 2-way ANOVA and post hoc Tukey honest significant difference (HSD) tests (α = .05).
  
  
  RESULTS
  Light irradiance and radiant exposure decreased as the thickness of the specimen increased (P < .05) regardless of the brand. The ranking from least to highest was BruxZir < ICE zircon = Wieland < Katana = Prettau Anterior. The zirconia brand, thickness, and cement type had a significant effect on the DC (P < .001). The DC decreased significantly as the thickness of the zirconia increased (P < .001). Katana and Prettau Anterior showed the highest DC and BruxZir showed the lowest.
  
  
  CONCLUSIONS
  The thickness of zirconia affects the DC of resin-based cements. The DC of the resin cements differed significantly between cements and among zirconia brands. More polymerizing time may be needed to deliver sufficient energy through some brands of zirconia.
authors.affiliation: Doctoral student, Department of Prosthetic Dentistry, University of Turku Institute of Dentistry, Turki Finland; and Visiting Scholar, Department of Operative Dentistry, University of North Carolina School of Dentistry, Chapel Hill, NC. Electronic address: sulaiman@unc.edu.
authors.forename: Taiseer A
authors.initials: TA
authors.lastname: Sulaiman
authors.affiliation: Assistant Professor, Department of Prosthetic Dentistry, University of Turku Institute of Dentistry, Turku, Finland.
authors.forename: Aous A
authors.initials: AA
authors.lastname: Abdulmajeed
authors.affiliation: Professor and Section Head of Material Science, Department of Operative Dentistry, University of North Carolina School of Dentistry, Chapel Hill, NC.
authors.forename: Terrence E
authors.initials: TE
authors.lastname: Donovan
authors.affiliation: Professor and Chair, Department of Operative Dentistry, University of North Carolina School of Dentistry, Chapel Hill, NC.
authors.forename: André V
authors.initials: AV
authors.lastname: Ritter
authors.affiliation: Assistant Professor, Department of Biomaterials Science, University of Turku, Institute of Dentistry and Laboratory Manager, Turku Clinical Biomaterials Centre, University of Turku, Turku, Finland.
authors.forename: Lippo V
authors.initials: LV
authors.lastname: Lassila
authors.affiliation: Professor, Department of Biomaterials Science, University of Turku, Institute of Dentistry and Welfare Division, Turku, Finland.
authors.forename: Pekka K
authors.initials: PK
authors.lastname: Vallittu
authors.affiliation: Professor, Department of Prosthetic Dentistry, University of Turku, Institute of Dentistry and Clinic of Oral Diseases, Turku University Central Hospital, Turku, Finland.
authors.forename: Timo O
authors.initials: TO
authors.lastname: Närhi
mesh_terms: D002516:Ceramics / Q000737:chemistry*; D003764:Dental Materials / Q000737:chemistry*; D006801:Humans; D008027:Light; D055115:Light-Curing of Dental Adhesives / Q000379:methods*; D008422:Materials Testing; D058105:Polymerization; D011829:Radiation Dosage; D019279:Resin Cements / Q000737:chemistry* / Q000528:radiation effects; D055116:Self-Curing of Dental Resins / Q000379:methods*; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods; D013499:Surface Properties; D013997:Time Factors; D015019:Yttrium / Q000737:chemistry*; D015040:Zirconium / Q000737:chemistry*
chemical_list: D003764:Dental Materials; C528569:Rely-X; D019279:Resin Cements; C499362:yttria stabilized tetragonal zirconia; C103502:Variolink; D015019:Yttrium; D015040:Zirconium