title: Light transmittance of zirconia as a function of thickness and  microhardness of resin cements under different thicknesses of zirconia.
abstract: OBJECTIVE
  The objective of this study was to compare microhardness of resin cements under different thicknesses of zirconia and the light transmittance of zirconia as a function of thickness.
  
  
  METHODS
  A total of 126 disc-shaped specimens (2 mm in height and 5 mm in diameter) were prepared from dual-cured resin cements (RelyX Unicem, Panavia F and Clearfil SA cement). Photoactivation was performed by using quartz tungsten halogen and light emitting diode light curing units under different thicknesses of zirconia. Then the specimens (n=7/per group) were stored in dry conditions in total dark at 37°C for 24 h. The Vicker's hardness test was performed on the resin cement layer with a microhardness tester. Statistical significance was determined using multifactorial analysis of variance (ANOVA) (alpha=.05). Light transmittance of different thicknesses of zirconia (0.3, 0.5 and 0.8 mm) was measured using a hand-held radiometer (Demetron, Kerr). Data were analyzed using one-way ANOVA test (alpha=.05).
  
  
  RESULTS
  ANOVA revealed that resin cement and light curing unit had significant effects on microhardness (p < 0.001). Additionally, greater zirconia thickness resulted in lower transmittance. There was no correlation between the amount of light transmitted and microhardness of dual-cured resin cements (r = 0.073, p = 0.295).
  
  
  CONCLUSIONS
  Although different zirconia thicknesses might result in insufficient light transmission, dual-cured resin cements under zirconia restorations could have adequate microhardness.
authors: Gazi University, Faculty of Dentistry, Department of Prosthodontics, Ankara, Turkey. isilcekic@gmail.com
authors: Isil
authors: I
authors: Cekic-Nagas
authors: Ferhan
authors: F
authors: Egilmez
authors: Gulfem
authors: G
authors: Ergun
authors: Bekir-Murat
authors: BM
authors: Kaya
mesh_terms: D006244:Hardness; D006245:Hardness Tests; D008027:Light; D008422:Materials Testing; D019279:Resin Cements; D015040:Zirconium
chemical_list: D019279:Resin Cements; D015040:Zirconium; C028541:zirconium oxide
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