title: Microhardness of a resin cement polymerized by light-emitting diode and halogen lights through ceramic.
abstract: OBJECTIVE
  This study evaluated the curing efficiency of light-emitting diode (LED) and halogen [quartz tungsten halogens (QTH)] lights through ceramic by determining the surface microhardness of a highly filled resin cement.
  
  
  METHODS
  Resin cement specimens (Variolink Ultra; with and without catalyst) (5-mm diameter, 1-mm thick) were condensed in a Teflon mold. They were irradiated through a ceramic disc (IPS Empress 2, diameter 5 mm, thickness 2 mm) by high-power light-curing units as follows: (1) QTH for 40 seconds (continuous), (2) LED for 20 seconds, and (3) LED for 40 seconds (5-second ramp mode). The specimens in control groups were cured under a Mylar strip. Vickers microhardness was measured on the top and bottom surfaces by a microhardness tester. Data were analyzed using analysis of variance (ANOVA) and a post hoc Bonferroni test at a significance level of p < 0.05.
  
  
  RESULTS
  The mean microhardness values of the top and bottom surfaces for the dual-cured cement polymerized beneath the ceramic by QTH or LED (40 seconds) were significantly higher than that of light-cured cement (p < 0.05). The top and bottom surface microhardness of dual-cured cement polymerized beneath the ceramic did not show a statistically significant difference between the LED and QTH for 40 seconds (p > 0.05).
  
  
  CONCLUSIONS
  The efficiency of high-power LED light in polymerization of the resin cement used in this study was comparable to the high-power QTH light only with a longer exposure time. A reduced curing time of 20 seconds with high-power LED light for photopolymerizing the dual-cured resin cement under ceramic restorations with a minimum 2-mm thickness is not recommended.
authors.affiliation: Department of Dental Materials, School of Dentistry/Research Center for Science and Technology in Medicine, Tehran University of Medical Sciences, Tehran, Iran. hoshmand@sina.tums.ac.ir
authors.forename: Tabassom
authors.initials: T
authors.lastname: Hooshmand
authors.forename: Nasrin
authors.initials: N
authors.lastname: Mahmoodi
authors.forename: Alireza
authors.initials: A
authors.lastname: Keshvad
mesh_terms: D000538:Aluminum Silicates / Q000737:chemistry* / Q000528:radiation effects; D003442:Crowns; D055117:Curing Lights, Dental / Q000145:classification*; D001840:Dental Bonding / Q000379:methods*; D003764:Dental Materials / Q000737:chemistry / Q000528:radiation effects; D003776:Dental Porcelain / Q000737:chemistry* / Q000528:radiation effects; D006244:Hardness / Q000528:radiation effects*; D019279:Resin Cements / Q000737:chemistry / Q000528:radiation effects*
chemical_list: D000538:Aluminum Silicates; D003764:Dental Materials; C075815:IPS-Empress ceramic; D019279:Resin Cements; D003776:Dental Porcelain; C103502:Variolink