title: Effect of different light curing methods on mechanical and physical properties of resin-cements polymerized through ceramic discs.
abstract: OBJECTIVE
  The aim of this study was to compare the polimerization ability of three different light-curing units (quartz tungsten halogen, light-emitting diodes and plasma arc) and their exposure modes (high-intensity and soft-start) by determination of microhardness, water sorption and solubility, and diametral tensile strength of 5 dual-curing resin cements.
  
  
  METHODS
  A total of 720 disc-shaped samples (1 mm height and 5 mm diameter) were prepared from different dual-curing resin cements (Duolink, Nexus, Bifix-QM, Panavia F and RelyX Unicem). Photoactivation was performed by using quartz tungsten halogen (high-power and soft-up modes), light-emitting diode (standard and exponential modes) and plasma arc (normal and ramp-curing modes) curing units through ceramic discs. Then the samples (n=8/per group) were stored dry in the dark at 37°C for 24 h. The Vickers hardness test was performed on the resin cement layer with a microhardness tester (Shimadzu HMV). For sorption and solubility tests; the samples were stored in a desiccator at 37°C and weighed to a constant mass. The samples were weighed both before and after being immersed in deionized water for different periods of time (24 h and 7 days) and being desiccated. The diametral tensile strength of the samples was tested in a universal testing machine at a crosshead speed of 0.5 mm/min. Data were analyzed statistically by nonparametric Kruskal Wallis and Mann-Whitney U tests at 5% significance level.
  
  
  RESULTS
  Resin cement and light-curing unit had significant effects (p<0.05) on microhardness, diametral tensile strength, water solubility and sorption. However, no significant differences (p>0.05) were obtained with different modes of LCUs.
  
  
  CONCLUSIONS
  The study indicates that polymerization of resin cements with different light-curing units may result in various polymer structures, and consequently different mechanical and physical properties.
authors.affiliation: Department of Prosthodontics, Faculty of Dentistry, Gazi University, Ankara, Turkey. isilcekic@hacettepe.edu.tr
authors.forename: Isil
authors.initials: I
authors.lastname: Cekic-Nagas
authors.forename: Gulfem
authors.initials: G
authors.lastname: Ergun
mesh_terms: D002516:Ceramics / Q000737:chemistry / Q000528:radiation effects*; D003188:Composite Resins / Q000737:chemistry; D006245:Hardness Tests; D055115:Light-Curing of Dental Adhesives / Q000379:methods*; D008422:Materials Testing; D058105:Polymerization / Q000528:radiation effects*; D019279:Resin Cements / Q000528:radiation effects*; D012995:Solubility; D013499:Surface Properties; D013718:Tensile Strength; D013997:Time Factors
chemical_list: D003188:Composite Resins; D019279:Resin Cements