title: Evaluation of light curing distance and mylar strips color on surface hardness of two different dental composite resins.
abstract: BACKGROUND
  Hardness is one of the basic properties of dental materials, specially composite resins which is relevant to their polymerization. The aim of this study was to evaluate the effect of light curing distance and the color of clear Mylar strips on surface hardness of Silorane-based (SCR) and Methacrylate-based composite resins (MCR).
  
  
  METHODS
  40 samples of MCRs (Filtek Z250) and SCRs (Filtek P90) were prepared in size of 5 mm×2 mm (80 samples in total). The samples divided into 8 groups (10 samples in each one) based on the color of clear Mylar strips (white or blue) and distance from light curing source (0 mm or 2 mm). All the samples cured for 40 second and stored in incubator for 24 hours in 37°C temperature. Surface hardness test was done by Vickers test machine and the collected data were analyzed by one-way ANOVA and paired T-test by using SPSS software version 13 at significant level of 0.05.
  
  
  RESULTS
  MCRs cured with blue Mylar strips from 0 mm distance had the highest (114.5 kg/mm(2)) and SCRs cured with white Mylar strips from 2 mm distance had the lowest (42.2 kg/mm(2)) mean of surface hardness. Also, the results of comparison among SCRs and MCRs showed significant differences among all groups (all P values <0.01).
  
  
  CONCLUSIONS
  The hardness decreased as the distance increased and the blue Mylar strips provided higher hardness than clear ones. Also, Filtek Z250 showed higher hardness compared to Filtek P90.
authors.affiliation: Restorative Dentistry Department, Torabinejad Dental Research Center and Dental Materials Research Center, School of Dentistry, Isfahan University of Medical Sciences and Islamic Azad University (Khorasgan branch), Isfahan, Iran.
authors.forename: Seyed Mostafa
authors.initials: SM
authors.lastname: Mousavinasab
authors.affiliation: Restorative Dentistry Department, Islamic Azad University (Khorasgan branch), Isfahan, Iran.
authors.forename: Mehrdad
authors.initials: M
authors.lastname: Barekatain
authors.affiliation: Graduated Dentistry Student, Islamic Azad University (Khorasgan branch), Isfahan, Iran.
authors.forename: Elahe
authors.initials: E
authors.lastname: Sadeghi
authors.affiliation: Dentistry Student, Dental Students Research Center, School of Dentistry, Isfahan University of Medical Sciences, Isfa-han, Iran.
authors.forename: Farzaneh
authors.initials: F
authors.lastname: Nourbakhshian
authors.affiliation: Dentistry Student, Dental Students Research Center, School of Dentistry, Isfahan University of Medical Sciences, Isfa-han, Iran.
authors.forename: Amin
authors.initials: A
authors.lastname: Davoudi
keywords: Light curing; methacrylate-based composite resin; silorane-based composite resins; vickers hardness.