title: Effect of light curing units on marginal adaptation and hardness of Class II composite resin restorations.
abstract: OBJECTIVE
  The aim of this study was to test the influence of different curing protocols on dentin marginal adaptation and the hardness of two composites.
  
  
  METHODS
  Three light-curing-units (LCUs): Quartz-Tungsten-Halogen (QTH: 541 mW/cm2), Argon-Ion-Laser (AL: 277 mW/cm2), and Plasma-Arc-Curing (PAC: 1818 mW/cm2) and two composites FiltekZ250 (F) and Tetric Ceram HB (TC) were tested. Sixty standardized "vertical-slot-Class II-cavities" were prepared at the mesial surface of bovine incisors and divided into six groups (n=10). Composites were placed using the Single Bond adhesive system and cured in 2 mm increments according to the manufacturers' instructions. After polishing, epoxy replicas were processed for scanning electron microscopy (SEM) marginal adaptation analysis at 500x magnification. The specimens were then sectioned transversally to the dental long axis, embedded in polyester resin, then polished and submitted to the Knoop hardness test at gingival and occlusal portions of the restoration. Data were analyzed using two-way analysis of variance (ANOVA) and Tukey's test (p=0.05).
  
  
  RESULTS
  The gap margins ranged between 4.3 to 5.8 microm, and no statistically significant differences were revealed in marginal adaptation for LCUs or for composites (p>0.05). Location influenced hardness (p=0.01). The occlusal portion presented significantly higher KHN than the gingival portion for all composite-LCU combinations. Regardless of the LCU used, TC produced statistically significant lower hardness values (ranging between 82.8 to 110.7 KHN) than F (ranging between 105.9 to 117.3 KHN).
  
  
  CONCLUSIONS
  Hardness and gap formation were not dependent on the LCUs tested in this study. Different resin composite was found to be a significant factor with regards to hardness but not gap formation.
authors.affiliation: Department of Restorative Dentistry Clinical Dentistry, Piracicaba School of Dentistry, University of Campinas, Piracicaba, SP, Brazil. lara_cavalcante@yahoo.com.br
authors.forename: Larissa Maria
authors.initials: LM
authors.lastname: Cavalcante
authors.forename: Alessandra Resende
authors.initials: AR
authors.lastname: Peris
authors.forename: Nick
authors.initials: N
authors.lastname: Silikas
authors.forename: Luiz André Freire
authors.initials: LA
authors.lastname: Pimenta
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D002417:Cattle; D003188:Composite Resins / Q000528:radiation effects*; D018772:Dental Marginal Adaptation; D003793:Dental Restoration, Permanent / Q000145:classification / Q000379:methods; D006219:Halogens; D006244:Hardness / Q000528:radiation effects; D054020:Lasers, Gas; D008027:Light; D044367:Phase Transition; D011897:Random Allocation; D018709:Statistics, Nonparametric; D014978:Xenon
chemical_list: D003188:Composite Resins; C444701:Filtek Z250; D006219:Halogens; C121818:Tetric ceram; D014978:Xenon