title: Influence of irradiation time on subsurface degree of conversion and microhardness of high-viscosity bulk-fill resin composites.
abstract: OBJECTIVE
  To evaluate the influence of irradiation time on degree of conversion (DC) and microhardness of high-viscosity bulk-fill resin composites in depths up to 6 mm.
  
  
  METHODS
  Four bulk-fill materials (Tetric EvoCeram Bulk Fill--TECBF; x-tra fil--XF; QuixFil--QF; SonicFill-SF) and one conventional nano-hybrid resin composite (Tetric EvoCeram--TEC) were irradiated for 10, 20, or 30 s at 1,170 mW/cm(2). DC and Knoop microhardness (KHN) were recorded after 24-h dark storage at five depths: 0.1, 2, 4, 5, and 6 mm. Data were statistically analyzed using ANOVA and Bonferroni's post-hoc test (α = 0.05).
  
  
  RESULTS
  With increasing bulk thickness, DC and KHN significantly decreased for TEC. TECBF and SF showed a significant decrease in DC and KHN at 4-mm depth after 10-s irradiation, but no decrease in DC after 30-s irradiation (p > 0.05). XF and QF demonstrated no significant DC decrease at depths up to 6 mm after irradiation of at least 20 s. At 4-mm depth, all materials tested achieved at least 80 % of their maximum DC value, irrespective of irradiation time. However, at the same depth (4 mm), only XF and QF irradiated for 30 s achieved at least 80 % of their maximum KHN value.
  
  
  CONCLUSIONS
  Regarding DC, the tested bulk-fill resin composites can be safely used up to at least 4-mm incremental thickness. However, with respect to hardness, only XF and QF achieved acceptable results at 4-mm depth with 30 s of irradiation.
  
  
  CONCLUSIONS
  Minimum irradiation times stated by the manufacturers cannot be recommended for placement of high-viscosity bulk-fill materials in 4-mm increments.
authors.affiliation: Department of Endodontics and Restorative Dentistry, School of Dental Medicine, University of Zagreb, Gunduliceva 5, 10000, Zagreb, Croatia, tarle@sfzg.hr.
authors.forename: Z
authors.initials: Z
authors.lastname: Tarle
authors.forename: T
authors.initials: T
authors.lastname: Attin
authors.forename: D
authors.initials: D
authors.lastname: Marovic
authors.forename: L
authors.initials: L
authors.lastname: Andermatt
authors.forename: M
authors.initials: M
authors.lastname: Ristic
authors.forename: T T
authors.initials: TT
authors.lastname: Tauböck
mesh_terms: D003188:Composite Resins / Q000737:chemistry* / Q000528:radiation effects*; D006244:Hardness; D008422:Materials Testing; D013314:Stress, Mechanical; D013499:Surface Properties; D013997:Time Factors; D014783:Viscosity
chemical_list: D003188:Composite Resins