title: Influence of light-exposure methods and depths of cavity on the microhardness of dual-cured core build-up resin composites.
abstract: OBJECTIVE
  The purpose of this study was to evaluate the Knoop hardness number (KHN) of dual-cured core build-up resin composites (DCBRCs) at 6 depths of cavity after 3 post-irradiation times by 4 light-exposure methods.
  
  
  METHODS
  Five specimens each of DCBRCs (Clearfil DC Core Plus [DCP] and Unifil Core EM [UCE]) were filled in acrylic resin blocks with a semi-cylindrical cavity and light-cured using an LED light unit (power density: 1,000 mW/cm2)at the top surface by irradiation for 20 seconds (20 s), 40 seconds (40 s), bonding agent plus 20 seconds (B+20 s), or 40 seconds plus light irradiation of both sides of each acrylic resin block for 40 seconds each (120 s). KHN was measured at depths of 0.5, 2.0, 4.0, 6.0, 8.0, and 10.0 mm at 0.5 hours, 24 hours, and 7 days post-irradiation. Statistical analysis was performed using repeated measures ANOVA and Tukey's compromise post-hoc test with a significance level of p<0.05.
  
  
  RESULTS
  For both DCBRCs, at 0.5 hours post-irradiation, the 20 s and 40 s methods showed the highest KHN at depth of 0.5 mm. The 40 s method showed significantly higher KHN than the 20 s method at all depths of cavity and post-irradiation times, except UCE at depth of 0.5 mm (p<0.05). The 120 s method did not result in significantly different KHN at all depths of cavity and post-irradiation times (p>0.05). In DCP, and not UCE, at 24 hours and 7 days post-irradiation, the B+20 s method showed significantly higher KHN at all depths of cavity, except the depth of 0.5 mm (p<0.05).
  
  
  CONCLUSIONS
  KHN depends on the light-exposure method, use of bonding agent, depth of cavity, post-irradiation time, and material brand. Based on the microhardness behavior, DCBRCs are preferably prepared by the effective exposure method, when used for a greater depth of cavity.
authors.affiliation: Nagasaki University Hospital, Clinic of Fixed Prosthodontics, Nagasaki, Japan, Clinic of Fixed Prosthodontics, Nagasaki University Hospital, Nagasaki, Japan.
authors.forename: Keiichi
authors.initials: K
authors.lastname: Yoshida
authors.affiliation: Nanjing University, The Stomatological Hospital Affiliated Medical School, Department of Prosthodontics, Nanjing, China, Department of Prosthodontics, The Stomatological Hospital Affiliated Medical School, Nanjing University, Nanjing, China.
authors.forename: Xiangfeng
authors.initials: X
authors.lastname: Meng
mesh_terms: D000704:Analysis of Variance; D003188:Composite Resins / Q000737:chemistry / Q000528:radiation effects*; D006245:Hardness Tests; D055115:Light-Curing of Dental Adhesives / Q000379:methods*; D008422:Materials Testing; D055668:Photochemical Processes / Q000528:radiation effects; D058105:Polymerization / Q000528:radiation effects; D015203:Reproducibility of Results; D019279:Resin Cements / Q000737:chemistry / Q000528:radiation effects*; D013499:Surface Properties / Q000528:radiation effects; D013997:Time Factors
chemical_list: C469237:Clearfil Core; D003188:Composite Resins; D019279:Resin Cements; C500741:Unifil Core