title: Hardness gradients of dual-polymerized flowable composite resins in simulated root canals.
abstract: BACKGROUND
  Information is lacking of the polymerization depth of dual-polymerized flowable composite resin foundation materials in simulated root canals.
  
  
  OBJECTIVE
  The purpose of this study was to investigate the hardness gradients and the polymerization depth of dual-polymerized flowable composite resin foundation materials in simulated root canals.
  
  
  METHODS
  Slots in steel split cylinders with 1 open end were filled with the following 6 materials: Luxa Core, Para Core, Clearfil DC Core, Multi Core Flow, Gradia Core, and Core-Flo DC. After filling, they were subjected to a light intensity of 1250 mWcm(-2) with a light-emitting diode light through their open ends for 20 seconds. The resulting specimens were stored in a light-proof box at 37°C, and the Knoop hardness gradients of each polymerized material were measured after 0.5 hour, 24 hours, and 120 hours. The surface readings were obtained in 1-mm intervals at 1 mm to 10 mm away from the open ends. The collected data were analyzed by 2-way ANOVA and the Student-Newman-Keuls test (α=.05).
  
  
  RESULTS
  Before the Knoop hardness numbers of the 6 materials became stable, they decreased gradually in depth at each time point (P<.001). However, the depths at which they became stable differed. The Knoop hardness numbers of Luxa Core and Core-Flo DC reached stability at a depth of 3 mm, Para Core at 4 mm, and Clearfil DC Core, Multi Core Flow, and Gradia Core at 5 mm. Additionally, at 120 hours after exposure, the ratios of the Knoop hardness numbers at a depth of 5 mm to those at 1 mm were 63.08% for Luxa Core, 70.48% for Clearfil DC Core, 81.38% for Para Core, 80.49% for Gradia Core, 86.30% for Multi Core Flow, and 96.28% for Core-Flo DC.
  
  
  CONCLUSIONS
  In simulated root canals, the flowable composite resin foundation materials tested had better polymerization under dual polymerizing than under chemical polymerizing, and their chemical-polymerized capabilities could determine the definitive polymerization depth.
authors.affiliation: Lecturer, Department of Prosthodontics, Central Laboratory of Stomatology, Stomatological Hospital Affiliated Medical School, Nanjing University, Nanjing City, China.
authors.forename: Hong
authors.initials: H
authors.lastname: Ding
authors.affiliation: Associate Professor, Department of Prosthodontics, Central Laboratory of Stomatology, Stomatological Hospital Affiliated Medical School, Nanjing University, Nanjing City, China. Electronic address: mengsoar@nju.edu.cn.
authors.forename: Xiangfeng
authors.initials: X
authors.lastname: Meng
authors.affiliation: Professor, Department of Prosthodontics, Central Laboratory of Stomatology, Stomatological Hospital Affiliated Medical School, Nanjing University, Nanjing City, China.
authors.forename: Xiaoping
authors.initials: X
authors.lastname: Luo
mesh_terms: D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry*; D055117:Curing Lights, Dental / Q000145:classification; D003624:Darkness; D003786:Dental Pulp Cavity; D006244:Hardness; D006801:Humans; D055115:Light-Curing of Dental Adhesives / Q000295:instrumentation; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry; D011092:Polyethylene Glycols / Q000737:chemistry; D058105:Polymerization; D011109:Polymethacrylic Acids / Q000737:chemistry; D011140:Polyurethanes / Q000737:chemistry; D019279:Resin Cements / Q000737:chemistry*; D055116:Self-Curing of Dental Resins / Q000295:instrumentation / Q000379:methods; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors
chemical_list: C469237:Clearfil Core; D003188:Composite Resins; C470230:Gradia; C483522:LuxaCore; D008689:Methacrylates; C509715:MultiCore Flow; D011109:Polymethacrylic Acids; D011140:Polyurethanes; D019279:Resin Cements; C111840:flowable hybrid composite; C029824:urethane dimethacrylate luting resin; C020946:triethylene glycol dimethacrylate; D011092:Polyethylene Glycols; D017438:Bisphenol A-Glycidyl Methacrylate