Hardness gradients of dual-polymerized flowable composite resins in simulated root canals

Statement of problem Information is lacking of the polymerization depth of dual-polymerized flowable composite resin foundation materials in simulated root canals. Purpose 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. Material and 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