Influence of Light Irradiation Modes on the Polymerization of Light-curing Resins in a Root Canal Model

抄録

 Purpose: Fiber posts with resin cores have been widely used as direct build-up materials for the restoration of endodontically treated teeth. However, the influence of light irradiation mode, including the irradiation intensity and time, on resin polymerization in the apical root canal remains an open research problem. This in vitro study investigated the influence of light irradiation mode on the polymerization of different light-curing resins with and without a fiber post.

 Methods: A translucent fiber post, namely i-TFC Luminous fiber, was used in combination with five commercial light-curing resins: i-TFC System Universal (UN), i-TFC System Blue (BL), i-TFC Luminous core LC flow (LC), Filtek U (FU), and MI core LC flow (MI). Each resin was filled into an artificial root canal model (diameter: 3 mm, depth: 15 mm) with or without the fiber and light-cured using a handy light-curing unit in two irradiation modes: mode-F3: 2,000 mW/cm² for 3 s, and mode-10: 1,200 mW/cm² for 10 s×3. The cured resins were characterized by their polymerization ratios, depths, and optical transmittances.

 Results: The polymerization ratio of each resin was significantly higher in mode-10 than in mode-F3 with and without the fiber post. In the fiber-post groups with mode-10, the polymerization ratio was over 96% for each resin. In the fiber-post groups with mode-F3, the polymerization ratio of each resin was relatively low: 90.5±3.6 for UN, 92.8±4.8 for BL, 85.2±3.7 for LC, 92.7±2.3 for FU, and 75.1±5.2 for MI. The polymerization depth of each resin with the fiber post reached 15 mm for each mode. The LC resin produced the highest optical transmittance, followed by the UN, BL, MI, and FU resins.

 Conclusion: Longer light irradiation and the use of a fiber post were found to be essential to achieve sufficient resin polymerization in the apical root canal.