Depth of Cure of Resin-Based Composites Irradiated With Three Types of Light-Curing Units at Different Output Intensities

Aim Dental light-curing units (LCUs) are used at Matsumoto Dental University Hospital (MDUH). However, the time of installation of the same type of light irradiator varies, which affects the output intensity of the LCU. The purpose of this study was to evaluate the performance of LCU with different output intensities by comparing the depth of cure (DOC) of resin-based composites (RBCs). Materials and methods The output intensities of three types of LCUs, namely Pencure 2000(Morita, Osaka, Japan), DC BlueLEX Plus (Yoshida, Tokyo, Japan)​​​​​​​, and Candelux (Morita, Osaka, Japan), were measured using a commercial dental radiometer, namely Bluephase Meter II (Ivoclar Vivadent, Schaan, Liechtenstein). The units with the highest and lowest output intensities were selected and used. The RBC, either Body A3 or Opaque A3 (Premise, Kerr, Brea, USA)​​​​​​​, was inserted into a cylindrical mold with an inner diameter of 4 mm and depth of 8 mm, and light irradiation was performed using an intervening polyester strip for 30 s. After removing the unpolymerized portions of the RBC from the mold with a plastic spatula, the long axis of the cured portion was measured with a digital caliper (n=10). Results The highest DOC was observed when the RBCs were cured with Pencure 2000 at 1513 mW/cm², the highest output intensity. The DOC was significantly greater when the LCU was positioned at 0 mm than at 8 mm from the RBC surface, and the DOC of Body A3 was greater than that of Opaque A3 (p<0.05). Moreover, a positive correlation was observed between output intensity and DOC. The output intensity of LCUs in the same model also varied, which affected the DOC. Conclusion Increasing the output intensity at the tip of the light guide of the LCU also increased the DOC of the RBC. Increasing the irradiation distance from 0 mm to 8 mm decreased the DOC of the RBC. The DOC of the opaque-shade RBC was smaller than that of the body-shade RBC when curing was conducted with the same LCU.