Effect of light guide tip diameter of LED-light curing unit on polymerization of light-cured composites

Objective: The aim of this study was to investigate the influence of the diameter of the light guide tip on the polymerization of light cured composites when light guide tips of different diameters were used with an light-emitting diode (LED)-unit. Methods: An LED-unit was used with three light guide tips of 4, 8 and 10 mm diameter. Variations of light illuminance with irradiation time of each light guide tip were measured with a lux meter. Two Composites were exposed for 10, 20, 30 or 40 s. Thereafter, the depths of cure of the specimens were measured by the scraping method, and Knoop hardness was measured at 0.5 mm intervals. Results: The relative light illuminances from the 8 mm tip and 10 mm tip were 45 and 32% of that of the 4 mm tip. The depth of cure for the 4 mm tip was significantly greater than the others. At a depth of 2.0 mm, the 4 mm tip produced significantly greater hardness than the others. The depth of cure of composite irradiated for 10 s using the 4 mm tip corresponded to those of composites irradiated for 20 s using the 8 mm tip and for 30 s using the 10 mm tip. Thus, when the irradiation time was extended, Knoop hardness of the 4 mm tip was not significantly different from the others. Significance: This study showed that the polymerization of light cured composite was affected by the diameter of the light guide tip of the LED-unit.