Effect of the light-emitting diode units on the depth of polymerization of a composite

Abstract

The physical characteristics of composite resins strongly influence their clinical durability. The purpose of this study was to evaluate the influence of different light-emitting diode units on the Knoop hardness (KHN) and plasticization (P) of a composite resin. Disc-shaped specimens (5 x 2 mm) of the Filtek Supreme (3M ESPE) methacrylate-based nanofilled composite were light-cured using second-generation light-emitting diode (LED2) Bluephase 16i (Vivadent) or third-generation (LED3) Ultralume LED 5 (Ultradent) curing units at 1390 and 800 mW/cm2 of irradiance, respectively. After 24 h, KHN was measured with 50-g load for 15 s, and was evaluated by percentage reduction of the hardness after 24 h immersed in absolute alcohol at top and bottom surfaces. Data were subjected ANOVA and Tukey’s test at a pre-set alpha of 0.05. LED2 device showed higher KHN than LED3 (p < 0.05), top surface of composite cured with LED 2 showed higher softening resistance after alcohol storage than bottom surface (p < 0.05), but there was difference on the plasticization values between curing devices and between the top and bottom surface of composite cured with LED3 (p > 0.05). The highest irradiance promoted higher KHN, but overall not affected the plasticization.