Abstract
The purpose of this study was to evaluate the microhardness of resin-based materials polymerized with a LED (light-emitting diode) light-curing unit (LCU) and a halogen LCU. Twenty cylindrical specimens (3.0 mm in diameter and 2.0 mm high) were prepared for each tested material (Z100, Definite and Dyract). Specimens were light-cured with two LCUs (Ultraled and Curing Light 2500) for either 40 or 60 s on their top surfaces. Hardness was measured on top and bottom surfaces of each specimen. Statistical analysis was done by ANOVA and Tukey's test (p<0.05). There was no significant difference in hardness between LED LCU and halogen LCU for Z100 and Dyract on top surface. Conversely, lower hardness was recorded when Definite was light-cured with the LED LCU than with the halogen lamp. On bottom surface, hardness was significantly lower for all materials light-cured with LED LCU. Z100 was harder than Dyract and Definite regardless of the light curing unit. There was no significant difference in hardness between the exposure times on top surface. Higher hardness was obtained when the materials were light-cured for 60 s on bottom surface. The tested LED was not able to produce the same microhardness of resin-based materials as the halogen LCU.
Highlights
Halogen lamps are the most frequently used sources for polymerization of resin-based dental materials
Light-curing unit - Top: there was no significant difference in hardness between LED and halogen lamp for Z100 and Dyract
Lower hardness was obtained when Definite resin composite was light-cured with the LED light-curing unit (LCU)
Summary
Halogen lamps are the most frequently used sources for polymerization of resin-based dental materials. Their benefits include low cost technology while their drawbacks involve the production of high temperatures and decline of irradiance over time due to bulb and filter ageing [1,2]. Different technologies for light curing composite resins like plasma arc lamps, laser and LED (light emitting diode) have been developed and investigated [3,4,5]. The visible light of a LED is produced by quantummechanical effects differently from halogen lamps that need heating of metal filaments. The light emitted by LED lamps is much more efficient. Some studies have reported worse properties of resins cured with LED light-curing units (LCUs) compared to those cured with halogen lamps [7,8]
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