This study compared the dentin shear bond strengths of currently used dentin bonding agents that were irradiated with an LED (Elipar FreeLight, 3M-ESPE) and a halogen light (VIP, BISCO). The optical characteristics of two light curing units were evaluated. Extracted human third molars were prepared to expose the occlusal dentin and the bonding procedures were performed under the irradiation with each light curing unit. The dentin bonding agents used in this study were Scotchbond Multipurpose (3M ESPE), Single Bond (3M ESPE), One-Step (Bisco), Clearfil SE bond (Kuraray), and Adper Prompt (3M ESPE). The shear test was performed by employing the design of a chisel-on-iris supported with a Teflon wall. The fractured dentin surface was observed with SEM to determine the failure mode.

The spectral appearance of the LED light curing unit was different from that of the halogen light curing unit in terms of maximum peak and distribution. The LED LCU (maximum peak in 465 ㎚) shows a narrower spectral distribution than the halogen LCU (maximum peak in 487 ㎚). With the exception of the Clearfil SE bond (P < 0.05), each 4 dentin bonding agents showed no significant difference between the halogen light-cured group and the LED light-cured group in the mean shear bond strength (P > 0.05).

The results can be explained by the strong correlation between the absorption spectrum of cam-phoroquinone and the narrow emission spectrum of LED.