Purpose: The influence of irradiation conditions on tensile bond strength(TBS)was evaluated using Clearfil Mega Bond(MB, Kuraray Noritake Dental)and Clearfil Mega Bond 2(MB2, Kuraray Noritake Dental) which contain a highly active photopolymerization catalyst. Methods: The surface of human teeth was ground with wet SiC paper up to 600 grit to prepare the dentin surface. The prepared surface was then conditioned by applying primer of MB, followed by bonding agent of MB. The applied bonding agent

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... as light-irradiated from approximately 2.0 mm, 7.0 mm and 12.0 mm above the adherend surface under the following conditions: 1. Using a halogen irradiation device (XL3000, 3M ESPE, USA)for 10 seconds, 2. Using a conventional LED light irradiation device(PenCure, Morita)for 10 seconds, and 3. Using a high-output LED light irradiation device(PenCure 2000, Morita)in high-power mode for 3 seconds. The resin composite was filled and cured by the XL3000. TBS was determined after 24-hour storage in water at 37℃(n=5) . Results: In the case of the irradiation distance of 2.0 mm, MB2 attained enough TBS under the conditions of high-output LED light irradiation by the PenCure 2000 in high-power mode for 3 seconds. However, when the irradiation distance was long, MB2 could not attain enough TBS with 3 seconds of irradiation and enough TBS was attained only when irradiating with the PenCure for 10 seconds. Conclusion: Even if the irradiation distance of PenCure was long, MB2 attained enough TBS. In addition, it was possible to obtain sufficient TBS by conducting light irradiation for 10 seconds, even when the irradiation distance was longer.