Influence of irradiation sequence on dentin bond of resin inlays

The relationship between the order in which a dual-cured resin cement is light activated and the bond strength of resin inlay materials to dentin was examined. Also evaluated was the setting time with various irradiation sequences. Lite-Fil CR/Imperva Bond (Shofu) and Clearfil CR/CR Cement (Kuraray) were employed. Ten specimens, 4 mm in diameter by 4 mm deep, were made with each material for each condition and bonded to bovine dentin with the respective bonding agent and cement. Order of light activation was: 1) no light activation; 2) premix activation of only the liquid prior to mix, 3 seconds for Lite-Fil and 25 seconds for Clearfil; 3) postplacement activation, 30 seconds for Lite-Fil and 40 seconds for Clearfil; and 4) premix and postplacement activation, 3 seconds and 30 seconds for Lite-Fil and 25 seconds and 40 seconds for Clearfil. Samples were stored in water for 24 hours and shear strength tested. The setting time with no activation and premix activation was measured according to the ISO #7489 standards. Bond strengths (MPa) were 1) 4.41, 2) 13.07, 3) 6.34, and 4) 14.81 for Lite-Fil, and 1) 0.37, 2) 2.44, 3) 0.52, and 4) 2.51 for Clearfil. No light activation or only postplacement activation resulted in lower bond strengths with a 4.0 mm-thick specimen. The setting time of the cement mix with premix activation was shorter than with no activation. Light activation of these dual-cure cements is essential. Premix activation of only the liquid resulted in bond strengths similar to those obtained with combined pre- and postplacement activating.