Light shielding effect of overlaying resin composite on the photopolymerization cure kinetics of a resin composite and a dentin adhesive

Objectives The purpose of this study was to simultaneously determine the impact of exposure times and incremental resin composite overlaying thickness on the cure kinetics of a light activated composite and a dentin adhesive at selected depths of a simulated restoration. Methods Levels and kinetics of polymerization of a light activated resin composite (Z250, 3M-ESPE) and dentin adhesive (Excite, Ivoclar) cured with a halogen light unit (Demetron, Kerr, USA) operating at low/medium intensity (500 mW/cm2) for different exposure durations (20 and 60 s) were measured at selected depths (0.3, 0.6 and 1 mm) using a modified calorimetric analyzer (DSC 25, METLLER-TOLEDO). Results Final polymerization levels of materials up to 1 mm through the composite are not significantly different while the light shielding effect of incremental resin composite overlaying progressively reduces their reaction rates. Significance Prolonged irradiation time at low/medium energies is effective for proper conversion of a resin composite and dentin adhesive; 60 s irradiation time provides the maximum obtainable conversion through the dental resin composite for thicknesses up to 1 mm.