Light shielding effect of overlaying resin composite on the photopolymerization cure kinetics of a resin composite and a dentin adhesive.
OBJECTIVE
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 1mm) using a modified calorimetric analyzer (DSC 25, METLLER-TOLEDO).


RESULTS
Final polymerization levels of materials up to 1mm through the composite are not significantly different while the light shielding effect of incremental resin composite overlaying progressively reduces their reaction rates.


CONCLUSIONS
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 1mm.
Apicella
Antonio
A
CRIB Centro di Ricerca Interdipartimentale sui Biomateriali, University of Naples, Federico II, Naples, Italy. apicella@unina.it
Simeone
Michele
M
Aversa
Raffaella
R
Lanza
Alessandro
A
Apicella
Davide
D
D002152:Calorimetry, Differential Scanning; D003188:Composite Resins / Q000737:chemistry* / Q000528:radiation effects; D017220:Dentin-Bonding Agents / Q000737:chemistry* / Q000528:radiation effects; D006801:Humans; D007700:Kinetics; D008027:Light; D008029:Lighting / Q000295:instrumentation; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry / Q000528:radiation effects; D011108:Polymers / Q000737:chemistry / Q000528:radiation effects; D011829:Radiation Dosage; D013499:Surface Properties; D013997:Time Factors
D003188:Composite Resins; D017220:Dentin-Bonding Agents; C420130:Excite cement; C444701:Filtek Z250; D008689:Methacrylates; D011108:Polymers