Curing Condition Affects Monomer Conversion of Self-adhesive Resin Cements

Objectives: This study evaluated the Degree of Conversion (DC) of self-adhesive and conventional dual-cured resin cements after 5, 10, and 20 minutes in clinical simulations when light from curing unit is attenuated by the presence of indirect pre-cured resin discs or when curing light is totally blocked by the restoration.

Methods: Two dual-cured self-adhesive (RelyX Unicem, 3M ESPE and Clearfil SA Luting,  Kuraray Med.) and two conventional resin cements (RelyX ARC, 3M ESPE and Clearfil Esthetic Cement, Kuraray Med.) were tested. The resin cements were applied to the surface of a horizontal attenuated-total-reflectance unit and were light-cured (Optilux 501, Demetron/Kerr) either through a glass slide or through pre-cured 2-mm thick pre-cured resin disc (shade B2, Sinfony, 3M ESPE) for 40s, or were allowed to self-cure (autopolymerizing mode). Infrared spectra were obtained after placing cements, and 5, 10, and 20 min after curing. The degree of conversion was calculated using standard techniques of observing changes in aliphatic-to-aromatic peak ratios pre- and post-curing. Data (n=5) were analyzed by two-way repeated measures ANOVA and Tukey's post-hoc test (pre-set alpha of 5%) within each brand.

Results: All autopolymerizing groups exhibited lower DC than groups exposed to curing light. All groups exhibited higher DC at the end of 20-min DC analysis than at 5- min interval. Most resin cements showed lower DC under indirect restoration than when they were exposed to direct light. Self-adhesive and conventional resin cements showed similar behavior when exposed to different curing conditions.

Conclusions: Light-activation is important to ensure high DC for self-adhesive and conventional dual-cured resin cements. When resin cements depend solely on the self-curing mode, clinicians should wait at least 20 min to allow the material to achieve better polymerization before adjusting and polishing procedures.