Clinical Relevance Self-cure after tack cure could result in a lower polymerization shrinkage in some resin-based luting cements, which is closely related to lower degree of cure. SUMMARY Objectives: To evaluate the effect of tack cure on polymerization shrinkage (PS) of resin-based luting cements. Methods and Materials: One composite resin cement, Duo-Link (Duolink); two self-adhesive resin cements, RelyX U200 (U200) and G-CEM LinkAce (GCem); and one resin-modified glass ionomer cement, RelyX Luting Plus (Luting+), were used for measuring PS in light-cure (LC group), self-cure (SC group), and two tack-cure modes that were light cured (TC-LC group) or self-cured (TC-SC group) after tack cure. PS was measured by a modified bonded disc method for 1600 seconds and analyzed with two-way analysis of variance and Tukey honestly significant difference test. To investigate the effect of tack cure on light cure or self-cure, data were analyzed with an independent-samples t -test with tack cure as a variable. The significance level was 5%. Results: Regarding cure mode, Duolink showed a significantly lower PS in the TC-SC group compared with the other groups. Luting+ showed a significantly lower PS in the TC-SC group than in the SC group. U200 showed a significantly lower PS in the self-cure groups compared with that in the light-cure groups. The PS of GCem was not affected by cure mode. Regarding cements, Luting+ showed the highest PS, followed by GCem, Duolink, and U200 ( p <0.05). Self-cure of Duolink and Luting+ was negatively affected by tack cure, while light cure was not affected. U200 and GCem were not affected by tack cure either in the self-cure or light-cure groups. Conclusion: For the tested cements, tack cure decreased the PS of Duolink and Luting+ when they were self-cured after tack cure. When the cements were light cured after tack cure, PS was not affected by tack cure in any cement.
SUMMARY The aim of this study was to evaluate the polymerization behavior and depth of cure (DOC) of recently introduced resin composites for posterior use: highly filled flowable composite and composites for bulk fill. A highly filled flowable (G-aenial Universal Flo [GUF]), two bulk-fill flowables (Surefil SDR Flow [SDR] and Venus Bulk fill [VBF]), and a bulk-fill nonflowable composite (Tetric N-Ceram Bulk fill [TBF]) were compared with two conventional composites (Tetric Flow [TF], Filtek Supreme Ultra [FS]). Linear polymerization shrinkage and polymerization shrinkage stress were each measured with custom-made devices. To evaluate DOC, the composite specimen was prepared using a mold with a hole of 4 mm depth and 4 mm internal diameter. The hole was bulk filled with each of the six composites and light cured for 20 seconds, followed by 24 hours of water storage. The surface hardness was measured on the top and the bottom using a Vickers microhardness (HV) indenter. The linear polymerization shrinkage of the composite specimens after photo-initiation decreased in the following order: TF and GUF > VBF > SDR > FS and TBF ( p <0.05). The polymerization shrinkage stress of the six composite groups decreased in the following order: GUF > TF and VBF > SDR > FS and TBF ( p <0.05). The mean bottom surface HV of SDR and VBF exceeded 80% of the top surface HV (HV-80%). However, the bottom of GUF and TBF failed to reach HV-80%. A highly filled flowable (GUF) revealed limitations in polymerization shrinkage and DOC. Bulk-fill flowables (SDR and VBF) were properly cured in 4-mm bulk, but they shrank more than the conventional nonflowable composite. A bulk-fill nonflowable (TBF) showed comparable shrinkage to the conventional nonflowable composite, but it was not sufficiently cured in the 4-mm bulk.