Dual-cure core build-up composites are designed to chemically-cure in addition to light-cure to promote a high level of cure at depths beyond the capability of light-curing alone. Objectives: This study evaluated the hardness of dual-cure core composites over time with and without light activation. Methods: FluoroCore (tooth-color and blue), and Corestore2 (white, universal and blue) were tested in dual- and self-cure modes in nylon molds (6mm diameter and 6mm high). In dual-cure mode FluoroCore was irradiated for 40s and Corestore2 for 20 & 40s using Optilux 500. Six Barcol hardness readings were obtained at the stated setting time (10m for FluoroCore and 5m for Corestore2) and 1, 2, 5, 10, 30m and 2 days. Results: The top surface of dual-cure samples showed slight but insignificant increases in Barcol hardness for the time periods tested. B/T values for FluoroCore tooth-color and blue were 45% and 29% at 0m and improved to 64% and 62% at 10m. Hardness was not detectable in self-cure FluoroCore up to 10m, although the 2 day values were similar to those of the bottom surface, which were at or below 80% that of the top surface. In general, Corestore2 bottom hardness of dual-cure samples was not detectable until 5m for the 40s samples and 10m for the 20s samples, although 2 day B/T value exceeded 85% for white and universal and the 40s Corestore2 blue at 94%. The dual-cure bottom hardness of the 20s samples were almost identical to the self-cure values at all time periods. Conclusions: The dual-cure B/T values were very low at 0m. Although they improved with time, the values did not achieve 90% except Corestore2 blue (94%) at 2 days. Dual-cure (vs. self-cure) improved the early bottom values. However, at 2 days the values were essentially the same, except for Corestore2 blue.

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