Long term post-cure conversion of bulk-fill composites

Objectives: To follow the degree of conversion (DC) of two commercial bulk-fill composite materials (Tetric EvoCeram Bulk Fill and Tetric EvoCeram Bulk Fill Flow/Ivoclar Vivadent) for up to seven days post cure.
Methods: DC was determined with Raman spectroscopy by comparing the relative change of band at 1640 cm-1 to the reference band at 1610 cm-1 of uncured and cured material.For each material,five samples were prepared.The cylindrical sample (d=3 mm,h=6mm) were light cured with irradiance of 1090 mW/cm2 for 20 seconds.After curing,the samples of Tetric EvoCeram Bulk Fill and Tetric EvoCeram Bulk Fill Flow were stored at 37oC.DC was measured immediately after curing (0 days),1 day post-cure and 7 days post-cure.Statistical analysis was performed using a dependent samples t-test.
Results: DC values (%) were (0 days/1 day/7 days):Tetric EvoCeram Bulk Fill 58.3/66.4/71.5; Tetric EvoCeram Bulk Fill Flow 71.6/80.1/80.7.After 1 day post-cure,the DC increase was statistically significant for all the composites tested.Additionally,the DC increase was significant after 7 days post-cure for Tetric EvoCeram Bulk Fill.

Conclusions: A long term post-cure DC increase was observed for both tested bulk-fill composites,suggesting that mechanical properties and biocompatibility develop gradually over at least seven days.This may be due to the alternative photoinitiator systems and polymerization modifiers used in bulk-fill materials.