Effect of Temperature on Post-cure Polymerization of Bulk-fill Composites

Objectives: To investigate the 24h post-cure polymerization and the effect of temperature on the post-cure polymerization of one conventional and three bulk-fill composite materials.

Methods: A conventional composite GrandioSO (GR) and three bulk-fill composites: Tetric EvoCeram Bulk Fill (TECBF), Quixfil (QF) and X-tra fil (XF) were investigated. The samples were cured for 20s with irradiance of 1090mW/cm(2). Composite samples were divided into two groups: the "room-temperature" group (RT, n=5) and the "body-temperature" group (BT, n=5) and they were stored in dark at 20°C and 37°C, respectively. Measurements of degree of conversion (DC) were made immediately after curing (0h) and 24h post-cure (24h). To analyse the extent of post-cure DC increase, the DC values of 0h-RT/24h-RT and 0h-BT/24h-BT were compared. To analyse the difference in DC between RT and BT, the DC values of 0h-RT/0h-BT and 24h-RT/24h-BT were compared.

Results: DC increase 24h post-cure was significant for all composites and ranged between 6.3% and 8.2% in RT and between 12.5% and 15.7% in BT. All composites demonstrated a higher DC in 24h-BT compared to 24h-RT. The difference was statistically significant for GR, TECBF and QF.

Conclusions: All composites demonstrated a significant post-cure effect after 24h. Post-cure temperature increase from 20°C to 37°C yielded a higher post-cure DC increase.

Clinical Significance: Due to the temperature effect on the final DC, studies performed at composite samples at room temperature may record more inferior properties than these attained in the oral cavity.