Influence of temperature on bulk-fill composites’ post-cure degree of conversion

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 20 seconds with irradiance of 1090 mW/cm². For each composite, 10 samples were prepared and randomly divided into two groups: the “room-temperature group” (RTG, n=5) and the “body-temperature group” (BTG, n=5) which were stored in dark at 20°C and 37°C, respectively. Degree of conversion (DC) was determined by means of Raman spectroscopy. DC measurements were made at the sample surface immediately after curing (0h) and 24h post-cure (24h). To analyze the extent of post-cure DC increase, 0h-RTG/24h-RTG and 0h-BTG/24h-BTG were compared for each composite by dependent samples t-test. To analyze the difference in DC between RTG and BTG, the DC values of 0h-RTG/0h-BTG and 24h-RTG/24h-BTG were compared for each composite by independent samples t-test.

Results: DC values (%) (0h/24h) for RTG were: GR 60.5/68.6, TECBF 59.3/65.6, QF 64.4/72.6, XF 63.6/71.5; for BTG: GR 58.0/73.8, TECBF 61.6/76.7, QF 65.8/78.3, XF 60.9/75.0. DC increase 24h post-cure was significant for all composites and ranged between 6.3%-8.2% in RTG and 12.5%-15.7% in BTG. Since there was no significant difference between 0h-RTG and 0h-BTG for each individual composite, equal initial DC for both groups was assumed. The impact of temperature on post-cure behavior was evaluated by comparing 24h-RTG/24h-BTG. All composites demonstrated higher DC in 24h-BTG compared to 24h-RTG. The difference was statistically significant for GR, TECBF and QF, while for XF only a trend of increase was observed.

Conclusion: Post-cure temperature increase from 20°C-37°C yielded higher post-cure DC increase, which should be taken into account while investigating composite properties.

This study was supported by Croatian Science Foundation.