Degree of Conversion and Surface Hardness of Two Nano- Composites Compared to Three Other Tooth-colored Restorative Materials

The aim of the laboratory study was to evaluate the degree of conversion (DC) and surface hardness of two nanofilled resin composite restorative materials compared to three other tooth-colored restorative materials. A light-emitting diode curing unit was used to photo-activate a hybrid composite (FiltekTM Z250), two nanofilled composites (Tetric® EvoCeram, FiltekTM Supreme XT), a nano-ionomer (KetacTM N100) and a compomer (Dyract® eXtra). After 24 hours dry storage in the dark at 37°C, the DC was determined using Fourier transformation infrared spectroscopy (FTIR). A microhardness tester was used to measure the Vickers Hardness Number (VHN). Data for DC and VHN were analyzed using one-way analysis of variance with Tukey’s multiple comparison test, and by using Pearson’s correlation test (P = 0.05 for statistical significance). The highest mean value for DC was obtained with Tetric EvoCeram (79.4 ± 6.7%). Filtek Z250 showed a significantly lower mean DC (58.3 ± 1.8%) than any of the other tested materials (P <0.001). Filtek Supreme XT, Ketac N100, Dyract eXtra and Tetric EvoCeram showed no significant DC differences among them (P >0.05). Filtek Z250 had the highest VHN (97.6 ± 2.8 MPa), while the lowest value was recorded with Tetric EvoCeram (55.3 ± 2.9 MPa). The VHN was significantly different among all tested materials (P <0.001). A significant and highly negative correlation existed between the DC and surface hardness (r = 0.736, P <0.01). The study concluded that Nanofilled composites may have a higher DC and a reduced VHN compared to hybrid composites, with clinical implications. Correlation between these two properties for various nanofilled materials requires further investigation.