Degree of conversion and surface hardness of two nanocomposites compared to three other tooth-colored restorative materials

ABSTRACT

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 [Filtek[TM] Z250], two nanofilled composites [Tetric[restricted] EvoCeram, Filtek[TM] Supreme XT], a nano-ionomer [Ketac[TM] N100] and a compomer [Dyract[restrected] 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