Correlation of the degree of conversion with the amount of elutable substances in nano-hybrid dental composites.

OBJECTIVES This study's purpose was to measure and compare the degree of conversion (DC) and the amount of elutable substances from modern resin-based composites (RBCs) as function of polymerization time. One nano-hybrid RBC based on tricyclodecane-(TCD)-urethane (Venus(®) Diamond) and two conventionally formulated RBCs (TetricEvo Ceram(®), Filtek™ Supreme XTE) were considered. METHOD DC (n=5) was investigated in real time for 5min by Fourier transform infrared spectroscopy (ATR-FTIR) in a filling depth of 2mm at varied irradiation times (5, 10, 20, 40s). After storing the specimens in ethanol/water for 7 d at 37°C the eluates were analyzed by gas chromatography/mass spectrometry. Results were statistically analyzed using a multivariate analysis (α=0.05) an independent t-test (p<0.05) and a Pearson correlation analysis. RESULTS In all groups increasing curing time resulted in a significant increase in DC. For TetricEvo Ceram(®) a high significant inverse correlation was found between DC and the amount of eluted camphorquinone (CQ, Pearson correlation coefficient=-0.88), ethylene glycol dimethacrylate (EGDMA, -0.73), 4-N,N-dimethylaminobenzoic acid ethylester (DMABEE, -0.87), triethylene glycol dimethacrylate (TEGDMA, -0.68), Tinuvin P (-0.71) and bisphenol-A-polyetheylene glycol dimethacrylate (BisEMA, -0.84). Unexpectedly DC and the amount of eluted methyl acrylate (MAA) correlated directly (0.72). In the specimens of Venus(®) Diamond a significant inverse correlation was found between DC and the amount of eluted CQ (-0.69) and TEGDMA (-0.50), whereas in the specimen of Filtek™ Supreme XTE DC correlated with CQ (-0.96), EGDMA (-0.70), DMABEE (-0.87), TEGDMA (-0.92) and MAA (-0.92). SIGNIFICANCE This study demonstrated a strong inverse correlation between DC and elutable substances in RBCs. Both evaluation methods emphasis the importance of an adequate polymerization (20, 40s), since short curing-times (5, 10s) resulted in lower DC and higher amount of eluted substances with toxic potential.