Effect of modulated irradiation time on the degree of conversion and the amount of elutable substances from nano-hybrid resin-based composites.

OBJECTIVES: The aim of our study was to analyse whether the irradiation time and/or the modulation of irradiation time influence the degree of conversion (DC) and the amount of elutable substances from modern nano-hybrid resin-based composites (RBCs). MATERIALS AND METHODS: The DC was recorded in real time for 5 min by means of attenuated total reflectance-Fourier transform infrared spectroscopy (n = 5) on the lower surface of 2-mm-thick samples irradiated with continuous and modulated irradiation times for 20 s and 40 s. The modulated times comprise a short polymerisation (2 s or 5 s) followed by a rest period of 1 min and an additional polymerisation to complete 20 s and 40 s of polymerisation (2 s + 18 s, 5 s + 15 s, 2 s + 38 s and 5 s + 35 s). After storing the specimens in ethanol/water for 7 days at 37 °C, the eluates were analysed by gas chromatography-mass spectrometry. Results were statistically analyzed using a one-way ANOVA analysis (α = 0.05). RESULTS: The effect of irradiation time on DC is similar in all three analyzed materials, showing a significant increase in DC by increasing irradiation time from 20 s to 40 s, while the DC is not influenced within one irradiation time (20 s or 40 s) by the modulation of time. CONCLUSIONS: The type and amount of eluates are strongly dependent from the material and the irradiation protocol. CLINICAL RELEVANCE: An interrupt irradiation of RBCs is clinically feasible, reducing in general the amount of elutable substances at similar DC as the corresponding continuous polymerisation.

Investigation of different bleaching conditions on the amount of elutable substances from nano-hybrid composites.

OBJECTIVES: To analyse the influence of irradiation time, aging before bleaching, and bleaching technique (home bleaching vs. in-office bleaching) on the amount of elutable substances from modern nano-hybrid resin-based composites (RBCs). METHODS: Specimens (n=5) of three nano-hybrid RBCs (Venus(®) Diamond, Tetric EvoCeram(®) and Filtek™ Supreme XTE) were irradiated for 5, 10, 20 and 40s. The degree of conversion (DC) was measured in real-time with Fourier transform infrared spectroscopy (FTIR). Specimens were bleached either directly after irradiation or after aging (1.5 or 6 month in distilled water at 37°C) with Opalescence(®) PF15% for 6h (simulation of home bleaching) or PF35% for 0.5h (simulation of in-office bleaching) and incubated in ethanol/water (3:1) at 37°C for 7d. The eluates were analyzed by gas chromatography/mass spectrometry. Unbleached specimens at the above mentioned irradiation times were used as controls. RESULTS: Bleaching increases the amount of elutable substances. This amount is generally stronger influenced by aging than by polymerization time or concentration of the gel. 2-Hydroxyethyl methacrylate was found in amounts up to 334.14 (106.91) µmol/l (Tetric EvoCeram(®), irradiation time 5s; bleaching with 15% CP) as a destruction product. Diethoyxdimethylsilane was found in all eluates from bleached specimens, but not in the control groups. This substance may be formed by oxidation of 3-methacryloxy-propyltrimethoxysilane, indicating that the bond between inorganic filler and organic matrix might be weakened after bleaching. SIGNIFICANCE: Bleaching gels might alter the physical properties of resin-based composites, especially at low irradiation times and fresh placed restorations.

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.