The degree of monomer conversion (DC) values of three different dental composites were examined using three different methods: surface microhardness (ratio of bottom/top), Fourier-transform infrared (FT-IR), and differential scanning calorimetry (DSC). Two of the dental composites included in the study were nanohybrid (Dentsply Neo Spectra ST HV and Omnichroma), and one was a microhybrid-labeled newly marketed composite containing nanoparticles (Dentac Myra). Composite discs were prepared according to the methodology for all methods and analyzed (2 mm thickness × 5 mm diameter). Surface microhardness values were measured in Vickers Hardness Number (VHN), while FT-IR and DSC values were obtained in percentage (%). Significant differences were observed in both bottom/top surface microhardness values and DC values obtained from FT-IR. However, there was no statistical difference in the ratio of bottom/top microhardness values. Neo Spectra ST HV exhibited superior performance in both microhardness and monomer conversion compared to the other two composites. Newly marketed Myra showed values close to Omnichroma. It was found that the values obtained by the DSC method were parallel to those obtained by FT-IR. In conclusion, the structure of dental composites leads to different mechanical properties. Additionally, DSC measurements and FTIR spectra were found to be complementary techniques for characterizing monomer conversion values.

Carbon nanotubes have become widely used due to their superior physiochemical properties, and so knowledge of their toxicity has become important. In this study, the toxic effects of nanotubes on Caenorhabditis elegans have been investigated. Multi-walled carbon nanotubes were characterized by transmission electron microscopy and particle size analysis. Upon exposure to the nanotubes at concentrations of 100 to 500 mg/L for 3 to 15 days, numbers and body lengths of the nematodes were not altered, but body thickness was raised and body movements were slightly decreased. A new type of toxicity-reproduction assay was performed to see the effect of multi-walled carbon nanotubes. The circular-form aggregation of starved larvae was counted. The number of aggregations was reduced with the increasing nanotube concentration by ∼27%. The concentration-dependent reduction was confirmed by counting the eggs in a single worm which demonstrated the negative effect of multi-walled carbon nanotubes on reproduction when the nematodes were subjected to prolonged exposure.