@article{tirapelli_panzeri_panzeri_pardini_zaniquelli_2004,  title={Radiopacity and microhardness changes and effect of X-ray operating voltage in resin-based materials before and after the expiration date},  volume={7},  ISSN={1516-1439},  url={https://doi.org/10.1590/S1516-14392004000300006},  DOI={10.1590/S1516-14392004000300006},  number={3},  journal={Materials Research},  publisher={ABM, ABC, ABPol},  author={Tirapelli, Camila and Panzeri, Fernanda de Carvalho and Panzeri, Heitor and Pardini, Luiz Carlos and Zaniquelli, Osvaldo},  year={2004},  month={Jul},  pages={409–412} }