1. Postgraduate Program in Dentistry, School of Health Sciences; Pontifical Catholic University of Rio Grande do Sul (PUCRS) - Av. Ipiranga, P.O.Box 6681, 90619-900; Porto Alegre Brazil.
2. Materials and Nanoscience Laboratory; Pontifical Catholic University of Rio Grande do Sul (PUCRS), P.O. Box 1429, 90619-900; Porto Alegre Brazil.