作者单位:Univ Penn, Penn Dent Med, Div Restorat Dent, Philadelphia, PA 19104 USA[1]Univ Fed Rio Grande do Sul, Sch Dent, Acad Dent, Porto Alegre, RS, Brazil[2]Univ Fed Rio Grande do Sul, Sch Dent, Dept Oral Pathol, Porto Alegre, RS, Brazil[3]Univ Fed Rio Grande do Sul, Inst Basic Hlth Sci, Dept Morphol Sci, Rua Sarmento Leite 500, Porto Alegre, RS, Brazil[4]