I think I’ve always associated “Ipanema” with “Ipana,” as in the toothpaste brand. (Sort of dates me, I know. Apparently it was brought back to market in 2011 as a “retro brand.”) Hey, I’m sure the girl has a great smile, although we’re not specifically told that in the song.
But it won’t surprise you to find out that there is nothing about dental hygiene here. Ipanema is a beach in Rio de Janeiro, and there was a bar about a block from there where the composer Antonio Carlos Jobim and the poet Vinicius de Moraes liked to sit and drink beer. They noticed a lovely 18-year-old girl often walking by on the sidewalk, either down to the beach or home from school (although it’s not clear how they knew where she was going). Her name was Hélo, short for Heloisa Eneida Menezes Pais Pinto. So inspired were they by her loveliness and her way of walking (“sheer poetry,” according to de Moraes) that they wrote the song on the spot, using the traditional manuscript material of bar napkins.