Tolkien was a folklore buff.
And the vagina dentata, incidentally, is an old old folk motif.
There were rumors of same regarding Vietnamese prostitutes:
"Vagina Dentata" and "Incurable Venereal Disease" Legends http://links.jstor.org/sici?sici=0043-373X...%3E2.0.CO%3B2-Y
Same say it's simply a male fantasy:http://books.google.com/books?id=0ZdGvkFFr...SqIuYVOcL150fI8
Old folk songs deal with this, and related matters, though many have been expurgated. For instance, you're unlikely to be aquainted with this:
The Twelve Days of Christmas" is less ingenious, ranging through "Twelve twitching testicles, eleven lecherous Lesbians, ten tired trollops, nine naughty nuns, eight useless eunuchs, seven sex-starved spinsters, six convicted vicars, five queer choir boys, four Girl Guides, three Boy Scouts, two virgin maids, and my Lord Montague of Burleigh."http://www.folklore.ms/html/books-and-MSS/...-fowke-HTML.htm