AustLit

'A dentist tells one of his patients the story of how he became a dentist in spite of wanting to be a dustman: one of his neighbors, despite being nearly toothless, always had his bin full of toothpaste which he tested on locked-up animals. This toothpaste is supposed to make sure people never have to clean their teeth again, but has a horrible taste. The old man gets a taste of his own medicine and transforms into a giant tooth, which the patients think becomes the dentist's sign. The story ends with the dentist telling a similar story to another child of how he became a dentist in spite of wanting to be a ballerina, revealing that the story is made up.' (https://en.wikipedia.org/wiki/Unbelievable_(short_story_collection))