Original comment from former Mark Master's Braces Galleries:
episode "The Retainer"
Omri Katz as Marshall Teller feels uneasy about getting a retainer. He remembers when a boy Patrick LaBrecque as Steve got his large (fantasy) headgear. There are many scenes where Steve wears his headgear that enables him to hear dogs talking to him. When Marshall eventually gets his retainer from his dentist he takes it out to look at it. At the end of the episode he takes it out again to show it to a dog. Then the dog leaves behind Steve's old headgear and you can clearly see the removable brace attached to it.
http://www.imdb.com/title/tt0101088/http://www.imdb.com/title/tt0569409/http://www.fernsehserien.de/index.php?serie=2396