I was able to catch this short on the DVD for "The Fantastic Planet". It starts out with live action. Patients are calmly strolling around an apparent mental facility of some type. A group of them get together and create a story. The story they come up with is shown in animation.
It involves a dentist who pulls all of the teeth out of the patients who come to visit him. The teeth are then sold to rich people who want them. I would think that word of mouth would quickly kill off his business...but apparently not. Anyway, we are shown a patient get all of his teeth removed. The patient passes out and the dentist lugs his body all the way out to the countryside (on foot no less!). The patient wakes up and follows the dentist back to the city.
While in the city, a group of policemen start following the patient. The policemen walk onto the grounds of a high school and mysteriously turn into kids. The "kids" then end up in an anatomy class. By the way...we are occasionally treated to a view of some sort of monster riding around on a bicycle.
How does the mysterious creature factor into this dental fiasco? For those of you whose interest is now piqued, you will have to watch the short to see how this all ends up. Or you can do yourself a favor and skip it. 1/10