If there's one thing you'll learn from watching the Joe McDoakes comedies is that Joe's neighbor, Marvin, is a total idiot! While he loves fixing things, they invariably end up completely mucked up.
The story begins with Marvin announcing he's now a dentist as he's completed his dental correspondence school coursework. Joe it not impressed and does not want Marvin looking at his teeth...so Marvin resorts to tricking Joe into breaking a tooth. Then, Marvin simply refuses to take no for an answer and Joe is subjected to dentistry that makes W.C. Fields in "The Dentist" look like a paragon by comparison!
If you are squeamish about going to the dentist, this film certainly won't help this at all...and will likely make it worse. If so, do NOT watch the film. However, it is funny and worth seeing...even if it does make you cringe a bit to watch.