Like that one dude said, button down shirt with a tie is a no no. In fact, my interviewer at one of the schools made fun of a previous applicant who was sporting the button down shirt and a tie with a suit. He just shook his head in disgust, these guys can't even dress themsleves
Shirt with a tie without a jacket is more acceptable although you might look like a 6th grader on the day of his history presentation.
Shirt with a tie with the white coat is of course perfectly fine and looks very professional. But if you're a dentist, you're doing physical **** so it's probably not a good look to wear something so restricting. If you're like an orthodontist and you don't have to get your hands dirty, shirt with a tie under a white coat would be great.
French cuff aka double cuff is usually associated with wealth. Kinda gives the wearer an heir of arrogance. So it would be kind of frowned upon for a young person in even the most appropriate fields like business, law, banking, etc to wear French cuff shirts. Even if they are plain white, french cuff shirts tend to be a little bit more ostentatious. For instance, a French cuff shirt is a big no no for interviews. Not just dental school interviews but interviews at a law firm or an investment bank.
But that's just a traditional and conservative view. It's like saying you shouldn't have sex before marriage. Get outta here with that garbage. In fact, I think it would actually be a good idea for dental students to wear a shirt and tie when they see patients. It makes you look more professional and it'll be easier for patients to trust you and respect your authority. Who wouldn't feel safer with a student who looks well put together in a shirt and tie over a scrub ass disheveled dude
with a raggedy polo shirt on and abercrombie cargos and ****?