I shadowed a dentist for a month or so the summer between my fresh/soph years of undergrad, so I put that on my AMCAS. It wasn't brought up in any of my interviews so I can't really tell you whether it helped or not. Ended up with 9 interviews and 6 acceptances for reference.
The only reason why I wrote it down really on my application was to use it as proof in case an interviewer were to ask me how sure I was about choosing medicine among other healthcare professions, but that honestly that kind of question didn't show up at all. 😵