For observership you meant shadowing right? If that’s the case then you should go to dental offices and ask them if it’s okay for you to shadow. That’s what I did. Some of them needs resume so be prepared.
It all depends on your visa status...If you don't have either a GC or US citenzenship, there are courses for international students 6 months or even a year where you can have your hands on experience and LORs.