It's very simple as like a paypal transfer or any other scan transfer. Their is a scan code for the crypto in many trusted and big exchanges.The dentist have to just create an account their. Then need to take a copy of QR code to scan. They have to paste on the dentist hospital.When the customers came to the hospital, they need to do ask of patients to scan code abd send the crypto. Once the payments made by them, they can give treatment to that patients.
as advised by many, it is not a wise move to use centralised exchanges even if it is a reputable exchange to store your crypto. why not download and install your own wallet like electrum? if a dentist or any other medical professional wants to be paid by crypto, they can easily search now via internet. they are well educated people so reading over the net is no problem with them. though they can make mistake in choosing a trading platform. but better to store their funds in a non-custodial wallet where they have full control of their funds. they can easily generate their address and post it.
people will also get curious with btc or crypto if they have something like that posted on their office doors.