Can an orthodontist hold your records because of unpaid bill?

Yes, an orthodontist or any healthcare provider, may hold onto and refuse you a copy of your dental or medical records for non-payment, but some state laws are very specific about exactly how an account balance has to be handled before medical records can be withheld

Generally, they are permitted to hold onto your health or dental records in cases wherein you had failed to pay after multiple warnings and reminders that doing so might lead to suspension of services and your credit score takes a big hit and you might see a significant drop in your overall credit ratings due to your dental account and other medical debts falling to a collections department