This has not been the case in my experience. Dentists have always told me exactly how much I owe them, and the one time I forgot a payment, they called me and texted me to let me know and I resolved it in a matter of minutes.

Meanwhile a hospital visit sent me a bunch of bills in the mail ranging from $50 to $100, they refused to tell me the total sum even when I visited in person, and when I missed one $50 payment I was sent to collections a year later.