FULL DISCLOSURE It’s important to know the price before you agree to the procedure. Often patients sit down for a routine cleaning and checkup, only to find they have a problem. The dentist offers to take care of the situation on the spot, and the patient agrees  but then is socked with a surprising bill at the end of the visit.

That happened to Monica Gagnier of Beacon, N.Y., on a recent visit to her Manhattan dentist for a twice-yearly cleaning. Looking to save money, Ms. Gagnier was careful to tell the office when she made the appointment that she wasn’t due to get X-rays and didn’t need to see the dentist for a checkup. Without those two items, she figured she would save more than $100 on her bill.

During the cleaning, however, the hygienist told her that her gums were infected and she needed antibiotic shots. Her total bill was $400.

“The antibiotics may well have been necessary,” Ms. Gagnier said. “But what I hate is being hit by surprise costs and treatments when I’m lying on my back, my mouth is wide open, and I can’t talk about it.”

You should always be given an opportunity to discuss any treatment, sitting up, without equipment in your mouth, says Dr. Messina. In addition, whenever you are facing an invasive dental procedure that is not an emergency, it makes sense to refuse treatment on the spot and get a second opinion, says Elizabeth Rogers, a spokeswoman for Oral Health America, a nonprofit advocacy and education group based in Chicago.

The range of prices on treatments like root canals, for instance, can easily differ by $1,000 or more.

SPREADING THE COST Patients can often space out treatments or negotiate payment plans with the dentist for extensive work. Working with the dentist on payments, says Dr. Mark Wolff, associate dean at the New York University College of Dentistry, is much better than putting the bill on your credit card and paying high interest.