Feb 6, 2015 3 min read

DEAR DOCTOR K: I had knee replacement surgery several years ago. More recently, I had my hip replaced. I am scheduled to have a root canal next month. Do I need to take antibiotics before my dental procedure?

DEAR READER: Almost any type of dental work — extractions, gum surgery, root canals, even routine cleanings — can injure the gums and other soft tissues of the mouth. The most obvious evidence of this is that they bleed.

Bacteria live inside our mouth. When gums are injured, bacteria from the mouth can enter the bloodstream. From there, bacteria can travel to places throughout the body — including the new joints that are created by hip or knee implants. A bacterial infection of a new artificial joint can ruin the joint. That will make a second operation necessary. Your implant can become infected even years after surgery.

Because of this theoretical risk from dental work, during most of my medical career the authorities recommended that people who have had hip or knee replacements take antibiotics before an invasive dental procedure. That is, the experts thought the benefits of taking “prophylactic” (preventive) antibiotics were likely to outweigh the risks.

In more recent years, however, large studies have changed expert opinion. The studies have shown that the risk to an artificial joint from dental work conducted without antibiotics is very low. More important, the overuse of antibiotics has been shown to create bacteria that are resistant to antibiotics — a growing risk.

For these reasons, professional dental and orthopedic groups now say preventive antibiotics aren’t required for people with artificial joints. But they still recommend that you let your dentist know about your artificial joint: There may be some dental procedures that the dentist or oral surgeon thinks may cause an unusually large number of bacteria to get into your bloodstream.

To be clear, I’m not saying that no one needs preventive antibiotics before and during a dental procedure. People with certain heart conditions, for example, should get preventive antibiotics before and during most dental procedures. This does not include routine dental cleaning.

People with these heart conditions are at greater risk for a disease called endocarditis, a bacterial infection of the heart’s valves or inner lining. It can cause lasting damage to the heart.

To reduce the risk of endocarditis, you will likely need to take a preventive antibiotic if you:

n have an artificial heart valve;

n have had infective endocarditis in the past;

n have a transplanted heart with valve problems;

n were born with certain heart problems that were not repaired, were repaired recently, or were repaired but continue to cause problems.

You may also need to take preventive antibiotics before dental procedures if you have cancer, HIV infection or hemophilia. Also tell your dentist and other doctors if you have a condition that puts you at greater risk of infection.

Finally, you may have taken antibiotics before having dental work in the past. Ask your doctor or dentist if that is still necessary.

Dr. Komaroff is a physician and professor at Harvard Medical School. To send questions, go to AskDoctorK.com, or write: Ask Doctor K, 10 Shattuck St., Second Floor, Boston, MA 02115.