Smoking and other types of tobacco use may increase the pain of temporomandibular joint disorders, a new study suggests.

Temporomandibular joint disorders, commonly known as TMJ, are a group of conditions that cause pain and dysfunction in the jaw joint and surrounding muscles. Symptoms include radiating pain in the jaw, face or neck; limited movement or locking of the jaw; and a painful clicking when the mouth opens or closes.

The cause of a person's TMJ problem is often not clear, but it can stem from damage to the joint from arthritis or an injury.

Smoking has not been established as a risk factor for TMJ development, but research has shown that among people with certain painful conditions -- such as fibromyalgia and chronic back pain -- tobacco users tend to have more severe pain.

To see whether this might be true of TMJ patients, researchers at the Mayo Clinic in Rochester, Minnesota, assessed 606 patients seen at their center over two years.

Overall, they found, there was no clear link between TMJ pain severity and current tobacco use -- whether smoking or chewing tobacco.

However, the findings changed when the researchers focused on the 55 percent of patients who did not have myofascial pain -- that is, their TMJ was caused by arthritis or other pain in the joint, rather than problems in the jaw muscles.

Among these patients, current tobacco users were between four and five times more likely to have moderate to severe pain.

Dr. Toby N. Weingarten and colleagues report the findings in the medical journal Pain.

It's not clear why tobacco users would have worse TMJ pain -- or why that would be the case only for those without myofascial involvement.

Smoking is thought to speed degeneration in the spinal bones, and it's possible that the same could occur in the temporomandibular joint, Weingarten's team notes. However, they add, the fact that smokers do not have higher TMJ rates argues against that theory.

Whatever the reasons for the findings, the study suggests that quitting smoking could help ease some patients' TMJ pain, the researchers write. Former tobacco users, they note, were no more likely than non-users to have moderate or severe pain.

SOURCE: Pain, December 15, 2009.