Eve Glazier, M.D., MBA, is an internist and associate professor of medicine at UCLA Health. Elizabeth Ko, M.D., is an internist and assistant professor of medicine at UCLA Health. Send your questions to askthedoctors@mednet.ucla.edu.

Dear Doctors: I saw my dentist for pain in an upper molar, but the X-ray was normal. My nose was also plugged up, and she said it might be my sinuses. I started doing a saline rinse, and after a few days the pain had gone. Why would having a sinus infection give you a toothache?

Dear Reader: Tooth pain that arises from inflammation or infection in the sinuses is fairly common. The sinuses are an important part of the respiratory system. They are four pairs of air-filled cavities that work together to warm, humidify and filter the air we breathe. They also produce mucus. The mucus acts as a lubricant and serves as a first line of defense for the immune system.

The four pairs of sinuses are in the lower forehead, on either side of the nose, behind the nose and in the bony structures of the cheeks. The mucus they produce forms a thin, sticky layer on the inner tissues. These tissues are lined with minute, hairlike structures known as cilia. This ingenious system helps the cilia capture and entrap dirt, dust and pathogens. The cilia propel the mucus down the nasal passages into the throat. Swallowing directs it into the esophagus and on to the stomach.

If a pathogen or allergen causes the sinus tissue to get inflamed and swollen, a condition known as sinusitis, the flow of mucus can get blocked. This creates pressure in the sinuses. Sinusitis can be uncomfortable. Symptoms include headache, postnasal drip, congestion, fatigue, a sensation of pressure in the ears and muted hearing. When the congestion is in the maxillary sinuses, tooth pain can occur. This pair of sinuses sit just above the upper molars in the cheekbones. Pressure there can irritate the roots of the teeth and cause a dull ache or pain that mimics a toothache.

Over-the-counter medication, such as nasal decongestant sprays or antihistamines, can help. These medications target specific symptoms, including mucus production, inflammation and congestion. The saline rinse you did can help loosen thick mucus and make it easier to expel. Saline rinse also helps clear the sinus cavities of dust, pollen and other debris and allergens. For sinus rinse, always use distilled or sterile water. You can also boil water for three minutes, then cool it. Tap water can contain microorganisms that, if they get into your sinuses, can cause serious and sometimes deadly infections.

Eve Glazier, M.D., MBA, is an internist and associate professor of medicine at UCLA Health. Elizabeth Ko, M.D., is an internist and assistant professor of medicine at UCLA Health.