What can swollen lymph nodes be a sign of?

From the symptoms you described (painful & swollen gums), it seems like you have a case of acute pericoronal tissue infection (meaning inflammation of the tissue around the crown of the wisdom tooth). This is commonly observed when there is a food (bacteria) trap caused by the partially erupting wisdom tooth. If left unattended, the infection may spread and cause your lymph nodes or face to swell too. Removal of the infected wisdom tooth is the most common treatment method and it will help to prevent any future infection.

Lymph node swelling can be caused by infections, cancers and inflammatory diseases. By far the most common cause is infection. Infection from the surrounding areas that drain into the lymph nodes such as the legs, abdomen, groin area can lead to the swelling of the lymph node. If there is recurrent swelling, these areas should be examined to exclude a persistent source of infection. Often a course of antibiotics may be given to see if the lymph node swelling settles. If the lymph node is persistent, you should see your doctor to get this assessed.