Sore in back of gums

A sore behind the last tooth may come from gum irritation, an erupting wisdom tooth, an ulcer, or a dental infection.

The area behind a molar contains gum overlying bone and, sometimes, a partially erupted third molar. Food trapping, cheek trauma, plaque around the tooth, or a small ulcer can inflame this tissue.

Rinse gently with warm salt water, brush the area with a small soft toothbrush, and avoid picking or placing chemicals on the sore. A dentist may examine the gum, test the tooth, and take an X-ray if a wisdom tooth or deeper infection is suspected.

Arrange dental care if the sore persists, recurs, bleeds easily, or is accompanied by tooth pain, bad taste, swelling, or difficulty opening the mouth. Seek urgent help for spreading facial swelling, fever, trouble swallowing, or breathing.

Ask whether the sore is caused by the gum, a wisdom tooth, an ulcer, or an infected tooth, and whether an X-ray is needed. Ask which treatment will remove the cause and how to keep the area clean while it heals.