Dental abscesses occur when bacteria is able to reach the pulp of a tooth, or grows deep in the space between the teeth and gums. Infection develops, which can cause an abscess. Bacteria may gain access to these areas for several reasons, including:

• Untreated decay. Deep cavities that lead to the inner tooth and affect the pulp are among the most common causes of a tooth abscess.
  
  
• Cracked tooth. Fractures or cracks in the enamel and dentin can allow bacteria into the pulp, which may lead to infection and abscess. This is a common cause of tooth abscesses.
  
  
• Periodontal disease. Gum disease causes the gums to pull away from the teeth, creating deep pockets of space between the teeth and gums. If food particles become stuck in these pockets, bacteria may grow and an abscess can develop in the gums.
  
  
• Unrepaired restorations. Weakened dental restorations (e.g., fillings) may break down over time and allow bacteria access to the pulp, potentially causing an infection and abscess.