Periodontitis is an inflammation of the tooth-supporting tissues caused by the lack of timely brushing and rinsing after eating, where food residues or soft plaque become calculus under the calcification of saliva. This condition requires tooth cleaning, which is a procedure performed around the teeth, and does not require root canal treatment. If periodontitis progresses further and bacteria from the periodontal pocket reach the root tip, it can cause inflammation around the tooth including the root tip. This may lead to a pathological condition of the dental nerve. If the root tip inflammation is caused by the retrograde action of periodontitis, root canal treatment is necessary because it affects the dental nerve. If there is no concurrent inflammation of the dental nerve, direct periodontal treatment can be performed. However, if retrograde root tip inflammation has occurred, then root canal treatment of the tooth is required.