To remove the infected ‘devital’ pulp tissue that has been infected due to caries, trauma, and lost its vitality; canal treatment is applied to clean the infected area and treat the inflammation. Deep caries or trauma-induced hot-cold sensitivity, throbbing, night pain, and severe pain are common symptoms when the nerve tissue of the tooth, the pulp, enters an inflammatory phase. On the other hand, the root canal may still be infected even when no sign of pain or tenderness is observed. Teeth may lose their vitality due to fillings, size reductions following crown-bridge construction or due to other different reasons. Such devital teeth do not cause any pain due to full damage on the nerve tissue and if the patient does not show up to routine controls, he/she can spend a long time being unaware of this. The long-term presence of infected teeth in this way; leads to an inflammation at the root end characterized by bone destruction, known as apical ostitis. While no chronic symptoms would be observed in this inflammatory condition; in case of acute exacerbations, it may cause the swelling of the tooth, pus, and severe pain. If infected teeth are not treated on time, the inflammation would worsen and become untreatable after a certain period, leading to tooth loss. In the later stages of inflammation, cystic formations occur at the root end.