The duration of pain from inflammation to necrosis of the pulp is uncertain. Some affected teeth have chronic pulpitis with a long duration, lasting 0.5-1 year or even longer, and patients may complain of a long history of painful hot and cold irritation. In chronic pulpitis, there is usually no severe spontaneous pain, and many patients do not receive timely treatment because they can tolerate it until the pulp is chronically necrotic. The pain of acute pulpitis is very characteristic, as the affected tooth usually presents with severe spontaneous pain that radiates to the ipsilateral head and neck, and the pain is not continuous but paroxysmal. The pain is usually more pronounced at night, increasing when lying down and decreasing when sitting up. In acute pulpitis, if left untreated, nerve necrosis can occur over a week’s time.