Toothache at night and no pain during the day is likely to be a symptom of acute pulpitis or an acute attack of chronic pulpitis, typically manifested as toothache at night and no pain during the day, correlated with body position, pain can occur spontaneously without stimulation, or may be induced when eating hot or cold irritating food. The main reason why pulpitis hurts at night and not during the day is because the human body is in a lower position at night when the head is lying down, the blood supply to the pulp cavity increases and it is easy to be congested with blood and inflammatory secretions increase, stimulating and producing pain. During the day, the pain is relieved with the filling of the pulp chamber in the standing or sitting position. In addition, the pain may not be easily noticed during the day because the attention is focused on things such as study and work, and at night the attention is distracted and the discomfort is easily noticed. The main causes of pulpitis are infection, physical injury and chemical stimulation.1. Infection: Most pulpitis is caused by bacterial infection, usually not paying attention to oral hygiene or other inflammatory diseases in the mouth, which can easily lead to bacterial growth and cause pulpitis, the majority of acute attacks of chronic pulpitis, toothache at night and no pain during the day, the occurrence of septicemia can have pulsating pain; 2. Physical Injury: frequent consumption of hot, cold, sour and sweet food, or excessive heat production caused by dental surgery to stimulate the teeth, as well as the occurrence of trauma, causing damage to the pulp and blood vessels in the pulp cavity, causing poor blood flow in the pulp cavity, which may cause pulpitis; 3, chemical stimulation: such as chemical stimulation of the pulp by filling restorative materials when dealing with cavities, which may induce pulpitis, and the phenomenon of toothache at night and no pain during the day. In addition, it may also be caused by other diseases, such as gingivitis, periapical periodontitis, etc. It is recommended to seek medical advice to identify the cause of this symptom and treat it for the cause. To pay attention to the oral hygiene environment, do adhere to the morning and evening brush teeth, rinse the mouth after meals, actively seek medical advice when there is inflammation in the mouth, follow medical advice to take anti-inflammatory drugs, if necessary, surgical repair.