Toothaches caused by pulpitis often occur at night and the pain is so severe that it is impossible to sleep. The pulp is located in the pulp chamber and is connected to the rest of the body by a narrow apical foramen. The pulp is surrounded by a hard dentin wall except for the apical foramen, so once inflammation occurs, it is not easy to establish drainage, allowing inflammatory exudate to accumulate. The increased pressure in the pulp cavity can easily spread to the entire pulp, causing the increased pressure in the pulp cavity to compress the nerve and thus produce severe pain. Therefore, once the pulp cavity is opened, the pressure drops and the pain abruptly decreases. The causes of pulpitis are physical, bacterial, idiopathic and chemical factors. Chemical factors: extreme temperature changes, such as high speed, continuous drilling and grinding of the tooth, failure to pad deep cavities with silver amalgam fillings, repeated external temperature stimulation and, rarely, electrical stimulation. Physical factors: acute dental trauma, such as traffic accidents, athletic competition, violent fights that expose the teeth to violent impact or injury, mechanical trauma such as traumatic occlusion, chronic bite trauma dentition caused by overfilling or other restorations. Bacterial factors: Pulpitis is supposedly an infectious disease, and bacteria are an important causative factor for pulp disease. There are three main methods that may lead to pulp infection: dental infection, periodontal infection and blood-borne infection. Bacteria can directly infect the exposed pulp in cases of caries, traumatic fractures and accidental pulp exposure during drilling and grinding, wedge-shaped defects, severe wear and tear of exposed pulp in the elderly, fractured or worn out pulp of malformed central cusps, malformed lingual fossa or malformed lingual sulcus without enamel coverage at the base, and cryptic fractures deep to the pulp cavity. If the dentin covering the pulp tissue is very thin, bacteria and their toxic products can cross the dentin tubules to reach the pulp cavity and cause pulp infection; bacteria may also reach the root tip through the periodontal tissue and enter the pulp cavity through the apical foramen to cause retrograde infection. Pulpitis caused by blood borne infection is quite rare.