Pulpitis is caused by bacterial infection. The oral cavity is an environment with bacteria, and if teeth are not brushed promptly after eating, bacteria can break down food into lactic acid, leading to demineralization of the teeth. This further infection causes tooth decay and the formation of cavities. In addition to these cariogenic factors, pulpitis may also be due to periodontitis or the destruction of periodontal supporting tissues, leading to a retrograde infection. There are also large amounts of bacteria in the periodontal pocket. If the periodontal pocket is deep enough to reach the root apex, it may sometimes cause retrograde apical periodontitis. Moreover, if the teeth are malformed and are accidentally bitten off or broken during the eruption process, this can also cause inflammation of the dental nerve, which is pulpitis.