Cavities are a type of dental hard tissue defect caused by bacterial infection, and represent a chronic, progressive, destructive disease. In the early stages of a cavity, if only the enamel layer is involved with simple demineralization of the tooth, then remineralization treatment can be conducted. This scenario is the only reversible one where the cavity can heal itself. If the cavity progresses to the dentin layer, then it cannot heal by itself and requires timely intervention by drilling to remove the decayed part and performing a filling treatment. If the infection is not controlled in time, bacteria can further cause the dental nerve to become purulent and necrotic, leading to symptoms of pulpitis or apical periodontitis. In such cases, timely root canal treatment is necessary.