The narrowing of the dental arch is more common in clinical practice and can be detected by an experienced physician by observing the smile movement. However, the disease is mainly diagnosed by clinical examination. If the patient’s upper and lower models are observed and the posterior teeth are found to be retruded, it indicates maxillary narrowing, and some patients may also exhibit narrowing of the upper and lower jaw arches, and then the upper and lower jaws need to be treated with arch expansion. The narrowing of the dental arch is often accompanied by high arch of the palatal lid, which is mainly caused by genetic factors, while some patients are caused by bad habits, such as poor nasal airway, frequent oral breathing, uneven force on the upper dental arch, and easy formation of high arch of the palatal lid and narrowing of the dental arch. Some children have the bad habit of gnawing fingers, which is also easy to cause the narrowing of the dental arch.