Usually, when we talk about “deflated mouth”, we mainly mean that the upper lip and skin are sunken inward, while the lower lip is protruding. So what exactly is “deflated mouth” all about? In fact, the cause of “deflated mouth” is relatively complex, generally not only the lips and other soft tissue problems, in most cases also accompanied by skeletal deformities. As we know, the upper teeth grow in the upper jaw, and the lower teeth grow in the lower jaw. If the upper jaw is underdeveloped, it will cause a depression in the middle of the face, which generally manifests itself as a sunken upper lip, a lack of fullness of the skin, and a collapsed nose. In most cases, there is also an abnormality in the bite of the teeth. Normally, the upper teeth are slightly to the outside of the lower teeth, but in patients with “deflated mouth”, the lower teeth are often to the outside, resulting in a “backbite” or even no bite contact. If the lower jaw is developing normally, the deformity is not serious, but if it is accompanied by an overdevelopment of the lower jaw, the deformity will be more pronounced and the so-called “deflated mouth” will be more pronounced, resulting in a more aged appearance. Sometimes the upper jaw is normally developed and the lower jaw is overdeveloped, which can also cause the illusion of a “deflated mouth”, but the main problem is the abnormal development of the lower jaw. The development of the jaw is mainly related to genetics, and bad habits can also have an impact. In addition, some patients with cleft lip and palate also have secondary underdevelopment of the upper jaw, while these patients have shorter than normal upper lips and surgical scars, so their “deflated mouth” is often more serious. Orthodontic treatment can correct the malformation of the teeth, but for patients with jaw developmental abnormalities, combined treatment with orthognathic surgery is required.