What does it mean when the lower teeth overlap the upper teeth?

When the lower teeth cover the upper teeth, it is called "underbite" (commonly known as "di bao tian"), which usually refers to anterior crossbite malocclusion. This condition may be caused by congenital diseases, respiratory disorders, systemic diseases, and other factors.

1. Congenital Diseases

Congenital cleft lip and palate are primary causes of anterior crossbite malocclusion. Cleft lip and palate can lead to excessive suture proliferation and altered bone surface growth. Additionally, post-surgical scar tissue may restrict jaw development. Among the malocclusions associated with cleft lip and palate, anterior crossbite or complete arch crossbite often results from underdevelopment of the maxilla.

2. Respiratory Diseases

Chronic tonsillitis, for example, may cause adenoid hypertrophy. To maintain airway patency and reduce pressure and irritation, the tongue tends to move forward, thereby pulling the mandible forward, potentially leading to anterior crossbite and mandibular protrusion.

3. Systemic Diseases

Pituitary hyperfunction can result in excessive secretion of growth hormone. If this condition persists beyond epiphyseal closure or develops after fusion of the growth plates, it may lead to symptoms such as acromegaly, mandibular protrusion, and anterior or full-arch crossbite.

Besides the above causes, genetic factors may also contribute to the development of underbite. If this condition significantly affects a patient's daily life, medical consultation and orthodontic treatment at a hospital are recommended.