&；nbsp； &；nbsp；&；nbsp；&；nbsp； "Underbite" is also known as anterior crossbite, which is one of the most common deformities in clinical practice. &；nbsp； Anterior crossbite can occur during the milk tooth stage, mixed dentition stage, and permanent tooth stage. Generally speaking, the earlier the correction, the better. Some parents believe that milk tooth crossbite is not a big deal and will be corrected automatically after all the teeth are replaced. Is this really the case? No. Crossbite deformity patients will severely affect the growth and development of the oral cavity, face, and jawbone, limiting the development of the middle 1/3 of the child's face while overdeveloping the lower 1/3. Such children appear to have a crescent-shaped face when viewed from the side, affecting both aesthetics and function. If not corrected during the milk tooth stage, the opportunity for treatment will be lost, and after the replacement of teeth, it usually continues to form permanent tooth crossbite. The crossbite appearance becomes more severe with age. If not corrected during the growth and development period, by adulthood, even with effort, the crossbite relationship of the teeth can be corrected, but serious skeletal deformities must be surgically corrected. Therefore, from a preventive perspective, crossbite (underbite) should be treated as early as possible. There are also such cases in clinical practice where after the correction of milk tooth crossbite, anterior crossbite reappears after the permanent teeth erupt, requiring another round of correction at the Department of Stomatology, Dongwu Hospital, Suzhou. However, it should be emphasized that although the anterior teeth are in a crossbite relationship, these cases are basically dental crossbites rather than skeletal crossbites, making the correction relatively easier. Therefore, it is necessary to correct milk tooth crossbite. Besides severely affecting appearance, it also significantly impacts the patient's chewing function. The anterior teeth cannot perform cutting functions, and due to the impact of crossbite on mandibular movement, the chewing function of the posterior teeth will also significantly decrease. It also affects the patient's speech function, making some sounds unclear, thus impacting communication and learning. In summary, underbite should not be left untreated, and the earlier the treatment, the better. &；nbsp；