Jaw Defects

BySimeon A. Boyadjiev Boyd, MD, University of California, Davis
Reviewed/Revised Sep 2022

The jaw can be missing, deformed, or incompletely developed at birth.

Birth defects, also called congenital anomalies, are physical abnormalities that occur before a baby is born. "Congenital" means "present at birth." (See also Introduction to Birth Defects of the Face, Bones, Joints, and Muscles.)

Birth defects of the jaw include

  • Micrognathia: A small lower jaw

  • Agnathia: Part of or all the lower jaw is missing

  • Maxillary hypoplasia: Underdevelopment of the upper jaw (maxilla)

Micrognathia is a small lower jaw (mandible). Pierre Robin sequence and Treacher Collins syndrome, which are disorders characterized by several defects in the head and face, are associated with a small lower jaw. If the lower jaw is too small, the infant may have difficulty eating or breathing. Surgery to extend the jaw may correct or diminish the problem.

Agnathia, a condition in which a part of or the entire lower jaw is missing, is a severe malformation. Often the infant also has abnormalities of the ears, temporal bone, saliva glands, the muscles used in chewing, and facial nerve. Treatment of agnathia consists of reconstructive surgery with bone grafts and other tissue grafts to improve the appearance and function of the jaw.

Maxillary hypoplasia is underdevelopment of the upper jaw (maxilla). It causes a flat mid-face, which makes the lower jaw appear to stick out. Treatment of maxillary hypoplasia involves surgery to reposition the upper jaw and align it with the lower jaw.

Hypertelorism and Maxillary Hypoplasia
Hide Details
This person has hypertelorism (widely spaced eyes; left) and maxillary hypoplasia (small upper jaw; right).
© Springer Science+Business Media

Diagnosis of Jaw Defects

  • Imaging tests

Doctors diagnose all of these defects by assessing the degree of jaw underdevelopment with x-rays and computed tomography (CT) of the face.

Because abnormal genes may be involved in birth defects of the jaw, affected babies should be evaluated by a geneticist. A geneticist is a doctor who specializes in genetics (the science of genes and how certain qualities or traits are passed from parents to offspring). Genetic testing of a sample of the baby's blood may be done to look for chromosome and gene abnormalities. This testing can help doctors determine whether a specific genetic disorder is the cause and rule out other causes. If there is a genetic disorder, families may benefit from genetic counseling.

Test your KnowledgeTake a Quiz!
Download the free MSD Manual App iOS ANDROID
Download the free MSD Manual App iOS ANDROID
Download the free MSD Manual App iOS ANDROID