Broken down into its literal definition, mandibular hypoplasia means a jawbone that is incomplete. "Mandibular" is the anatomical term that refers to the lower jaw or mandible and "hypoplasia" is a medical term that refers to an underdevelopment or growth of a body part. Mandibular hypoplasia, therefore, is the incomplete or underdeveloped development of the lower jaw. Micrognathism, a condition where the lower jaw is undersized, is another term that means essentially the same thing.
Mandibular hypoplasia is often a congenital condition, but it can also occur as a result of trauma or injury. The cause of congenital mandibular hypoplasia can vary, and a cause is not always identified in pediatric patients born with this facial malformation. Likewise, mandibular hypoplasia may be just one of several specific underdevelopments that are the result of a birth defect. Other areas that may be affected include the ears, upper jaw, and nose.
Clinically, this condition can present as a deviated chin with asymmetrical facial features surrounding the mouth. Complications can occur and will largely depend on the severity of the condition, but can include difficulty breathing, chewing and swallowing, which can lead to sleep apnea and weight loss or failure to thrive in infants. In some cases, a tracheostomy or feeding tube may be necessary until surgical correction can be achieved.
Mandibular hypoplasia is often classified according to the Pruzansky Classification System, developed in 1969. Since then, other classification systems have been developed that created subclasses of the original ordering system. Pruzansky classified mandibular hypoplasia as grade 1, 2, or 3. Grade 1 refers to mandibles that are small in size regardless of normal configuration. Grade 2 refers to jaws that are hypoplastic, or underdeveloped, and can fall into subclasses a or b depending on the malformation. Grade 3 refers to a jaw that is severely underdeveloped or malformed.
Treatment for mandibular hypoplasia requires reconstructive surgery. The extent of the surgery depends on the degree of underdevelopment and configuration of the surrounding facial bones and muscles. In essence, the jaw is reconstructed with a series of bone grafts. Reconstructive surgery is usually performed by an oral or maxillofacial surgeon, who will evaluate the condition and make recommendations based on medical history, development, severity of the condition, and age. This type of reconstructive surgery is quite complex, as the lower jaw serves many purposes and functions in addition to being a primary facial feature of an aesthetic nature. However, many surgeries are quite successful in both improving facial features and correcting or alleviating complications that may occur due to hypoplasia.