Broken down into its literal definition, mandibular hypoplasia means a jaw that is incomplete. "Mandibular" is the anatomical term referring to the lower jaw or jawbone and "hypoplasia" is a medical term that refers to an under development or growth of a part of the body. Mandibular hypoplasia therefore is the incomplete or under-development of the lower jaw. Micrognathism, a condition where the lower jaw is undersized, is another term meaning essentially the same thing.
Mandibular hypoplasia is often a congenital condition, but can also come about as a result of trauma or injury. The cause of congenital forms of this condition can vary and a cause is not always identified in pediatric patients born with this facial malformation. Similarly, it may be only 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 may present as a deviated chin with asymmetrical facial features surrounding the mouth. Complications can occur and will depend largely 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 tracheotomy or feeding tube may be necessary until surgical correction can be achieved.
Mandibular hypoplasia is often graded based on the Pruzansky Classification System, developed in 1969. Other classification systems have been developed since 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 mandibles that are hypoplastic, or underdeveloped, and may fall into subclasses a or b depending on the malformation. Grade 3 refers to a mandible that is severely underdeveloped or malformed.
Treatment for mandibular hypoplasia requires reconstructive surgery. The extent of the surgery is dependent on the degree of underdevelopment and configuration of the surrounding facial bones and muscles. In essence, the mandible is rebuilt with a series of bone grafts. Reconstructive surgery is typically 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 besides being a primary facial feature of an aesthetic nature. Nonetheless, many surgeries are quite successful at both improving facial features and correcting or alleviating complications that can occur because of hypoplasia.