An underbite is a dental malocclusion condition where the lower jaw protrudes foreward abnormally, partially overlapping with the upper teeth due to the imbalanced development of the upper and lower jaw. In frontal view the chin of an underbite patient only looks relatively bigger. In profile view the chin stands out from the face like an outstretched drawer. The functional interference in an undebite arrangement includes speech difficulty for syllables that require teeth-tongue cooperation and also biting dysfunction to some extent. However its interference to smile is the most unbearable thing for most of the underbite sufferer. They feel awkward every time laughing because their smiling looks unnatural. These functional abnormalities and every day problems imposed by an underbite condition drive the sufferer seeking medical help. For adult underbite patient non surgical intervention may not help much as the bone abnormalities of the mandible is already formed.


The young man in this page is tall and handsome. Yet he had trouble with smile because of his underbite jaw. At the time when he saw Dr. Ma he already acquired many information regarding underbite occlusion. Still he had never expected such a great improvement in smile after his surgery. His primary goal was to improve facial figure, chewing and speech function. It turned out the facial expression change of smile mostly satisfied him. He told Dr. Ma, at his follow-up visit, that he never need to hold his laugh anymore since his surgery. The surgery he underwent was mandibular sagittal split osteotomy underbite correction, during surgery his mandible bone was splited sagittaly, set back and internally fixed in an ideal position.

Though the chin shows no protruding in frontal view, it still looks too big to the rest parts of his face for this underbite patient. After surgery this unbalanced look improved.

underbite profile
In profile view the signs of underbite show clearly. These includes the long and protruding chin and the blurred labial-chin angle. The correction surgery set back the chin bone and these unwanted appearance were improved.

underbite smile
When laughing the protruding lower set of teeth shows clearly, so they are reluctant to smile. The correction surgery converts the smile to a sweet one.

During the sagittal split osteotomy the mandible bone of this young man was cut split in a special way and then re-fixed in a retrieved manner to restore the normal bite relationship of the upper and lower set of incisor teeth. The correction of the malocclusion led to the recovery of the malfunction caused by the underbite arrangement of the jaws.

As the mandible bone was cut into three pieces and re-fixed the incision on the bone needs about three to four months to health completely. During this period of time hard food should be avoided.

Some candidates wondering if they could cut the mandible bone smaller to make the face narrow during the set back surgery of the mandible bone. The answer is no. Because when the mandible bone is set back firm fixation is required. Removal of the mandible bone makes this fixation difficult. A compromised fixation will in turn interfere the finial cosmetic result of the surgery.

Why surgery could change the smile of an underbite patient? In an underbite situation the mandible bone is over developed and over protruding to the front, so the soft tissue and the skin over the chin area is tight. The predisposed tension in this area prevents the free movement of the skin and muscle in this area to produce a proper expression. Even worse the underbited front part of the teeth show completely when smile, the abnormal underbited occlusion giving an unnatural look. The surgery of Saggital Split Osteotomy of the mandible bone reduces the protruding degree of the chin and tension applied on the skin and soft tissue in this area is relived, the facial expression muscle can move more freely. At the same time the occlusion relationship of the exposed incisor teeth at smile restored to normal. All of these changes make the smile of an underbite patient more charming and sweetly. Most of the time this smile improvement is so profound that could astonish friends and relatives.

By: mafushun

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