Lower Jaw Underbite Surgery: Correcting the Bite at Its Root

You look in the mirror and notice your chin seems to "jut forward," your lower teeth protrude over your upper teeth, and your profile has a "crescent" or concave shape? You may have tried braces but still find the bite misaligned, or you have been advised to get a chin implant yet something still feels unresolved. This is a very real concern for many people whose underbite is caused by a protruding lower jaw. This article helps you understand what lower jaw underbite surgery is, when intervention is truly needed, and why a chin implant alone cannot mask the root of the problem.

What Is a Lower Jaw Underbite, and Why Is It More Than Just a Tooth Issue?

An underbite (anterior crossbite) is a condition in which the lower front teeth sit outside the upper front teeth when biting down, the reverse of a normal bite. Medically, an underbite can stem from three different groups of causes, and identifying the correct group determines the direction of treatment.

• Dental underbite: the lower front teeth tilt forward or the upper teeth tilt inward, while the jawbone structure remains balanced.
• Skeletal underbite: the lower jaw overgrows and protrudes forward, or the upper jaw is underdeveloped and set back, or a combination of both.
• Combined underbite: both skeletal and dental misalignment are present.

The "protruding jaw" case you are concerned about usually falls into the group of underbites caused by the lower jawbone. In that situation, the problem lies not in the teeth but in the very bony framework that supports the face. This is the key reason why correcting the teeth or adding a chin implant alone is not enough.

When Is Lower Jaw Underbite Surgery Needed?

Not everyone with an underbite needs to undergo surgery. For a mild dental underbite, braces (orthodontics) alone may bring the bite back into the correct position. However, lower jaw underbite surgery is usually considered when:

• The jaw misalignment is pronounced, with the lower jawbone protruding significantly in a way that orthodontics cannot compensate for.
• The crossbite causes difficulty with chewing, biting and tearing food, or speech.
• The patient has passed the growth phase and the jawbone has stabilized (typically from late adolescence onward).
• There is a psychological impact, with prolonged loss of confidence due to the appearance of the facial profile.

The decision on whether to operate must be based on a direct examination, a lateral cephalometric X-ray (cephalometric), CT imaging, and a bite analysis. The doctor will measure the angles and skeletal relationships to determine whether the true "culprit" is the lower jaw, the upper jaw, or both. Results vary from person to person, depending on individual constitution and the degree of misalignment.

The Lower Jaw Setback Technique in Underbite Surgery

Corrective jaw surgery for treating an underbite belongs to the field of orthognathic surgery (maxillofacial skeletal correction). The goal is to bring the bony framework into a balanced relationship, so that the bite and the contours of the face are corrected at the same time.

Cutting and Setting Back the Lower Jaw (BSSO)

For an underbite caused by a protruding lower jaw, the technique commonly applied is the Bilateral Sagittal Split Osteotomy (BSSO). The doctor makes incisions inside the mouth to avoid leaving scars on the skin, cuts the bone along the planned lines, and then slides the lower jaw backward to the correct bite position. The bone is then fixed in place with specialized plates and screws.

It May Be Combined With Advancing the Upper Jaw

If the cause is an underdeveloped, set-back upper jaw, the doctor may combine the procedure with advancing the upper jaw forward (the Le Fort I technique). In many combined underbite cases, two-jaw surgery achieves a more harmonious relationship than operating on a single jaw alone. The specific approach is always personalized according to each individual's imaging analysis.

Why Must Braces and Surgery Go Hand in Hand?

One point many people are unaware of: corrective jaw surgery rarely stands alone. The treatment process for a skeletal underbite usually involves three coordinated phases between the orthodontist and the surgeon.

• Pre-surgical braces: realigning the teeth onto the correct axis within each dental arch, so that when the jaw is moved into its new position, the two sets of teeth fit together.
• Corrective jaw surgery: moving the bony segment into the planned relationship.
• Finishing braces after surgery: fine-tuning the bite for a precise fit and stabilizing the result over the long term.

If orthodontics is skipped, the jaw may be set back but the teeth on both sides will not fit together, leading to a misaligned bite, poor chewing, and a tendency to relapse. For this reason, braces are not an "optional extra" but an inseparable part of the treatment journey.

Why Can't a Chin Implant Alone Mask an Underbite?

This is a common misconception. A chin implant only affects the soft tissue and the chin contour at the front of the face; it does not change the position of the jawbone or the underlying crossbite at all. For a person with an underbite caused by a protruding lower jaw:

• A chin implant cannot correct the condition where the lower teeth overlap the upper teeth.
• In some cases, intervening in the wrong place can even make the lower face look more protruded.
• The chewing and speech problems caused by the crossbite remain unchanged.

In other words, a chin implant addresses the cosmetic "tip," while corrective jaw surgery addresses the structural "root." Sometimes, only after correcting the jaw does the doctor consider further refining the chin area, if it is truly necessary.

Medical Notes: Contraindications, Risks, and Complications

Corrective jaw surgery is a major intervention that must be performed at a properly accredited hospital with adequate anesthesia, monitoring, and recovery care — not as a service at a spa or an unlicensed cosmetic facility. Honestly presenting the limitations below is essential for you to make an informed decision.

Some cases require caution or are contraindicated:

• People who have not finished the bone growth phase (the bone is still changing).
• People with uncontrolled underlying conditions: cardiovascular disease, diabetes, or bleeding disorders.
• Pregnant women, and people with an acute maxillofacial infection.
• People with unrealistic expectations or who are not ready for a lengthy treatment journey.

Possible risks and complications:

• Swelling, bruising, and soreness in the maxillofacial area during the early recovery phase.
• Temporary numbness of the lips and chin due to nerve involvement; most recovers gradually, though it can sometimes be prolonged.
• Infection, bleeding, or issues affecting the fixation plates and screws.
• A mild bite misalignment requiring additional orthodontic fine-tuning, or a risk of relapse.

No surgery is absolutely safe, and no one can guarantee an identical result for everyone. The outcome depends on individual constitution, the initial degree of misalignment, adherence to post-operative care, and coordination with orthodontics. Following the schedule for follow-up visits, hygiene, and diet as instructed plays a very important role in the healing process.

Advice and an Invitation to Consult

An underbite caused by a protruding lower jaw is a problem of bony structure, so the durable approach is to address the root correctly through corrective jaw surgery combined with braces, rather than trying to mask it with a chin implant. The most important step is to be examined, imaged, and carefully analyzed in order to determine which group of underbite you belong to and which treatment path is right for you.

If you are uncertain about lower jaw underbite surgery and want to clearly understand your options, come and meet Dr. Vo Thanh Sang — a Level I specialist in aesthetic plastic surgery in Ho Chi Minh City — for a direct examination and honest advice. Contact the hotline 079 7479 222 to book an appointment and discuss your specific case in detail.