Mandibular prognathism / Underbite correction surgery

I. Overview of an underbite

Underbite, as known as Mandibular prognathism, is the condition that the lower jaw protrude excessively compared to the upper jaw, causing an imbalance in facial structure. This condition not only affects facial aesthetics but also results in many functional issues such as difficulties in eating, speaking, temporomandibular joint pain and affecting the patient's mental health negatively.

Restoring confident for 2000-born woman by performing underbite correction jaw surgery

II. Common causes

1.  Genetics

According to numerous science journals, as well as from our own data collected at Viet My Plastic Surgery Hospital. Genetics is the most common cause of underbite. If a close family member such as parent or grand parent possesses an underbite, the likelihood of that trait get passed down to the next generation is much higher. 

2. Environmental factor

Bad habits develop and maintain during childhood such as tongue-thrusting, finger sucking, or biting lip affect the growth process of the jaw and lead to developing condition of an underbite.

3. The uneven growth of the jaw bone

The lower jaw develops excessively or the upper jaw develops poorly, leading to the misalignment of the jaw structure.

III. Underbite treating surgery indication

Underbite treating surgery is indicated for cases with:

• Severe underbite that can’t be treated with simple orthodontic methods.
• Severe misalignment between the upper and lower jaws, greatly affects the chewing function and facial aesthetics.
• Patients who need an improvement in the appearance and life quality.

IV. The process of underbite correction surgery

Orthognathic Surgery is a complex process, requiring the close collaboration between the oral and maxillofacial surgeons, orthodontic surgeons and other relating experts. The procedure consists of the following steps:

1. Examination and treatment planning

• Clinical assessment: The doctor will examine the treating areas, taking X-Rays images of patient's skeleton, and collect jawbone samples to assess the condition of the jaw bone and bite joint.
• Analyze the face: The doctor will use advanced 3D simulation software to construct the expected post-surgery face, this step helps patients visualize the outcome and set realistic expectation. 
• Accurate planning: Based on the collected information about the patient’s jaw structure and personal desire. The doctor then carefully pick the appropriate treatments methods and planning them in order to reach the optimize results.

2. Take dental impressions before the surgery

Dental impressions are imprints of mouth internal parts. They storing information about the shape of the teeth, gums and oral structures. These information can be used to diagnose problem with the mouth and planning treatment accordingly.

• Determine the current bite: Examine and measure the misalignment between the upper and lower jaws.
• Accurate treatment planning: Using specialize imaging device to collect image that can be used by computer software to construct a 3D model of the jaw. Based on that 3D model, the doctor make a detailed treatment plan, including the positions of the bone portion that need to reposition. 
• Predict the post-surgical results: Stimulate the new bite and ensure the alignment between both jaws meet both the functional requirements and aesthetic desires.
• Support in the fabrication of orthodontic appliances (if needed): In the cases requiring orthodontics before or after the surgery, the 3D model can be used as input for manufacturer to provide custom appliances for the patient. 

3. Jaw (orthognathic) surgery

Jaw surgery changes your jaw bone structures by altering their shape, position or both. They can be used to treat condition such as temporomandibular joint disorders, malocclusion (under and over bite) and obstructive sleep apnea. 

3.1: BSSO – Bilateral Sagittal Split Osteotomy

Bilateral sagittal split osteotomy is a corrective jaw surgery that aim to reposition the lower jaw in order to treat certain conditions. During the procedures, the lower jaw will be separated from the upper jaw and the moving either upward or forward into the desired position. 

When is a Bilateral Sagittal Split Osteotomy needed?

The appropriate candidate for this procedure should match at least one of these criteria:

• The lower jaw develops excessively, protruding greatly compared to the upper jaw.
• Patients having underbite conditions, yet the upper jaw develops normally.

The procedure detailed

• Mandibular osteotomy: The surgeon will perform a vertical cut on both sides of the mandible, near the joint position. After that, the jawbone is pushed back to the planned position to achieved the ideal bite.
• Bone Fixation: The jaw bone after adjustment will be fixed using screws or titanium plates to ensure stability.

Advantages

• The incisions is made within the oral cavity. Therefore, it leaves no external scars.
• Fast execution time (approximately 2 to 3 hours).

3.2: Lefort I Osteotomy

Lefort Osteotomy is the common name for a group of methods used to treat facial deformities by reallocating bone in the upper jaw and mid face area. Among them Lefort I is the most common procedure used for treating jaw misalignment.

When is a Lefort I Osteotomy needed?.

The appropriate candidate for this procedure should match at least one of these criteria:

• The upper jaw develops poorly, recessed compared to the lower jaw.
• In cases where the upper jaw is unbalanced and misaligned, affecting the facial aesthetics and bite functions.

The procedure

• Maxillary osteotomy: The surgeon will perform a stretching cut across the upper jaw bone (Lefort I line), separating the jaw from the skull.
• Remove the upper jaw: The upper jaw is brought forward or adjusted as necessary to achieve the balance.
• Fixing the upper jaw: The bone is fixed using screws or fixation plates.

Advantages

• Significantly improve facial appearances and bite joint structure.
• Can be combined with adjusting the width of the upper jaw or changing the height of the face.

3.3: Double Jaw Surgery (bimaxillary osteotomy)

Double Jaw Surgery is performed when treating either half (lower, upper) jaws can not fully cured the conditions or help the client achieve their desired appearances. 

When is Double Jaw Surgery needed?

The appropriate candidate for this procedures often have symptom that need adjustment in both upper and lower jaw. 

• Both the upper and lower jaws are severely imbalanced, greatly affecting the facial aesthetics and bite functions.
• Complex cases of jaw misalignment combined with a asymmetric chin or other issues.

The procedure

• Lefort I Osteotomy: The upper jaw is brought forward or adjusted in the direction according to the plan.
• BSSO Osteotomy: The lower jaw is pushed backward, aligned with the upper jaw.
• Adjust in detail: Both of the jaws are adjusted in parallel to ensure harmony of the bite and face.
• Bone fixation: Use screws and fixation plates to fix both jaws after the surgery.

Advantages

• Comprehensive effectiveness, improving both the chewing function and facial aesthetics.
• Suitable with complex cases that performing either previous surgery method can treat.

3.4: Genioplasty surgery

Genioplasty is the type of surgery that restructure your chin by cut and reposition its bone. 

When is a genioplasty surgery needed?

Different from the previous methods, the appropriate candidate for this procedures do not need to have jaw issue: 

• An underbite caused by long or excessive protruded chin while the upper and lower jaw bones are still balanced.
• Genioplasty surgery can be done separately or combined with jaw correction surgery.

The procedure

• Cutting the chin bone: The surgeon will cut through the tip of the chin bone, then push it backwards or adjust it to the desired position.
• Chin bone fixation: The bone is fixed using screws or titanium fixation plates to ensure no displacement. 

Advantage

• Improve the facial contours in cases where the chin is the main cause of an underbite.
• The surgery is less invasive compared to jaw correction surgeries.

3.5: Combined jaw and facial contouring surgeries

In some cases, an underbite is accompanied with other deformities such as crooked face, crooked chin, or an imbalance of the entire face. In these cases, the doctor will make a comprehensive treatment plan, including:

• Adjusting both of the jaws.
• Combined with surgery that treat the cheekbone and chin areas as well as other facial features to achieve the optimal aesthetics results.

4. After the surgery and post-operative care:

The post operative care play a crucial roles in helping the patients achieve the optimized results. Patients must follow strictly the guideline provide by the doctor.

4.1: Post-operative diet

Because underbite correction surgery affects the ability to chew and bite joint function, having appropriate diet that match each recovery phases is required to help client having an efficient recovery period. 

First period: the first 1 to 2 weeks after the surgery

• Complete liquid form food: you should only eat liquid food such as soup, runny porridge, smoothie, milk, sour-free juices, which helps prevent pressure on the jawbone.
• Eat in small bites: Drink or eat using a small spoon to minimize jaw movements.

Second period: 2 to 4 weeks after the surgery

• Soft food: Gradually move on to eating soft food such as dense porridge, thin noodles, rice, or mashed potatoes.
• Avoid chewing hard: Do not eat hard food such as seeds, crunchy bread, or fried food.

Third period: After 4 weeks

• Practice to chew softly: You can start eating soft food like stewed meat, steamed fish or boiled vegetables, but remember to chew them thoroughly.
• Continue to avoid eating hard and chewy food: Avoid food that can put pressure on the jaw such as bubble gum, ribs, or dishes that require force to bite.

4.2: Rest and take care of the operative area

Rest properly

• Avoid strenuous activities: In at least the first 4 weeks, avoid sporty activities or strenuous exercising that can affect your face.
• Sleep in the right posture: Sleep with your head elevated (using a higher pillow than usual) to reduce swellings and improve blood circulation.
• Enough resting period: Sleep in 7 to 9 hours every night, avoid stress or overwork during the recovery period.

Jaw care and oral hygiene

• Clean gently: Use a soft-bristled toothbrush and mouthwash prescribed by the doctor to keep your mouth clean and prevent infection.
• Cold compressing in the first 48 hours: Help reduce swellings and pain. Then, you can move to warm compressing following the doctor’s instructions.
• Follow the prescribed medicines: Use pain relievers, anti-inflammatory drugs or antibiotics as prescribed by the doctor.

V. Advantages of underbite shaping surgery

1. Improve facial aesthetics: the surgery helps your face become more balanced, bring harmony into the facial structure and appearances.

2. Restore chewing function: Bite joint adjustment helps patients eat and chew more comfortably.

3. Enhance confidence and life quality: With the new appearance, patients become more confident in communications and their daily life.

VI. Some important notices

• Watch for abnormal signs: If you experience symptoms such as persistent pain, high fever, excessive bleeding or numbness that does not subside, contact the doctor immediately.
• Do not move your jaw spontaneously: Avoid activities such as yawning or biting hard in the beginning to avoid affecting the healing jawbone.
• Regular check-ups: Attend scheduled check-ups so that the doctor can monitor your recovery and provide new guidelines if necessary.

* The results achieved depend on each individual’s physiology.