Mandibular asymmetry refers to a condition where the lower jaw (mandible) exhibits differences in size, shape, or position between the left and right sides of the face. While slight facial asymmetry is normal, significant disproportion is a common dentofacial deformity that affects a person’s appearance and the proper functioning of the mouth. Corrective surgery is the primary treatment to restore symmetry, improve functional mechanics, and achieve facial harmony. This process involves multiple stages of preparation, a precise surgical technique, and a dedicated recovery period.
Defining Mandibular Asymmetry and Diagnosis
Mandibular asymmetry is characterized by differences in the mandible’s size and volume, leading to a noticeable deviation of the chin and lower facial third. Causes include developmental issues, such as hemimandibular elongation or hyperplasia involving excessive growth on one side. Acquired conditions like trauma, tumors, condylar resorption, or functional problems like uncorrected bite interference can also contribute. This imbalance often causes functional issues, most notably malocclusion, where the upper and lower teeth do not align correctly, and may contribute to temporomandibular joint (TMJ) discomfort.
The diagnostic process begins with a thorough clinical examination to assess the alignment of the dental midlines and the degree of chin deviation relative to the facial midline. A full understanding of the skeletal discrepancy requires advanced imaging. Cone Beam Computed Tomography (CBCT) is the preferred radiographic technique because it provides a three-dimensional view of the bony structures, allowing for precise measurement of the asymmetry.
Two-dimensional imaging, such as orthopantomography, may be used as an initial screening tool, especially in younger patients due to lower radiation exposure. The data gathered from these scans and the clinical assessment determine if the skeletal structure is the primary cause of the asymmetry. This information is then used to plan the necessary surgical movements to bring the lower jaw back into symmetry with the facial skeleton.
Pre-Surgical Planning and Preparation
The preparatory phase requires close collaboration between the oral surgeon and the orthodontist. Most patients undergo pre-surgical orthodontic treatment, often lasting between 12 and 18 months, before the operation is scheduled. This initial phase, called dental decompensation, involves moving the teeth into positions they would naturally occupy over a correctly aligned jawbone.
Teeth may have shifted over time to compensate for the underlying skeletal asymmetry, creating an unstable bite. Pre-surgical orthodontics removes this dental camouflage, which temporarily worsens the skeletal problem’s appearance. This step is necessary to ensure the teeth will fit together perfectly once the jawbones are surgically repositioned. Once the teeth are aligned on their respective arches, the surgical planning phase begins.
Advanced planning is accomplished using Virtual Surgical Planning (VSP), which utilizes the patient’s CBCT scans to create a precise 3D computer model of the jaw and face. The surgical team digitally performs the bone cuts and moves the mandibular segments into the ideal, symmetrical position. This virtual rehearsal allows for precise measurement of the required movements and helps predict the final aesthetic and functional outcomes. The VSP process culminates in the creation of custom surgical guides and splints, which are physical molds used during surgery to ensure the jaw segments are fixed exactly as planned.
The Surgical Procedure
The correction of mandibular asymmetry is performed under general anesthesia in a hospital setting, typically using a Bilateral Sagittal Split Osteotomy (BSSO). This procedure accesses the lower jawbone through incisions made entirely inside the mouth, avoiding external facial scars. The surgeon first makes an incision along the gum line of the lower jaw to expose the bone.
The BSSO technique involves making controlled bone cuts (osteotomies) on both sides of the mandible, specifically in the ramus area. These cuts split the mandible into two segments on each side: a proximal segment attached to the jaw joint and a distal segment containing the teeth. The bone segments are then moved to the new position determined by the VSP plan, correcting the deviation and size discrepancies.
In cases of significant asymmetry, the jaw may be rotated or moved forward on one side and backward on the other to align the lower jaw with the upper jaw and the facial midline. Once the jaw is in its corrected position, the segments are stabilized using small, biocompatible metal plates and screws, which provide rigid fixation. If bone interference prevents a passive fit, additional bone removal may be required to avoid stressing the joint before the internal incisions are closed with dissolvable sutures.
Recovery and Long-Term Functional Outcomes
The immediate post-operative period involves a hospital stay, typically for one to two days, where pain and swelling are carefully managed. Patients should expect significant facial swelling, which usually peaks within 48 to 72 hours following the procedure. Keeping the head elevated, even while sleeping, and using cold compresses helps minimize this initial inflammation.
Discomfort is managed with prescribed medication and generally subsides substantially within the first week. A soft or liquid diet is required for approximately four to six weeks to prevent pressure on the healing bone segments while they fuse together. While initial swelling reduces rapidly, residual swelling can take three to six months to fully resolve, revealing the final contour of the corrected jaw.
A common temporary side effect is numbness or tingling in the lower lip and chin, caused by the manipulation of the nerves that run through the mandible. Sensation typically returns gradually over three to six months, though a small percentage of patients may experience a degree of permanent sensory change. The long-term functional outcomes focus on achieving a stable and proper bite (occlusion), which improves chewing and speaking efficiency and contributes to the patient’s quality of life. Most patients return to desk-based work within the fourth week, with full return to normal activity requiring several months.