Double Jaw Surgery for Severe Underbite Correction

Understanding Severe Underbite and Bimaxillary Anatomy

A severe underbite, known clinically as a skeletal Class III malocclusion, is a craniofacial discrepancy where the lower dental arch and jaw rest anterior to the upper jaw. While minor dental discrepancies can be managed with orthodontic tooth movement alone, severe presentations typically involve a structural skeletal disharmony. This presents as either maxillary hypoplasia (an underdeveloped or retruded upper jaw), mandibular prognathism (an overdeveloped or protruding lower jaw), or a combination of both. When both the maxilla and mandible contribute to the malocclusion, single-jaw repositioning is anatomically insufficient, necessitating bimaxillary orthognathic surgery, colloquially termed double jaw surgery for severe underbite correction.

The anatomical structures involved in double jaw surgery underbite correction are complex and closely integrated with vital neurovascular bundles and airway spaces. The upper jaw (maxilla) forms the floor of the nasal cavity and the anterior floor of the maxillary sinuses, while carrying the superior alveolar nerves and blood supply from the descending palatine and maxillary arteries. The lower jaw (mandible) houses the inferior alveolar nerve within the mandibular canal, which provides sensation to the lower lip, chin, and teeth. Furthermore, the position of both jaws dictates the volume of the retropalatal and retroglossal pharyngeal airway, meaning corrective osteotomies directly influence respiratory mechanics, masticatory function, and temporomandibular joint (TMJ) biomechanics.

Aetiology: Causes and Developmental Factors in Skeletal Class III

Skeletal Class III malocclusion arises from a multifaceted interplay of polygenic inheritance and environmental influences during craniofacial growth. Genetic predisposition plays a primary role; individuals with a family history of mandibular prognathism frequently exhibit similar growth patterns, as seen in historical familial lineages and contemporary genetic mapping. Disruption in the growth vectors of the spheno-occipital synchondrosis—the cartilaginous growth centre at the base of the skull—can restrict forward midfacial translation, leading to midface retrusion. Additionally, congenital anomalies, such as cleft lip and palate, often induce severe maxillary restriction secondary to early surgical scarring and intrinsic tissue deficiency.

Environmental and functional factors can exacerbate or mimic skeletal discrepancies during childhood development. Chronic upper airway obstruction, typically caused by hypertrophic adenoids, chronic allergic rhinitis, or deviated nasal septa, promotes habitual mouth breathing. This alters resting tongue posture, depressing the tongue against the floor of the mouth rather than the hard palate, depriving the maxilla of natural lateral and anterior expansive forces. Hormonal imbalances, such as excessive growth hormone secretion, and childhood habits can also modulate jaw development. In adult surgical candidates, systemic factors including bone mineral density, nutritional status, and lifestyle habits directly affect skeletal stability and bony consolidation post-osteotomy.

Clinical Presentation and Functional Consequences

Patients presenting with severe skeletal Class III malocclusion display distinct extraoral and intraoral characteristics. Extraorally, the facial profile is characteristically concave, with a prominent chin point (pogonion), flattened paranasal areas, deficient cheekbone projection, and an inverted lip relationship where the lower lip sits proud of the upper lip. Intraorally, the lower incisors bite in front of the upper incisors (anterior crossbite), often accompanied by posterior crossbites and severe dental compensations, where maxillary incisors naturally tip forward (proclination) and mandibular incisors tilt backward (retroclination) in an instinctive biological attempt to achieve contact.

The functional morbidity of an uncorrected severe underbite extends across multiple physiological domains. Masticatory efficiency is substantially compromised because normal shearing and grinding incisal contacts are absent, forcing patients to crush food using atypical vectors, which can lead to gastrointestinal strain and poor dietary variety. Speech articulation, particularly the pronunciation of sibilant ('s', 'z') and labiodental ('f', 'v') sounds, is frequently impaired. Furthermore, the abnormal biomechanical loading across the stomatognathic system places asymmetrical stress on the articular disc and condyles of the temporomandibular joints, predisposing patients to myofascial pain, internal disc derangement, and accelerated joint degeneration.

Diagnostic Workup, Cephalometrics, and Virtual Surgical Planning

The comprehensive evaluation for double jaw surgery underbite correction requires meticulous multidisciplinary assessment involving consultant oral and maxillofacial surgeons and specialist orthodontists. Clinical examination assesses facial symmetry, soft-tissue dynamics, incisor show at rest and upon smiling, and joint range of motion. High-resolution Cone-Beam Computed Tomography (CBCT) provides three-dimensional volumetric imaging of the maxillofacial skeleton, capturing airway dimensions, bone thickness, and the precise path of the mandibular canal relative to tooth roots. Digital dental models, obtained via intraoral optical scanners, allow precise assessment of occlusal intercuspation.

Computer-aided surgical simulation and Virtual Surgical Planning (VSP) represent the modern standard of care. Using dedicated orthognathic software, clinicians perform computerized cephalometric tracing (measuring angular and linear skeletal relationships such as SNA, SNB, and ANB angles) and simulate osteotomy cuts. The maxilla and mandible are digitally repositioned to optimise facial aesthetics, occlusal stability, and pharyngeal airway volume. Custom stereolithographic surgical splints or patient-specific surgical guides and pre-bent titanium plates are then fabricated using additive 3D printing, translating the virtual simulation into sub-millimetre operative precision in the surgical theatre.

Classification and Staging of Skeletal Discrepancies

Orthognathic classification builds upon Edward Angle’s dental classification but categorises discrepancies at the skeletal base level. Skeletal Class III is formally defined by a negative ANB angle, where the subnasale-to-nasion-to-supramentale relationship indicates that the apical base of the mandible lies anterior to that of the maxilla. Surgeons further subclassify the condition based on the primary site of deformity: pure maxillary hypoplasia with normal mandibular length (Type A), normal maxillary position with pure mandibular prognathism (Type B), or combined maxillary deficiency and mandibular excess (Type C). Vertical discrepancies, such as vertical maxillary excess or deficiency, and transverse discrepancies (maxillary constriction) often coexist.

Asymmetry staging is critical, as many Class III patients exhibit concurrent yaw, roll, or pitch rotational deformities of the jaw complex. Lateral chin deviation and asymmetrical occlusal planes (canted occlusal plane) require differential three-dimensional movements during double jaw surgery underbite correction. Staging also accounts for dental compensation severity; decompensation through presurgical orthodontics is required to move teeth into their ideal positions relative to their respective jawbones, intentionally worsening the visible underbite temporarily so that the true skeletal discrepancy can be fully corrected surgically.

Treatment Modalities: Orthodontic Camouflage versus Double Jaw Surgery

Management of an underbite depends on the patient's skeletal maturity and discrepancy severity. In growing children, interceptive dentofacial orthopaedics—such as reverse-pull face masks or bone-anchored maxillary protraction—can guide skeletal growth. In skeletally mature adolescents and adults with mild skeletal discrepancies, orthodontic camouflage may be considered. Camouflage involves extracting lower premolars and retracting lower anterior teeth while advancing upper incisors. However, in moderate-to-severe cases, camouflage compromises periodontal health by pushing roots outside the alveolar bone housing, leaves facial concavity unaddressed, and risks narrowing the posterior airway space.

For severe skeletal Class III discrepancies, bimaxillary (double) orthognathic surgery combined with comprehensive orthodontic treatment is the definitive, evidence-based gold standard. While single-jaw surgery (mandibular setback alone) was historically common, extensive isolated mandibular setbacks significantly reduce retroglossal airway volume, increasing the risk of secondary obstructive sleep apnoea. Double jaw surgery—advancing the maxilla to correct midface retrusion and modestly setting back or rotating the mandible—optimises facial balance, safeguards airway patency, and achieves superior long-term occlusal and skeletal stability compared to single-jaw movements.

Step-by-Step Surgical Procedure: Le Fort I and BSSO

Double jaw surgery for underbite correction is performed under general anaesthesia with nasotracheal intubation, ensuring unobstructed access to the oral cavity. The operation begins with the Le Fort I maxillary osteotomy. An incision is made in the maxillary vestibular mucosa above the tooth roots. Using precision reciprocating saws or piezoelectric instruments, horizontal bone cuts are made through the anterior and lateral maxillary sinus walls, the nasal septum, and the pterygomaxillary junction. The maxilla is gently down-fractured and mobilised, allowing the surgeon to advance, vertically reposition, or expand the upper jaw into its planned position using an intermediate 3D-printed surgical splint.

The repositioned maxilla is rigidly secured to the stable infrazygomatic crests and piriform rims using low-profile, biocompatible titanium miniplates and monocortical screws. Attention is then directed to the lower jaw for the Bilateral Sagittal Split Osteotomy (BSSO). Mucosal incisions are placed along the external oblique ridge of the mandible. The surgeon carefully exposes the medial and lateral cortices of the mandibular ramus, identifying and preserving the inferior alveolar neurovascular bundle as it enters the mandibular foramen.

Controlled horizontal, vertical, and sagittal bone cuts are made through the ramus and body of the mandible. The bone is split into a proximal segment (bearing the condyle and TMJ articulation) and a distal segment (bearing the dentition). The distal segment is repositioned to interlock with the newly positioned maxilla using the final occlusal splint. The proximal condylar segment is seated passively within the glenoid fossa to maintain joint health, and the overlapping bony segments are rigidly fixed using bicortical positional screws or miniplates. Incisions are thoroughly irrigated and closed with resorbable sutures.

Postoperative Recovery, Healing Timeline, and Dietary Progression

Hospital stay following double jaw surgery underbite correction typically ranges from one to three days. Modern rigid internal fixation with titanium hardware eliminates the historical need to wire the jaws completely shut (intermaxillary fixation). Instead, light guiding elastics (rubber bands) are applied to orthodontic brackets to guide the bite into the new occlusion while allowing limited movement. Facial swelling and soft-tissue bruising peak around 48 to 72 hours post-surgery before progressively subsiding over three to four weeks. Sleeping with the head elevated at a 45-degree angle significantly assists lymphatic drainage and reduces oedema.

Dietary rehabilitation follows strict stages to safeguard bone union. For the first two to three weeks, patients must adhere strictly to a non-chew, high-calorie liquid and smooth pureed diet (such as blended soups, smooth yoghurts, and nutritional supplements). From weeks four to six, light fork-mashable foods (such as soft dal, thoroughly cooked khichdi, scrambled eggs, and well-steamed vegetables) are introduced. Active chewing of firm or resistant foods is strictly prohibited until osteotomy union is confirmed clinically and radiographically, typically around eight to twelve weeks post-surgery. Post-surgical orthodontic refinement generally resumes four to six weeks postoperatively to fine-tune the intercuspation.

Potential Complications, Neurosensory Changes, and Management

As with all major surgical interventions, bimaxillary osteotomy carries known risks that require clinical vigilance and informed management. Neurosensory alteration is the most frequent sequela. Traction or manipulation of the inferior alveolar and mental nerves during BSSO routinely causes temporary paraesthesia (numbness, tingling, or altered sensation) of the lower lip and chin. While neurosensory recovery is progressive over 6 to 18 months, a minor percentage of patients may experience permanent, localized sensory deficits. The infraorbital nerve may similarly experience transient neuropraxia, leading to temporary midfacial numbness.

Other potential complications include postoperative haemorrhage, surgical site infection, non-union or delayed union of the osteotomy segments, hardware loosening, and skeletal relapse. Skeletal relapse—the tendency of the jaws to migrate toward their original position—is minimised through rigid internal fixation, meticulous condylar seating during surgery, and careful postsurgical orthodontic control. In regions where use of smokeless tobacco, gutka, paan, or smoking is prevalent, strict preoperative and postoperative cessation is mandatory, as nicotine and toxic alkaloids severely impair microvascular perfusion, dramatically increasing the risk of wound dehiscence, hardware infection, and non-union.

Emergency Red Flags and When to Seek Urgent Clinical Care

While routine postoperative symptoms like swelling, mild oozing, and moderate discomfort are expected, patients and carers must recognise critical warning signs requiring immediate emergency medical evaluation. Acute airway compromise is the most critical emergency. Any sudden difficulty breathing, progressive stridor (high-pitched breathing sounds), inability to swallow oral secretions, or severe swelling elevating the floor of the mouth requires immediate attendance at an emergency department or direct contact with the surgical team.

Additional red flags include brisk, bright red oral or nasal haemorrhage that does not stop with gentle pressure, sudden shifting of the dental occlusion where teeth no longer meet the splint, severe refractory pain unalleviated by prescribed analgesia, and spiking fever above 38.5°C accompanied by foul-tasting discharge from intraoral suture lines. Furthermore, new-onset visual disturbances, persistent uncontrolled vomiting that risks aspiration, or severe unilateral calf pain and chest pain (signs of thromboembolism) warrant urgent, immediate hospital assessment.

Evidence and further reading

The contemporary protocols governing double jaw surgery underbite correction are rooted in extensive clinical literature and international guidelines published by bodies including the British Association of Oral and Maxillofacial Surgeons (BAOMS), the International Journal of Oral and Maxillofacial Surgery, and the American Journal of Orthodontics and Dentofacial Orthopedics. Systematic reviews consistently demonstrate that bimaxillary surgery for severe skeletal Class III malocclusion yields superior stability, more favourable soft-tissue aesthetics, and lower risk of postoperative airway compromise compared to large isolated mandibular setback procedures.

Long-term stability studies corroborate that rigid internal fixation with titanium plates and screws provides predictable skeletal retention, with skeletal relapse rates under 10% in non-syndromic populations when presurgical orthodontic decompensation is properly executed. Furthermore, patient-reported outcome measures (PROMs) documented across maxillofacial research demonstrate statistically significant and durable improvements in oral health-related quality of life, masticatory capacity, and psychological well-being following successful bimaxillary correction of severe underbite.