Open Bite Causes, Chewing Difficulties, and Treatment Options

Understanding Open Bite and Craniofacial Anatomy

An open bite is a form of malocclusion where a distinct gap persists between the opposing maxillary (upper) and mandibular (lower) teeth when the jaw is fully closed in centric occlusion. In a healthy physiological bite, the upper incisors overlap the lower front teeth vertically by approximately two to three millimetres, a relationship termed overbite. When an anterior open bite develops, the incisors and canines fail to make contact, shifting the entire functional chewing load onto the posterior molars and premolars. This malocclusion fundamentally alters dental biomechanics, masticatory muscle efficiency, and the structural balance of the craniofacial skeleton.

Anterior open bite is clinically distinguished from posterior open bite, in which the back teeth do not touch while the incisors meet. Craniofacial anatomy plays a defining role in how these anomalies manifest. Clinicians differentiate between a purely dental open bite—where the alveolar bone and basal jaw bases are normally positioned but the teeth have under-erupted or tilted—and a skeletal open bite. A skeletal open bite involves divergent jaw bases, characterised by a steep mandibular plane angle, an increased lower anterior facial height, and a clockwise rotation of the mandible relative to the cranial base.

Aetiology: Primary Causes and Contributing Risk Factors

The development of an anterior open bite is multifactorial, arising from an interplay between genetic predispositions and environmental influences. Non-nutritive sucking habits during early childhood, such as prolonged thumb or dummy sucking beyond the age of three, exert mechanical forces that restrict the vertical eruption of incisors while allowing posterior teeth to over-erupt. Similarly, atypical swallowing patterns—commonly referred to as a tongue thrust—and chronic tongue-resting postures between the dental arches create continuous, low-magnitude forces sufficient to maintain an anterior space and disrupt normal occlusal development.

Upper airway obstruction represents another significant aetiological driver. Chronic mouth breathing resulting from enlarged adenoids, hypertrophic tonsils, severe allergic rhinitis, or nasal septal deviation forces the mandible to posturally drop and the tongue to depress to maintain an open pharyngeal airway. This continuous postural alteration stimulates excess posterior alveolar growth, rotating the mandible downward and backward. In adults, sudden or progressive open bite causes may include temporomandibular joint (TMJ) pathology, specifically degenerative joint disease, idiopathic condylar resorption, or rheumatoid arthritis, which leads to loss of condylar height.

Clinical Presentation and Functional Impairments

The clinical presentation of an anterior open bite extends beyond visible cosmetic misalignment. One of the most debilitating functional consequences involves severe chewing difficulties. Because the anterior dentition cannot achieve incisal contact, patients cannot shear, incise, or bite into basic foods like sandwiches, apples, or fibrous vegetables. Instead, individuals are forced to tear food using their canine or premolar teeth, or place oversized food boluses directly onto the molars, leading to inefficient mastication and subsequent digestive discomfort.

Speech articulation is frequently compromised. The persistent gap between the incisors allows air to escape abnormally during phonation, commonly producing a sigmatism or lisp when pronouncing sibilant consonants such as 's', 'z', 'sh', and 'ch'. Furthermore, patients frequently exhibit lip incompetence, where the upper and lower lips cannot close passively at rest without straining the mentalis (chin) muscle. This chronic mouth posture promotes oral dryness, increasing the long-term risk of dental caries and gingival inflammation, while uneven occlusal loading can trigger muscular strain and temporomandibular disorders.

Diagnostic Evaluation, Imaging, and Differential Diagnosis

Accurate diagnosis of an open bite requires a rigorous clinical examination combined with specialised dental imaging. The orthodontist begins with an extraoral assessment to evaluate facial proportions, lip competence at rest, and the presence of excess gingival display. Intraorally, the clinician measures the exact negative vertical overlap in millimetres, assesses transverse arch width, checks for dental wear facets, and examines tongue posture during static rest and dynamic swallowing. Digital impressions or plaster models are captured to construct three-dimensional occlusal maps.

Radiographic assessment is essential to establish an accurate differential diagnosis between dental and skeletal discrepancies. A lateral cephalometric radiograph is analysed to measure angular and linear relationships, such as the sella-nasion to mandibular plane angle and the ratio of posterior to anterior facial height. In cases where progressive open bite, facial asymmetry, or joint discomfort is reported, cone-beam computed tomography (CBCT) or magnetic resonance imaging (MRI) of the temporomandibular joints is performed to rule out active condylar resorption, osteoarthritis, or internal disc derangement.

Classification and Staging of Open Bite Malocclusion

Classification systems categorise open bites based on location, underlying skeletal morphology, and severity of vertical separation. By location, cases are split into anterior (affecting incisors and canines), posterior (affecting premolars and molars), or complete open bite, where only the most distal molars make occlusal contact. Morphologically, they are classified as dentoalveolar, where the skeletal jaw bases are within normal limits, or skeletal, defined by hyperdivergent facial growth, short mandibular rami, and increased lower facial height.

Severity staging is determined by the maximum vertical dimension of the interincisal gap measured at the central incisors. A mild anterior open bite exhibits a vertical separation of less than two millimetres. A moderate open bite presents with a gap measuring between two and four millimetres, typically extending laterally to the canines. A severe open bite exceeds four millimetres of vertical separation, often extending bilaterally into the premolar region, leaving the patient with only one or two points of posterior occlusal contact.

Evidence-Based Anterior Open Bite Treatment Modalities

The selection of an anterior open bite treatment depends fundamentally on the patient's biological age and whether the malocclusion is dentoalveolar or skeletal. In growing children, interceptive orthodontics yields favourable results. Interventions include habit-breaking appliances (such as palatal cribs or spurs) combined with myofunctional therapy to retrain resting tongue posture. If airway obstruction is identified, early referral to an ear, nose, and throat (ENT) specialist for adenotonsillectomy can restore nasal breathing and normalise vertical facial growth.

In non-growing adolescents and adults with mild to moderate dental open bites, orthodontic camouflage is common. Modern protocols frequently employ clear aligners or fixed braces combined with temporary anchorage devices (TADs), which are micro-screws placed in the alveolar bone. TADs enable predictable intrusion of over-erupted maxillary and mandibular molars, which allows the mandible to autorotate upward and forward, closing the anterior gap without causing undesirable extrusion of the incisors.

For severe skeletal open bites in adults, orthognathic surgery combined with comprehensive orthodontics remains the gold standard. This typically involves a Le Fort I maxillary osteotomy to superiorly reposition (impact) the posterior maxilla, sometimes combined with a bilateral sagittal split osteotomy (BSSO) of the mandible. Maxillary impaction allows the lower jaw to swing upward into an optimal functional relationship, restoring facial balance, incisal overlap, and functional masticatory mechanics.

Clinical Pathways: What to Expect During Treatment

Undergoing orthodontic or surgical correction follows a structured clinical pathway. The process begins with comprehensive records: high-resolution photographic imaging, digital intraoral scanning, and cephalometric radiographs. During the active orthodontic phase, fixed bracket systems or sequential clear aligners are fitted. If micro-screws (TADs) are required for molar intrusion, they are inserted using a small amount of local anaesthetic in a brief, minimally invasive procedure. Patients attend regular review appointments every six to eight weeks for appliance adjustment and tracking.

For patients undergoing combined orthodontic and orthognathic surgical care, the initial orthodontic phase aligns the dental arches independently over twelve to eighteen months, which may temporarily make the open bite appear larger. The surgical phase takes place under general anaesthesia in a hospital setting, where the bony segments are repositioned and rigidly fixed with biocompatible titanium plates and screws. A brief hospital stay of one to two nights is standard, followed by a final phase of finishing orthodontics to settle the intercuspation.

Post-Treatment Recovery, Retention, and Managing Relapse Risk

Recovery timelines depend on whether the intervention was non-surgical or surgical. Non-surgical orthodontic movement typically involves mild dental tenderness for two to four days after adjustments, manageable with simple analgesics. Following orthognathic surgery, initial soft-tissue recovery takes two to four weeks, during which a strictly modified liquid-to-soft diet is essential to protect healing bone osteotomies. Mild facial swelling, temporary numbness in the lower lip or palate, and nasal congestion are normal post-operative sequelae.

Long-term stability is one of the most critical challenges in anterior open bite treatment due to high biological relapse rates. Retention protocols must be rigorous and lifelong. Standard practice involves a combination of bonded fixed retainers behind the anterior teeth and rigid vacuum-formed retainers worn overnight. Because persistent or recurrent tongue thrusting can re-open the bite, concurrent speech and myofunctional therapy is often prescribed to establish a stable swallowing pattern and habitual palate-resting tongue position.

Complications, Long-Term Maintenance, and Oral Health Risks

Without appropriate intervention, a persistent anterior open bite leads to significant long-term oral complications. Excessive, non-physiological chewing forces on posterior molars accelerate occlusal tooth wear, enamel micro-fractures, and abfraction lesions. The periodontium around these heavily loaded teeth may experience heightened bone loss if plaque control is compromised. Conversely, attempting excessive orthodontic extrusion of front teeth to close a large gap increases the risk of external apical root resorption and compromised periodontal support.

Surgical interventions carry specific potential complications, including temporary or permanent neurosensory alterations to the inferior alveolar or infraorbital nerves, infection at osteotomy sites, or post-surgical relapse if underlying condylar disease was undetected. Long-term oral health maintenance requires immaculate plaque control, regular professional scale and polish appointments, consistent nighttime retainer wear, and routine follow-up examinations to identify and treat early signs of vertical relapse or joint dysfunction.

Red Flag Symptoms and When to Seek Urgent Clinical Assessment

Patients must be aware of specific warning signs that necessitate prompt specialist assessment. The sudden development of an open bite in an adult who previously possessed a normal occlusion is a primary red flag. This presentation frequently signals acute pathology within the temporomandibular joints, such as rapidly progressing idiopathic condylar resorption, severe osteoarthritis, or inflammatory joint effusion, and demands urgent specialist rheumatological and maxillofacial investigation.

Other red flags include intractable, unilateral joint pain accompanied by significant restricted jaw opening (trismus), clicking that progresses to closed lock, or rapid facial asymmetry. Following orthognathic surgery, immediate medical attention is required if a patient experiences active haemorrhage from the nose or mouth, high-grade fever, worsening asymmetric swelling, sudden inability to bring teeth together according to the surgical splint, or severe persistent neurosensory loss.

Evidence and further reading

The contemporary management of anterior open bite is guided by extensive peer-reviewed orthodontic and maxillofacial research. Systematic reviews published by the Cochrane Collaboration and guidelines from the British Orthodontic Society highlight that early habit-interception therapies in the primary and mixed dentition significantly reduce the need for complex surgical interventions later in life. Literature in the American Journal of Orthodontics and Dentofacial Orthopedics establishes that molar intrusion via temporary anchorage devices provides a reliable, minimally invasive alternative to surgery for moderate dentoalveolar discrepancies.

For severe skeletal disharmonies, clinical trials and longitudinal cohort studies in the International Journal of Oral and Maxillofacial Surgery confirm that two-jaw orthognathic surgery delivers the highest predictability and aesthetic outcome, provided tongue posture and respiratory function are simultaneously managed. Long-term stability data emphasise that passive retention alone is often insufficient without neuromuscular and respiratory rehabilitation. Further detailed guidance on malocclusion classification and treatment protocols can be accessed through the British Orthodontic Society, the American Association of Orthodontists, and clinical guidelines published by the National Institute for Health and Care Excellence (NICE).