An underbite, formally known as Class III malocclusion, is a condition where the lower jaw (mandible) protrudes past the upper jaw (maxilla). This skeletal pattern results in the lower teeth resting in front of the upper teeth when the mouth is closed.
Obstructive sleep apnea (OSA) is a serious sleep disorder characterized by repeated episodes of partial or complete collapse of the upper airway during sleep. These collapses reduce or stop airflow, causing a drop in blood oxygen levels and fragmented sleep. The severity of OSA is measured by the Apnea-Hypopnea Index (AHI), which records the average number of breathing disruptions per hour. The relationship between the two conditions stems from the fact that the bony structure of the face and jaw directly supports the soft tissues of the throat.
The Anatomical Connection Between Jaw Structure and Airflow
While a receding lower jaw is the more common anatomical risk factor for OSA, an underbite significantly alters the craniofacial complex and affects airway dimensions. A skeletal Class III relationship is often associated with underdevelopment of the upper jaw, known as maxillary retrusion. This positioning can shorten the length and depth of the nasopharynx, the upper part of the airway behind the nose.
This structure means the soft palate and tongue base may have less bony support, narrowing the space for air. Furthermore, some underbite profiles are linked to a vertical growth pattern, often called a high-angle pattern. This vertical discrepancy can result in a smaller total upper airway volume, making the throat more susceptible to collapse when muscles relax during sleep.
Surgical correction of an underbite highlights the airway risk. The most common procedure, mandibular setback surgery, moves the lower jaw backward to align the bite. This backward movement is a known risk factor for narrowing the Posterior Airway Space (PAS). Narrowing the PAS can induce or worsen existing OSA symptoms by crowding the tongue and soft tissues into the throat. Therefore, the craniofacial structure must be carefully evaluated pre-treatment to ensure the airway is not compromised by the bite correction.
Identifying Sleep Apnea in Patients with Underbites
The diagnostic process involves a combined assessment of the bite, the facial skeleton, and sleep-time breathing patterns. An initial clinical evaluation includes a physical examination of the patient’s tonsils, tongue size, and the relationship between the jaws. This helps identify anatomical features that may contribute to airway restriction.
Imaging Techniques
Detailed imaging is used to measure the available airway space. Lateral cephalometric X-rays and Cone-Beam Computed Tomography (CBCT) scans analyze the skeletal components. These techniques allow clinicians to measure the Posterior Airway Space (PAS) and the Superior Pharyngeal Airway Space (SPAS) to quantify the throat volume. Specific measurements, such as the ANB angle (sagittal jaw relationship) and the SN-GoMe angle (vertical facial pattern), help classify the severity of the skeletal discrepancy.
Polysomnography (PSG)
Imaging alone cannot confirm sleep apnea, as it only shows the anatomical structure while the patient is awake. A formal sleep study, or polysomnography (PSG), remains the definitive test to confirm the diagnosis and determine severity. The PSG monitors brain activity, oxygen levels, heart rate, and breathing effort. This data is used to accurately calculate the AHI and confirm if the anatomical obstruction is functionally causing sleep apnea.
Corrective Treatments for Jaw-Related Airway Obstruction
Treating OSA in the presence of an underbite requires correcting the skeletal discrepancy while simultaneously ensuring the airway is enlarged or maintained.
Pediatric Orthopedic Management
For growing children with an underbite caused by a deficient maxilla, specialized orthodontic and orthopedic management is often the first step. Treatment uses a reverse-pull headgear or a face mask, often combined with Rapid Maxillary Expansion (RME), to advance the upper jaw. This forward movement widens the nasal cavity and the nasopharyngeal airway, leading to a significant increase in the volume of the breathing passage.
Surgical Intervention (Adults)
In adult patients with a severe skeletal underbite and confirmed OSA, the definitive treatment is orthognathic surgery. This surgery corrects the bite by moving the maxilla forward and the mandible backward, but it must be meticulously planned to protect the airway. To actively treat the sleep apnea, the surgical plan often incorporates a Maxillomandibular Advancement (MMA) component. The entire jaw complex is advanced slightly forward to pull the soft tissues and tongue base with it, significantly increasing the airway volume.
Mandibular Advancement Devices (MADs)
MADs are a common non-surgical treatment for mild to moderate OSA, working by holding the lower jaw forward during sleep to prevent airway collapse. However, for patients with a pre-existing underbite (Class III malocclusion), a traditional MAD is generally complex or contraindicated. The device functions by advancing the jaw, which can worsen the forward position of the lower teeth relative to the upper teeth, potentially aggravating the dental alignment. In these cases, the focus shifts to surgically correcting the underlying skeletal issue or using other non-MAD therapies.