The term Class 3 occlusion describes a specific type of malocclusion, or imperfect bite alignment, where the lower jaw is positioned too far forward relative to the upper jaw. This condition is commonly known as an underbite. When the jaws are closed, the lower teeth overlap the upper teeth, a relationship known as a reverse overjet.
Anatomy and Definition of Class 3 Occlusion
Occlusion classifications are determined by the relationship of the first permanent molars. In a Class 3 malocclusion, the lower first molar is positioned too far forward compared to the upper first molar. This forward position of the lower arch defines the classification. The misalignment can stem from two underlying causes: dental or skeletal.
A dental Class 3 malocclusion occurs when the teeth are misaligned, but the jaw bones are normally positioned. The lower teeth are simply too far forward relative to the upper teeth. Conversely, a skeletal Class 3 malocclusion involves a discrepancy in the size or position of the jaw bones. This skeletal issue results from an overgrowth of the lower jaw (mandibular prognathism), an undergrowth of the upper jaw (maxillary deficiency), or a combination of both.
Diagnosis also considers the relationship of the incisors, where the lower front teeth are positioned in front of the upper front teeth. This condition can range in severity from an edge-to-edge relationship to a reversed overjet. In some instances, a patient may exhibit a “pseudo-Class 3” where premature contact during biting causes the lower jaw to shift forward. Identifying whether the cause is dental, skeletal, or postural is part of the diagnostic process.
Factors Contributing to Development
The underlying cause of most Class 3 occlusions is a genetic predisposition that influences jaw growth patterns. A family history of a prominent lower jaw or other skeletal anomalies increases susceptibility to the condition. This hereditary component dictates the size and position of the maxilla and mandible, making the skeletal relationship the primary factor in the development of most Class 3 cases.
While genetics play the primary role, environmental factors can also contribute, especially in skeletal cases. Childhood habits, such as prolonged thumb-sucking or pacifier use, can affect tooth alignment and jaw development. Dental factors, like improper tooth placement or early tooth loss, can also lead to misalignment, particularly in the milder, dental-only forms of Class 3.
Impact on Oral Function and Aesthetics
A Class 3 occlusion has functional and aesthetic consequences. Functionally, the misalignment of the teeth and jaws can impair mastication, leading to reduced chewing efficiency and difficulty biting into certain foods. The improper bite can also place abnormal stress on the temporomandibular joint (TMJ), which may result in jaw pain, discomfort, or chronic headaches.
Speech can also be affected, as proper tooth positioning is necessary for the articulation of certain sounds. Patients may experience speech impediments or distortions, particularly with sibilant sounds like ‘s’ and ‘z’. Beyond these functional issues, the characteristic facial profile associated with a severe Class 3 occlusion is often a primary concern. This profile is concave, featuring a prominent lower jaw and chin.
Corrective Treatment Options
The treatment strategy for Class 3 occlusion depends on the patient’s age and whether the malocclusion is primarily dental or skeletal. For growing patients, the goal is to modify jaw growth through interceptive orthodontics. This approach, often called Phase I treatment, is effective when initiated early, typically between ages six and ten, before skeletal growth is complete.
Early treatment often utilizes appliances like a reverse-pull headgear, or facemask, which applies forward pressure to the upper jaw. This encourages the maxilla to grow forward while attempting to restrict or redirect the growth of the lower jaw. Functional appliances, such as the Reverse Twin Block, can also be used to posture the mandible backward and induce changes in the skeletal relationship.
For adolescents and adults where skeletal growth is finished, treatment options are more limited and often more invasive. Mild to moderate dental Class 3 issues can be corrected through orthodontic camouflage, which uses braces or clear aligners to move the teeth into a better biting position. This process involves tilting the upper front teeth forward and the lower front teeth backward to compensate for the jaw discrepancy.
If the skeletal discrepancy is severe, orthognathic surgery, or jaw surgery, is usually required to achieve a stable and functional result. This procedure involves surgically repositioning the upper and/or lower jaw bones to correct the underlying skeletal misalignment. Surgical correction is typically performed after growth has ceased (around age 16 for females and 18 for males) and is almost always combined with comprehensive orthodontic treatment.