Skeletal malocclusion is a misalignment of the jawbones that affects both appearance and oral function. Unlike dental malocclusion, which only involves the teeth, skeletal malocclusion is caused by a size or position discrepancy between the upper jaw (maxilla) and lower jaw (mandible). This bone disharmony is the root cause of an improper bite. The condition impacts the facial profile, how teeth meet, and can influence speech and chewing.
Underlying Causes of Skeletal Malocclusion
The primary driver behind skeletal malocclusion is genetics. Hereditary factors and the genetic blueprint determine the size, shape, and growth patterns of the jawbones. This means a predisposition for the condition is often passed down through families.
While genetics play the largest part, other factors can contribute to a skeletal discrepancy during childhood. Prolonged habits like thumb sucking, pacifier use beyond age three, or tongue thrusting can influence jaw growth and tooth alignment. Trauma to the face or jaw during formative years can also alter development, leading to an imbalance. These environmental influences often act on a pre-existing genetic tendency.
Developmental issues during fetal growth can also result in skeletal malocclusions. Disruptions in the formation of the craniofacial region can lead to improper development of the maxilla or mandible. These congenital issues may appear as an isolated anomaly or as part of a broader syndrome affecting multiple body systems. Such early distortions can establish a lifelong skeletal imbalance if unaddressed.
Classification of Skeletal Malocclusions
Orthodontists classify skeletal malocclusions into three main categories based on the relationship between the upper and lower jaws. Class I represents a correct front-to-back jaw relationship, but with other skeletal issues like a vertical mismatch, such as an open bite or deep bite. The dental bite may appear relatively normal, but an underlying jaw disharmony related to facial length is present.
Class II malocclusion is recognized as an “overbite,” where the lower jaw is underdeveloped and positioned too far back relative to the upper jaw. This results in a convex facial profile, with a recessed chin and lower jaw. The upper front teeth may seem to protrude significantly, not because of their angle, but because the lower jaw does not extend far enough forward to support them properly.
Conversely, Class III malocclusion is known as an “underbite.” This condition is characterized by an overdeveloped lower jaw that juts forward or an underdeveloped upper jaw that is set back. The result is a concave facial profile, where the lower teeth and chin are more prominent. The lower front teeth sit in front of the upper front teeth, creating a clear misalignment.
Treatment Approaches
Treatment for skeletal malocclusion varies based on the patient’s age. In growing children and adolescents, the focus is on growth modification, which uses orthodontic appliances to guide jaw growth into a more favorable alignment. The goal is to correct the skeletal imbalance during development before it becomes permanent.
For a Class II malocclusion, functional appliances like headgear apply gentle, persistent forces to stimulate growth in the mandible. For a Class III malocclusion, a reverse-pull face mask might be employed to pull the upper jaw forward, encouraging its growth to catch up with the lower jaw. This early intervention can reduce the need for more invasive procedures later in life.
In adults whose jaw growth is complete, correcting a skeletal malocclusion requires a combination of treatments. Orthodontic braces are used to straighten the teeth within each jaw. Since the bone structure cannot be altered with braces alone, corrective jaw surgery, or orthognathic surgery, is necessary to reposition the jaws.
Orthognathic surgery is performed by an oral and maxillofacial surgeon to move the upper jaw, lower jaw, or both into a correct alignment. The surgeon makes precise cuts in the jawbones, repositions them, and secures them with small plates and screws. This procedure corrects the foundational skeletal problem, improving the bite and facial balance. A final period of orthodontic treatment follows surgery to ensure the teeth fit together in their new positions.
Related Functional and Health Concerns
Untreated skeletal malocclusion can lead to functional and health problems. A common issue is difficulty with chewing, as misaligned jaws prevent teeth from meeting properly. This makes breaking down food inefficient and can also lead to uneven and excessive force on certain teeth, causing premature wear, chipping, or fractures over time.
Speech can be affected by the position of the jaws and teeth, as certain sounds are formed by the interaction of the tongue with the teeth and palate. A skeletal discrepancy makes it difficult to articulate words clearly, leading to speech impediments. The misalignment can also force the tongue into awkward positions, creating habits that are difficult to break even after correction.
The jaw joints are also susceptible to problems. A misaligned bite places strain on the temporomandibular joints (TMJ), which connect the jaw to the skull. This stress can lead to temporomandibular disorders (TMD), characterized by jaw pain, clicking sounds, headaches, and difficulty moving the mouth. Over time, this can result in chronic pain and joint damage.
Skeletal malocclusions can be linked to breathing difficulties like obstructive sleep apnea. A small or recessed lower jaw may cause the tongue to fall back and block the airway during sleep, leading to repeated pauses in breathing. This condition disrupts sleep and reduces oxygen levels, which has long-term health consequences. Correcting the jaw position can help open the airway and alleviate these problems.