What is Retrognathia?

Surgeons who work on the head and neck, including ear, nose, and throat surgeons and oral surgeons, as well as dentists and orthodontists, often talk about the positions of the upper and lower jaw in three different ways. The first is from front to back, which is usually called the anterior-posterior plane. This is what you would see if you were to look at someone’s profile, or from the side. The second view is from across, which you can see in a face-forward view. The third one is vertical, which is best understood when looking at a person’s face from the side.

Retrognathia is a term that describes an abnormal position of the lower jaw. ‘Retro’ means that there is not enough growth and ‘gnathia’ refers to the jaws, specifically the lower jaw. When doctors describe someone as having retrognathia, they mean that the person’s lower jaw hasn’t grown enough in the front-to-back direction. This means that, when viewed from the side, the lower jaw is further back than it should be. There can also be deficiencies in vertical or crosswise growth, but these are usually less important unless planning for surgery. To sum up, when someone is said to have retrognathia, it means that their lower jaw hasn’t grown enough, especially in the front-to-back direction.

So why does being diagnosed with retrognathia matter? Firstly, it helps rule out associated conditions which could have wider health impacts. It also allows for appropriate referrals to orthodontics, with the potential need for surgery. Healthcare professionals who manage an airway need to be aware of it. Lastly, it’s important to understand that it can affect conditions like obstructive sleep apnea.

What Causes Retrognathia?

The mandible, or the lower jaw, forms near a structure known as Meckel’s cartilage, but it doesn’t actually stem from it. The mandible starts off as a dense mass of tissue, which eventually forms a bone by a process known as intramembranous bone formation. This means it forms directly from the tissue, rather than going through a cartilage stage first. By the time a baby is six weeks old in the womb, this process of bone formation begins.

The part of the mandible that joins with the skull at the temporomandibular joint, called the condyle, forms separately. This part undergoes endochondral ossification, which means it forms from cartilage and then turns into bone. This starts to happen around the tenth week of development inside the womb.

The mandible doesn’t just grow in one direction – it grows downwards and forwards. The bone in the front part gets slowly absorbed while more bone is added to the back part. Along with growth at the condyle, this helps the mandible grow in a downward and forward direction.

As children grow, doctors use charts to track their development, including height, weight, and growth rate. However, it’s important to remember that there can be a lot of variation between different children. Girls usually stop growing taller around the age of 17 or 18, while boys typically stop growing in their early twenties. For children with a mandible that’s too small or not formed properly, this growth process can finish much sooner.

Why is all this important? It’s really crucial in understanding when to do surgery to address a condition called retrognathia, where the lower jaw is set further back than the upper jaw. The timing of growth and development factors into deciding the best time for surgery on a case-by-case basis.

Risk Factors and Frequency for Retrognathia

There hasn’t been much large-scale research done on retrognathia, which refers to having a jaw that is set back further than normal. The small amount of research that has been done typically involves looking at specific, isolated groups of people. Generally, these studies look at retrognathia as it appears as a part of a craniofacial syndrome, which is a condition that affects the bones in the head and face.

Signs and Symptoms of Retrognathia

When examining a patient’s mouth, one of the first things doctors usually do is assess how the teeth align with each other. This method of rating teeth alignment was first created by Dr. Edward Angle, often considered the father of orthodontics. The system is based on how the first set of molars and the canines relate to each other. In Class 1 occlusion, the upper (maxillary) and lower (mandibular) teeth have a proper relationship. If the lower teeth are set back compared to the upper teeth, it is referred to as Class 2, which often suggests that the patient has a condition called “retrognathia”. Class 3 is when the lower teeth are more advanced than they should be, similar to a bulldog’s jaw structure.

Retrognathia is often associated with Class 2 occlusion, however, it’s worth noting that the teeth can hide this condition. This is because the body often compensates for skeletal discrepancies in the dental alignment. A quick examination can often reveal whether a patient is retrognathic. If their facial profile is excessively convex when viewed from the side, it may indicate retrognathia. For adults, as part of a standard airway check, the distance from the thyroid to the chin can also suggest a difficult airway and indicate retrognathia. This distance is typically less than the width of three fingers or around 7mm in people with underdeveloped lower jaws.

Radiology, specifically a type of X-ray called a lateral cephalometric radiograph, is an important tool in diagnosing retrognathia. By analyzing these radiographs in various ways, doctors can measure the relationship between the skull and the facial skeleton, which is useful for developing treatment plans for orthodontics and jaw surgeries.

The most common diagnosis associated with retrognathia in orthodontics and oral & maxillofacial surgery practices is mandibular AP hypoplasia. This condition often requires a surgical correction using a procedure called bilateral sagittal split osteotomy of the mandible.

Pierre-Robin sequence
Hemifacial microsomia
DiGeorge syndrome
Nager syndrome
Treacher Collins
Goldenhar syndrome
Mobius syndrome

It’s important to keep in mind certain associated conditions, especially in infants and children, that often come along with a small lower jaw. These conditions include:

Previous surgeries to the head and neck or instances of trauma can also lead to retrognathia. For example, a fall from a bicycle in childhood that caused an injury to the jawbone could result in restricted growth of the jaw, leading to a crooked face and a retrognathic appearance. Any hard blow to the chin or lower face can inhibit jaw growth and potentially lead to retrognathia, which is why it is essential to document the patient’s history thoroughly.

Testing for Retrognathia

The physical exam is one of the best methods to identify if a person has a smaller-than-average lower jaw, or what doctors call “retrognathia”. This exam is usually supplemented by a lateral cephalometric x-ray, a type of special x-ray that targets the side of the head. This x-ray is normally analyzed with a complicated set of measurements considering the whole head, which is not covered here.

These measurements help assess the size and position of the lower jaw in relation to the base of the skull, to confirm if a person has a smaller lower jaw or “mandibular hypoplasia”. As an example, one measurement known as the Sella-Nasion-B point angle (SNB) is typically around 80 degrees in white people. Therefore, if you have an SNB angle of 72 degrees, this could suggest that you have “retrognathia”.

Treatment Options for Retrognathia

Retrognathia, a condition where the lower jaw is set further back than the upper jaw, is often diagnosed in children between ages four to ten. If a child has a regular dentist, they are likely to be referred to an orthodontist for evaluation, ideally around age seven to eight. Since this condition is generally harmless with no other effects, the orthodontist may monitor the child using a series of x-rays. They might recommend treatment with non-surgical methods such as headgear or newer inside-the-mouth techniques to reposition the jaw. Children who do not regularly see a dentist or an orthodontist should be referred to one if this condition is suspected.

If there’s concern about breathing issues in a patient with retrognathia, it may be an indicator of a difficult-to-manage airway. Factors such as underdeveloped structures, anatomical distortion, and potential malpositioning of the epiglottis may need to be taken into account.

If retrognathia is detected in an infant, child, or even an older individual, and there are other signs that make the doctor suspect a syndrome or multiple issues, various conditions may be considered:

Pierre-Robin Sequence: The combination of retrognathia, a downward displacement of the tongue, and a cleft palate. There’s a high chance of breathing obstruction, and the situation can range from mild to severe. A patient with this condition will need to be referred to a craniofacial (skull and face) team for examination and treatment.

Hemifacial Microsomia: This is a part of conditions known as oculo-auriculo-vertebral (OAV) syndromes and refers to underdeveloped growth on one side (or both sides) of the face. This condition could affect not only the lower jaw and lower face, but also the midface, jaw joint, eyes, ears, and soft tissue. If detected in an infant, the patient will need evaluation and treatment from a craniofacial team.

Goldenhar Syndrome: Another OAV syndrome, the cause of this condition is unknown. It combines features of Hemifacial Microsomia with additional facial clefting, eye abnormalities, vertebral anomalies, and other findings. The patient will need a referral to a craniofacial team as well as an eye specialist for evaluation and treatment.

Treacher Collins Syndrome: This condition stems from a genetic mutation and results in a unique facial appearance with extreme retrognathia, slanting eyes, facial hypoplasia (underdevelopment), and ear deformities. These infants will need immediate and intense therapy.

Nager Syndrome: This disorder is similar to Treacher Collins syndrome, but its cause is unknown. The treatment approach is alike.

Mobius Syndrome: A rare condition with an unclear cause. It presents with a characteristic “mask-like face” due to paralysis of several cranial nerves, retrognathia, eye deformities, and other skeletal and limb abnormalities. The patient will need a referral to a craniofacial team for evaluation and treatment, along with any other specialists as needed.

When a person has a smaller-than-average lower jaw (a condition called “retrognathia”), it could be due to a variety of medical conditions. Here are some possibilities:

Hemifacial microsomia
Pierre-Robin sequence
Goldenhar syndrome
Treacher Collins syndrome
Nager syndrome
Mobius syndrome

What to expect with Retrognathia

The outlook is generally good, unless the condition of having a receding chin, also known as retrognathia, leads to more serious health problems. These can include obstructive sleep apnea, a disorder where breathing repeatedly stops and starts during sleep, issues with the joint that connects the jaw to the skull called temporomandibular joint dysfunction, or is part of a more severe syndrome.

Possible Complications When Diagnosed with Retrognathia

Retrognathia, a condition where the lower jaw is set further back than the upper jaw, can cause several issues. Most commonly, it leads to a type of misalignment of the teeth known as Angle class II malocclusion. This makes chewing troublesome. It can also potentially cause psychological distress, particularly for young people, due to the facial abnormality.

Another likely issue related to retrognathia is obstructive sleep apnea. This is because the condition can cause a narrower and more restricted airway, making breathing during sleep problematic. Additionally, managing the airways can be substantially more challenging in individuals with retrognathia.

Common Problems:

Angle class II malocclusion – makes chewing difficult
Psychosocial stigmas – can cause psychological distress, especially in adolescents
Obstructive sleep apnea – likelihood is increased due to a narrower airway
Airway management issues – makes it more challenging to maintain clear airways

Preventing Retrognathia

If you or your child’s lower jaw seems to be set back further than normal (a condition called “retrognathia”), you should make an appointment with a general dentist or orthodontist for a check-up. These dental professionals can evaluate the situation and recommend the necessary next steps.