An underbite is a class III orthodontic malocclusion that occurs when the lower jaw is pushed forward. In a normal bite, the front teeth should slightly overlap the lower teeth. An underbite is when the lower front teeth and jaw are positioned in front of the upper front teeth and jaw. There are two classifications of underbites, including:
Dental underbites form due to teeth misalignment. They are typically caused by crossbites, which is when the upper and lower teeth do not align correctly when biting down. Crossbites occur when some bottom teeth are located outside the upper teeth when the two jaws are in occlusion (closed).
When a crossbite appears in the front of the mouth, rather than the sides, it is a dental underbite. The teeth are positioned slightly forward but the entire lower jaw does not protrude forward (stick out).
Skeletal underbites form through the malformation of the jawbone. This type of malocclusion is usually genetic (present at birth). In some cases, the cause of an underbite can be from jaw malformation (skeletal), teeth misalignment (dental), or both.
The primary causes of an underbite include:
An overbite (class II malocclusion) is the opposite of an underbite. It occurs when the upper teeth and jaw overlap the lower teeth and jaw. This form of malocclusion is common but less common than a class I malocclusion (minor teeth overcrowding).
Underbites and overbites should never go uncorrected. If they are left untreated, severe pain, jaw problems, and dental conditions can result over time. Common complications of an untreated underbite include:
An underbite increases a person’s risk of tooth enamel damage due to the severity of misalignment. In turn, as the enamel wears away, cavities are more likely to develop.
Uncorrected underbites can result in sleep apnea disorder, which is linked to mouth breathing and heavy snoring. A blockage in the upper airway while sleeping causes the disorder, which results in breathing that repeatedly “stops” and “starts.”
These conditions are more common in overbites than in underbites. However, they can occur in underbites if the cause of the underbite is an abnormally small upper jaw and small airway.
If left untreated, an underbite can lead to temporomandibular joint and muscle disorders (TMJD). They are a group of disorders that cause dysfunction and extreme pain in the jaw and surrounding muscles that control jaw movement. People with TMJ disorders experience different kinds of pain, such as headaches, earaches, and discomfort when opening or closing the mouth.
Other complications of untreated underbites include:
Underbites are commonly found in children and adolescents. Although, the misalignment usually resolves once permanent teeth fully erupt. If you are concerned your child may have a true underbite, it is crucial to make an appointment with a local orthodontist to discuss whether treatment is necessary or not.
Treatment for an underbite depends on the patient’s age and the severity of misalignment:
If a baby is born with a severe underbite, a growth modification device helps position their jaw correctly early on. Some underbites form due to birth defects, such as a cleft lip and palate. The earlier you seek treatment for your child's underbite, the less likely surgery will be necessary later in life.
If a severe underbite isn’t noticeable or present at birth, orthodontists recommend waiting until your child turns seven years of age to seek treatment. Around this age, primary teeth shed and permanent teeth begin to erupt.
If an underbite is not corrected in early childhood, it is more likely that other dental conditions and jaw issues have developed into adulthood.
Treatment is still possible for adults, but choices are limited since the jaw and teeth have fully developed. Depending on the patient, surgery is usually necessary at this stage of life.
Common treatment options include:
Extracting baby (primary) teeth is a common underbite treatment option for babies and children. Extracting teeth early on makes room for permanent teeth to grow in straight. Orthodontists try to avoid extracting an adult’s permanent teeth, but in severe cases, treatment may be necessary to allow the teeth to move freely.
Braces are typically the best dental underbite treatment option for younger children, adolescents, and some adults. Braces are for both aesthetic and functional reasons, not only to correct a patient’s smile, but also to realign their jaw. A patient visits their orthodontist every four to eight weeks until the braces are removed. Braces are left on for 18 months to three years.
Invisalign, and other types of orthodontic-approved clear aligners, can correct minor underbites caused by tooth crowding. Invisalign can also fix teeth that are tilted the wrong way. However, if the underbite is caused by skeletal issues, surgery, or more invasive orthodontic treatment (e.g., palatal expansion or surgery) is needed.
In addition to braces, reverse pull headgear may be necessary. The device consists of pads that attach to the forehead and chin with a facemask frame in between. Patients connect rubber bands from the anchorage device on their braces to the frame.
Headgear shifts the upper jaw forward, which aligns the upper and lower jaws over time. Using headgear to correct an underbite at a young age eliminates the need for jaw surgery later in life.
Upper jaw expanders fit over a few back teeth in the upper jaw with a screw in the middle. You can activate an RPE by turning the screw a small amount each day, which creates tension between the two palatal bones. The goal is to widen the maxilla (upper jaw), expand the dental arch, and move the teeth within the bone. Over time, the jaw widens. In most cases, palatal expansion treatment takes 3 to 6 months.
Jaw surgery for an underbite is expensive (up to $40,000) but may be necessary for severe cases, such as fully developed adults. Surgery consists of an in-depth exam, X-rays, and administration of general anesthesia. Then an oral surgeon cuts, reshapes, and repositions the patient’s jawbone.
This type of jaw surgery, also called orthognathic surgery, requires orthodontic treatment and coordination between the orthodontist and the oral surgeon.
Cobourne, Martyn T., and Andrew T. DiBiase. Handbook of Orthodontics. Elsevier, 2016.
“Orthodontic Treatment Options.” American Association of Orthodontists, www.aaoinfo.org/orthodontic-treatment-options/.
Proffit, William R., et al. Contemporary Orthodontics. Elsevier/Mosby, 2019.