What Is an Underbite? A Straightforward Guide to Causes, Severity, and Treatment
Last updated: May 2026
The short version: an underbite is when your lower front teeth sit in front of your upper front teeth when you close your mouth. The opposite of an overbite. Less common, more often skeletal, and (in most cases) genuinely fixable.
About 5 to 10% of people have some degree of underbite. Most of those are mild and don’t need treatment. The ones that do need treatment fall into a wide range, from “a few months of clear aligners” to “braces plus jaw surgery.” The right answer depends entirely on what’s actually causing the underbite, how severe it is, and how old you are.
This guide is the version we wish every parent and adult patient had before their first consult.
What an Underbite Actually Is
In a healthy bite, your upper front teeth sit slightly in front of your lower front teeth when your mouth is closed. That overlap is normal. It’s the overlap that lets you bite into things cleanly.
An underbite is the reverse. The lower teeth jut out past the upper teeth, or sit in front of them, when the mouth is closed. The technical name is Class III malocclusion (a category that orthodontists use to classify how the upper and lower jaws relate).
An underbite is different from an overbite, where the upper teeth overlap the lower teeth too much. Both involve the bite being misaligned, but they’re caused by different things and treated differently.
There are two basic kinds of underbite:
Dental underbite. The teeth themselves are misaligned, but the jaws are roughly in the right position. This is the easier case. Braces or clear aligners can usually fix it.
Skeletal underbite. The lower jaw is positioned forward of where it should be, or the upper jaw is set back. The teeth are following the jaws. This is the more complex case and may need orthopedic treatment (jaw growth modification in kids) or surgery (in fully grown adults). Most severe underbites are skeletal.
About 70 to 80% of underbites we see are at least partly skeletal in nature. This matters because skeletal underbites do not self-correct, and they tend to worsen with continued jaw growth, which is why early evaluation matters more for underbites than for many other bite issues.
Underbite vs. Overbite: How They Compare
A quick comparison, because patients ask about both all the time.
Overbite: Upper front teeth overlap the lower teeth too much. Most common bite issue. Often dental (the teeth are the problem) and treated with braces, Invisalign with elastics, or both. Roughly 70% of people have some overbite; only about 25% need treatment. More on overbites here.
Underbite: Lower front teeth sit in front of upper teeth. Less common (5 to 10% of people). More often skeletal. Earlier intervention matters more because skeletal underbites worsen with jaw growth, while overbites can sometimes be corrected later in life.
The shorthand: overbite is usually about the teeth and can wait. Underbite is usually about the jaw and benefits from earlier action.
What Causes an Underbite
There’s no single cause. Most underbites result from a combination of:
Genetics. The biggest factor. If a parent or grandparent has an underbite, the children often have similar jaw structure. Family-line underbites are well-documented; certain royal lineages historically carried pronounced Class III patterns.
Jaw growth disharmony. The upper and lower jaws grow at different rates during childhood. When the lower jaw outgrows the upper, the result is an underbite, even without any external factor. This is often where the genetic contribution actually shows up.
Childhood oral habits. Prolonged thumb-sucking, pacifier use past about age 3, tongue-thrusting (pushing the tongue forward against the teeth when swallowing), and mouth breathing can all contribute, especially when combined with a genetic predisposition. These habits alone rarely cause a severe underbite, but they can push a borderline case into a clinical one.
Injury to the face or jaw. Less common but real. A childhood facial injury that affects the lower jaw can disrupt normal growth.
Certain rare medical conditions. A small number of craniofacial syndromes (Crouzon, Treacher Collins, others) include underbite as a feature. These are diagnosed by specialists well before orthodontic evaluation.
What does NOT cause an underbite, despite being commonly blamed: late teething, getting braces “too early,” allergies, or pacifier use before age 2. These either don’t contribute or contribute negligibly.
How to Tell Mild From Severe
Here’s the part most patients want to know: how bad is mine?
Mild underbite: The lower teeth slightly cross in front of the upper teeth, but not by much. Often the lower teeth just sit edge-to-edge with the uppers, or barely in front. Many adults with mild underbites have lived their whole lives without treatment and have no functional problems. The face looks normal. Chewing is fine.
Moderate underbite: The lower teeth clearly sit in front of the upper teeth, with a visible reverse overlap of 1 to 4 millimeters. The jaw alignment is noticeably off, but not dramatically. Some functional issues may appear: difficulty biting cleanly through food, mild speech effects on certain sounds (s, sh, th), and visible asymmetry in the lower face.
Severe underbite: The lower teeth sit well in front of the upper teeth, often with a gap of 5 millimeters or more. The lower jaw juts out visibly. There are usually real functional problems: trouble chewing properly, ongoing speech difficulties, jaw pain or TMJ symptoms over time, headaches, and significant impact on facial profile.
The thing severity does not tell you: whether you need treatment. A mild dental underbite in a healthy adult often doesn’t need anything. A moderate skeletal underbite in a kid is much more likely to need active treatment now than that adult is.
How to Fix an Underbite at Every Age
Treatment depends on three things: severity, whether it’s dental or skeletal, and how old the patient is. Bone growth is the variable that changes the playbook.
Kids (ages 7 to 10): The window for the easiest fixes
This is the best time to treat an underbite, by a wide margin. The lower jaw is still growing, the upper jaw can still be expanded, and orthopedic appliances can change the trajectory of jaw growth in ways that become impossible after puberty.
Common options at this age:
- Reverse-pull (face mask) headgear with a palate expander. Looks intimidating in pictures, very effective at pulling the upper jaw forward while expanding it. Worn at home, usually nights only, for 6 to 12 months.
- Upper jaw expander alone in mild cases where the upper jaw is just narrow.
- Limited braces to address dental components of the bite.
- Frankel III or other functional appliances in select cases.
If you catch an underbite at age 7 or 8, you may avoid surgery entirely. If you wait until 15, surgery becomes much more likely. This is the single biggest reason the American Association of Orthodontists recommends a first orthodontic evaluation by age 7.
Teens (11 to 17): Treatment is still effective but the options narrow
By the teenage years, the upper jaw has largely finished growing, but the lower jaw is still active. This shifts the available treatments. Full braces or Invisalign can correct dental underbites and many mild skeletal cases. More significant skeletal underbites may need treatment that combines braces with orthopedic surgery later, or extractions to compensate dentally for what the skeleton won’t allow.
This is also when functional appliances stop being as effective. The window for changing jaw growth is closing.
Adults: Treatment without growth requires different tools
Adults can still have their underbites corrected, but the lever of jaw growth is gone. The options become:
Dental underbite (the teeth are the problem): Braces or Invisalign for adults can move the teeth into proper alignment without touching the skeleton. Treatment usually takes 18 to 24 months. Most mild underbites can be addressed this way.
Skeletal underbite (the jaw is the problem): Two paths exist. Camouflage orthodontics moves the teeth to mask the underlying jaw mismatch. Works for moderate cases and avoids surgery, but doesn’t change the face profile and has limits on how dramatic the correction can be. Orthognathic surgery (jaw surgery) actually repositions the jaws. Combined with braces before and after, this fully corrects severe underbites and changes the facial profile. It’s a significant procedure, usually requiring a few days in the hospital and several weeks of recovery, but the results are durable and the technology has improved substantially over the past two decades.
An honest orthodontist will tell you which category your case falls into and what’s realistic. Camouflage treatment that gets pushed past its limits leads to compromised results.
Why You Shouldn’t Wait on an Underbite
For most orthodontic issues, waiting a year or two has minimal consequences. Underbites are the exception. Three reasons:
Skeletal underbites worsen with growth. The lower jaw is one of the last facial bones to finish growing, and in a Class III pattern, it can continue advancing through the late teens and even into the early twenties. A 10-year-old with a mild underbite can become an 18-year-old with a severe one if nothing is done.
The cost of treatment increases dramatically with age. A reverse-pull headgear and expander combination for a 9-year-old costs a few thousand dollars and 12 months. The same case treated at 25, after the jaw has finished growing, may require surgical correction at a total cost of $20,000 to $40,000 (most of which is the hospital and surgeon, not the orthodontist) plus 18 months of braces.
Function gets harder to restore later. Chewing patterns, jaw joint function, and speech all adapt around an underbite over years. Correcting a 30-year-old’s underbite means undoing decades of compensation; correcting an 8-year-old’s underbite means guiding normal development.
The orthodontic community recommends a first evaluation by age 7. For underbites specifically, that timing is more than a recommendation. It’s the difference between simple orthopedic treatment and complex surgical correction.
Frequently Asked Questions
Can an underbite fix itself?
A truly mild dental underbite occasionally improves slightly as adult teeth come in. A skeletal underbite does not fix itself and typically worsens. If a child has any sign of underbite at the age 7 evaluation, the recommendation is almost always to actively monitor rather than wait and see.
Can Invisalign fix an underbite?
For mild to moderate dental underbites, often yes. Invisalign with elastics can move teeth into proper bite alignment when the skeletal foundation is roughly correct. For severe or primarily skeletal underbites, Invisalign alone usually isn’t enough; braces with surgery may be needed, depending on the case.
Does underbite surgery hurt?
The surgery itself is done under general anesthesia, so there’s no pain during the procedure. Recovery involves swelling, soreness, and a soft-food diet for several weeks. Most patients are back to normal activity within 6 weeks and back to a normal diet within 3 months. Pain is managed with prescribed medication during the early recovery and shifts to over-the-counter relief within the first two weeks for most patients.
Are underbites more common in some ethnic groups?
Class III malocclusion (the technical name for underbite) is more prevalent in some East Asian populations than in European-descended populations. Genetics drive most of this difference. The treatments don’t differ by ethnicity, but the prevalence does.
Will an underbite affect speech?
Sometimes. The “s,” “z,” “sh,” and “th” sounds are most likely to be affected because they depend on precise positioning of the upper and lower front teeth. Many people with mild underbites compensate without noticeable effects. Moderate to severe underbites are more likely to produce noticeable speech changes, which usually improve substantially after correction.
If You’re Worried About a Possible Underbite
Whether you’re a parent who noticed your kid’s lower jaw looks more prominent than it used to, an adult who has lived with a mild underbite and is starting to wonder whether it’s worth treating, or you’ve been told you may need surgery and want a second opinion, the right next step is an evaluation by an orthodontist.
At Wax Ortho, the consultation is free. Dr. Wax has treated thousands of bite cases across Linden, Highland, and Flushing, Michigan since 2014. We’ll tell you whether your case (or your child’s) needs treatment now, can wait, or doesn’t need anything at all. No pitch, no pressure, just an honest read on what you’re dealing with.
About the Author
Dr. Nicole Wax, DDS, MS Orthodontics
Dr. Wax is a board-trained orthodontic specialist and a Diamond Plus Invisalign Provider, a designation from Align Technology recognizing the top 1% of Invisalign providers by case volume. She holds a DDS from The Ohio State University and an MS in Orthodontics from the University of Detroit Mercy. She founded Dr. Wax Orthodontics in 2014 and has helped thousands of families across Linden, Highland, and Flushing, Michigan find a smile that feels like them. Dr. Wax is a member of the American Association of Orthodontists and was named to the Flint & Genesee Group’s 40 Under 40 in 2024.