Underbites: What You Need to Know
- nnrortho
- Jun 26
- 4 min read
Updated: Jul 22
If you've noticed that your child's bottom teeth sit on top of or in front of their top teeth, or that their lower jaw appears more prominent, they may have what's known as a Class III bite, commonly called an underbite.
An underbite can affect much more than appearance. It can impact chewing, speech, tooth wear, jaw function, and self-confidence. The good news is that when identified early, we can often guide growth and significantly improve the outcome.
What Is an Underbite?
In an ideal bite, the upper front teeth should fit slightly in front of the lower front teeth. With an underbite, the opposite occurs. This is called a crossbite.
Not every underbite looks the same. Some children have only a few front teeth in crossbite, while others have a more significant discrepancy involving the entire jaw.
Common signs include:
Upper and lower front teeth biting edge to edge
Lower teeth sitting in front of the upper teeth
A prominent lower jaw or chin
Difficulty biting into foods
Excessive wear on the front teeth
A facial profile that appears "concave," with the chin looking more forward
How Do You Develop an Underbite?
Most underbites are genetic. Children often inherit the size and position of their jaws from their parents.
An underbite may develop because:
The upper jaw doesn't grow enough.
The lower jaw grows more than expected.
A combination of both occurs.
What Can We Do Early?
Early orthodontic treatment can take advantage of a child's natural growth.
For many younger children with an underbite caused by a narrow or underdeveloped upper jaw, we may recommend Phase I treatment using an upper expander together with a facemask.
Upper Expander
An upper expander gently widens the upper jaw over several months. This creates more room and helps correct a narrow upper arch.
Facemask Therapy
Once expansion has begun, a facemask (a type of headgear) is worn outside the mouth, usually in the evenings and while sleeping. Gentle elastic forces encourage the upper jaw to grow forward while helping improve the relationship between the upper and lower jaws.
Treatment is most effective while children are still growing—typically between 7 and 10 years of age. Starting at the right time gives us the best opportunity to reduce the severity of the underbite and, in some cases, avoid more invasive treatment later.
Why Are There Usually Multiple Phases of Treatment?
Parents are often surprised to learn that early treatment may not eliminate the need for braces later with this type of bite.
That's because Phase I treatment focuses on guiding jaw growth or preventing harm from bad bites, not creating a final bite.
After early treatment:
The child continues growing.
Baby teeth continue falling out.
Permanent teeth continue erupting.
The jaws continue developing throughout adolescence.
Once all the permanent teeth have erupted, a second phase of treatment with braces or clear aligners is often needed to align the teeth, fine-tune the bite, and create the best long-term result.
Think of Phase I as correcting the foundation while the house is still being built. Phase II is the finishing work that creates a healthy, functional, and beautiful smile.
When Is Jaw Surgery Needed?
Unfortunately, not every underbite can be corrected with orthodontics alone.
If the discrepancy between the upper and lower jaws is severe—or if the lower jaw continues to outgrow the upper jaw during adolescence (growth potential)—jaw surgery may be the best option to achieve an ideal bite and facial balance.
Jaw surgery is not performed until growth is complete, usually around:
16–18 years for girls
18–20 years for boys
Treatment typically involves:
Braces before surgery to position the teeth correctly
Orthognathic (jaw) surgery performed by an oral and maxillofacial surgeon during braces treatment
Continued braces treatment after surgery to finalize the bite
Although the thought of surgery can sound intimidating, modern techniques are highly predictable, and for patients with severe skeletal discrepancies, surgery often provides the most stable and functional result.
It's important to remember that needing jaw surgery is not a failure of early orthodontic treatment. Early treatment may still improve the bite, reduce the severity of the problem, make future treatment simpler, and improve function during childhood.
The Importance of an Early Evaluation
The best time to assess a child with a possible underbite is around age 7. At this age, we can determine whether growth guidance is appropriate or whether careful monitoring is the best approach.
Every child grows differently, and no two underbites are exactly alike. An early orthodontic evaluation allows us to develop a personalized treatment plan that gives your child the best opportunity for a healthy, confident smile.
If you're concerned that your child may have an underbite, we'd be happy to evaluate their growth and discuss the treatment options that are most appropriate for them.
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