Short answer. A crooked or uneven smile usually starts in one of four places: the teeth (crowding, a shifted midline or a tilted bite), the gums (an uneven gum line), the jaws (one side grew more, or the jaw slides sideways to close) or the lips and facial muscles. Most smiles are slightly asymmetric, and studies show that people without dental training miss differences an orthodontist sees. Tooth and bite causes are fixed with braces or aligners, a crossbite in a child with an expander, and an unevenly grown jaw with braces and jaw surgery. A smile that droops suddenly is a medical emergency: call 911.
By Rodrigo F. Viecilli, DDS, PhD, board-certified orthodontist at Limestone Hills Orthodontics in Austin, TX, who has treated more than 5,000 patients.
What makes a smile look crooked or uneven
| Cause | What it looks like | Usual fix |
|---|---|---|
| Crowded, rotated or tipped teeth | Teeth at different heights or angles, or one tooth sticking out | Braces or clear aligners |
| Midline shift | The line between the two upper front teeth is off center, or does not line up with the lower teeth | Braces or aligners, often with rubber bands; sometimes a plan for a missing tooth |
| Tilted bite (canted occlusal plane) | More teeth or gum show on one side; the line of the teeth slopes | Braces, sometimes with miniscrews; jaw surgery when the jaw itself is tilted |
| Uneven gum line | Some teeth look short because more gum covers them | Gum contouring by a periodontist, often after braces level the teeth |
| Crossbite with a jaw shift (children) | The lower jaw slides to one side as the teeth close, and the lower midline and chin move with it | A palatal expander |
| Jaw asymmetry | The chin sits off center or one side of the face is longer | In adults, braces combined with jaw surgery |
| Lips and facial muscles | One side of the lip rises higher while the teeth are straight | Usually normal variation; any sudden change needs a doctor |
More than one cause is common. A tilted bite often comes with a chin that is off center, and an uneven gum line often follows teeth that erupted at different heights. That is why the first step is diagnosis: photographs, a 3D scan of the teeth and jaws, and a look at how the jaw moves when the teeth close.
What people actually notice
Small asymmetries are normal, and people without dental training are forgiving. In a study that showed altered smile photos to orthodontists, general dentists and lay people, the dentists and lay people did not notice the upper midline shifted by 4 mm, and orthodontists rated it less attractive only at 4 mm. Every group noticed a front tooth tipped by 2 mm. Lay people noticed a tilted line of the front teeth once it reached 3 mm.
A later study found that lopsided changes look worse than matched ones on both sides: every group noticed when one front tooth was 2 mm narrower than its partner. Young adults in another study accepted midline shifts up to about 2.4 mm. In practice, tipped teeth, uneven tooth heights and a sloping smile line matter more to how a smile looks than a perfectly centered midline.
How common facial asymmetry is
Among 1,460 patients evaluated at the University of North Carolina dentofacial clinic, 34% had visible facial asymmetry. The chin was involved in 74% of them and the bite was tilted in 41%. When the chin was off center, it pointed to the left 80% of the time. These were patients seeking treatment for jaw problems, so the figures are higher than in the general public.
Uneven smiles in children: check for a crossbite
When the upper back teeth close inside the lower ones on one side, many children slide the lower jaw sideways to fit the teeth together. The lower midline and the chin shift with it, and the smile looks crooked. In a randomized trial of children with this kind of crossbite, it did not correct on its own in the untreated group. In another trial of 110 children, a fixed expander called a quad-helix corrected the crossbite in 28 of 28 children treated in orthodontic specialist clinics.
That is one reason orthodontists recommend a first check around age 7; see your child’s first orthodontist visit. More is in crossbites in children, crossbite treatment and palatal expanders.
How each cause is fixed
- Teeth. Crowding, rotations and tipped teeth are straightened with braces or Invisalign. A limited correction of a few front teeth can take 6 to 12 months.
- Midline and tilted bite. Rubber bands and wire adjustments move the midline; miniscrews can level a mildly tilted bite.
- Gums. Once the teeth are level, a periodontist can reshape an uneven gum line.
- A narrow upper jaw. An expander in a growing child, or miniscrew-assisted expansion (MARPE) in older teens and adults.
- The jaws. When one side of the jaw grew more than the other, braces combined with jaw surgery after growth ends correct the face as well as the bite; see surgical orthodontics and jaw surgery vs braces.
- The lips. Straight teeth under an asymmetric lip line do not need orthodontics.
Typical treatment times for each kind of problem are in how long braces take, and crowding itself is explained in what causes crooked teeth.
When an uneven smile is an emergency
A smile that suddenly droops on one side can be a stroke, especially with numbness, arm weakness, trouble speaking, loss of balance or vision changes. The American Stroke Association’s B.E. F.A.S.T. signs are balance, eyes, face drooping, arm weakness and speech difficulty, and T is time to call 911, even if the symptoms go away. Any sudden weakness on one side of the face needs a doctor right away, not an orthodontist.
Uneven smile questions, answered
Is it normal to have an uneven smile?
Yes. Most faces and smiles are slightly asymmetric. In studies, lay people did not notice the upper midline shifted by 4 mm, while tipped teeth and a sloping smile line stood out sooner. An uneven smile is worth checking when it bothers you, when the bite feels off, or when it appeared suddenly.
Can braces fix a crooked smile?
When the cause is the teeth or the bite, yes: braces or aligners straighten teeth, center the midline and level a tilted bite. When the cause is the jaw, braces are combined with jaw surgery or, in children, an expander. When the cause is the lips, braces do not change it.
Why is my smile higher on one side?
The usual reasons are a tilted bite, where the teeth on one side sit higher, an uneven gum line, or lip muscles that lift more on one side. Photographs and a 3D scan show which one it is, and the fix depends on the cause.
Can a crossbite cause an uneven smile?
Yes. In children, a crossbite on one side often makes the lower jaw slide sideways when the teeth close, shifting the lower midline and the chin. Trials show it does not correct on its own, and a palatal expander usually fixes it.
How long does it take to fix an uneven smile?
It depends on the cause. A limited correction of a few front teeth can take 6 to 12 months, a full bite correction usually 18 to 24 months, and treatment combined with jaw surgery 24 to 36 months.
Limestone Hills Orthodontics is on RM 2222 in Northwest Austin. The first visit is free for new patients who have not been in orthodontic treatment in the last 12 months. Book a free orthodontic consultation or call (512) 720-6399.
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