A smile can look crooked while every tooth is perfectly straight, because three different things are being confused: the face, the dental midline, and the tilt of the bite plane. Facial asymmetry and a crooked smile get talked about as though they are one problem with one fix. They are not. The face can be slightly uneven left to right. The centre line between the front teeth can sit off the middle of the face. The biting plane can be tilted rather than level. Each is assessed differently, each has different causes, and treating the wrong one is a common way to spend a lot of effort and change nothing.
Key takeaways
- Minor facial asymmetry is normal and close to universal. Perfect symmetry does not exist, and a 2023 longitudinal study in the European Journal of Orthodontics found asymmetry already present in normal children by age six.
- Prevalence figures vary enormously by method, from about 4.7 per cent for clinically significant asymmetry, to 34 per cent in a University of North Carolina dentofacial clinic review, to over 50 per cent when assessed radiographically. These measure different things.
- Sudden or newly developing facial asymmetry, drooping, numbness or weakness needs prompt medical assessment, not a cosmetic dental one.
- Facial asymmetry, a dental midline shift and a canted occlusal plane are three separate findings. They can occur together but they are diagnosed and treated separately.
- Miller's study found the dental midline is exactly centred in only around 70 per cent of people, and upper and lower dental midlines fail to coincide in roughly three quarters of the population.
- Causes range from normal developmental variation and a functional mandibular shift through to muscular causes and condylar hyperplasia, which is excessive and often progressive growth of one jaw condyle.
Read this first: when asymmetry needs a doctor, not a dentist
If facial asymmetry has appeared suddenly or is getting noticeably worse, that needs prompt medical assessment rather than a cosmetic dental appointment. This applies particularly to new drooping on one side of the face, new numbness, new weakness, difficulty closing one eye, a change in speech, or an asymmetry that has developed over days or weeks rather than being something you have always had.
New facial asymmetry is not a cosmetic issue and should not be framed as one. Sudden facial weakness can have serious medical causes that need urgent attention, and the right first call is a doctor or an emergency department, not a dentist. If you are unsure how urgent it is, treat it as urgent. Nothing in the rest of this article changes that.
The remainder of this article is about long standing, stable asymmetry that has been part of your face for as long as you can remember. That is a very different situation, and it is usually a normal variation rather than a problem.
Where this article fits
The existing article on why a smile looks off centre is about the centre line itself: whether the join between the two upper front teeth lines up with the middle of the face, and what can be done about it. This article is about the face that line sits on.
That distinction is the whole reason this article exists. Plenty of people go looking for a fix for an off centre smile when the teeth are centred correctly on a face that is itself slightly uneven. Moving the teeth in that situation may make the mismatch worse rather than better. Related reading sits in the articles on how crooked teeth are straightened, why one tooth looks longer than the others and digital smile design, which covers how a proposed change is planned against the face rather than against the teeth alone.
Minor facial asymmetry is normal
Some degree of left to right difference is close to universal, and it is not a defect. A 2023 longitudinal study published in the European Journal of Orthodontics found facial asymmetry already present in normal children by the age of six, which places it as a normal developmental feature rather than something that has gone wrong later. Faces grow, and the two halves do not grow in perfect step.
The reported prevalence, though, varies enormously depending on how it is measured, and it is worth seeing the range rather than one headline figure. A retrospective clinical review of patients at the University of North Carolina dentofacial clinic found 34 per cent of 1,460 patients had clinically apparent facial asymmetry. Other studies report figures as low as about 4.7 per cent for clinically significant asymmetry, with chin deviation in 5.7 per cent and nasal pyramid deviation in 3.4 per cent. Assessed radiographically, reported figures exceed 50 per cent.
Those numbers are not in conflict so much as answering different questions. Visual assessment, photographic assessment and radiographic assessment measure different structures at different thresholds. A radiograph picks up skeletal differences no one can see. A clinic review counts what a clinician judged noticeable in a population that had come in seeking treatment. A community study using a stricter definition of clinically significant will return a smaller figure. None of them is the definitive number, and anyone quoting a single percentage as the prevalence of facial asymmetry is oversimplifying.
Three findings that get confused
Most of the confusion in this area comes from three separate findings being treated as one. The table below separates them, along with who assesses each and what should raise concern.
| Finding | What it means | What usually causes it | Who assesses it | Red flag signs |
|---|---|---|---|---|
| Facial asymmetry, soft tissue and skeletal | Overall left to right imbalance of the face, involving soft tissues, bone or both | Normal developmental and genetic growth variation, and less commonly condylar hyperplasia or a muscular cause | Dentist, orthodontist, and a doctor or specialist where a medical cause is possible. Three dimensional imaging may be needed | Any asymmetry that is new, worsening, or accompanied by numbness, weakness or drooping |
| Dental midline shift | The centre line between the upper front teeth does not sit on the middle of the face | Tooth size differences, crowding, early tooth loss, drifting, or a face that is itself slightly uneven | Dentist or orthodontist, assessed against facial landmarks rather than against the other teeth alone | A shift that has appeared or increased in an adult, which can indicate tooth movement or loss |
| Canted occlusal plane | The biting plane is tilted rather than level, so one side sits higher than the other | Uneven vertical jaw growth, an underlying skeletal asymmetry, or long standing tooth position differences | Dentist or orthodontist, often with photographs and three dimensional imaging | A cant that is progressing, or one associated with joint pain or a changing bite |
| Functional mandibular shift | The lower jaw slides to one side to find a comfortable bite, so the face looks uneven when the teeth are together | A bite discrepancy such as a crossbite that forces the jaw off its natural path | Dentist or orthodontist, by comparing the jaw at rest with the jaw in full closure | Joint clicking, locking, pain, or a shift that is increasing |
| Sudden or new asymmetry | A change in facial appearance over days or weeks rather than a long standing feature | Requires medical diagnosis. Possible causes include nerve and muscular conditions such as Bell's palsy, among others | A doctor or emergency department, urgently. Not a cosmetic assessment | All of it. New drooping, numbness, weakness or speech change needs prompt medical care |
The dental midline, and how often it is actually centred
An off centre dental midline is statistically normal rather than unusual. Miller's study, cited widely across orthodontic sources, found the dental midline is exactly centred in only around 70 per cent of people. The upper and lower dental midlines fail to coincide with each other in roughly three quarters of the population. That means a large share of people walking around with what most would call a nice smile have a midline that would not survive a ruler.
Perception studies back that up. A 2025 study indexed in PMC on occlusal plane and midline preferences in asymmetrical faces found that a dental midline deviation of up to about 2mm toward the direction of chin or nose deviation, or up to about 1mm in the opposite direction, was rated as aesthetically acceptable by both laypeople and dental professionals. The direction of the deviation mattered, not just the amount. A midline that drifts the same way the face already leans is tolerated better than one that fights it.
The practical lesson is that centring the teeth on the face is not always the same as centring them on each other, and a plan built purely on measurements between teeth can look worse than the starting point. The midline is judged against the face.
A tilted bite plane is its own finding
A canted occlusal plane means the biting surface is tilted rather than level, and it reads to the eye as a crooked smile even when every tooth is straight and the midline is fine. It shows up clearly when someone bites on a flat object such as a spatula and a photograph is taken from the front: the object sits at an angle rather than parallel to the eyes.
A cant tilting in the same direction as a mandibular shift is a recognised association, and canting and facial asymmetry often occur together. That does not make them the same thing. They are diagnosed separately, they may need three dimensional imaging to characterise properly, and management ranges from orthodontic camouflage for milder presentations through to orthognathic surgery in severe skeletal cases. Jaw surgery is not something Lumi Dental provides, and cases in that range are referred to a specialist team.
What causes long standing facial asymmetry
Most stable asymmetry comes from normal developmental and genetic variation in how the two halves of the face grew. That is the largest category and it needs no treatment at all. Beyond that, several recognised causes are worth knowing about.
A functional mandibular shift
A bite discrepancy can force the lower jaw to slide to one side in order to close comfortably. The jaw itself may be symmetrical, but the face looks uneven whenever the teeth are together. This one is worth identifying because it is often correctable by addressing the bite, and because a long standing shift can influence how the jaw grows in younger patients.
Muscular causes
Residual weakness after a condition such as Bell's palsy can leave a lasting difference in how the two sides of the face move and rest. This is a medical history question as much as a dental one, and it changes what a cosmetic plan can reasonably achieve, since the asymmetry is in movement rather than in the teeth.
Habitual one sided chewing
Chewing consistently on one side is listed among the contributing factors to facial asymmetry. It sits at the milder end and it is often a consequence of something else, such as a sensitive or missing tooth on the other side, which is a reason to have the cause looked at rather than simply trying to change the habit.
Condylar hyperplasia
Condylar hyperplasia is excessive and often progressive growth of one jaw condyle, the part of the lower jaw that forms the joint near the ear. It causes the jaw to deviate, changes the bite over time and can bring joint dysfunction with it. Because it can progress, an asymmetry that is changing in an adult is a reason for proper assessment rather than watchful waiting.
What can be done, and in what order
The order of operations matters more than the treatment list. The first step is working out which of the three findings is actually present, and whether more than one is. That means looking at the face at rest and smiling, comparing the jaw at rest with the jaw in full closure to pick up a functional shift, checking the midline against facial landmarks rather than against the lower teeth, and checking whether the bite plane is level. Three dimensional imaging is used where a skeletal component is suspected.
From there, options range widely. A functional shift may be addressed by correcting the bite discrepancy causing it. A midline discrepancy within the range people find acceptable may need nothing at all. A mild cant may be managed with orthodontics. Restorative work such as bonding or veneers can soften how an asymmetry reads without changing the underlying structure, and a trial smile or mock up is a sensible way to see whether a proposed change actually improves things before committing. Severe skeletal cases are referred for specialist surgical assessment. What should not happen is a cosmetic plan built on the assumption that straighter teeth will fix an uneven face.
Common questions
Is it normal to have an asymmetrical face?
Yes. Minor facial asymmetry is close to universal and perfect symmetry does not exist. A 2023 longitudinal study in the European Journal of Orthodontics found asymmetry already present in normal children by age six. Reported prevalence ranges from about 4.7 per cent for clinically significant asymmetry to 34 per cent in a University of North Carolina clinic review and over 50 per cent on radiographic assessment, depending entirely on how it is measured.
Why does my smile look crooked when my teeth are straight?
Usually because the finding is not in the teeth. The face itself may be slightly uneven, the dental midline may sit off the facial midline, or the bite plane may be tilted. A canted occlusal plane in particular reads as a crooked smile even when every tooth is perfectly aligned, which is why straightening alone would not change it.
What causes one side of the jaw to grow bigger than the other?
Condylar hyperplasia is the recognised cause of excessive and often progressive growth of one jaw condyle, leading to jaw deviation, a changing bite and sometimes joint dysfunction. Because it can progress, an asymmetry that is getting worse in an adult should be assessed rather than watched. Normal growth variation accounts for most mild differences.
Can chewing on one side cause facial asymmetry?
Habitual one sided chewing is listed among the contributing factors, though it sits at the milder end of the list alongside developmental variation, functional shifts and muscular causes. It is often a symptom of something else, such as discomfort or a missing tooth on the other side, so the more useful question is why you are avoiding that side.
Is facial asymmetry the same as a crooked bite?
No. They are separate findings that often occur together. Facial asymmetry is an overall left to right imbalance of the face. A crooked bite may involve a dental midline shift, a canted occlusal plane or a functional mandibular shift, each of which is assessed and treated in its own right. Confusing them is the most common reason a cosmetic plan misses the mark.
When should I worry about facial asymmetry?
When it is new or getting worse. Sudden or newly developing asymmetry, drooping, numbness, weakness, difficulty closing an eye or a change in speech needs prompt medical assessment rather than a cosmetic dental appointment. Long standing asymmetry that has been part of your face for as long as you can remember is a different situation and is usually normal variation.
Can braces fix facial asymmetry or only tooth position?
Orthodontics primarily changes tooth position, and it can address a dental midline shift, a functional mandibular shift caused by a bite discrepancy, and some mild canting through camouflage. It does not change the underlying skeleton. Severe skeletal asymmetry is managed with orthognathic surgery by a specialist team, which is outside the scope of general or cosmetic dentistry.
Talking it through
If your smile looks crooked in photographs and you are not sure whether the issue is your teeth, your midline or your face, the team at Lumi Dental in Melrose Park offers a complimentary cosmetic consultation. That starts with working out which of the three findings is present, because the answer changes everything that follows. Other current offers are listed on the current deals page, and a written quote can be prepared before any treatment is agreed. If your asymmetry is new or changing, please see a doctor first.
This article is general information only and is not personal dental or medical advice. Facial proportions, bite and jaw growth vary from person to person, and treatment suitability and outcomes vary. Please speak with a dentist, orthodontist or doctor about your own circumstances before making a decision.
