What does a midline shift mean?
When you smile, the line between your two upper front incisors is usually expected to line up with an imaginary line running down the centre of your face and with the centre line of your lower front teeth. When one of these lines moves to the right or left, this is called a “midline shift” or “midline deviation”. Small differences are found in many people and often go unnoticed; more marked shifts can affect both appearance and the way the teeth bite together.
A midline shift is a finding, not a diagnosis in itself. What really matters is why the shift has happened, because a shift caused by teeth moving out of place is handled differently from one caused by asymmetric growth of the jaw.
Causes of a midline shift
Tooth-related causes
- Crowding: When space is short, teeth can be pushed to one side as they line up. See crowded teeth.
- Gaps between teeth: Gaps on one side can allow teeth to drift in that direction. See gaps between teeth.
- Differences in tooth size: A small or differently shaped lateral incisor can affect the midline.
Jaw-related causes
Uneven growth of the right and left sides of the upper or lower jaw, the jaw sliding to one side as it closes, or conditions such as a crossbite can affect the midline. Sometimes the jawbone is symmetrical but the lower jaw slides sideways on closing because the teeth meet too early at one point; in that case the shift may be “functional”. For skeletal differences, see our page on skeletal jaw problems.
Missing teeth or teeth lost early
When a baby tooth is lost early, a tooth is congenitally missing or the space left by a tooth extracted in adulthood stays empty for a long time, the neighbouring teeth can tip into the gap. Over time this drift can also affect the centre line of the front teeth. This is why monitoring space loss in children matters; see orthodontics for children.
Habits
Long-term thumb sucking, pushing the tongue to one side or always chewing on the same side can affect the balance of the teeth and jaws, especially during growth. Whether a habit is still present is taken into account when planning treatment.
How is it assessed?
Assessment starts with an orthodontic examination. Your orthodontist usually looks at:
- The position of the upper and lower midlines relative to the centre of the face and to each other
- Whether the lower jaw slides sideways as the mouth opens and closes
- The bite relationship of the back teeth (whether the right and left sides are the same)
- Missing, small or differently shaped teeth
- X-rays, an intraoral scan and photographs if considered necessary
With this information, the aim is to understand whether the shift comes from the teeth, the jaw or both. Sometimes, if a slight shift causes no functional problem and its appearance does not matter to the patient, monitoring it without treatment can also be an option.
Orthodontic treatment options
Clear aligners
For many tooth-related, mild to moderate midline shifts, clear aligner treatment can be considered. In planning, the order and amount of each tooth movement is set digitally; if needed, attachments, interproximal reduction (IPR) or elastics are added to the plan. Suitability is decided at the examination and according to the features of the case; see What is Invisalign?
Fixed braces
Where the teeth need more extensive movement or root movements need more control, fixed braces may be preferred. For a general comparison of which method may suit you, see clear aligners or braces?
Further assessment if the jaw is the cause
If the shift comes from asymmetric growth of the jawbone, moving the teeth alone may not fully align the midline or may change the tilt of the teeth more than is desirable. In growing children, appliances that guide jaw growth may be considered (see our guide to appliances). In adults who have finished growing, marked skeletal asymmetries may require surgical options to be assessed alongside orthodontics; see When is orthognathic surgery needed? This decision is made after a detailed examination and, where necessary, together with the relevant specialists.
If a tooth is missing
If the shift is due to a missing tooth, orthodontic treatment may aim to close the space or to open it to a suitable width for a future implant or prosthesis. This planning is usually done together with other treatments; see implants and orthodontics.
After treatment
Once the midline has been corrected, the retention period is important for the teeth to hold their new position. Retainer wear and check-ups continue as your orthodontist recommends; see retention treatment.
Frequently asked questions
Should a slight midline shift be treated?
Not every shift needs treatment. If there is no problem with the bite and the shift does not bother you in terms of appearance, it can be monitored. The decision is made by weighing the examination findings together with your expectations.
Can a midline shift be corrected with clear aligners alone?
In many tooth-related cases, clear aligners can be considered. Where the jaw is the cause or extensive tooth movement is needed, different methods or additional treatments may be required.
Does the midline have to be exactly centred to the millimetre?
In most cases small differences are not visible and do not affect function. The aim of treatment is a healthy bite and a balanced-looking smile; your orthodontist discusses the achievable result at the examination.
I have noticed a midline shift in my child. What should I do?
Especially if you see the jaw sliding sideways on closing, it is useful to book an orthodontic assessment. See early orthodontic treatment.
For questions, you can call 0312 911 60 36 or use the form on the contact page.
This page is for general information only; diagnosis and the treatment plan are determined by an examination and your orthodontist's assessment.
