Top 10 Reasons Teeth Become Crooked or Shift Over Time

How we ranked these reasons

These reasons are ordered roughly from the most fundamental, the pattern you are born with, to the ones that tend to appear later in life, such as gum disease, ageing and a retainer that is no longer worn. That is an editorial judgement drawn from NHS and professional guidance, not a survey, and it does not claim to show how common each reason is. Several usually act together, a clinician may weigh them differently for you, and a tooth that has moved is not always the result of something you did. The list is meant to explain why teeth go where they go, so that you can ask better questions, not to assign blame.

Crooked, crowded and shifted: what the words mean

People use crooked to cover several different things. Crowding means there is not enough room, so teeth overlap or twist. Spacing means there is too much room, so gaps show. A bite problem, which orthodontists call a malocclusion, means the upper and lower teeth do not meet well, for example an overbite, underbite, open bite or crossbite. Shifting means teeth that were once straighter have moved, which can happen in childhood as adult teeth come through, or in adulthood. The NHS explains that orthodontic treatment is used to straighten teeth and correct the bite, and that dentists refer people when there is a concern. Knowing which of these you have helps you make sense of the ten reasons below, because different causes lead to different patterns.

1. Inherited jaw and tooth pattern

Family resemblance does not stop at the face. The size and shape of the jaws, the position of the lower jaw relative to the upper one, the width of the dental arches and even the size of individual teeth tend to run in families, which is why a child can end up with an overbite or underbite similar to a parent's. Research in this area is complex and the exact share of genetics versus environment is hard to pin down, so no one can promise how a particular child's teeth will turn out. What is clear is that many bite patterns are not caused by anything the patient or parent did. A dentist can often spot an inherited pattern early and keep an eye on it, and an orthodontist can decide if or when treatment would help. Watch out for self-blame, or for believing a bite problem can be fixed by habits alone.

2. Teeth too big for the jaw, or too small

The jaws have only so much room, and the adult teeth need to fit in a row along them. When the teeth are large relative to the jaw, they crowd, overlap, twist or sit outside the arch, with upper canines and lower front teeth often affected. When teeth are small or the jaw is wide, spaces appear between them. This mismatch is usually inherited and is very common, which is one reason crowding is among the most frequent reasons people ask about braces. It is not something brushing, diet or a mouthguard can change. Treatment can create or close space by moving teeth, reshaping the sides of teeth, widening an arch in some cases or, sometimes, removing teeth. A dentist can tell whether crowding is mild or whether a referral makes sense. Watch out for treating crowding as a hygiene fault, since crowded teeth are harder to clean but are not crowded because of poor cleaning.

3. Baby teeth lost early or kept too long

Baby teeth act as place-holders for the adult teeth. If one is lost early, usually to decay or injury, neighbouring teeth can drift into the gap, leaving too little room for the adult tooth underneath, which may then come through crooked or become blocked. The opposite problem is a baby tooth that stays when it should have fallen out, which can push the adult tooth to come through in the wrong place, for example behind or in front of the baby tooth. The NHS stresses looking after children's teeth from the first tooth and having regular check-ups, and a dentist may suggest watching, removing a retained tooth or, rarely, fitting a space maintainer. Ask the dentist about this if baby teeth are lost much earlier or later than expected. Watch out for pulling a loose or stubborn baby tooth at home without advice.

4. Thumb, finger and dummy habits

Sucking a thumb, finger or dummy puts steady pressure on the teeth and the roof of the mouth. Over months and years, this can tip the upper front teeth forward, stop the front teeth meeting and narrow the upper arch. The NHS advises that these habits are normal in young children and that most children stop on their own, but that continuing once the adult teeth begin to arrive, at around age six or seven, can affect how the teeth come through. How much damage occurs depends on how long, how often and how hard the habit continues. Many changes improve once the habit stops, though some bite changes need orthodontic help. A dentist, health visitor or school nurse can offer ideas that avoid shaming a child. Watch out for punishments or bitter-tasting paints, which are more likely to cause distress than to end the habit.

5. Tongue position and mouth breathing

The tongue, lips and cheeks balance each other and shape the dental arches as a child grows. A tongue that pushes forward when swallowing or rests low in the mouth, and long-term breathing through the mouth because of blocked nasal passages, have been linked in some studies to a narrower upper jaw, an open bite or a longer face. The evidence is mixed, and it is difficult to tell whether the habit causes the bite or the bite causes the habit, so any claim that one thing is the single cause should be treated with caution. If a child snores heavily, always breathes through the mouth or has a persistent lisp, a dentist, GP or orthodontist can look at the possible causes together. Treatment may involve the nose, throat, speech or teeth. Watch out for products that promise to retrain the tongue or reshape the jaw without any examination.

6. Missing, extra or buried teeth

Some people are born with fewer teeth than usual, most often one or more second premolars or upper lateral incisors, and others have an extra tooth that crowds the rest. In some cases, a tooth forms but gets stuck in the jaw, with upper canines the best-known example. Each of these changes the space available, so teeth tilt, drift, twist or fail to appear. These are developmental differences that appear before birth and are no one's fault. They are usually found on a routine dental X-ray or because a tooth has not come through when it should, and an orthodontist or a dentist with a special interest can plan the best approach, which sometimes involves a team including a surgeon or restorative dentist. Early detection gives the most options. Watch out for ignoring a baby tooth that has not fallen out by the time the adult tooth should be arriving, since it can be a clue.

7. Injury and decay

A knock to the mouth can push a tooth out of line, damage the nerve or loosen it, and sports and falls are common causes in children and teenagers. Decay can destroy part of a tooth or lead to its removal, which leaves a gap that neighbouring teeth tilt into over time. Large fillings and crowns that change a tooth's shape can also alter how teeth meet. Preventing these is partly within reach, through a well-fitted mouthguard for contact sport, brushing twice a day with fluoride toothpaste, cutting down how often sugary food and drink are consumed and keeping up with dental check-ups, all of which are standard NHS advice. After an injury, see a dentist promptly, even if nothing looks wrong, because problems can appear later. Watch out for leaving a gap after losing a tooth, since filling the space is easier early than after neighbouring teeth have moved.

8. Gum disease in adults

Teeth sit in bone and are held there by the gum and ligament around them. Gum disease, which the NHS describes as a common problem caused by plaque, can damage that support, so teeth become loose and can drift, spread apart or tip forward, often most noticeably at the upper front teeth. Many people first see the change as a new gap or a tooth that sticks out and assume their teeth have shifted for no reason. Bleeding gums when brushing, bad breath, receding gums or loose teeth are signs worth a dental visit. Treatment starts with thorough cleaning and home care, and orthodontic movement is only considered once the gums are healthy, because moving teeth in inflamed gums can make things worse. Seeing a dentist early gives a chance of stopping the problem. Watch out for assuming new gaps are cosmetic only, as they can point to a gum problem.

9. Wisdom teeth

Wisdom teeth are often blamed for pushing the front teeth into crowding, particularly the lower ones in late teens and twenties. The evidence that they do so is weak. Studies have found that the lower front teeth tend to crowd with age even in people who never had wisdom teeth, and NICE advised the NHS to stop routinely removing problem-free wisdom teeth to prevent crowding. Wisdom teeth can cause other problems, such as infection or damage to the tooth in front, and these are valid reasons for a dentist to recommend removal. If you are worried that a wisdom tooth is affecting your teeth, a dentist can assess it with an examination and, if needed, an X-ray, and explain the risks and benefits of any surgery. Watch out for removing healthy wisdom teeth in the hope of preventing crowding, or for expecting removal to straighten teeth that are already crowded.

10. Ageing and stopping retainer wear

Teeth are never completely fixed. The ligaments around them keep responding to forces from the lips, cheeks, tongue and biting throughout life, and small changes with age are normal, with the lower front teeth the classic example. The British Orthodontic Society and NHS both stress that teeth tend to move back after braces unless a retainer is worn as advised, which is why many orthodontists recommend long-term retention. People who had braces years ago and stopped wearing retainers often notice crowding returning. Some movement can also happen if a fixed retainer wire breaks or detaches without being noticed. Wearing the retainer as directed is the main thing within your control, and an orthodontist or dentist can check it. Watch out for a retainer that no longer fits comfortably, since forcing it on can hurt the teeth, and contact the practice instead.

Common myths about crooked teeth

A few explanations come up again and again and are worth correcting. Sleeping on one side, resting your chin on your hand or chewing on one side are often blamed, but there is little good evidence that these ordinary habits move teeth enough to matter, unlike habits that apply steady pressure for hours, such as thumb sucking. Another myth is that braces make teeth weaker or that teeth straighten themselves with age, when in fact most irregularity stays or slowly worsens. It is also untrue that straight teeth always mean a good bite, or that crooked teeth always need treatment. Some people are happy with their smile and healthy, and treatment is a choice. If a claim sounds too simple, ask your dentist or orthodontist.

What you can and cannot change

It helps to separate causes into three groups. Some are built in, such as the inherited jaw pattern, the size of teeth and missing, extra or buried teeth, and nothing in daily life changes them. Some are partly in your hands, such as stopping a thumb or dummy habit in good time, preventing decay, protecting teeth in sport and cleaning well to avoid gum disease. And some are matters of upkeep, particularly wearing retainers after treatment. Straight teeth are not a sign of good care and crooked teeth are not a sign of neglect. Teeth can be straightened at almost any age if the gums and teeth are healthy, though the aim and the approach differ. For general reassurance, many people have some degree of irregularity, and whether to treat it is a personal choice.

When to ask a dentist or orthodontist

See a dentist if teeth are moving noticeably, if a gap or a tooth that sticks out has appeared in adulthood, if gums bleed or recede, if a baby tooth has not come out at the expected time or if a child still sucks a thumb or dummy once adult teeth are coming through. A dentist can explain what is happening, treat any underlying problem and refer to an orthodontist if appropriate. NHS orthodontic treatment in England is free for under-18s who have a clear clinical need, assessed using the Index of Orthodontic Treatment Need, and is limited for adults, so many people choose private care. Check that your clinician is registered with the General Dental Council, and ask for a written plan and costs before agreeing to anything. A second opinion is always reasonable.

Key takeaways

Teeth become crooked or shift for ten common reasons: an inherited jaw and tooth pattern, a mismatch between tooth and jaw size, baby teeth lost early or kept too long, thumb and dummy habits, tongue position and mouth breathing, missing, extra or buried teeth, injury and decay, gum disease, the often over-blamed wisdom teeth, and ageing combined with stopping retainer wear. Many are not within anyone's control, and some can be helped by prevention, early dental visits and wearing retainers. If your teeth are moving, ask a dentist to find out why before deciding what to do. This is general information, not personal medical advice, and your own dentist or orthodontist is the right person to assess your mouth.

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This guide is for general information only. It is not a diagnosis, treatment plan, or substitute for advice from a registered dentist or orthodontist.