My teeth are shifting: why it happens, and how fast it progresses

A tooth is not like a nail fixed into the bone; there is a thin layer of connective tissue between the root and the bone, and a tooth can move throughout life, even if only very slightly. The American Association of Orthodontists (AAO) writes that tooth movement is a natural, lifelong process linked to the constant renewal of bone, and that the forces on the teeth when you speak, bite and chew push them in that direction. When teeth are lost or their support weakens, this natural movement turns into noticeable shifting.

Shifting has four separate sources, and their speeds are very different from one another. The details of the front teeth fanning out are on the page about gaps opening between teeth; here the real question is how fast the shifting progresses, which kind can be watched and which should not be left.

The first source is an extraction gap. In a study at the Leeds Dental Institute comparing 100 patients with a back tooth that had no opposing tooth left against 100 people matched for age, sex and bone level, 92% of the unopposed teeth had grown longer. The average overeruption was 1.68 millimetres, with some cases approaching 4 millimetres; in the comparison group the figure was 0.24 millimetres. Overeruption was clearly greater in the upper jaw than in the lower. The same research group's second study found that the teeth on either side of the gap tipped into it, and that the tooth in front of it could also rotate; the tipping of the tooth behind the gap was sometimes very pronounced.

The speed of the movement has been measured too. In a study published in the Journal of Dental Research that followed 116 untreated gaps at the back of the mouth with successive X-rays, the distance between the teeth on either side of the gap shortened by less than 1 millimetre on average in the first year; the fastest narrowing happened in the first 2 years after the extraction and slowed progressively in the following years. The authors write that after the first 2 years the movement is generally slow and small.

This finding also corrects a widespread belief. In a study of 111 patients published in JADA and followed for a median of 6.9 years, in most patients missing a single back tooth the distance between the neighbouring teeth shortened by 1 millimetre or less, overeruption of the opposing tooth stayed at 1 millimetre or less in 99% of cases, and bone loss next to the neighbouring teeth was 1 millimetre or less in 83% of cases. The authors suggest that with a single gap at the back, immediate treatment may not be essential for most patients, and that it should instead be followed with regular check-ups. The figures from the two studies do not match exactly; one measured overeruption on plaster models, the other with X-rays and a different method. The shared message is this: with a single gap at the back, shifting is real but usually slow and limited.

The second source is gum disease, and this picture should be taken much more seriously. A review in the Journal of Periodontology writes that in patients with gum disease, teeth moving out of place because of bone loss (pathologic tooth migration) has been reported in 30% to 55.8%, and that it is often the complaint that brings the patient to the dentist. A study examining the records of 370 patients in Iran found a rate of 11.4% (35 of 314 patients with gum disease), and none of those with mild gum disease had migration; migration became more common as the disease became more severe. In other words, if your front teeth are shifting, there may be advanced bone loss behind it.

The review also stresses that migration has no single cause: bone loss is the main factor, but pressure from the tongue, cheeks and lips, pressure within inflamed gum pockets, bite problems and habits such as lip biting also play their part. The same review also notes that after gum treatment in the early stages, teeth that have shifted sometimes move back on their own. That is a concrete benefit of going early.

The third source is not wearing a retainer after brace treatment. The NHS writes that after braces come off, a retainer has to be worn to stop the teeth moving back to where they were. The AAO notes that straight after treatment there is a settling period in which teeth are most prone to moving back, that not wearing a retainer for even a few days can make the teeth shift noticeably, and that a retainer will often be needed for life.

The fourth source is age itself. The AAO writes that teeth naturally shift as we get older, that this can cause crowding of the lower front teeth or gaps between the upper teeth, and that bite problems do not correct themselves and can get worse over time. This is a slowly progressing change that is usually painless; however, if gum disease comes with it, the speed changes.

The situations in the first list progress slowly and can be dealt with at a planned appointment. If a point from the second list applies, see your dentist without waiting for your next check-up.

The sequence below is the assessment to expect at the dentist for shifting teeth. Take your old photographs, and any old X-rays you have, with you to the appointment.

1. 1

   Start at home: photos from the same angle

   Once a month, take a photo in the same light and from the same angle, with your teeth together and while smiling. Comparing them is the simplest evidence to show your dentist whether the shifting is really progressing. Old wedding or holiday photos help too.

2. 2

   Floss and food getting stuck

   If floss now slides without any resistance through a gap it used to squeeze through, or if food has started getting stuck in a new place, the contact between two teeth may have opened. Note which gap it is.

3. 3

   Gum measurements and a mobility test

   The dentist measures the gum pocket around each tooth and checks for bleeding and looseness. This is the key step that tells apart whether the shifting comes from gum disease or from a gap.

4. 4

   X-rays

   The bone level around the roots, where the missing teeth are and the tilt of the neighbouring teeth can be seen on an X-ray. If you have old X-rays, comparing them shows how fast the movement is.

5. 5

   Bite and habits

   Which tooth touches first when the mouth closes, signs of clenching, and habits such as tongue thrusting and lip biting are asked about and checked. The review notes that many habits are associated with migration and that they are hard for the dentist to spot; tell them about any you know of.

6. 6

   Putting things in order according to the cause

   If there is gum disease, that is treated first; moving teeth or filling gaps is only planned once the gums have settled. If the cause is a gap, a decision is made on whether to fill it and whether orthodontic correction is needed.

There is no single treatment for shifting; what is done depends on where the shifting comes from.

The following are wrong decisions often seen with this complaint. We set them out so that you can ask the right questions, whichever dentist you see.

The timings vary with the source of the shifting and the treatment carried out. The sequence below is a general framework; the plan of the dentist who examines you comes first.

1. The first 2 years after an extraction

   The measurement study found that the teeth on either side of the gap move closer fastest during this period. If you are thinking of filling the gap, ask for the gap and the opposing tooth to be measured at check-ups during this time; if there is a change, you will have data to base the decision on.

2. After the first 2 years

   The movement usually slows and stays small. At regular check-ups, comparing photographs and X-rays may be enough.

3. The months after gum treatment

   As the inflammation settles, looseness can lessen, and teeth that shifted in the early stage can partly move back. Moving teeth or filling gaps is usually planned once this healing is seen.

4. After brace treatment

   The AAO writes that at first you may be asked to wear the retainer all the time except when eating and brushing, and later only at night. When the retainer is abandoned, shifting can start again.

We are not giving a single figure here, because behind shifting teeth there may be a single gap that only needs monitoring, or advanced bone loss that needs gum treatment and orthodontics. These are the items that determine the scope:

The source of the shifting

A gap, gum disease, not wearing a retainer and age follow entirely different paths and fall within the remit of different clinicians.

The scope of gum treatment

There are different stages, from a professional clean to deep cleaning below the gum line and surgery.

Whether orthodontic correction is needed

There is a big difference between a new retainer and a full repeat treatment.

The number of missing teeth

Filling a single gap and planning several missing teeth together are jobs on a different scale.