How Teeth Move: The Biology Behind Orthodontics
For adults curious about braces or aligners: the periodontal ligament, pressure and tension, bone remodelling, force levels, faster treatment, root resorption and relapse. The core point: a tooth is not pushed through solid bone. Bone is removed ahead of it and rebuilt behind it, which takes months, and the risk of teeth moving back remains long term.
5.0 from 550+ Google reviews
Open 8am to 8pm, seven days
Free parking at the door
CQC & GDC registered
No referral needed
Clinically reviewed by Dr Ibraheem Ijaz, dentist · GDC 301711
Medical disclaimer: This page is for general information only. It does not replace an examination or treatment by a dentist.
Dr Ibraheem Ijaz, principal dentist, reviewed this page. He is a General Dental Practitioner with a BDS, a BSc (Hons), an MSc (Leeds), a PG Dip in Implant Dentistry and a PG Cert in Restorative and Aesthetic Dentistry.
How do teeth move?
Teeth move as the bone and ligament around each root are removed on one side and rebuilt on the other, says a 2018 narrative review.
The force comes from an appliance: the British Orthodontic Society (BOS) uses “brace” and “appliance” for a device that applies force to move teeth or correct the bite, including removable aligners. Our pages on fixed braces and straightening teeth with removable aligners describe each.
What is the periodontal ligament?
The periodontal ligament is a thin layer of fibrous tissue, about 0.2 mm wide on average, that attaches each tooth root to its bone.
A 2018 narrative review describes collagen fibre bundles with cells, nerves, blood vessels and fluid that hold the tooth in its socket while it withstands chewing. It says the ability of teeth to move through bone relies on this ligament. Its transseptal fibres run between neighbouring teeth and help keep them in line. Our page on the structure of a tooth explains the root and its surroundings.
What happens on the pressure and tension sides?
Under the classic pressure-tension theory, a tooth shifts in its ligament space within seconds of a force, squeezing one side and stretching the other.
In this account, blood flow falls on the pressure side and holds steady or rises on the tension side, a 2018 narrative review explains. If the force is sustained, oxygen levels shift within minutes and messengers such as prostaglandins and cytokines are released, starting inflammation with no bacteria involved. The net result is bone removal on the pressure side and bone formation on the tension side.
Laboratory and animal methods are widely used in this research, and a 2006 review says laboratory results should be checked against animal studies.
How is bone remodelled around a moving tooth?
Bone remodelling pairs two cell types: osteoclasts remove bone where the ligament is compressed, and osteoblasts build bone where it is stretched.
Signals such as RANK ligand and osteoprotegerin help regulate this turnover, a 2018 narrative review explains, and new bone and ligament fibres form on the side the tooth moves away from. So the socket is reshaped around the tooth.
Questions about this treatment? Book online or call the practice.
Do lighter forces work better?
The systematic reviews below have not firmly established an ideal force level.
Heavy force cuts off blood flow on the pressure side, killing cells there (hyalinisation); some always occurs clinically, a 2018 narrative review explains. A 2009 systematic review of 39 studies, three in humans and most in rats, says hyalinisation is considered undesirable but its possible link with tissue stress, and with the speed of movement after the first phase, has had little attention.
A 2003 systematic review, mostly of animal experiments, found no evidence identifying an optimal force. A 2019 systematic review of 12 randomised studies of fixed braces moving teeth bodily, without tipping, only one at low risk of bias, found 50 to 250 cN (centinewtons) moved teeth at a similar rate, and forces above 250 cN were slightly faster but came with adverse effects. It concluded that 50 to 100 cN seem optimal for movement and comfort and may cause fewer side effects, though the lack of strong evidence calls for careful interpretation.
Why does orthodontic treatment take months?
Treatment takes months because every step of movement depends on bone being removed and rebuilt. A 2018 narrative review notes that better brackets and wires cannot shorten treatment indefinitely, because the biological response sets the limit.
A 2015 Cochrane review of surgery to speed this up found four small trials of corticotomy, cuts through the outer layer of the jaw bone, in 57 people aged 11 to 33, all at unclear risk of bias. Teeth moved slightly faster over one to three months, but the evidence was low quality, no trial reported total treatment time and none reported data on harms. The authors called for longer studies to confirm any benefit.
What is the risk of root resorption?
Root resorption is shortening of a tooth root, which a 2018 narrative review links to inflammation during tooth movement that is not kept in check.
A BOS patient leaflet says minor root changes happen with all brace work and are not usually a problem. Occasionally they can be more serious, and the people at risk can often, but not always, be identified.
A 2021 overview of 28 systematic reviews, 20 of moderate or high quality, found root resorption more common and more severe with fixed braces, especially with heavy force, intrusion (pushing a tooth into the bone), torque (tilting the root), longer treatment, extractions and large root-tip movements, particularly of upper front teeth. Evidence on most other factors was insufficient, high-quality studies were few, and cause and effect between root resorption and treatment mechanics had not been confirmed. It recommends avoiding heavy, continuous forces and large root movements over long treatment.
If you have questions about root resorption, raise them with your dental team before or during treatment.
Why do teeth move back after orthodontic treatment?
Teeth tend to move back, called relapse, and BOS links the risk to the bone and gums around them needing time to adjust.
BOS says the jawbone and gums may need a year or more to settle, and the early months after the brace comes off carry a particular risk. Even in the longer term the risk remains, and BOS advises keeping up retention. Settling and retention overlap: retainers hold the teeth while the tissues adapt.
The cause of a rotated tooth turning back has been questioned. Stretched gum fibres were assumed to pull it back, but a 1996 study in dogs found them torn and disorganised rather than stretched, and a 2008 study of erupting dog teeth suggested factors other than the fibres straightening may be responsible. These are animal findings, not results in people.
Our page on retention after treatment covers retainers, and our page about teeth moving back after braces covers relapse. If your teeth start to shift once treatment has finished, show them to a dentist.
Frequently asked questions
How fast do teeth move with braces?
Less than a millimetre a month, in one trial. In 25 people having four premolars removed for braces, canines pulled back with a spring moved about 0.71 mm a month in the upper jaw and 0.57 mm in the lower. As a single small trial, it may not apply to other teeth or appliances.
Why can heavy force delay early tooth movement?
Heavy force kills squeezed ligament cells, so bone beside it must first be removed from behind, a 2018 narrative review explains. Movement waits for this undermining resorption. Light force only reduces blood flow, so bone-removing cells clear that bone quickly and directly (frontal resorption). In treatment, some blocked blood flow is almost impossible to avoid, so both occur.
Why might a pause in tooth movement help the roots?
A pause may let the root surface heal. A 2015 systematic review of 21 human studies concluded that pausing tooth movement seems to help reduce root resorption by allowing the resorbed outer layer of the root to heal. It noted flaws such as no control group. If you have questions about root resorption, ask your dental team.
Can vibration or light speed up tooth movement?
Evidence suggests not, for vibration or light. A 2023 Cochrane review of 23 trials with younger patients and adults rated all evidence low to very low certainty. It suggests vibration and photobiomodulation (low-level laser or LED light) give no additional benefit in shortening treatment; light may have a limited benefit for single stages, read cautiously: its clinical significance is questionable.
Is the inflammation that moves teeth an infection?
No. A 2018 narrative review describes this inflammation in the ligament as aseptic, meaning no bacteria are involved, and as part of how remodelling is triggered. After several days, the review says, the response moves from an acute phase to a longer, proliferative phase involving bone-forming, bone-removing and ligament cells.
Book a consultation.
Online in under a minute, or call and speak to a real person.
You can book online or call the practice, open 8am to 8pm, Monday to Sunday. Orthodontic treatment at Deepcar Dental Care is for adults only, with fixed metal, ceramic and lingual braces and clear aligners provided by our dentists.
Our page about orthodontic treatment and our guide to orthodontic treatment explain what treatment involves.
334 Manchester Road
Deepcar, Sheffield S36 2RH
0114 288 2121
Contact us
Opening hours
Open 8am to 8pm, seven days
Free parking at the door