Ankylosed Teeth and Orthodontics: When a Tooth Cannot Be Moved

What ankylosis is

Ankylosis describes the pathological fusion of the cementum or dentine of a tooth root directly to the surrounding alveolar bone. Normally, teeth are suspended in their sockets by the periodontal ligament (PDL) — a fibrous connective tissue that acts as a shock absorber and provides the biological mechanism for orthodontic tooth movement. In ankylosis, the PDL is partially or completely obliterated and replaced by a direct bone-to-tooth union. Without a functional PDL, the tooth behaves as if it is rigidly embedded in the jaw rather than suspended within it. The tooth cannot respond to orthodontic force in the usual way, and applying force to an ankylosed tooth risks damaging adjacent teeth and bone rather than moving the ankylosed tooth itself.

How ankylosis develops

Ankylosis most commonly follows trauma to the tooth or supporting structures. A tooth that has been luxated, avulsed and replanted, or subjected to a significant blow can undergo replacement resorption — a process where the immune system gradually replaces root cementum and eventually root dentine with alveolar bone. Infection, periapical pathology, and dentoalveolar surgery can also disrupt the PDL and initiate ankylosis. In some patients, particularly children, primary (deciduous) molars undergo idiopathic ankylosis with no identifiable cause, resulting in infraocclusion as the surrounding jaw continues to grow downward while the ankylosed tooth remains at its original height. A genetic predisposition has been identified in some families with multiple affected primary molars.

How ankylosis is detected

Three methods are used in combination to diagnose ankylosis. The percussion test is the simplest: when tapped with a dental instrument, an ankylosed tooth produces a dull, solid, high-pitched sound quite different from the hollow, lower resonance of a normally suspended tooth. This test is clinically reliable but requires an experienced clinician for accurate interpretation. Radiographic assessment using a periapical or panoramic radiograph shows loss of the PDL space in the affected region, though early or partial ankylosis can be difficult to detect radiographically. Cone beam computed tomography (CBCT) provides a three-dimensional view of the PDL and is the most sensitive imaging method for confirming the extent of bone-tooth fusion, particularly when treatment planning decisions depend on an accurate diagnosis. Infraocclusion — where the tooth sits below the occlusal plane — is a reliable clinical indicator of long-standing ankylosis in growing patients.

Infraocclusion in children and its consequences

Infraocclusion refers to the submerging appearance of an ankylosed deciduous molar as the jaws grow and adjacent teeth erupt to a higher occlusal level while the ankylosed tooth stays put. In mild cases, infraocclusion causes only a minor step in the dental arch. In severe cases, the ankylosed molar can become deeply buried beneath the gum and bone, with the adjacent permanent teeth tipping significantly over it. The consequences include: blocked eruption or ectopic displacement of the underlying second premolar, tipping of adjacent first permanent molars, loss of arch length as adjacent teeth drift, bone deficiency on the affected side of the arch, and in extreme cases, the ankylosed tooth becoming entirely submerged. The rate of submergence is related to the rate of jaw growth — it is fastest during the pubertal growth spurt and in patients with rapid vertical facial development.

Why ankylosed teeth cannot be moved orthodontically

Orthodontic tooth movement depends on the piezoelectric and biological response of the PDL to sustained mechanical force. Pressure on the PDL stimulates osteoclastic resorption on the compression side, while tension on the PDL stimulates osteoblastic bone deposition on the tension side — the combination produces tooth movement through bone. An ankylosed tooth has no functional PDL. Applying orthodontic force to it does not produce the expected PDL response. Instead, force is transmitted directly to the bone, which can cause root resorption of the ankylosed tooth itself or tipping of adjacent teeth if the force is redirected. In rare clinical situations, very short-duration high-force techniques or surgical luxation have been used to attempt movement of partially ankylosed teeth, but these approaches are not predictable and are not standard practice.

Treatment options — decoronation, extraction, monitoring

The optimal treatment for an ankylosed deciduous molar with a present, erupting successor premolar is often monitoring until the premolar is ready to erupt, then extraction of the ankylosed molar timed carefully to allow the premolar to complete its eruption. Where infraocclusion is severe and causing significant arch disruption, extraction is preferred earlier. Decoronation is a surgical procedure in which the crown and most of the root are removed but the ankylosed root fragments are intentionally left in the bone. This preserves the alveolar bone volume — critically important in growing patients and in those being planned for a future implant — while eliminating the functional problems caused by the retained tooth. For ankylosed permanent teeth in adults, extraction followed by space closure orthodontically or space maintenance for a future implant are the two main pathways, chosen based on arch length, the adjacent teeth, and the patient's restorative needs.

Implant planning after extraction of an ankylosed tooth

When an ankylosed permanent tooth is extracted, the subsequent treatment depends heavily on whether adequate bone volume is preserved. Decoronation, when performed at the right developmental stage, has been shown to preserve significantly more alveolar bone than conventional extraction — a crucial consideration since dental implants require a minimum bone width and height. In young patients who have not yet finished growing, implant placement should be deferred until facial growth is substantially complete, which is typically around 18 to 20 years in females and up to 21 in males. Placing an implant in a growing jaw causes the implant to behave like an ankylosed tooth itself — it will fall progressively into infraocclusion as the jaw continues to grow. Orthodontic treatment is often required before implant placement to ensure the space is the correct width and the adjacent tooth roots are appropriately diverged to allow implant positioning.

Managing spaces adjacent to ankylosed teeth

Ankylosed teeth cause adjacent teeth to tip and drift, creating arch length discrepancies that must be corrected before definitive restoration. Orthodontic treatment is frequently needed to upright tipped molars, create or restore the correct space for a replacement tooth, and ensure root parallelism. In patients where the space has been lost significantly due to prolonged drift, space regaining is more complex and may involve distal movement of the drifted molar. Temporary anchorage devices (TADs) and skeletal anchorage are particularly useful in these situations because they allow movement of multiple teeth without requiring reciprocal anchorage from teeth that may already be compromised. A multidisciplinary treatment plan coordinating the orthodontist, oral surgeon, and restorative dentist is essential.

NHS vs private treatment for ankylosis

NHS treatment for ankylosed deciduous teeth and their orthodontic consequences is generally available for eligible patients under 18, particularly where the IOTN score reflects the severity of the arch disruption or the difficulty of premolar eruption. Surgical procedures including decoronation are available via NHS oral surgery referral. For adults with ankylosed permanent teeth requiring orthodontic space management and implant planning, NHS coverage depends on the specific clinical circumstances; complex restorative and implant work is often private. An orthodontic assessment with a specialist is the best starting point to understand the full treatment pathway and associated costs.

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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.