Tooth resorption is loss of hard dental tissue, but not from decay. This means that the substance of a tooth is broken down by certain specialised body cells and then absorbed. Resorption thus causes some of a tooth, generally in the root area, to just disappear.
In the developing child there is a natural physiological resorption of the roots to allow for the exfoliation, or shedding of the first set of teeth at the appropriate time. This is completely normal. In the adult however, resorption is considered pathological, i.e. abnormal.
The problem can affect one or several teeth of the permanent dentition and the precise presentation can vary according to location.
Resorption is broadly classified as either internal or external, depending on whether it is initiated outside the tooth or from the pulpal cavity within it. It involves a complex interaction between various types of specialised body cells such as inflammatory cells, resorbing cells, cytokines and enzymes, and the hard dental tissue.
The stimulus for this process to begin is reckoned to be physical pressure or damage, or chemical due to pathogenic bacterial toxins.
External root resorption often occurs without obvious symptoms, unless a tooth is sufficiently damaged to become mobile. Otherwise it is usually only picked up on radiographic examination, i.e. X-rays.
The condition is further defined according to its location as either cervical or apical and the causes can include;
- periodontal (gum) disease
- stimulus due to orthodontic treatment
- stimulus from an unerupted, impacted tooth
- cysts or tumors
Internal root resorption can result from
- internal bleaching – a whitening procedure used to treat a single, dead tooth.
- stimulus from a necrotic tooth pulp – ie where the nerve inside the pulp has died off.
Known Causes And Appropriate Treatment
Dental resorption can occur as a result of traumatic injury which causes damage either to the periodontal ligament (with subsequent external root resorption) or from pulpal injury and death (with infection ensuing).
The periodontal ligament is a specialized type of fibrous connective tissue, which forms a kind of sling between the jaw bone and the root of the tooth. The ligament suspends it within the jaw bone socket, allowing for slight movement which protects against shock damage.
If damage occurs where the root is still immature and developing, there is often a good chance of recovery and a fair long term prognosis for the tooth. In older patients, however, the damage is less easily repaired.
Treatment is geared towards stabilizing a mobile tooth and immediate root-canal therapy, to clean out the pulp where the dead tissue lies.
Periodontitis, or gum disease can, in its later stages, damage the periodontal ligament – leaving the root surface exposed and vulnerable to action by cells called osteoclasts, monocytes and macrophages. The actions of these cells can result in dissolution and resorption to varying degrees. This kind of resorption has been associated especially with certain types of pathogenic, i.e. harmful bacteria.
Orthodontic treatment, by its very nature, puts pressure on the periodontal ligament to facilitate bone resorption to allow the tooth to move. Subsequently, sometimes there follows the appearance of patches of resorption along the sides of the root or from the apex (tip of the root).
Such occurence is an inherent risk of orthodontic treatment and it is perhaps desirable for a series of radiographs to be taken during extended treatment, in order to pick up incidences of undue root resorption. Where it occurs, it is often necessary to postpone active treatment for a few months to halt the resorptive process. The longer the duration of treatment, or the greater the distance of teeth movement required, the greater is the risk of unwanted root resorption.
Once orthodontic treatment is complete there is usually substantive repair and recovery.
The unerupted tooth
An unerupted tooth can exert pressure against a neighboring root, to cause resorption similar to that from orthodontic treatment. Typical examples include the forward-leaning lower wisdom tooth which is impacted against the back of the standing second molar and causes damage where the two meet. Similarly, the misdirected movement of an upper canine which presses against the root of an upper lateral incisor.
Treatment depends on the extent of damage and the possibility of removal of an impacted wisdom tooth, or orthodontic treatment in the case of a mis-aligned upper canine, in order to encourage it to erupt and then bring into alignment.
Tumor or odontome
Pressure from a dense tumor or an odontome can be sufficient to induce resorption in an adjacent tooth in some cases.
Occasionally, resorption can occur without any obvious cause, but where a cause is evident then treatment is directed towards removing that causative factor and treating a damaged tooth as necessary.
Sometimes this might involve root-canal therapy and/or splinting.
Tooth resorption is fortunately not a common problem, but can be challenging to deal with when it occurs.