Root resorption – an introduction

17 Root resorption – an introduction


Hard tissues are protected from resorption by their surface layers of blast cells. It appears that as long as these layers are intact, resorption cannot occur. Although bone, dentine and cementum are mesenchymal, mineralized tissues composed mainly of collagen and hydroxyapatite, they differ markedly in their susceptibility to resorption.


Two mechanisms are involved in resorption of hard tissue:


1. The trigger

2. A reason for the resorption to continue.

The trigger mechanism in root resorption is a root surface detached from its protective blast cell layer. Detachment may follow any damage to the protective blast layer. For the resorption to continue, a stimulus is required, e.g. infection or a continuous mechanical force.


Root resorption always starts at a surface, and is termed internal if emanating from the root canal wall and as external if emanating from the root surface.


Internal resorption is rare in permanent teeth. Radiographically, it is characterized by an oval-shaped enlargement of the root canal space. Histological examination reveals resorption of the internal aspect of the root by multinucleated giant cells adjacent to granulation tissue in the pulp. There are different theories regarding the origin of the pulpal granulation tissue involved in internal resorption. The most logical explanation is that it is pulp tissue that is inflamed because of an infected coronal pulp space. In addition to the requirement of the presence of granulation tissue, root resorption takes place only if the odontoblast layer and predentine are lost or altered.


Traditionally, a pink tooth has been thought pathognomonic of internal root resorption; the pink colour is caused by granulation tissue in the coronal dentine undermining the crown enamel. However, a pink tooth can also be a feature of a specific type of external root resorption, namely peripheral inflammatory external root resorption (detailed later in this chapter), which must be ruled out before a diagnosis of internal root resorption is made. A pink tooth can also be due to pulpal haemorrhage.


There are different forms of external root resorption described in man. The underlying mechanism is understood for some of these, whereas other forms are still unexplained and therefore termed idiopathic. A classification system for external root resorptions that have a known mechanism has been proposed in man and is as follows:


1. Surface resorption

2. Replacement resorption associated with ankylosis

3. Inflammatory resorption.

This classification system works for external root resorption in cats and dogs as well.



SURFACE RESORPTION


A surface resorption is initiated subsequent to injury of the cementoblast layer. The denuded root surface attracts clast cells, which will resorb the cementum for as long as osteoclast-activating factors are released at the site of injury, usually a few days. When the resorption stops, cells from the periodontal ligament will proliferate and populate the resorbed area, resulting in deposition of reparative dental tissue (new cementum).


It is thought that minor traumas caused by unintentional biting on hard objects, bruxism, etc. can cause localized damage to the periodontal ligament and trigger this type of resorption. The process is self-limiting and reversible.



REPLACEMENT RESORPTION


Replacement resorption results in replacement of the dental hard tissue by bone. When a surface resorption stops, cells from the periodontal ligament will proliferate and populate the resorbed area. If the resorption is large it will take some time for these cells to cover the entire surface. Cells from the nearby bone may then arrive first and establish themselves on the resorbed surface. Bone will thus be formed directly upon the dental hard tissue. This results in fusion between bone and tooth, i.e. ankylosis. This can be seen as a form of healing; the bone has accepted the dental hard tissue as part of itself and the tooth becomes involved in the normal skeletal turnover. So, during consequent remodelling of bone, both dental hard tissue and bone will be resorbed. When the resorptive process is over, the osteoblasts will form bone in the resorbed area. In this way the dental tissues will gradually be replaced by bone. In short, ankylosis is a form of healing of root surface resorption, which from a clinical standpoint may be undesirable.

Related posts:

  1. Chronic gingivostomatitis with extraction leading to partial cure
  2. Tooth shortening and endodontic therapy
  3. Chronic gingivostomatitis as a consequence of periodontitis and iatrogenic injuries
  4. Enamel dysplasia

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Sep 3, 2016 | Posted by in SMALL ANIMAL | Comments Off on Root resorption – an introduction

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