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==Introduction==  

==Introduction==  

[[File:Explorer probe and dental resorption.jpg|200px|right|thumb|Explorer probe being used to identify tooth resorption in the 4th premolar]]

Feline tooth resorption or feline odontoclastic resorptive lesions (RL) (also been referred to as cervical line lesions, neck lesions, dental resorptive lesions and feline caries) affect more than one third of adult domestic cats and are the second most common [[:Category:Oral Diseases - Cat|oral problem seen in cats]] (after [[periodontitis]]), with prevalence increasing with age. <font color="red">(picTR1) </font color>

[[File:Explorer probe and dental resorption.jpg|200px|right|thumb|Image 6: Explorer probe being used to identify tooth resorption in the 4th premolar]]

[[File:Cat mandibular radiograph 1.jpg|200px|right|thumb|Tooth resorption]]

Feline tooth resorption or feline odontoclastic resorptive lesions (RL) (also referred to as cervical line lesions, neck lesions, dental resorptive lesions and feline caries) affect more than one third of adult domestic cats and are the second most common [[:Category:Oral Diseases - Cat|oral problem seen in cats]] (after [[periodontitis]]), with prevalence increasing with age (image 1).

On examination, there is a loss of dental tissue on the [[Enamel Organ#Crown|crown]] or at the neck of the [[:Category:Teeth - Anatomy & Physiology|teeth]]. The crown may be completely resorbed with the remaining root covered with [[Gingiva|gingiva]].

On examination, there is a loss of dental tissue on the [[Tooth - Anatomy & Physiology#Crown|crown]] or at the neck of the [[:Category:Teeth - Anatomy & Physiology|tooth]]. The crown may be completely resorbed with the remaining root covered with [[Gingiva|gingiva]].

==Aetiology and Pathogenesis==

==Aetiology and Pathogenesis==

The aetiology and pathogenesis of FORLs has not yet been demonstrated but is almost certainly multifactorial. Possible hypotheses that have been suggested include, the texture of the diet, abnormal calcium regulation, [[Hypervitaminosis A|hypervitaminosis A]], mechanical stress, [[Developmental Dental Conditions|anatomical abnormalities of the teeth]], [[:Category:Cat Viruses|viral infections]] and plaque bacteria and [[Periodontal Disease|periodontal disease]].

The aetiology and pathogenesis of FORLs has not yet been demonstrated but is almost certainly multifactorial. Possible hypotheses that have been suggested include, the texture of the diet, abnormal calcium regulation, [[Hypervitaminosis A|hypervitaminosis A]], mechanical stress, [[Developmental Dental Conditions|anatomical abnormalities of the teeth]], [[:Category:Cat Viruses|viral infections]] and plaque bacteria and [[Periodontal Disease|periodontal disease]].

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.

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. However bone, [[dentine]] and [[cementum]] are mesenchymal, mineralized tissues composed mainly of collagen and hydroxyapatite, and they differ markedly in their susceptibility to resorption.

Two mechanisms are involved in resorption of hard tissue:

Two mechanisms are involved in resorption of hard tissue:

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

The trigger mechanism in root resorption is a root surface detached from its protective blast cell 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. Histological examination reveals resorption of the internal aspect of the root by multinucleated [[Giant Cells|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), 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:

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. Histological examination reveals resorption of the internal aspect of the root by multinucleated [[Giant Cells|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), 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:

# Surface resorption

# Surface resorption

# Replacement resorption associated with ankylosis

# Replacement resorption associated with ankylosis

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

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

'''SURFACE RESORPTION''' - is initiated subsequent to injury of the [[cementoblast]] layer. It is thought that minor traumas caused by unintentional biting on hard objects, bruxism, etc. can cause localized damage to the [[Enamel Organ#Periodontal Ligament|periodontal ligament]] and trigger this type of resorption. The process is self-limiting and reversible.

'''SURFACE RESORPTION''' - is initiated subsequent to injury of the [[cementoblast]] layer. It is thought that minor traumas caused by unintentional biting on hard objects, bruxism, etc. can cause localized damage to the [[Tooth - Anatomy & Physiology#Periodontal Ligament|periodontal ligament]] and trigger this type of resorption. The process is self-limiting and reversible.

'''REPLACEMENT RESORPTION''' - results in replacement of the dental hard tissue by [[Bones - Anatomy & Physiology|bone]]. When a surface resorption stops, cells from the periodontal ligament will proliferate and populate the resorbed area. 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. 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.  

'''REPLACEMENT RESORPTION''' - results in replacement of the dental hard tissue by [[Bones - Anatomy & Physiology|bone]]. When a surface resorption stops, cells from the periodontal ligament will proliferate and populate the resorbed area. 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. 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.  

The lesions can be detected by means of a combination of visual inspection, tactile examination with a [[Dental Explorer|dental explorer]] and [[Intra-Oral Radiography - Small Animal|radiography]].

The lesions can be detected by means of a combination of visual inspection, tactile examination with a [[Dental Explorer|dental explorer]] and [[Intra-Oral Radiography - Small Animal|radiography]].

===[[Oral Examination - Small Animal|Oral Examination]]===

====[[Oral Examination - Small Animal|Oral Examination]]====

Visual inspection and tactile examination with a dental explorer will only identify end-stage lesions, i.e. when the process involves the crown and has resulted in an obvious cavity.  

Visual inspection and tactile examination with a dental explorer will only identify end-stage lesions, i.e. when the process involves the crown and has resulted in an obvious cavity.  

Signs on visual inspection which are consistent with RLs:

Signs on visual inspection which are consistent with RLs:

* Focal hyperplastic gingival tissue covering the tooth defect. This gingival covering is usually, but not always, inflamed.  <font color="red">(picTR2)</font color>

* Focal hyperplastic gingival tissue covering the tooth defect. This gingival covering is usually, but not always, inflamed (image 2).

* Red spot on crown of the tooth as seen in the images <font color="red">TR3 and TR4</font color>

* Red spot on crown of the tooth as seen in the images (images 3 and 4).

* Missing/fractured teeth; site may have inflamed covering gingiva and/or bony swelling. <font color="red">TR5</font color>

* Missing/fractured teeth; site may have inflamed covering gingiva and/or bony swelling (image 5).

* Root fragments  

* Root fragments  

===[[Intra-Oral Radiography - Small Animal|Intra-Oral Radiography]]===

====[[Intra-Oral Radiography - Small Animal|Intra-Oral Radiography]]====

A definitive diagnosis can only be made after an examination and intra-oral radiography with the cat [[Oral Examination Under General Anaesthesia|under general anaesthesia]]. The lesion can be felt as a concavity using a sharp explorer probe. <font color="red">Pic TR6</font color>. Lesions are often only detected once the calculus has been removed.

A definitive diagnosis can only be made after an examination and intra-oral radiography with the cat [[Oral Examination Under General Anaesthesia|under general anaesthesia]]. The lesion can be felt as a concavity using a sharp explorer probe (image 6). Lesions are often only detected once the calculus has been removed.

Visualisation is aided by drying the teeth using the air stream from a dental air-water syringe. With normal teeth, the marginal gingiva will lift away from the tooth when the air is directed at the base of the [[Enamel Organ#Crown|crown]], but with RLs, the soft tissue seems “stuck” to the underlying tooth. General anaesthesia is imperative as examination of these lesions in a conscious cat is painful.  

Visualisation is aided by drying the teeth using the air stream from a dental air-water syringe. With normal teeth, the marginal gingiva will lift away from the tooth when the air is directed at the base of the [[Tooth - Anatomy & Physiology#Crown|crown]], but with RLs, the soft tissue seems “stuck” to the underlying tooth. General anaesthesia is imperative as examination of these lesions in a conscious cat is painful.  

Radiography will identify lesions that are localized to the root surfaces within the [[Enamel Organ#Alveolar Bone|alveolar bone]], which cannot be detected by clinical methods. Radiography is also required to confirm the diagnosis and to assess the extent and type of the lesion. Radiographs often reveal a lesion that is more advanced than originally suspected from the clinical examination. <font color="red">PicTR7</font color>

Radiography will identify lesions that are localized to the root surfaces within the [[Tooth - Anatomy & Physiology#Alveolar Bone|alveolar bone]], which cannot be detected by clinical methods. Radiography is also required to confirm the diagnosis and to assess the extent and type of the lesion. Radiographs often reveal a lesion that is more advanced than originally suspected from the clinical examination (image 7).

[[Radiographic Interpretation of Tooth Resorption - Small Animal|Radiographic Features of RLs]]: <br>

[[Radiographic Interpretation of Tooth Resorption - Small Animal|Radiographic Features of RLs]]: <br>

a) loss of integrity of the periodontal ligament space <br>

a) Loss of integrity of the periodontal ligament space. <br>

b) loss of the lamina dura<br>

b) Loss of the lamina dura.<br>

c) irregularities on the root surface<br>

c) Irregularities on the root surface.<br>

d) diffuse decrease in radiodensity of the entire root compared with adjacent roots<br>  

d) Diffuse decrease in radiodensity of the entire root compared with adjacent roots.<br>  

e) radiolucent areas within the root dentine often extending into the crown dentine<br>  

e) Radiolucent areas within the root dentine often extending into the crown dentine.<br>  

f) replacement of root substance by bone-like tissue. <br>

f) Replacement of root substance by bone-like tissue. <br>

g) resorbing roots present with clinically missing crown <br>

g) Resorbing roots present with clinically missing crown. <br>

For more information see [[Radiographic Interpretation of Tooth Resorption - Small Animal|radiographic interpretation of tooth resorption]].

For more information see [[Radiographic Interpretation of Tooth Resorption - Small Animal|radiographic interpretation of tooth resorption]].

===Classifying the Lesions===

====Classifying the Lesions====

Classification of tooth resorption : <font color="red">(American Veterinary Dental College classification) pictures</font color>

Classification of tooth resorption :  

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==Treatment==

==Treatment==

Historically, restoration of the tooth surface has been recommended for the treatment of accessible lesions that extend into the dentine and do not involve pulp tissue. However, several studies have shown that tooth resorption continues and the restorations are lost. Consequently, the use of restoration of odontoclastic lesions as a major treatment technique cannot be recommended.

Historically, restoration of the tooth surface has been recommended for the treatment of accessible lesions that extend into the dentine and do not involve pulp tissue. However, several studies have shown that tooth resorption continues and the restorations are lost. Consequently, the use of restoration of odontoclastic lesions as a major treatment technique cannot be recommended.

===Conservative Management===

====Conservative Management====

This consists of monitoring the lesions clinically and radiographically. This approach is recommended for lesions that are not evident on clinical examination, i.e. only seen radiographically, and there is no evidence of discomfort or pain. In general practice, most lesions are only diagnosed when pathology is extensive and conservative management is rarely an option.

This consists of monitoring the lesions clinically and radiographically. This approach is recommended for lesions that are not evident on clinical examination, i.e. only seen radiographically, and there is no evidence of discomfort or pain. In general practice, most lesions are only diagnosed when pathology is extensive and conservative management is rarely an option.

In most cases, extraction or coronal amputation of an affected tooth is indicated. Preoperative radiographs are mandatory to allow selection of the appropriate treatment option.

In most cases, extraction or coronal amputation of an affected tooth is indicated. Preoperative radiographs are mandatory to allow selection of the appropriate treatment option.

===Extraction===

====Extraction====

Teeth with resorption are notoriously difficult to extract, as the root is resorbing and being replaced by bone-like tissue. Moreover, there are areas of ankylosis, i.e. fusion of bone and tooth substance, along the root surface.  

Teeth with resorption are notoriously difficult to extract, as the root is resorbing and being replaced by bone-like tissue. Moreover, there are areas of ankylosis, i.e. fusion of bone and tooth substance, along the root surface.  

Teeth affected by resorption can be extracted using a closed technique, but an open technique is usually less traumatic to the tissues and easier to perform. The teeth are often prone to fracture so an open technique allows good access to any root fragments remaining.  

Teeth affected by resorption can be extracted using a closed technique, but an open technique is usually less traumatic to the tissues and easier to perform. The teeth are often prone to fracture so an open technique allows good access to any root fragments remaining.  

===Coronal Amputation===

====Coronal Amputation====

The indications for, and outcome of, coronal amputation have been well documented and the procedure is recommended for selected cases, but needs radiographic monitoring at regular intervals postoperatively to ensure that the root is resorbing and that healing is uneventful. In brief, the technique involves raising a gingival flap to expose the margin of the alveolar bone. The crown of the affected tooth is amputated using a small round bur. A small amount of root tissue is also removed with the bur, just enough to ensure that the intentionally retained root(s) is (are) apical to the alveolar margin. The gingival flap is replaced and sutured in place. This technique is only appropriate for teeth that do not have any radiographic evidence of [[Endodontic Conditions|endodontic disease]] (ie. periapical inflammation) or [[periodontitis]], and teeth in cats with gingivostomatitis should be removed entirely.

The indications for, and outcome of, coronal amputation have been well documented and the procedure is recommended for selected cases, but needs radiographic monitoring at regular intervals postoperatively to ensure that the root is resorbing and that healing is uneventful. In brief, the technique involves raising a gingival flap to expose the margin of the alveolar bone. The crown of the affected tooth is amputated using a small round bur. A small amount of root tissue is also removed with the bur, just enough to ensure that the intentionally retained root(s) is (are) apical to the alveolar margin. The gingival flap is replaced and sutured in place. This technique is only appropriate for teeth that do not have any radiographic evidence of [[Endodontic Conditions|endodontic disease]] (ie. periapical inflammation) or [[periodontitis]], and teeth in cats with gingivostomatitis should be removed entirely.

{{Learning

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