Contributors: Lisa Milella, Alex Smithson

 Species: Feline   |   Classification: Miscellaneous

Introduction

  • The bulk of the tooth (roots and most of the periodontium) can only be visualized by means of intra-oral radiographs.
  • Around 70% of cats over 3 years have some form of dental disease and as much as 70% of the pathology in the mouth may go undetected without dental radiography.

Radiographic considerations

  • Fine detail screens are required.
  • Non-screen film (eg dental film, size 2) or a small flexible cassette and screen is ideal for nasal chambers.
  • To accurately assess each tooth in a cats mouth 10 films should be taken :
    • Upper incisors, upper left canine (anterior-posterior oblique and lateral), upper right canine (anterior-posterior oblique and lateral), upper left maxillary premolars and molar, upper right premolars and molar, lower canines and incisors, lower right mandibular teeth, lower left mandibular premolars and molar.
  • Full mouth radiographs are more likely to be of benefit in older cats.
  • Dental film sizes 0/1 and 2 are ideal.
  • A useful screen for FORLS (feline odontoclastic resorptive lesions   Odontoclastic tooth resorption (resorptive lesions)  ) in cats over 3 years old which do not show lesions clinically consists of 2 films: right mandibular premolars and molar, left mandibular premolars and molar. This makes use of the fact that the most frequently first affected teeth are 307 and 407 (left and right 3rd mandibular premolars - though 1st visible - respectively). Lesions present on the roots can thus tbe detected and x-ray survey expanded where necessary.
  • As technology advances many dentists and veterinary dentists have started using digital x-ray systems for intra-oral radiographs   Dental radiography: digital 01    Dental radiography: digital 02  . A sensor is placed in the patient's mouth instead of an x-ray film and exposed   Dental radiography: digital sensor  . Both direct and indirect systems are available.
  • Direct digital: the image is transferred directly via the sensor to a computer. The advantages of using direct digital systems are that a much lower exposure is required and the time saved during procedures. The software package allows one to view and enhance images and provides images in more detail. Currently there are 3 systems available - Kodak, Eva and Schick. Disdvantages are cost and size of sensor (only size 2 is available as yet). Despite this, the direct system offers the greatest benefit over traditional dental film and processing.
  • Indirect digital: the image is transferred via a digital accessing system from the sensor to a computer. The advantages of using indirect digital systems are that a much lower exposure is required and both film sizes 2 and 4 are available. The software package allows one to view and enhance images and provides images in more detail. Disadvantages are the cost of sensor renewal (its potential for scratches/damage), sensor size limitation and slower image production compared to direct digital.

Restraint

  • Dental radiography requires general anesthesia   General anesthesia: overview  . This is the only way to obtain accurate projections and avoid trauma to film, sensor or operator!

Indications

  • Some lesions may be detected clinically but the full extent of the lesion or disease can only be accurately assessed with radiographs.
  • Much pathology will be detectable only with radiography.
  • With the high incidence of feline odontoclastic resorptive lesions, feline dentistry should not be performed without the use of radiography.

Radiographic anatomy

Normal anatomy

  • See radiograph showing normal anatomy of the mandible   Teeth: normal anatomy of mandible - radiograph  :
    • Mandibular canal (red).
    • Lamina dura and periodontal ligament space (yellow).
    • Crown.
    • Roots.
    • Dentine (more dentine is deposited with age) (blue).
    • Pulp chamber and root canal (narrows with age) (green).
    • Alveolar bone.

Dental formula

  • Maxilla:catI1I2I3CP2P3P4M.
  • Mandibula:catI1I2I3C P3P4M .
  • Carnassial teeth: P4and M1(Red: single rooted; green: double rooted; blue: triple rooted).
  • Adontia (congenital absence of teeth) and oligodontia (only few teeth present) are rare but it is more common for cats to show hypodontia (one or more missing teeth).
  • Supernumerary incisors and premolars are common and cause problems with eruption and deviation of permanent teeth.
  • Impacted and unerupted teeth should be differentiated from missing teeth by intra-oral radiography   Radiography: intra-oral parallel and bisecting angle  .
  • Pre-extraction radiographs are useful and help detect anatomical variations.

Variation in size

  • Microdontia (very small teeth) and macrodontia (abnormally large teeth) have been reported.

Variation in shape

  • Images   Teeth: upper third premolar with extra root - radiograph    Teeth: upper third premolar with extra root   show an extra root on the upper 3rd premolar up to 10% of cats may have an extra root on this tooth.

Interpretation

Appearance

Developmental/ structural defects

  • Images   Teeth: fused tooth 01    Teeth: fused tooth 02  show a developmental abnormality there is gemination (partial splitting/twinning) of the crown.
  • Fusion may also occur where two teeth fuse to form one large, abnormal tooth.

Periodontal disease

  • External root resorption and bone loss may occur as a result of periodontal disease   Periodontal disease  .
  • See   Teeth: periodontal disease - radiograph   (horizontal bone loss evident over mandibular molar).

Gingivostomatitis

  • Inflammation of gingiva plus mucosa   Gingivitis and stomatitis  .
  • Full mouth series radiographs essential.
  • Perfect extractions required - presence of disease teeth, root remnants and atomized material will prevent cure!

Endodontic disease

  • With age, the root canal space becomes narrower as more dentine is deposited. If the pulp becomes inflamed and necrotic, this process will stop.
  • See   Teeth: crown fractures 01 - radiograph   which shows a relatively wide pulp chamber for a 10 yr old cat.
  • With time the necrotic pulp will cause inflammation and destruction at the root apex. Image   Teeth: crown fractures 02 - radiograph  shows loss of the periodontal ligament space and large periapical radiolucency.
  • Radiography is a requirement if certain procedures such as root canal therapy are to be performed.

Resorptive lesions

External resorption:

  • Occurs when tooth material is lost from the outside towards the inside. Various types exist, either idiopathic (cats) or secondary to inflammation, eg periodontitis.
  • Resorptive lesions (RL/FORL 'feline odontoclastic resorptive lesions') are one of the most common oral conditions affecting cats today. The lesions often begin on the root surface or below the gingival margin and only in the final stages when a large degree of destruction has occurred, become visible clinically as a defect in the crown with associated gingivitis.All teeth clinically affected by resorptive lesions should be radiographedas often the lesion detected is only the tip of the iceberg. See image   Teeth: lower canines 01 - radiograph  which shows a radiograph of the small lesion detected clinically in   Teeth: lower canines 02  .
  • Resorptive lesions are found less commonly in dogs than cats but are found in areas of prolonged inflammation.
  • A grading system is used assessing whether the lesion is affecting just the enamel, involves the pulp or has significant weakened and destroyed the tooth.
  • Radiographic evaluation:
    • Assess the integrity of the lamina dura - with RL the periodontal ligament space and lamina dura are not always visible around the entire root. See   Teeth: resorptive lesion 01 - radiograph   (red).
    • RLs can appear as less radiodense areas on the crown or root surface. See   Teeth: resorptive lesion 01 - radiograph   (blue) and   Teeth: type 1 resorption - radiograph  .
    • Many roots disappear with no difference in opacity between the root and the alveolar bone   Teeth: type 2 resorption - radiograph  .
    • End stage lesions may show persistent roots with missing crowns. See   Teeth: end stage type 2 resorption - radiograph  .
  • Two types of  resorptive lesions occur:
    • Type 1 RL with no evidence of resorption of the roots.
    • Type 2 RL with resorption of the roots.
  • Treatment options are dependent on radiographic evidence of resoprtive change and remaining root anatomy.
    Do not assume resorbed. Do not assume will 'disappear' pain free. Do not atomize roots.

Internal resorption

  • Occurs when tooth material is lost from the inside towards the outside. Due to pulpitis (pulp inflammation), eg secondary to tooth fracture   Dental fracture  .

Oral and dental neoplasia

  • Most oral neoplasms are predominantly lytic and may also have some additional irregular new bone formation. Radiographic differentiation often not possible.
  • Bone lysis resulting in 'floating teeth' indicates rapid change and is more frequently found with aggressive malignancies.
  • Slower growth by less aggressive tumors tends to move teeth rather than destroy them or cause rapid bone density loss.
  • Soft tissue tumors: squamous cell carcinoma   Mouth: squamous cell carcinoma  , fibrosarcoma, and malignant melanoma are most common malignant oral soft tissue tumors   Mouth: neoplasia  and can not be differentiated radiographically.
  • Squamous cell carcinoma   Mouth: squamous cell carcinoma  is the most common oral tumor affecting cats and will invade bone. The fine detail obtained by using intraoral film will help assess bone involvement or not. SCC accounts for 70% of oral tumors in cats.
  • Squamous cell carcinoma (SCC) commonly affects soft tissue including the base of the tongue and results in signs of pain, eg ptyalism, difficulty eating.
    SCC lesions often mimic other dental disease, eg periodontal disease, biopsy and radiograph any abnormal (especially asymmetrical) lesions.
  • Fibrosarcomas are another tumor affecting the oral cavity in cats. Typically the tumor presents as a diffuse fibrous swelling with significant bone lysis on radiographs.
  • Bone tumors: mandibular osteosarcoma and multilobular osteochondrosarcoma (= chondroma rodens) are most common malignant bone tumors. The latter is characterized by multilobulated dense new bone formation on the surface of flat bones of the skull and mandible. Rare in cats.
  • Benign oral masses: acanthomatous epulis is a histologically benign but radiographically aggressive lesion (lytic with irregular margins).

Other oral and dental disorders

  • Dental anomalies in size, shape and number of teeth are common. Dental radiographs made at young age can help determine the presence of crowns prior to eruption.
  • Periodontal disease   Periodontal disease  and tooth root infection can be recognized radiographically as widening of the lucent periodontal space and horizontal loss of alveolar bone, periapical lucencies, pathologic tooth root fractures.
  • Trauma: fractures of the mandible and maxilla are much better assessed with the use of intra-oral radiographs and treatment can be planned to avoid important oral structures.
  • Osteitis: common due to local spread of inflammatory and infective disease, tooth abscess.
  • Osteomyelitis: true osteomyelitis is rare in cats
  • Monitor treatment or complications of treatment (root fragments). See   Teeth: radiodense root remnant - radiograph  .

Additional studies

  • Magnetic resonance imaging   Magnetic resonance imaging: basic principles   is a very useful tool in aiding the diagnosis of soft tissue problems associated with the oral cavity. MRI is used to view soft tissue rather than bone so is superior to radiographs and CT scans in demonstrating the extent of soft tissue tumors. In feline medicine it is extremely useful in diagnosing nasopharyngeal tumors.
  • MRI is also useful for assessing the disk damage in cats with temporomandibular joint problems. Damage occurs to the TMJs following trauma.
  • CT   Computed tomography (CT)  is superior to MRI in evaluating bony tumors. CT scans give extremely good detail of the skull base and good detail of the nose. Ideally a CT scan is useful for evaluating the extent of tumors involving the nasal cavity.