Contributors: Lisa Milella, Alex Smithson

 Species: Canine   |   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 dogs 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 4) or a small flexible cassette and screen is ideal for nasal chambers.
  • Radiography should be performed for any teeth showing pathology or suspected pathology after careful probing.
  • Full mouth radiographs are not commonly performed but are of benefit in dogs showing gingivostomatitis or requiring investigation of orofacial pain where a focus/ foci of pathology cannot be identified clinically/ on probing.
  • Ensure that adentulous areas (missing teeth) area imaged especially where signs of inflammation (eg gingivitis) are seen; root remnants are common!
  • Size 2 (periapical) film is ideal for most teeth. Canines and other teeth in large breeds may require size 4 (occlusal) dental film.
  • The number of films required for a full mouth series depends on the size of the dog but includes:
    • Upper incisors, upper left canine (anterio-posterior oblique and lateral), upper right canine (anterio-posterior oblique and lateral), upper left maxillary premolars and molars, upper right premolars and molars, lower canines and incisors, lower right mandibular premolars and molars, lower left mandibular premolars and molars, lower left canine anterio-posterior oblique +/- lateral, lower right canine anterio-posterior oblique +/- lateral.
  • As technology advances many dentists and veterinary dentists have started using direct digital X-ray systems for intra-oral radiographs. 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. Disadvantages are the cost and size of sensor - only size 2 is available as yet. This size limitation means that larger teeth may require two views, each of a different tooth portion (usually coronal/crown then radicular/root areas), to enable full assessment. 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. 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.
  • Accurate diagnosis, treatment planning and treatment monitoring requires examination of the whole tooth including root(s) and surrounding bone.

Radiographic anatomy

Normal anatomy

  • See Skull normal teeth - radiograph intra-oral DV Gingiva normal anatomy Endodontics and normal anatomy.

Dental formula

  • Maxilla: I1I2I3CP1P2P3P4M1M2.
  • Mandibula mandible :I1I2I3CP1P2P3P4M1M2M3
  • Carnassial teeth: p4andM1( Red: single rooted; green: double rooted; blue: triple rooted)
  • Anodontia (congenital absence of teeth) and oligodontia Skull oligodontia - radiograph intra-oral (only few teeth present) are rare but it is common in dogs for a few teeth to be missing (hypodontia).
  • Supernumerary incisors Teeth supernumerary and premolars are common and cause problems with eruption and deviation of permanent teeth (less frequent of a problem in cats).
  • Impacted and unerupted teeth should be differentiated from missing teeth by intra-oral radiography.
  • Pre-extraction radiographs are useful and help detect anatomical variations, eg supernumerary roots, which would complicate extraction etc.

Variation in size

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

Variation in shape

  • Extra roots may be seen, eg up to 10% of cats may have an extra root on the upper 3rd premolar.

Interpretation

Appearance
Developmental/ structural defects

  • Developmental abnormality, eg germination (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 Mandibular 1st molar and 4th premolar showing severe periodontal disease - radiograph.

Endodontic disease

  • With age, the root canal space becomes narrower as more dentine is deposited by the pulp. If the pulp becomes inflamed and necrotic, this process will stop Teeth pulpal necrosis 01 Teeth pulpal necrosis 02.
  • With time the necrotic pulp will cause inflammation and destruction of bone at the root apex.
  • Radiography is a requirement if certain endodontic procedures such as root canal therapy Endodontics: root canal therapy are to be performed.

Resorptive lesions

1) 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 Periodontitis.
  • Resorptive lesions (RL): all teeth clinically affected by resorptive lesions should be radiographed as often the lesion detected is only the tip of the iceberg.
  • 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 significantly 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.
    • RLs can appear as less radiodense areas on the crown or root surface.
    • Many roots disappear with no difference in opacity between the root and the alveolar bone.
    • End stage lesions may show persistent roots with missing crowns.
  • 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 resorptive change and remaining root anatomy.
    Do not assume resorbed. Do not assume will 'disappear' pain free. Do not atomize roots.

2) 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.
    Lesions may mimic other dental disease eg periodontal disease; biopsy and radiograph any abnormal (especially asymmetrical) lesions!
  • Soft tissue tumors: squamous cell carcinoma, fibrosarcoma, malignant melanoma are the most common malignant oral soft tissue tumors and can not be differentiated radiographically. Relative prevalence:
    • Malignant melanoma (30-35%), invades bone, aggressive changes
    • Squamous cell carcinoma (SCC) is also a common oral tumor in dogs and will invade bone. The fine detail obtained by using intra-oral film will help assess bone involvement or not. SCC accounts for 20-30% of oral tumors in dogs.
    • Fibrosarcomas frequently affect the oral cavity in dogs (upto 20% of oral tumors). Typically the tumor presents as a diffuse fibrous swelling with significant bone lysis on radiographs.
    • Fibrosarcomas in dogs show marked variation in behavior and aggression.
  • Bone tumors Bone: neoplasia : 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 Oral tumor: benign Non neoplastic oral masses :
    • Gingival hyperplasia Gingival enlargement common response to inflammation (gingivitis).
    • Dentigerous cysts, ameloblastoma, adamantinoma, odontoma Skull dental tumor - radiograph intra-oral , fibromatous epulis (POF peripheral odontogenic fibroma Oral masses: benign fibromatous epulis ), ossifying epulis (POF peripheral ossifying fibroma Oral masses: ossifying epulis ), are the most common benign oral and dental neoplasms. Characterized by expansile lytic mandibular or maxillary lesion with more or less well defined margins. (Rare in cats.)
    • Acanthomatous epulis Oral masses: acanthomatous epulis is a histologically benign but radiographically and clinically invasive, 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 and tooth root infection can be recognized radiographically as widening of the lucent periodontal space and horizontal loss of alveolar bone, periapical lucencies (dark halo around root apex), pathologic tooth root fractures.
  • Trauma: fractures of the mandible and maxilla are much better assessed with the use of intraoral radiographs and treatment can be planned to avoid important oral structures.
  • Osteitis: common due to local spread of inflammatory and infective disease, eg tooth abscess
  • Osteomyelitis: true osteomyelitis is rare in cats
  • Monitor treatment or complications of treatment (root fragments).

Additional studies

  • Magnetic resonance imaging 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 animals with temporomandibular joint problems. Damage occurs to the TMJs following trauma.
  • CT Computed tomography: head is superior to MRI in evaluating bony tumors. CT scans give extremely good detail of the skull base, TMJs and good detail of the nose. Ideally a CT scan is useful for evaluating the extent of tumors involving the nasal cavity Computed tomography: nasal chamber.