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A 1 year 10 month old male neutered Labrador Retriever presented to the Dentistry team at The Ralph with a one month history of discolouration of the crowns of  the right maxillary and mandibular canine teeth (104 and 404) with no visible signs of trauma to the surrounding soft tissues. He had been known to eat enthusiastically out of a rigid plastic slow feeder prior to presentation. 

The patient presented bright, alert and responsive. Cardiothoracic auscultation was unremarkable. His weight was 28.5 kg with a body condition score of 5/9. His behaviour was friendly and boisterous. A conscious oral assessment confirmed pink discolouration of the entire crown of the right maxillary canine tooth (104) and the coronal half of the crown of the right mandibular canine tooth (404).

Figure 1: Pink discolouration of the entire crown of the right maxillary canine tooth (104) and the coronal half of the crown of the right mandibular canine tooth (404).

The Dentistry team admitted the patient, and an anaesthetised examination including diagnostic probing, charting and dental radiography was performed. As part of the assessment of intrinsically discoloured teeth, the contralateral tooth is also radiographed, for comparison, and a significant additional pathology was present. Impaction of both the left and right mandibular first premolar teeth was noted (305 and 405). A mandibular dentigerous cyst was identified associated with 305. It was radiographically well-defined, extending from the distal aspect of the left mandibular canine tooth (304) to the mesial aspect of the second premolar tooth (307). The left mandibular second premolar tooth (306) had partial resorption of the root apices. The size of the cyst was moderately large, however it had not yet caused significant displacement expansion of the mandible, and therefore, no associated visual swelling was present.

Figure 2: Location of dentigerous cyst

Figure 3: Impaction of both the left and right mandibular first premolar teeth was noted (305 and 405).

Figure 4: A mandibular dentigerous cyst was identified associated with 305.

Treatment for the dentigerous cyst was deemed more urgent than the root canal treatments. Endodontic treatments were therefore postponed.

Loco-regional anaesthesia was provided by means of a left inferior alveolar block. The cyst was exposed from an intra-oral dorso-buccal approach, and its entire lining was surgically removed (enucleated). A large pedicle flap was elevated, extending from the distal aspect of the left mandibular canine tooth (304) to the distal aspect of the left mandibular second premolar (306). The thinned buccal bone was removed with rongeur forceps, and cyst lining was extirpated with a curette. A sample of the capsule was sent to the external laboratory for histopathology.

Figure 5: The surgical site of the dentigerous cyst after removal of the cyst lining.

The unerupted 305 and 405 and diseased 306 were extracted. Synthetic bone graft material (Synergy) was placed in the defect prior to surgical closure. Histopathology of the cystic lining confirmed the diagnosis and no neoplastic cells were identified.  Four weeks later he returned for his root canal procedure to the right maxillary and right mandibular canine teeth (104 and 404). Radiography showed early signs of bone ingress into the previous cyst defect. 

Figure 6: The completed root canal treatment to the right mandibular canine tooth (404)

Figure 7: The completed root canal treatment to the right maxillary canine tooth (104)

Dentigerous cysts are a type of odontogenic cyst derived from the enamel organ (the structure responsible for enamel formation), of the crown of an unerupted tooth. This leads to deposition of fluid, cyst formation and subsequent bone expansion, with progressive loss of integrity of the surrounding structures. While there is the possibility that a cyst can occur at the site of any unerupted tooth, mandibular first premolar teeth (305/405) are most commonly affected, followed by the mandibular third premolar teeth (307/407), mandibular incisor teeth and canine teeth. Brachycephalic breeds such as Boston terriers, Pugs and Boxers seem to be particularly susceptible to this condition due to dental overcrowding . 

While not uncommon in veterinary patients, the signs of dentigerous cysts can be subtle and can be easily missed on routine oral examination.  In some cases, the overlying tissues appear normal and the area is rarely painful, unless concurrent infection is present. In other individuals there may be associated visible oral swelling, sometimes with a hint of grey or brown discolouration (due to the colour of the fluid within the structure). If left long enough, these cysts can begin to damage the surrounding cortical bone, leading to facial asymmetry or a marked mass effect. If untreated (and particularly if bilateral disease is present), pathological fractures can result. 

Fine needle aspirate of a suspicious swelling may yield grey/brown fluid, however cytology of this fluid is rarely diagnostic. Diagnosis of these lesions requires imaging. Dental radiography is the most commonly performed modality, however CT (Computed Tomography) or CBCT (Cone Beam Computed Tomography), can also be useful, especially in large lesions to better appreciate collateral damage, involvement of other anatomical structures (such as the nasal sinuses in maxillary lesions and the proximity to the mandibular canal in mandibular lesions) and bone integrity.

There are two possible treatment methods for these cysts depending on their size and involvement of other structures. In the case of small lesions, identified early in the course of disease, the treatment of choice involves extraction of the causative unerupted tooth together with any adjacent teeth irreversibly damaged by the disease process. Following extraction, the epithelial lining of the cyst should be enucleated in its entirety, with a section submitted for histopathology. If the resultant deficit is large, then bone grafting materials such as Synergy (a synthetic material composed of a biphasic combination of β-Tricalcium Phosphate and Hydroxyapatite) or demineralised bone matrix (morcelised cancellous bone, processed to remove soft tissue, cells and marrow elements, freeze-dried and irradiated after packing), can be instilled into the resultant cavity. 

If the cyst is particularly large, or there is close proximity to vital structures, then a second treatment method has been proposed. This involves marsupialisation of the overlying gingival or mucosal tissue. The cyst is exposed via a mucoperiosteal flap and a section of the cyst lining is removed. A stoma is then created by suturing the edges of the cyst lining to the surrounding gingiva. This allows continued drainage of fluids while concurrently encouraging ingress of bone into the deficit, reducing it in size. Once the size of the lesion is more favourable, then traditional enucleation can be carried out as described above. 

In most cases, complete removal of the cyst lining along with any causative unerupted dentition is curative. This highlights the importance of further investigation in patients with missing dentition beyond the normal period of eruption (with no history of previous extractions), particularly in predisposed breeds.

While slow feeder bowls do have their benefits, it is also important to consider the possibility of oro-dental trauma that can be sustained from their use in highly food-motivated dogs such as Labrador retrievers. In these cases, alternatives such as forage mats or scatter feeding  may be a safer option and offer some enrichment.

Thank you for taking the time to read Ria’s article from our Summer newsletter! Head back to the Our Community page on our website to take a read of the rest of this edition of The Ralpher.

Bye for now!

Team Ralph 🐾