The ABCs of veterinary dentistry: D is for Dentigerous cyst

Dr David E Clarke BVSc Diplomate AVDC Fellow AVD
Registered Specialist, Veterinary Dentistry and Oral Surgery
Tracey Small BA (Soc Sc), VN, Dip VN (Dentistry)
www.dentalcareforpets.com.au

 

In this article we continue our journey through the alphabet looking at the letter D.

Introduction

Odontogenic cysts are epithelium lined structures that occur in the areas of the jaws containing teeth.1-3 Uncommon in dogs, they have been reported to include dentigerous cysts, periapical (or radicular) cysts, lateral periodontal cysts, odontogenic keratocysts and canine odontogenic parakeratinised cysts.1,3-6 Odontogenic cysts arise within islands of remnants of odontogenic epithelium (dental lamina, rests of Malassez) located in the periodontal ligament stroma.1 Dentigerous cysts are the most common odontogenic cysts in dogs.1,3,6-10

During odontogenesis, once the enamel has been formed, the enamel organ atrophies and becomes the reduced enamel epithelium.11,12 The reduced enamel epithelium is a closed sac that encompasses the crown of the tooth and is attached at the cemento-enamel junction (CEJ).11-13 When the tooth erupts through the gingiva, the enamel epithelium desquamates to form a ring of tissue around the CEJ and becomes part of the gingival attachment and is no longer a closed sac.6,12

When a tooth fails to erupt, the reduced enamel epithelium remains a closed sac around the crown of the tooth and fluid is drawn in by a process of osmosis resulting in a cyst.12,14 The cyst forms when fluid accumulates within the cyst lining consisting of epithelial cells derived from the reduced enamel epithelium.11,14 This cyst continues to expand compromising and destroying local bone, adjacent teeth and resorption of roots.11-15 Dentigerous cysts are therefore associated with unerupted teeth.11-15 Dentigerous cysts are usually painless, however, the fluid accumulation and proliferation of epithelial cells often cause local destruction to bone and adjacent teeth.11,12

Case study
Tilkah, an 18 month old, 15.5kg, spayed female Blue Heeler dog (Figure 1)

was treated for a dentigerous cyst. She was originally referred to the practice at eight weeks of age with a Class 2 malocclusion that also involved bilateral malposition of the mandibular deciduous canine teeth (704, 804).

704 was positioned distal to 604 and 804 was linguoverted and traumatising the hard palate on the palatal aspect of 504. At the initial visit, the displaced teeth were causing significant pain and possibly causing a dental interlock preventing normal elongation of the mandible.

Treatment involved extraction of 704 and 804 to relieve the trauma and allow the jaw to grow in length if the malocclusion was not of genetic origin.

The recommended revisit time was six months of age for review of the erupting permanent mandibular canine teeth, but due to family restrictions Tilkah returned for an occlusion assessment at 12 months of age.

On conscious examination it was noted that the mandible had not elongated, the left mandibular canine tooth (304) had erupted into an atraumatic position caudal to the left maxillary canine tooth (204), and the mandibular right canine tooth (404) was linguoverted causing trauma to the hard palate.

In addition, it was noted that the mandibular right first premolar (405) was not visible on probing and charting.

Treatment options for 404 included tooth extraction, crown amputation and direct pulp capping, or orthodontic movement were discussed with the owner, who chose crown reduction and pulp capping.

Tilkah was then admitted for treatment of 404 to alleviate trauma to the hard palate and to radiograph the presumed absent 405.

Pre-anaesthetic blood chemistry and haematology profile were within normal limits.

A 22 gauge intravenous catheter was placed in the right cephalic vein aseptically and a balanced electrolyte solution Hartmans™ 2.5ml/kg/hr commenced. A preanaesthetic of acepromazine 0.4mg, buprenorphine 150ug and atropine 0.84mg was given by subcutaneous injection.

Tilkah was induced with diazepam 4mg and ketamine 80mg via IV catheter 30 minutes later. Anaesthesia was maintained via #8 cuffed endotracheal tube using 1.5 – 3% isoflurane in oxygen. Anaesthetic monitoring included visual assessment, reflex activity, oxygen saturation, heart rate, expired CO2, respiratory rate and blood pressure. These parameters were recorded every five minutes on an anaesthetic monitoring form. IV fluids were increased to 5ml/kg/hr (77ml) throughout the surgery procedure. Tilkah was placed into right lateral recumbency and a warming blanket was placed over her to maintain body temperature.

Once Tilkah was stabilised a comprehensive oral examination was performed by the veterinary dental specialist and nurse.
Overall teeth were healthy, no gingivitis was present, some generalised calculus was recorded, tooth 404 was linguoverted and tooth 405 appeared missing (Figure 2). Dental radiographs were taken with a size 2 Sopix digital DR sensor plate. Radiographs of 405 (Figure 3)

revealed an unerupted tooth with no significant radiographic changes to the surrounding area and displacement of the crown in a coronal/distal direction and the root was tipped distally. Based on these findings a tentative diagnosis of a dentigerous cyst was made. The crown amputation and direct pulp capping were performed successfully, but due to anaesthetic considerations, a decision to extract 405 in four months when Tilkah would return for radiographs of the crown amputation and vital pulp therapy of 404 to assess tooth vitality was made and the owner informed.

Tilkah returned four months later for assessment and treatment of the unerupted 405 and to radiograph the vital pulp therapy of 404. Tilkah was found to be in good health and well hydrated. Anaesthesia was performed as previously described.

The patient was placed into left lateral recumbency. A local nerve block using 0.3mls of 3% mepivacaine into the mandibular right middle mental foremen using a dental aspirating syringe and carpule was performed, which blocks the inferior alveolar nerve, thereby anesthetizing the mandibular incisors and canine. Mepivacaine takes affect within two minutes and lasts for approximately 2-3 hours. A radiograph of the previous crown amputation and direct pulp capping showed a formed dentinal bridge and narrowing of the pulp canal, indicative of treatment success and tooth vitality.

A radiograph of the impacted 405 (Figure 4) showed an enlargement of the lesion and some alveolar bone loss associated with the distal aspect of 404.

A size 15 surgical blade was used to make an incision into the gingiva over the normal position of 405 extending from the mesial aspect of 406 to the distal aspect of 404. A No 2 Molt periosteal elevator was then used to elevate an envelope flap to expose the underlying area. The flap was retracted with a Minnesota retractor to visualise the impacted tooth (Figure 5).

A No. 2 winged Cislak dental elevator was used to sever the periodontal ligament supporting 405 which had a portion of the soft tissue (presumed to be a dentigerous cyst lining) attached to the CEJ (Figure 6).

The 405 with attached epithelial tissue was extracted with extraction forceps (Figure 7) and placed into a formalin pot for histopathology at Gribbles Pathology. A post extraction radiograph showed there was alveolar bone resorption along the distal surface of 404 and the mesial surface of the mesial root of 406 where the epithelial lining was adhered to.

The epithelial cavity lining was debrided using a No 2 Molt periosteal elevator (Figure 8) and placed into a separate formalin pot for histopathology.

The exposed root surfaces of 404 and 406 were curetted with a #5/6 Gracey curette. A radiograph was taken to confirm complete extraction of 405 and debridement of the cavity (Figure 9).

With confirmation of extraction of 405, the area was flushed and tricalcum phosphate was placed into the defect to the height of the alveolar bone and radiographed (Figure 10).

The gingiva was sutured closed with polyglycolic acid absorbable suture size 3/0 (Figure 11).

Tilkah was moved to a recovery cage. IV fluids were reduced to 2.5ml/kg/hr (38ml) for an hour. A subcutaneous injection of meloxicam 3mg for pain and inflammation was administered. At discharge, the client was instructed to feed soft chunks of meat for the next 10 days and to prevent Tilkah from chewing on any hard objects to allow the extraction site to heal. Medications were explained, oral meloxicam to the 15.5kg dose mark once daily and clindamycin 150mg capsules twice daily for 10 days. Maxigard™ gel (chlorhexidine free zinc and Vitamin C formula) was advised to use daily by placing a pea sized drop on both upper canines for regular oral hygiene. A revisit consultation was booked for two weeks time.

The owners were contacted by phone two days post-surgery, Tilkah was recovering well with no complications. The histopathology report noted: Macroscopy – “Tooth 405 and cyst”. A tooth with surrounding attached connective tissue and five tiny fragments of light tan non-descript tissue the largest of which measures 3mm x 1mm. The soft tissues from around the tooth are removed and placed into a single cassette with fragments of additional tissue and the tooth is placed into decalcification for further processing. Microscopy – Gingival cyst (multiple fragmented sections): The sections evaluated are fibrovascular connective tissue with multiple segments of the surface having an intact layer of stratified epithelial cells.

The epithelial cells are well differentiated with no outstanding atypical features. In some areas the underlying connective tissue is consistent with granulation tissue and some segments have mild local active inflammation composed of macrophages, lymphocytes, plasma cells and occasional neutrophils. The decalcified sections of tooth have no significant changes. Diagnosis – Gingival cyst: Dentigerous cyst. Comments – The gingival tissues provided are lined by stratified squamous epithelial cells with additional sections of a histologically normal tooth which is consistent with a dentigerous cyst. A diagnosis of dentigerous cyst was therefore confirmed by histopathology and the owners were informed of the result.

A revisit consultation two weeks post-surgery showed that the surgery site had healed, and sutures had dissolved (Figure 12).

The owners were shown how to brush Tilkah’s teeth and instructed to do so daily using the supplied Petosan toothbrush and toothpaste. An appointment was made for six months to radiograph the surgical site, to evaluate the success of enucleation of original cyst and to assess the health of bone structure and tooth vitality of 404 and 406. At this revisit, the area had healed well (Figure 13) and radiographs confirmed successful regrowth of previously lost bone (Figure 14).

Conclusion
Dentigerous cysts should be a primary consideration for any oral swelling or missing tooth in either jaw.3,6,16,17 The most commonly represented breeds are the brachycephalics and the most common area is the first premolar in the mandible.3,17
Because dentigerous cysts are often discovered as an incidental finding, the significance of a thorough oral examination and radiographs of all presumed missing teeth cannot be over emphasised.3,6,17 Treatment involves a surgical approach using a mucogingival-periosteal flap to accomplish removal of the unerupted tooth, complete enucleation of the cyst wall, curettage, osteoplasty, and bone grafting if bone defects are extensive.3,6,16,17 In the many cases, a bone graft is not necessary, as a healthy blood clot using the host’s own osteoblasts to replace bone lost is recommended. Prognosis is excellent when treated early and when the cyst is completely excised6,11,12,14,15 as early detection and treatment of dentigerous cysts prevents the continuation of local bone and tooth destruction.11,13-15 Histopathology of the epithelial lining is recommended.
It is recommended that follow up radiographs are performed six months later to confirm success of excision, to assess the regeneration of local bone, vitality of adjacent
teeth, periodontal support and root resorption.6,11,13-15

References:
• Poulet FM, Valentine BA, Summers BA. A survey of epithelial odontogenic tumours and cysts in dogs and cats. Vet Pathol 1992;29:369-380.
• Gardner DG. An orderly approach to the study of odontogenic tumours in animals. J Comp Pathol 1991;107:427-438.
• Verstraete FJM et al. Clinical signs and histological findings in dogs with odontogenic cysts: 41 cases. JAVMA 2011;239:1470-1476.
• Nicoll et al Odontogenix keratocyst in the dog. JAAHA 1994;30:286-289.
• Lommer MJ. Diagnostic imaging in veterinary dental practice. Perapical cyst. JAVMA 2007;230:997-999 Beckman BW. Radicular cyst of the premaxilla in a dog. JVD 2002;20:213-217.
• Verstraete FJM, Chamberlain TP. In: Oral Maxillofacial Surgery in Dogs and Cats. 2nd ed. Verstraete FJM, Lommer MJ and Arzi B. p463-464.
• Doran I, et al. Extensive bilateral odontogenic cysts in the mandible of a dog. Vet Pathol. 2008;45:58-60.
• Gardner DG. Dentigerous cysts in animals. Oral Surg Oral Med Oral Pathol. 1993;75:348-352.
• Kramek BA, O’Brien D, Smith FO. Diagnosis and removal of dentigerous cyst complicated by ameloblastic fibro-odontoma in a dog. J Vet Dent. 1996;13:9-11.
• Regezi JA, Sciubba JJ, Jordan RC. Cysts of the jaw and neck. In: Oral Pathology: Clinical Pathologic Correlations. 7th ed. 2017:245-268.
• D’Astous J. An overview of dentigerous cysts in dogs and cats. Can Vet J. 2011; 52(8): 905-7.
• Hale, FA. Dentigerous cysts an avoidable catastrophe. The CUSP, 2007; January; 1-5.
• Beckham B. The diagnosis and surgical removal of a dentigerous cyst associated with unerupted mandibular left first premolar in a Shih Tzu. Available at: http://www.veterinarydentistry.net/blog/wp…./01//Dentigerous-Cyst-Case-Report.pdf
• Niemiec Brook A. A Color Handbook Small Animal Dental, Oral & Maxillofacial Disease. Florida: CRC Press; 2012, pp. 118-119
• Lobprise Heide B. Blackwell’s Five-Minute Veterinary Consult Clinical Companion – Small Animal Dentistry. 2nd ed., Ames: Blackwell Publishing; 2012, pp. 178-182
• Verstraete FJM, Tsugawa AJ. Self assessment Colour Review of Veterinary Dentistry, 2nd ed, 2016.
• Babbitt SG, Krakowski Volker M, Luskin IR. Incidence of radiographic cystic lesions associated with unerupted teeth in dogs. J Vet Dent. 2016;33:523-531.

 

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