THE HEALTHY COLLIE: DENTITION
DENTIGEROUS CYST IN THE MANDIBLE OF A DOG

by Dr. David E. Hansen, D.V.M., Fellow AVD
Camloch Collies

Please refer to the previous article for terminology definitions

Patient History / Presenting Complaint
A 20-month-old, 60 pound spayed female Boxer was presented for assessment and treatment of a large mandibular swelling located caudal to the right mandibular canine tooth. The owner one-month prior had noticed the swelling. The dog had no history of trauma and did not seem painful. The swelling had been increasing in size. The owner is a licensed veterinary technician working for a board-certified internal medicine specialist. Initially skull radiographs and an ultrasound of the area revealed a fluid filled cyst in the bone. The cyst was aspirated multiple times through the ventral border of the mandible.

Preliminary Examination
On physical examination the only abnormalities were limited to the patient's right mandible and oral cavity. Her right mandible had a 15mm swelling extending from the caudal aspect of right mandibular canine tooth to the mesial aspect of the right mandibular third premolar tooth. The right mandibular second premolar tooth was in an elevated position on the swelling. The right mandibular first premolar tooth was not evident. (see Figure 1)

Figure 1: Swelling caudal to the canine tooth

Dental Radiograph
The patient was anesthetized. The survey intraoral radiographs of the anterior mandible showed a large round radioleucent area extending from the caudal aspect of the root of the right mandibular canine tooth, to 2 mm mesial to tooth right mandibular second premolar tooth.

Figure 2: Large cyst in right mandible

The right mandibular first premolar tooth and the roots of the right mandibular second premolar tooth appeared to be within the radioleucent area. (see Figure 3) A diagnosis of a dentigerous cyst of the right mandibular first premolar tooth was made.

Figure 3: First and second premolars involved

Surgical Procedure
Prior to starting the surgical procedure, a right caudal mandible local nerve block was placed. While waiting for the local block to take affect, a complete dental prophylaxis was done. A detailed oral examination revealed no other abnormalities other than a moderate amount of plaque.

An incision was made from the caudal aspect of right mandibular canine tooth extending distally around the labial side to the caudal aspect of the right mandibular second premolar tooth. A mucoperiosteal flap was raised off of the labial side of the mandible exposing the raised surface of the bone and unerupted right mandibular first premolar tooth. (see Figure 4)

Figure 4: First premolar exposed

The bone from right mandibular canine tooth, encircling the right mandibular first premolar tooth and extending to the right mandibular second premolar tooth, was removed diamond bur. The opening was enlarged revealing a large cyst with a very thin cortex of bone around it. The caudal root surface of the right mandibular canine tooth could be identified to the apex. The mesial root of the right mandibular second premolar tooth could be identified without any bone support. The right mandibular second premolar tooth was easily elevated and extracted. The right mandibular first premolar tooth was carefully extracted with the lining of the cyst wall. (see Figure 5)

Figure 5: After teeth and cyst are removed

The lining was elevated off the bone with a periosteal elevator. Special care was taken around the apex of the right mandibular canine tooth in an attempt to preserve its blood supply. The large cavity was flush with sterile saline and filled with a synthetic bone graft particulate. The flap was sutured in a simple interrupted pattern. (see Figure 6)

Figure 6: Post-op

Final radiographs were taken to document the fill of the cyst and for comparison later. (see Figures 7 and 8)

Figure 7: Post-op

Figure 8: Post-op

Aftercare
The patient made an uneventful recovery showing very little discomfort. A non-steroidal anti-inflammatory drug was to be given once daily only as needed by the patient. The owner was to flush the mouth twice daily after eating. The dog's regular kibble was to be soaked in water to soften it for a period of 5 days and the owner was to withhold chew toys, rawhides etc until the 6-month recheck to decrease the risk of a mandibular fracture. Exercise was to be restricted for 1 week. A recheck was scheduled in 14 days.

Follow-up
At the 14-day recheck, the patient was doing extremely well. The owner reported that the dog had not missed a meal. The mucosa was healing nicely. She had not shown any signs of pain. The owner was to start brushing the dog's teeth daily.

The patient was presented for follow-up radiographs 6-month post-op. She had not shown any signs of pain. The owner had not allowed the dog to chew on any hard objects. The mandible appeared normal on visual examination. The radiographs showed excellent remodeling of the bone and synthetic material. (see Figure 9)

Figure 9: 6 month post-op

The alveolar ridge height was maintained to an almost normal level, which will improve the strength of the mandible to prevent a pathologic fracture. There was a periodontal space evident along the caudal aspect of the right mandibular canine tooth. (see Figure 10)

Figure 10: 6 month post-op

The pulp chambers of the right mandibular canine tooth and the opposite mandibular canine tooth were of equal size. The pulp chamber of the right mandibular canine tooth was also smaller when compared to the radiograph taken 6-month previously. This indicates that the right mandibular canine tooth is still vital.

Discussion
This patient was not showing any obvious signs of pain. The sudden appearance of a enlarging growth was the only indication that a problem was developing. The initial skull radiographs were inadequate due to the overlapping right and left mandibles. The ultrasound did reveal a fluid-filled cyst, however it was done from the ventral border of the mandible so the right mandibular first premolar tooth was not evident as it was on the far side of the fluid. When first encountering a lesion like this in a young dog the first question is: Are all of the teeth present?

Dentigerous cysts can be divided into two basic types, eruption and follicular. Eruption cysts are a dilation of the normal follicular space surrounding a tooth crown during eruption and follicular cysts are dilations of the follicular space around the crown of a tooth that is unerupted or impacted. A cystic structure arises from the developing dental follicle at the neck of the tooth. If a tooth fails to erupt, the follicle remains and produces a sac. The cyst can be very invasive and expansile and requires thorough surgical removal and curettage. If there is incomplete removal of the lining the cyst is likely to recur.

Intraoral radiographs in young animals are indicated when there are teeth that are apparently absent It should not be assumed that the teeth are absent until proven so. Early treatment of impacted or non-erupted teeth may prevent the formation of dentigerous cysts. The formation of dentigerous cysts will result in much more tissue destruction and pain for the patient.

This case and the previous case demonstrated that a missing tooth is not necessarily missing at all, but not erupted. Many times there is a missing tooth because there was never an adult tooth bud present. Missing teeth are most commonly seen in small dogs, and in some larger breeds can be considered a serious fault. Permanent teeth are more frequently missing, and if a deciduous (baby) tooth is genetically not present, the permanent associated tooth should also be absent. Generally a tooth that is truly missing can only be distinguished from an unerupted or impacted tooth by obtaining radiographs of the site.

Developmental problems can be due to a specific inherited cause (genetic), probable genetic etiologies (theories), with a familial tendency, or due to congenital influences. Genetic describes conditions that are inherited. Congenital describes abnormalities present at birth, either inherited or due to conditions that occurred during pregnancy (eg, infection, drugs, injury). Familial describes conditions that affect a family to an extent that is considered greater than expected by random or chance circumstance.

Missing and extra (supernumerary) teeth share a familial tendency and may be hereditary in some cases and acquired in others. A dog can have both missing and extra at the same time. (see Figure 11)

Figure 11: 2 first premolars, but no second premolar

It is my personal observation that in the larger breed dogs, the most common missing teeth are one of the mandibular or maxillary first three premolars. Retained deciduous teeth can also delay the eruption of the permanent teeth. Even if the permanent tooth is not delayed in eruption, it may be deflected by the deciduous tooth and can contribute to malocclusion.

David E. Hansen, DVM., Fellow AVD, graduated from Kansas State College of Veterinary Medicine in 1987. In 1989 he and his wife, Krista, formed Camloch Collies. He developed an interest in advanced veterinary dentistry in 1990 and in 2001 became one of only 69 Fellows of the elite worldwide organization, Academy of Veterinary Dentistry.