Figure 1: Bony swelling of the rostral right mandible in a 7-month-old dog.Photos courtesy John Lewis Laga is a seven-month-old female spayed Labrador that presented with a bony swelling of the right rostral mandible. The swelling was noted a week prior to presenting to her primary care veterinarian. Physical examination was unremarkable except for abnormalities noted on the orofacial exam. A palpable bony swelling of the rostral right mandible measured approximately 4 cm in diameter (Figure 1). Intraorally, the right mandibular canine tooth (tooth 404) was displaced distally and was linguoverted, resulting in trauma to the palate. Tooth 403 was noted to be missing (Figure 2). Looking for a diagnosis Laga was placed under general anesthesia, and dental radiographs were obtained (Figure 3). Tooth 403 was found to be unerupted and malformed, and a cystic structure was centered at the crown of tooth 403, which resulted in displacement of teeth 402, 404, 405, and 406. Tooth 403 and its suspected cyst were surgically approached dorsally after extraction of teeth 401, 402, 404, 405, and 406. Tooth 403 was removed and a large cystic soft tissue structure was retrieved intact from the dorsal opening in the right mandible. The site was curetted, lavaged and closed with 4-0 poliglecaprone 25 in a simple interrupted pattern (Figure 4). Histopathology of the submitted soft tissue structure revealed a diagnosis of epithelial cyst, which when occurring in the area of an unerupted tooth, is consistent with a dentigerous cyst. Not every unerupted tooth results in formation of a dentigerous cyst. In a retrospective study spanning four years at a dental specialty practice, 136 dogs ranging in age from three months to 17 years were diagnosed with 213 unerupted teeth.1 Brachycephalic breeds are predisposed. Boxers, pugs, shih tzus, and Boston terriers are at the top of the breed predilection list.1 Out of 213 unerupted teeth radiographed in one study, cystic lesions were identified in 29 percent of these unerupted teeth.1 Since there is no way to predict which dogs’ unerupted teeth will develop cysts, I follow the general guideline to remove any unerupted tooth if the owner lets me. Another reason not to “wait and watch” unerupted teeth is the fact dentigerous cysts have been reported to occasionally malignantly transform to carcinomas.2 Surgical details Unlike Laga’s case, surgical removal of the cyst lining usually results in multiple small pieces, rather than a large, intact cyst. The cyst lining is usually very thin and comes out in unrewarding thin pieces of epithelium. It is important to take the time to meticulously curette the lining of the cyst away from the sclerotic bony wall of the defect. Removal of the cyst lining is referred to as enucleation. I usually use a small bone curette or a feline periosteal elevator to remove the lining. Remember to look for cyst lining on the inside of the raised flap, since some of the lining may be adherent to the underside of the flap. Depending on how the cyst has affected the adjacent teeth, further extractions may be necessary. In Laga’s case, five teeth were extracted either due to bone loss caused by the cyst or to allow for better visualization of the cyst. An allograft was placed into the defect, but the size of the defect and expense of the graft material precluded complete filling of the defect with graft material. In cases where bone graft is not placed, a fibrin clot likely fills the area and acts as scaffolding for bone to traverse the area. Follow-up radiographs of Laga’s mandible were obtained approximately one year later, which showed remodeling of the cystic structure to a radiographic appearance of consolidated bone of normal density (Figure 5). Dentigerous cyst The dentigerous cyst is a specific type of odontogenic cyst associated with an unerupted tooth. Dentigerous cysts arise due to a retained epithelial lining that surrounds the crown. This epithelial lining is normally shed when a tooth erupts. When a tooth does not erupt, fluid accumulation occurs within the epithelial lining, which results in expansion of the cyst over time and resultant bone loss. The teeth most likely to be unerupted are the mandibular first premolar teeth in dogs. Other sites include mandibular third molar, maxillary and mandibular incisor teeth, and mandibular canine teeth. Have you seen a dentigerous cyst in your practice? If not, one has probably seen you. [wonderplugin_slider id=138] John Lewis, VMD, FAVD, DAVDC, practices dentistry and oral surgery at Veterinary Dentistry Specialists and is the founder of Silo Academy Education Center, both located in Chadds Ford, Pa. References Babbitt SG, Krakowski Volker M, Luskin IR. Incidence of radiographic cystic lesions associated with unerupted teeth in dogs. J Vet Dent. 2016. Dec;33(4):226-233. Colbert S, Brennan PA, Theaker J, Evans B. Squamous cell carcinoma arising in dentigerous cysts. J Craniomaxillofac Surg. 2012. 40(8):e355-357.
