My colleagues and I recently visited Michele Goodman, VMD, and Colleen Clabbers, VMD, and their team at Elmwood Park Zoo in Norristown, Pa. The zoo recently unveiled its new facility, the Frank and Paige Engro Veterinary Health Center (Figure 1), where we performed a dental examination on Colby, a three-year-old male intact muntjac. Figure 1. The treatment room of the Frank and Paige Engro Veterinary Health Center at Elmwood Park Zoo. Visitors can observe procedures in real-time from the balcony. Photo courtesy Dr. John R. Lewis Patient overview Colby’s keeper noted the deer was missing his left maxillary canine tooth. The keeper was able to palpate the area of the missing tooth and felt a rough surface suggestive of a retained portion of crown and root. No tooth was found in his exhibit, and there were no other males Colby shared the exhibit with. The male Chinese muntjac (Muntiacus reevsii) has interesting (and large) maxillary canine teeth. They are approximately 50 mm long and 20 mm wide. Utilized for fighting and dominance displays with other males, large canine teeth can be challenging for ruminants that need to sufficiently chew their cud. Firmly rooted tall canine teeth could prevent lateral movement of the mandibles necessary for chewing and could adversely affect prehension of forage. The muntjac has a clever adaptation: the canines of mature muntjacs are not firmly fixed within their alveoli. Due to an abnormally wide periodontal ligament space, their canine teeth can move in not only a lateral direction but also in a rostral-caudal direction. Only mature canine teeth (i.e. completely erupted canines with closed roots) exhibit this degree of mobility. Immature canine teeth do not.1 Despite having short roots and being remarkably mobile, they have been described to be surprisingly difficult to extract.1 Surgical plan Our anesthetized examination of Colby showed evidence of a portion of the left maxillary canine tooth crown protruding through the gingiva (Figure 2). Dental radiography and conventional CT scan showed evidence of a tooth root approximately 25 mm long, with a wide periodontal ligament space and minimal bone separating the root and the nasal passage. Figure 2. Broken left maxillary canine tooth in a muntjac. The male Chinese muntjac has interesting (and large) maxillary canine teeth; approximately 50 mm long and 20 mm wide. Photo courtesy Dr. John R. Lewis We performed a regional nerve block at the left infraorbital foramen with bupivacaine. A gingival incision was made with a 15c blade directly over the tooth. A size 3 dental luxator, and winged dental elevators of size 5 and size 8 were used circumferentially to break down periodontal ligament gently. Once mobility was significantly increased, the root was grasped with a pair of large Blumenthal rongeurs and gently rotated in each direction before gentle coronal traction was placed to deliver it (Figure 3). A postoperative radiograph was obtained to confirm the removal of the entire root. The site was closed with a simple interrupted pattern using 5-0 poliglecaprone 25 (Figure 4). Figure 3. Root of the left maxillary canine tooth is retrieved with a closed technique using luxators, elevators and Blumenthal rongeurs doubling as extraction forceps. Photo courtesy Dr. John R. Lewis Fracture of canine teeth in muntjacs appears to be common. In a study of 76 males aged over two years, 41 percent were found to have broken one or both canines.2 Though muntjac canine teeth have been reported to be challenging to extract, Colby’s maxillary canine tooth root was cooperative and a full mucoperiosteal flap was not required. Incisions were limited to the gingiva and stopped at the mucogingival line. Figure 4. Closure of the extraction site with 5-0 poliglecaprone 25. Note the size of thecontralateral canine tooth! Photo courtesy Dr. John R. Lewis Dental morphology Dental morphology refers to the form and structure of teeth. Teeth can be classified as brachyodont or hypsodont based on their crown and root structure. All teeth of humans, carnivores, and pigs are brachyodont. Brachyodont teeth have a distinct crown and well-developed roots. The apices (singular: apex) of the roots are open for a limited time during eruption and development; therefore, the teeth do not continually grow or erupt. This contrasts with hypsodont teeth (seen in horses, rodents, and lagomorphs), which have a comparatively large reserve crown beneath the gingival margin and root structure that allows for continued growth and/or continued eruption during all or most of an animal’s lifetime. Hypsodont teeth can be divided further into two categories: radicular and aradicular hypsodont teeth. The cheek teeth of horses are an example of radicular hypsodont teeth. The apices of these teeth remain open for a significant portion of adult life, but they eventually close, after which continued growth of the tooth ceases, and occlusal wear is offset only by continued eruption. Cheek teeth and incisors of rabbits and some rodents are aradicular hypsodont (also called elodont) teeth, indicating a lack of true root structure along with lifelong tooth growth, which compensates for occlusal wear. Colby’s canine tooth root structure was similar to the brachyodont teeth we commonly see in dogs, except the apex was still open on inspection of the apex after extraction. Apical closure in dogs is complete by approximately one year of age. Though more pronounced in males, both sexes have canine teeth.3 Male muntjacs engage in intraspecies sparring and fighting. Muntjacs display dominance before fighting, in which they stand apart, hold their heads high and tilted towards each other, and take steps toward their opponent. At this point, either a subordinate male withdraws, or the muntjacs circle briefly before dropping their antlers and lunging forward. The muntjacs meet head-on and try to push their opponent backward. The aggressor attempts to use his canine teeth to strike downward on the back of his opponent’s neck. After a few blows, the loser usually runs away.3 Though Colby was the only male in his exhibit, he must have caught his tall canine on something. We were happy to help him and the doctors at Elmwood Park Zoo. John R. Lewis, VMD, DAVDC, FF-OMFS, practices and teaches at Veterinary Dentistry Specialists and Silo Academy Education Center in Chadds Ford, Pa. References https://www.wildlifeonline.me.uk/animals/article/water-deer-tusk-movement Chapman, N., Harris, S. & Stanford, A. 1994. Reeves' Muntjac Muntiacus reevsii in Britain: their history, spread, habitat selection, and the role of human intervention in accelerating their dispersal; Mammal Review 24: 113-160. https://animaldiversity.org/accounts/Muntiacus/
