Dental and Temporomandibular Joint Pathology of the North American Brown Bear (Ursus arctos horribilis, Ursus arctos middendorffi and Ursus arctos sitkensis)

Abstract

Museum specimens (maxillae and mandibles) from 393 North American brown bears (Ursus arctos) from Alaska were examined macroscopically according to predefined criteria and 204 specimens were included in this study. The specimens were acquired between 1905 and 2012. There were 99 specimens (48.5%) from male animals, 87 (42.7%) from female animals and 18 (8.8%) from animals of unknown sex. The ages of the animals ranged from neonate to adult, with 92 adults (45.1%) and 112 young adults (54.9%) included and neonates/juveniles excluded from the study. The number of teeth available for examination was 6,525 (76.2%); 8.6% of teeth were absent artefactually, 0.8% were deemed absent due to acquired tooth loss and 14.5% were absent congenitally. None of the brown bears had supernumerary teeth, persistent deciduous teeth or abnormally formed crowns. Only four of the specimens in the present population were affected by enamel hypoplasia and one specimen contained two mandibular fourth premolar teeth with one root instead of two. All 204 specimens displayed at least some degree of attrition/abrasion, affecting 63% of all teeth, ranging from mild wear of the enamel to deep abrasion associated with pulp exposure. Ten-times more adult than young adult specimens had abrasion causing pulp exposure, while more young adults showed mild attrition/abrasion. Dental fractures were noted in one-third of brown bears and in 3.0% of the total number of present teeth. More adult brown bears had dental fractures than young adults. There were 11 specimens (5.4%) that displayed overt periapical disease, affecting a total of 20 dental alveoli (0.22%), with adults significantly more affected than young adults. Some degree of periodontitis was seen in 145 specimens (71.1%), affecting 13.6% of all dental alveoli. Nearly one-third (29.9%) of skulls displayed skeletal and/or dental malocclusion, most commonly a level bite. Lesions consistent with temporomandibular joint (TMJ) osteoarthritis were found in 27 specimens (13.2%). Caries lesions were discovered in four specimens (2.0%), affecting eight teeth in total. Although the clinical significance of dental and TMJ pathology in the brown bear remains elusive, the occurrence and severity of some of these lesions may play an important role in the morbidity of this species.