Systematic Assessment of Mammalian Skull Specimens for Dental and Temporomandibular Joint Pathology

We have collaborated with the California Academy of Sciences and other museums for quite a while now to document the dental pathology of mammals of the western United States, including the bears, the marine mammals, the felids, and the canids, and the advantage of this technique that it allows for reproducible results across the species. Our protocol is an excellent means of enacting the scientific method. Past projects have been formative for veterinary students and pre-dental students, and collaborators have developed an understanding of normal maxillofacial anatomy, data analysis, and scientific writing.

The temporomandibular joint, or TMJ, is one of the most important joints of the body of mammals, as it affects breathing, eating, drinking, and other functions like protection. Information obtained from study of the TMJ and its disorders is crucial for conservational science, since it affects survival and fitness This protocol can provide insight into companion animal and exotic animal health, evolutionary biology, and ecology. This method is specific to the oral maxillofacial region of mammalian species.

The prerequisites for using this methodology are to have a good understanding of the normal anatomy of the species and to have a good working knowledge of dental pathology in general to recognize the lesions. Document the specimen information, including identification numbers, species, sex, and location of origin. Examine the skull for completeness of the anatomic structures.

Estimate the age of the specimen at the time of death based on the closure of cranial sutures. For the gray fox skull, young adults have open sutures at the base of the skull, while the sutures of older adults have closed. Consult pertinent literature for the time of cranial suture closure, as this varies for each target species.

Replace loose teeth with their corresponding alveolae. Inspect each dental quadrant successionally, and record the presence or absence of teeth. Classify the loss of each tooth as either congenitally absent or acquired tooth loss or artifactually absent.

Document any persistent deciduous teeth or supernumerary teeth. Examine the shape of the crown of each tooth and any visible root structure. Document the number of roots by examining the loose teeth out of their alveolae.

Examine the teeth for any extra roots. Use a metal or plastic periodontal probe and explorer to ascertain the texture of the alveolar bone for evidence of periodontitis. Attempt to insert the periodontal probe between the roots of each multi-rooted tooth to test for the presence of furcation involvement or exposure.

Depending on the number of roots, multiple areas should be tested for furcation. Examine each tooth for fracture as indicated by the loss of tooth substance with sharp edges. To determine if each fracture is complicated or uncomplicated, attempt to insert the probe into the pulp chamber from the fractured site.

Examine both sides of the skull and the teeth for evidence of periapical lesions that are characterized by expansion of the alveolar bone in the region of the apex of the tooth root with evidence of increased vascularization. Examine each tooth for attrition or abrasion indicated by the loss of tooth substance with a smooth, glassy appearance and rounded edges. Attempt to insert the explorer tip into the pulp chamber to determine pulp chamber exposure from the abraded region.

Inspect the bone components of the temporomandibular joint, including the head of the mandible, the condylar process, and the mandibular fossa of the squamous temporal bone. Check for evidence of temporomandibular joint pathology, while ruling out artifacts such as postmortem trauma, drawer damage, or preparation artifacts. Next, examine the skull for evidence of traumatic injury.

The current protocol results in a combination of objective and semi-subjective data, and the outcome depends on the accurate and repeatable assessment of specimens;for example, in Mirounga angustirostris, persistent deciduous teeth were observed, and supernumerary root was seen in Lynx rufus californicus. In Urocyon cinereoargenteus, stage two periodontitis was observed, characterized by increased vascularization of the alveolar bone. Stage three was characterized by moderate bone loss and furcation involvement.

Stage four was characterized by severe alveolar bone loss. Fractured teeth were observed in Callorhinus ursinus and periapical lesions in Enhydra lutris nereis. Temporomandibular joint osteoarthritis was observed in Puma concolor cougar with an irregular articular surface, subchondral bone exposure, and porosity of the mandibular condylar processes.

A specimen free of any detectable pathology or minimal disease or anatomic variation was found and documented to act as a standard for comparison. The most important aspects of this protocol are familiarity with a species'normal maxillofacial and dental anatomy, recognition of affected tissues, and diligent documentation of findings. Future studies of the TMJ will provide information on histology, biomechanics, and also observation of the animal in the wild.

This will put context of the pathology found in the museum specimen. Our work has provided a sound methodology for analysis and has yielded important reference points for comparative work with other species in other parts of the world.