Date Published: April 12, 2019
Publisher: Public Library of Science
Author(s): Uwe Kierdorf, Morten T. Olsen, Patricia Kahle, Catharina Ludolphy, Horst Kierdorf, Cyril Charles.
The systematic analysis of museum collections can provide important insights into the dental and skeletal pathology of wild mammals. Here we present a previously unreported type of dental defect and related skull pathology in five juvenile Baltic grey seals that had been collected in the course of a seal culling program along the Danish coast in 1889 and 1890. All five skulls exhibited openings into the pulp cavities at the crown tips of all (four animals) or two (one animal) canines as well as several incisors and (in one animal) also some anterior premolars. The affected teeth showed wide pulp cavities and thin dentin. Pulp exposure had caused infection, inflammation, and finally necrosis of the pulp. As was evidenced by the extensive radiolucency around the roots of the affected teeth, the inflammation had extended from the pulp into the periapical space, leading to apical periodontitis with extensive bone resorption. Further spreading of the inflammation into the surrounding bone regions had then caused suppurative osteomyelitis of the jaws. The postcanine teeth of the pathological individuals typically had dentin of normal thickness and, except for one specimen, did not exhibit pulp exposure. The condition may have been caused by a late onset of secondary and tertiary dentin formation that led to pulp exposure in anterior teeth exposed to intense wear. Future investigations could address a possible genetic causation of the condition in the studied grey seals.
The systematic analysis of mammalian skeletons from museum collections can provide important information on the spectrum and prevalence of anomalies and diseases of bones and teeth in the studied species [1–4]. The findings of such investigations are not only of interest with respect to comparative pathology, but also helpful in the assessment of population health and its changes over time. The results can thereby contribute to the identification of emerging health threats and to an effective population management.
Three complete and two fragmentary skulls of Baltic grey seals from the skull collection of the Natural History Museum of Denmark, University of Copenhagen, exhibited a similar spectrum of pathological dental and osseous changes. None of the other 204 grey seal skulls from the collection that were inspected in the course of our study showed comparable lesions.
On macroscopic and radiographic inspection, the five pathological grey seal skulls showed a similar spectrum of dental and bone lesions. All specimens exhibited openings into the pulp cavity at the crown tips of incisors and canines, and in one case (ZMUC 139) also of three anterior premolars (Table 1, Fig 3). Except for one specimen (ZMUC 155, both maxillary C unaffected), exposure of the pulp cavity through an opening at the crown tip was observed in all mandibular and maxillary canines from the five pathological skulls. In the affected teeth, both the tip of the enamel cap and the dentin overlying the pulp horn had thus been lost soon after eruption due to wear. No indication of fracturing of the tooth tips was observed. Except for specimen ZMUC 139, no exposure of the pulp cavity was recorded in postcanine teeth.
In the five grey seals exhibiting pathological skull changes, pulp exposure of incisors, canines and, in one skull also anterior premolars had occurred following the loss of the enamel layer covering the crown tip and the wearing away of the subjacent thin dentin layer overlying the pulp cavity. Normally, pulp exposure due to tooth wear is prohibited by the lifelong apposition of dentin that causes a progressive narrowing of the pulp cavity with age .