Abstract

Dental Trauma

Captive sea lions between the age of 18 months and three years often exhibit severe damage to their permanent dentition, with exposures of their pulp cavities. The affected teeth are usually the mandibular incisors, canines and premolars. It is suspected that the loss of tooth substance is caused through abrasion with non-dental structures. The aetiology of the condition is unclear as some animals have been observed to play with pebbles, or chew the structure of their pool, whilst other sea lions that show signs of severe tooth wear have not been observed to engage in such behaviour.

Because sea lions have a long growth period before reaching maturity, and do not have a postnatal primary dentition, the teeth of these animals, especially the roots of the canine teeth, have a prolonged period of development. Due to this long period of development the pulp cavities remain large and the apices stay dilated to facilitate root growth to maturity. These large pulp cavities have the feature of maintaining the vitality of the exposed pulp through the formation of "pulp polyps", but at the same time afford a very large space for harbouring bacteria once the pulp tissue has become necrotic.

Pulp necrosis is followed by periapical abscess formation, where the animals often exhibit a mandibular swelling, malaise and localised pain. The infection responds to systemic antibiotics, but usually recurs, occasionally forming an extra-oral sinus tract at the ventral aspect of the mandibular symphysis.

The principles of dental treatment in a veterinary environment must be balanced between three primary objectives:

 Predictability of treatment--avoiding any therapy that would not afford a very high degree of long term success.

 Speed of therapy--not jeopardising the animal's life through an unnecessarily prolonged general anaesthetic.

Minimal Surgical Trauma

In a captive environment these teeth do not have a functional use in the sea lion. Also the immature state of the pulp cavities and the apical foraminae are not commensurate with the principles of root canal treatment. At the same time pulp therapy to maintain the vitality of these teeth cannot be considered to be predictable, and the many teeth that are usually involved in each animal would require a very long general anaesthetic with no long-term benefit to the animal. Therefore in these cases extraction of the damaged teeth offers the most practical and beneficial therapy.

Extraction of the sea lion's canine teeth follows standard oral surgical principles, but the bulbous roots require judicious removal of alveolar bone before elevation is attempted so as not to fracture the mandible. The suture line of the mucoperiosteal flaps frequently breaks down in the aquatic environment, but the sockets heal through secondary intention within a short period of time. Postoperatively the animals exhibit normal feeding behaviour and the mandibles continue to develop normally.

Periodontal Disease

Dental Stains

Sea lions in captivity very frequently develop a black coating on their teeth. The gingival condition adjacent to these deposits is usually healthy. Histopathological opinion is that they are most likely to be the result of the activity of oral chromogenic bacteria and are not pathogenic to the animals.

Juvenile Periodontosis

Infrequently young animals may exhibit juvenile periodontosis, where there is a rapid progression of periodontal disease with alveolar bone destruction, purulent gingival discharge and tooth drifting in the jaws. There is usually a strong odour of halitosis. Macroscopically the teeth appear healthy and clean. The cause of the syndrome is almost certainly a host immune response, which is generally recognised as one of the most important factors in the aetiology of periodontal disease. Dental host response is described as the individual's resistance or susceptibility against the bacterial endotoxins being liberated from the bacterial plaque on the teeth. Juvenile periodontosis does not respond well to antibiotic therapy and extraction of the teeth is the treatment of choice.

Chronic Periodontitis

Some old sea lions can exhibit pain from their canine teeth that superficially appear healthy. Examination under sedation can reveal deep periodontal pockets with a purulent discharge, although the teeth that have bulbous roots will still be well retained in their sockets. A short-term course of antibiotics will control an acute phase of infection, but in the long term extraction of the effected teeth is the treatment of choice. The removal of these teeth can be challenging as these older animals have fully formed roots to their canines and the consistency of the alveolar bone is much less flexible than encountered in young animals. Equipment and instruments that match the size of the structures being worked on should be used to speed up the operation, otherwise the length of the anaesthesia will be unnecessarily prolonged.

Acknowledgments

PK wishes to thank John Lewis and Andrew Greenwood of the International Zoo Veterinary Group for the immobilisation and long term veterinary care of the animals; and the many genuinely caring marine mammal keepers for their help and enthusiasm.