(Nomenclature in this paper for anatomical orientation of the teeth will be the standard dental terms: Coronal and Apical, for direction towards or relationships to, the Distal and Proximal extremities of the tusk respectively.)

Abstract

Ten Pacific walrus aged between 4 and 6 years were housed in Moscow Zoo. Seven of the animals developed bilateral tusk abrasions, where the teeth were worn down to within 4.0 to 1.0 cm of the gingival margins. This occurred through normal "digging" behaviour at the bottom and the sides of their concrete lined pools. The animals exhibited various degrees of malaise and depression for over one year that gave cause for concern. Three of the fourteen tusks had their pulp cavities exposed. Facial swellings developed in all the affected animals and five walrus exhibited facial sinus tracts medial to the eyes, with a purulent discharge. The infections responded to oral antibiotic treatment, but recurred after the medication was stopped.

The anatomy of the permanently dilated apical foramen of the walrus tusk does not allow thorough debridement and precise obturation of the pulp cavity, which is a prerequisite of root canal therapy. Therefore endodontic treatment of these teeth is contraindicated.

Eight walrus were treated by bilateral tusk extractions under inhalation anaesthesia. One of the animals operated on was developing bilateral cataract and had his healthy tusks extracted for prophylactic reasons, as he was becoming increasingly disorientated with his environment and likely to damage his tusks.

Walrus tusks may be extracted by an internally collapsing technique or through a mucoperiosteal flap procedure. The walrus tusk, even when exhibiting a pulp cavity exposure, will have an irregular, reparative dentine plug of variable depth obstructing the canal. This barrier can extend close to the apical extremity of the tusk obliterating the guidance the pulp cavity may afford, thereby making the creation of a symmetrical, hollow tusk that is required for longitudinal sectioning, unpredictable.

The position of the walrus on the operating table was determined by the anaesthetist's requirements to maintain the animal. Sternal recumbency made access in performing the internally collapsing technique difficult and time consuming.

Thirteen tusks were removed through a flap procedure, while three were extracted through the internally collapsing technique. Most of the animals were eating within 24 hours after surgery. The sinus tracts healed, and the facial swellings or purulent discharges did not reoccur in any of the animals over a follow-up period of ten months.

On examining decalcified sections of one of the infected tusks, a thin layer of largely acellular dentine lined the pulpal surface of the dentinal wall. The junction of the dentinal plug and the pulpal wall of the tusk did not form a seal and pus extended to the abraded coronal surface. Some chronically inflamed pulp remains were observed in the infected tusk's pulp cavity. The microscopic features support a diagnosis of pulpitis and pulpal necrosis, which were secondary to pulpal exposure from the abraded surface. It appears that the speed of the abrasion was too fast to allow the formation of an organised secondary dentine barrier that could produce an impermeable seal.

Walrus tusks which have suffered severe abrasion to their coronal extremities should be judged to have had the vitality of their pulp tissues compromised and their extraction ought to be considered at signs of related pain, malaise, swelling or infection. At the same time such surgery must not be taken lightly and the team should be prepared for all eventualities. Depending on the operating position the animal is maintained in by the anaesthetist, in the author's opinion a flap procedure appears to be the most predictable for their tusk extraction. Conservative treatment for abraded or infected walrus tusks is not considered appropriate.

Acknowledgments

PK wishes to thank Andrew Greenwood and John Lewis of the International Zoo Veterinary Group for the immobilisation and peri-operative care of the animals; Maria Kouznetsova, Senior Veterinary Surgeon at Moscow Zoo for the long term pre- and postoperative care of the walrus; Anna Pavlova, Head Walrus Keeper at Moscow Zoo for her exceptionally caring and skilful management of the animals; Swissair who were very kind in carrying the team and the equipment; and Tanya Arzhanova, Assistant to the Director of Moscow Zoo for being the magician who made the complicated logistics of the whole procedure gel together.