Abstract

A group of 2.1 walruses (Odobenus rosmarus) with an estimated age of two years old was received at the Brookfield Zoo in Brookfield, Illinois, USA from the Parken Zoo, Eskatuna, Sweden. Three days following their arrival a dental examination of the tusks was performed. It revealed various levels of wear, but apparently healthy tusks. There were no signs of cracking, infection, or splitting. Careful observations of use of tusks in the exhibit were done in order to assess the value of various behavioral enrichment devises to decrease the expected rubbing of tusks and subsequent excessive wear. Photographs were taken in order to document changes in the tusks.

In order to decrease the likelihood of excessive tusk wear, an extensive behavioral enrichment and training program was implemented. This program included five training sessions per day, daily exhibit rotation through four exhibit areas and 36 behavioral enrichment devices (toys, ice, feeder tubes, etc.) offered on a rotating schedule.

After one month, weekly evaluations of the tusks revealed significant wear on 1.1 of the walrus tusks, despite a concerted effort to keep the animals from rubbing them. It was decided to attempt capping the tusks to decrease the amount of wear. If they continued to wear, eventually an area would be worn into the pulp cavity or worn thin enough they might crack below the level of the gum line.

The technique involved making impressions of the tusks in clay, followed by making a casting of the mold and then using that casting to create the ticonium cap. Ticonium is a chrome-nickel dental alloy used to make removable partial dentures. This was accomplished by first training the walrus calves to present a "mouth open" behavior and allowing complete manipulation of the tusks. They were then desensitized to both the procedure and the time necessary to accomplish it. The goal was to hold for up to three minutes with pressure on the tusks. This was the approximate minimal time necessary for the bonding material to join the cap to the tusk. After this was accomplished, and proper impressions were made and subsequently, the castings were produced.

The castings were made by a dental laboratory technician using the lost wax technique. The caps were first created in wax on the casts and then the wax was invested. The investment was heated and the wax was burned out. Then molten ticonium was cast into the investment. The caps were then recovered and polished. The interior was micro-abraded. The caps were placed on the tusks to check for fit and once that was confirmed, they were cemented with glass ionomer cement. The cement was mixed to proper consistency, placed into the caps, seated on the dried tusk and excess cement removed. The caps were held with apical pressure for four minutes until initial set of the cement.

To date, the animals still have caps in place and there has been no change in the conformation of the tusks. They continue to grow and appear to be wearing to a small degree only on the ends and sides of the caps. This procedure has shown to eliminate wear of the ivory on young walrus tusks and may lead to the development of normal appearing tusks as they mature.

Acknowledgments

The authors would like to thank Gregg Dye and the trainers at the Seven Seas Facility, Brookfield Zoo for their efforts in training the animals for the procedure.