you could try modelling kits. I made a ferrari 2005 f1 car using plastic pieces, paint and stickers and glue (believe me, the stickers were the hardest to apply) and took that in. They were impressed, all the interviewers commented along the lines 'oh wow'. If your going to do this, then choose one thats relatively complex, it gives you more to show off - about 70-80 pieces. Revell is the manufacturer. You can make boats, cars, and other stuff. Its probably best if you get 2, then you can use the first to practice and make the necesary mistakes to learn from.
Alternatively, and this is probably better, cast an impression yourself and fine down the edges and take that in. That looks good because you can show off your manual skills as well as your interest in dentistry. I did it at the Eastman Dental Hospital in Kings cross, london, as part of wkexp. Its a brilliant place to go to, you get to see what postgraduates do.