Actually, his tusks broke of by themselves about two years back. The people who heard ithe crack said that it sounded like a gun being fired. He had to endure som painfull teeth surgery after. That is why he wears those metal rings now. Here is a picture of how he used to look.
Thanks for the explaination Toddy... Poor Chieng Mai. there have been many cases I have heard about bull's tusks being broken off in zoos and in parks they sometimes look in obvious pain.