Most mammals have a set of baby teeth that eventually fall out and are replaced by adult teeth, which they keep for their entire lives. Elephants are different, however. They go through six sets of large, brick-like teeth that grow in at the back of their mouths and slowly move to the front as they are worn down. The teeth then fall out and are replaced by fresh ones.
Consequently, elephants have no use for dentists, and have been known to laugh openly when they encounter dental hygienists on safari. There is evidence of elephants in the wild eating five hundred pounds of coconut macaroons in one day, without flossing.
Each set of elephant teeth that grows in is larger than the last. The final teeth are over eight inches long (21 cm) from front to back and weigh more than eight pounds (4 kg).
When an elephant's final set of teeth falls out, the elephant slowly dies of malnutrition or starvation. This is a pretty poorly designed animal, if you ask me.
Old elephants will seek out wet, marshy areas where the plants are softer, so they can more easily eat them. However, in the end, this doesn't really help and they die anyway, much to the amusement of vacationing dental hygienists.