I just looked it up and apparently the iron is just to enhance the cutting surface. They do have teeth that replaced themselves indefinitely as well.
With beavers, the enamel is iron enhanced so it's stronger than the dentine behind. They wear unevenly, the back wearing down more easily than the front, which keeps the teeth sharp. They're incisors continue to grow indefinitely, but they don't get replacements if they lose one.
And bloodworms have copper teeth! I guess they get it from the sediments they live in. That blew my mind, so finding this out about reptiles is so wild.