I cant stop biting things , can anyone please tell me why ?

If I see a pen ,or a bottle cap , even a corner of a book I will the need to bite it. I feel pleasure doing it. The worst culprits are pens , bottle caps , chocolate bar wrappings , anything really. I want to know how I can stop and if anyone could tell me why I like doing it so much that would b great.. Is it my teeth or what ?