I had a chap in (oh, err, missus) this A.M. with a chip on the incisal edge of lower front tooth. He asked "Is my tooth knackered?". The answer turns out to be a resounding "NO!"
Our front teeth, in fact all our teeth, have a 'self-sharpening' mechanism built in. Evolution had equipped us with this mechanism because we haven't always had knives and forks easily to hand.
How does it work? The enamel on the outside of the tooth is somewhat harder than the dentine inside. When the dentine get exposed by natural wear the enamel starts to stand up relative to the dentine to create two sharp cutting edges. When the enamel is sticking up enough is chips off.
It's irritating but natural, and the only way to avoid the problem is to have all your meals by naso-gastric tube - yum.