Why do teeth have so many nerves

Mechanoreceptors they have to detect everything from light touch to deep pressure, stretch and vibration. It's pretty complex to go into but this is why 

I agree, my teeth are in a right state, mostly caused by a state licenced psychpath of a dentist I had as a child, you'd go in there for a check up feeling and looing normal and comes out looking and feeling like you'd been punched in the face. He used to use one of those hook things and lift your head off the couch where he was digging in with the hook so much. He would fill teeth without having drilled out all the bad bits so they rotted from inside.

I still hate and fear the dentist, I will have to have a private one for my next visit as the NHS one has stopped doing NHS. I wouldn't mind having to go private if you got a decent service, but most of the time you don't and they always seem to want you to have a load of cosmetic work done too, implants and stuff. Hygenists can be awful too, I don't see them anymore I flat out refuse after seeing one who left me with bleeding and inflamed gums and loose teeth.

I feel lucky that hair doesn't have the same nerves as teeth.  Just think of the pain if cutting hair meant cutting through nerves.

Mammals are unusual - compared to reptiles, fish and dinosaurs - in having three things, teeth that have different shapes for different functions, teeth that fit together very precisely, and teeth that do not replace themselves in adulthood. Mammalian teeth are therefore quite precious, an old elephant that has worn its molars down will die of starvation. The innervation of teeth prevents - to some extent - accidental breakage through biting on very hard objects.

A shark replaces teeth continuously, they will bite hard on iron bars. It makes little difference to them if they lose a dozen teeth. Tiger sharks in particular are very indiscriminate in what they will bite and indeed swallow.

some of us are fortunate to have a dentist !!   

I think a large part of it is to alert you of problems before they get even worse.

Teeth are an absolute menace and then you have the dentist….

Each tooth has nerves and blood vessels that are responsible for providing it with nutrients. The nerve is present in the root of the tooth. Once a tooth comes out of the gums, the nerves are no longer important for its function or health. The main function of the nerve is to sense hot and cold.

That's an AI response hooked from Google which I think it filched from the New Scientist so it might be pretty accurate.