"What's the point of having nerve endings in our teeth..."

"... when all it can do is hurt for the rest of your life, as they won't heal themselves or grow back if they get a cavity."

Explain it to me like I'm Five top 4 voted comments.

• To let you know if a living thing is living inside of your tooth eating away at your flesh under the tooth. 

• It might not have a purpose at all, as long as it doesn't get you killed before you have a chance to breed. Evolution is like that, it doesn't have a defined "goal". 

• Evolution does not have an "ideal design" - it simply evolves 'random things'. 

• If a the creature with the "random thing" gains advantage over creatures without the 'random thing' (or at least isn't disadvantaged by it) that creature may pass-it-on when it reproduces and more creatures get it. Also, if the "random thing" stops being useful due to other changes (such as creatures leaving the oceans/trees/suburbs/stable jobs) it won't disappear unless it's a pretty series disadvantage (gills, flippers, middle-class angst and a sense of personal wellbeing respectively)