Like other important organs, teeth have nerves for sensation and protection.
The diseased “nerve” removed in a root canal procedure is the common term for the combination of nerves and blood vessels that form pulp, the soft interior of the tooth.
There is also a bundle of nerve fibers in the ligament that attaches the tooth to the bone. Together, these nerves let the teeth integrate with muscles, the brain, and the temporomandibular joint, responsible for the up-and-down motion of the jaw, in the complex activity of chewing.
The ability to know where the teeth are at all times is called proprioception, and nerve sensation is necessary to guide the teeth. If your bite is not quite right after dental work, or if your teeth shift, you can sense it immediately.
The nerves also let the teeth perceive heat, cold, and pain and protect them from harm. These sensations can – warn of decay.
Often, if there is a large cavity, the tooth becomes sensitive to sweets, as part of the body’s defense mechanism.
Your mouth and tongue and lips have all the nerves you need to detect cold or hot. As for chewing motions, there aren’t any exposed nerves that relate chewing motions of your teeth. Your jaw muscles can sense that. To notice articles stuck between teeth? That’s nerves in your gums, BETWEEN teeth. Notice you can’t sense a particle of food ON your tooth. Nope, I think nerves in teeth are an ancient holdover of nerves from some evolutionary past, as someone said, possibly from nerves in the throat of fish where early ‘teeth’ were formed.
Nerves in teeth aren’t there to warn you of decay or ‘sweets’ because what can you do about a decayed tooth once it’s decayed enough to cause you intense pain? You can’t stop the decay at that point onward or reverse it (modern dentistry is only a recent invention).
About the only other evolutionary reason might be so you learn not to try to crack down too hard on hard foods. Crack down on a nut, and if it’s too hard you will break your tooth to pieces, which loses you a tooth, which isn’t good (need it for chewing), so the nerves give out pain to warn you to not do that again. Sounds neanderthal though to me. All you would need is one broken tooth (without nerves) and you could see it when you spit out. A visual warning. I think it’s from an evolutionary past when pain was needed to warn people of things when we were too stupid to figure it out otherwise.