Tooth nerve pain can be extremely severe.
Dentists call it "pulpitis", which looks like a funny kind of a word for a toothache, but it's made up of 2 other words: "pulp", which is the dental term for the nerve inside a tooth, and "itis" which means inflammation, like in tonsillitis or dermatitis.
So "pulpitis" means an inflammation of the tooth nerve. If the nerve buried deep inside the tooth becomes inflamed for whatever reason, it can be extremely painful.
How can such a tiny little nerve cause so much pain?
The problem is, the nerve is completely surrounded by a rock-hard, rigid tube: the tooth! If it gets a bit inflamed for any reason, it wants to swell up a little, like when you accidentally hit your thumb with a hammer. Your thumb can swell up, and it's a bit sore, but settles down in a few days.
BUT the nerve buried inside a tooth cannot swell up. So what happens is this; as the nerve tissue becomes inflamed, (maybe due to a cavity or to a knock on the tooth), it tries to swell up as tissue fluid leaks out of the tiny blood capillaries. The result is that the pressure inside the tooth goes up.
When the pressure inside the tooth goes up, two things happen. First, it hurts, because the nerve is being pinched. This is that constant, throbbing tooth nerve pain.
Second, the tiny blood capillaries inside the tooth also get compressed. This in turn starts to limit the blood flow to the tooth nerve. The pain begins to get worse.
What happens next depends on how badly the tooth nerve is inflamed.
Sometimes it can get better. Other times, it only gets worse.
If your tooth nerve pain has a chance of getting better, dentists call the type of inflammation "reversible pulpitis". This means that something can be done to reverse the situation, and get back to normal.
BUT if the nerve has become damaged by the pressure from the inflammation, then dentists will call this "irreversible pulpitis". It cannot be reversed. The process has gone too far. It's a bit like gangrene in a toe that has been frostbitten. The nerve will die.
However, the nerve will not die in one quick go. It usually dies in little sections, with the bit that is still alive continuing to cause pain. This situation is usually the cause of the worst tooth nerve pain of all. You will have a severe, constant throbbing ache. Anything hot or even warm will make it worse. Even the warmth from your cheek can affect the tooth.
At this point, only rinsing with cold water will help much. You have to keep sipping cold water and holding it next to the tooth. As soon as the water warms up a little, you have to spit it out and take another mouthful of the cold stuff.
The only solution with irreversible pulpitis is to get along to a dentist as quickly as you can. The treatment choices you face are limited to just 2; either get the tooth taken out, or else save the tooth with root canal treatment.You can read more about your options at getting a tooth pulled and root canal procedure.
In the meantime, if you can't get to a dentist quickly, there are some tricks that may help. Read more about this at toothache home remedies.
What about reversible pulpitis? Obviously something's wrong with the tooth for it to hurt like this, so my advice is the same - get along to a dentist as soon as you can. The quicker you let him take a look, the better the chances that he can fix the problem and get the tooth settled down for you.
Most times, it will just be a normal filling that's needed.
BUT if you wait, hoping it will settle down on it's own, you run a very big risk of your pulpitis drifting from "reversible" into "irreversible", which means much more tooth nerve pain, and more complicated (and expensive) treatment to put things right!
So if you're getting any kind of toothache, my best recommendation is to get a dentist to check it out as soon as possible. The earlier you get a problem looked, the quicker, simpler and cheaper it is!