Root canal! This word is associated with feelings of anxiety among many people. It shouldn't though! I've had a root canal before and I was falling asleep during the procedures! After a root canal, the tooth should feel perfectly normal within a couple of months.
Pain from a tooth that requires a root canal can only come from two sources: the dental pulp (nerve) or the bone surrounding it.
Pain from the nerve
After a root canal has been completed, it is very unlikely the pain is from the pulp, but still possible. A clue to whether the source of discomfort is from the dental pulp is whether you experience more pain with hot or cold foods.
The much more likely reason for you to still feel pain to temperature is that it's another tooth! Hopefully you don't need another root canal!
Your dentist will be able to determine if it is another tooth by placing something cold onto individual teeth to check.
Pain from the bone
Bone pain would cause pain when any physical forces are placed on the tooth. This could be tapping, biting or pushing.
The causes of pain from the bone are persistent infection, cracked tooth, high filling/crown.
A persistent infection means that the root canal will be need to redone or endodontic surgery. This is more likely to happen in long standing infections that have enlarged significantly and have mature types of bacteria.
A cracked root will lead to microbes travelling through the crack and causing an infection. Much of the time the tooth cannot be saved. A dentist will be able to tell a cracked root by probing in between the tooth and gums and sometimes even through an x-ray.
A high filling has the best prognosis because all it needs is removal of the offending high spots and it's good to go! When it is high, the tooth will have excessive forces which will cause it to be sore.
What should you do?
The best thing to do is of course to see your dentist or endodontist. They will be able to go through the investigations to determine the cause of your pain. There are some rare causes that involve other things of the mouth, but they're so rare it is out of the scope of this article.
To make yourself feel better, painkillers and sometimes antibiotics may help.