Believe it or not, many teeth that require root canal therapy do not cause pain. Just because there's no pain doesn't mean your tooth is okay. Your dentist and endodontist determine if you need a root canal by looking at your tooth's pulp. If it's damaged or infected, you'll need a root canal treatment, even if your tooth doesn't hurt.
If you see something that looks like a pimple near your damaged tooth, see your dentist right away. The "pimple," called a fistula, is a tunnel of tissue that drains pus from an infection. When this happens, you have no pain because the fistula keeps pressure from building in the tissue. It's important to know that the infection must be treated to prevent nearby tissues from becoming infected.