<< My sister went to the dentist today and they told her she needed 3 root canals. Well she didnt ask how they did it exactly. So thats why I am posting here. How do they do it exactly? >>
Wow, I was told I needed two root canals once, but not three (unless they're referring to the actual number of nerve canals that are damaged, not the number of individual teeth). If for some reason she doesn't feel that should be right because she's not having problems with those teeth, maybe she should get a second opinion.
Root canals are usually not that bad, but occassionally they can be painful. It depends on the individual, the dentist, and the extent of the damage. There is no reason a root canal HAS to be painful, it just depends on the individual circumstances.
What happens is that tooth decay threatens to enter (or has already entered) the nerve canal. When that happens, there are only two ways to deal with it; pull the tooth or do a root canal. Dentists are not fond of pulling people's teeth, and not just because it is the least expensive alternative.
Teeth can shift when theres a gap between them, creating more problems. Teeth are also a limited resource, you never know when you may have no other choice but to pull a few teeth, so its always best to save every tooth when you can (and if you can afford it).
In a root canal, the decay is removed and the nerve is essentially killed and stripped away. Some inert and stable material is put in the canal space to act as a sort of insulation. Then the tooth is restored usually by bonding a crown to it. There can be some discomfort for several hours after, which can be mitigated by taking an anti-inflammatory/pain-reliever before your dental appointment (only if the person has no problems tolerating such things as Advil) and as necessary for pain after getting home.
In most cases of pain or discomfort, the nerve is ALREADY so inflammed by invading decay that the root canal itself isn't the primary source of the discomfort. Within 24 hours, the tooth should actually begin to feel better than it did before the root canal.
I lived with an aching/sensitive tooth for a year before having a root canal done, and I would trade that for 3 or 4 hours of discomfort any day. In my case, within 24 hours I was wondering why I didn't have it done sooner.