Hi..root canal is usually done when there is a big hole in the tooth due to decay. Or tooth damage due to accident. In these cases nerve area of tooth gets infected. Patient may or may not have pain. But it has to be solved by repairing the tooth and making it strong and chewable again. Sensitivity, pain, food Lodgement are other symtoms Regards

If the age permits, the damage can be seen by the x-ray, & roots are intact , it can be qualified for the RCT

I agree with dr Vishwas!

Before answering I would like to give a little information about the tooth. The tooth has three parts. First The outer covering commonly known as enamel which protects (second) the inner living tissue know as the pulp of the tooth  and third the gums surrounding the tooth A tooth qualifies for a root canal for the following reasons- 1.decay approaching or involving pulp 2. Infection in roots 3. Gum disease which has enabled the spread of germs inside the root 4 traumatic exposure of the inside pulp of tooth 5micro trauma over a period of time due to heavy biting forces which may lead to death of inside pulp of tooth. 6 hyper sensitivity  not resolved by other treatments 7 intentional root canal for certain cases