I've had a dead tooth since I was a teenager. DDS recommended root canal. Is it really necessary?

did your dentist give you a reason for suggesting a root canal now? Are you having pain? Is there an abscess or swelling? Ask your dentist for more information. If you are still uncomfortable with the response get a second opinion. 

If your tooth is darkening or has a cyst at the end of the root then a root canal would be indicated. If you elect not to get a root canal since it is apparently not hurting you then in my practice we would monitor it with an xray every year and a half. If a cyst begins to develop then get the root canal. At some time in your life, a root canal will most likely be needed. Hope this helps. :)