How can a tooth I had a root c on hurt?

I had a root c on one of my molars about 2 years ago, I didn't have the money for a crown so I have just left it hollow this whole time and been sure to clean the hollow cavity out after eating anything. A few days ago I started getting pain in the tooth. How is this possible? doesn't a root c completely remove the nerve? The pain is definitely in the tooth itself and not below or in the gum, I can poke it from the inside and pinpoint exactly where it is.