Root canal treatment is necessary If the nerve of a tooth is inflamed or already dead. In many cases this makes it possible to save the diseased tooth. A root infection does not have to be painful, and sometimes you only discover it with a cold test or an x-ray. It might also be necessary to renew an old root canal filling before replacing a crown or a filling. With an surgical microscope and modern treatment methods even the finest branches of the root canals can be followed to effectively eliminate the focus of inflammation.