In cases where the tooth despite proper root canal treatment is still infected and inflamed at the end of the root it should be treated directly and surgically. In this case the tooth is not extracted but the infection or cyst is removed directly through a surgical incision
In cases where there is a thick post inside the canal or teeth that need control after previous treatment and the root end lesion has not yet healed or the previous root filling has spread beyond the root; the root of the tooth requires surgery