This post is a search for the knowledge of the community. Since December 2000 one of my friends has had pain in the lower left quadrant of my mouth always in one particular tooth. The pain is a dull, deep, gnawing, crushing pain that he describes as being with him 24 hours a day. Its intensity varies, but it is always there. It is completely ruling his life. The pain started with a crown preparation of tooth #20 in December of 2000. After tooth #20 was extracted (July 2003) the pain immediately jumped to tooth #19. Two years later (July...