Lyn,
Have you ever heard of a condition called Mandibular Tori? It is a very common condition (about 20% of the population has it). It is a bony protrusion from the lower jaw below the teeth (towards the tongue). I had the very same scare you are having now when I felt the bump in my lower jaw. Though my onc was originally stumped, my dentist recognized it as Mandiubular Tori right away. (Has your dentist had a look?) It is perfectly benign. With all you have been through, wouldn't it be nice to hear the words "benign" about this?
You can Google "Mandibular Tori" and it will take you to some pretty ugly pictures that may or may not look like what you are describing. Here is a link as well.
http://www.dental.mu.edu/oralpath/ca...25/case25a.htm
I wish you only the very best and am hoping that once you run it to ground you will find that this can be crossed off your worry list.
Cynthia