The silvery thing is called a tuning fork. I think it's just a way to objectively test the ability of the patient to feel that particular sensation at particular points. I don't think it can determine whether nerve damage is permanent or temporary. But that's just my own reasoning...maybe someone else here knows otherwise.

I would guess that testing the ability to feel cold is likewise not an indication of temporary vs. permanent damage.

But to answer you other question, yes, I have spots where I can't feel the vibrations and/or cold.