A low DC voltage is produced by the thermocouple when the two junctions are at different temperatures. This voltage is referred to as the thermoelectric voltage. This thermoelectric voltage is produced by the temperature gradient along the thermocouple wires.
Re: What's causes the electric shock type pain in a tooth Hi DM69. I'm not a dentist but I'm pretty sure its the erosion of your tooth exposing the pulp, I had the exact same feeling in my tooth before I had it extracted a month ago, so I feel your pain.
The electric shock headaches do sound like the pain from an inflamed cranial nerve, perhaps the occiptal one, perhaps another (there are eight to choose from). This may also be causing the pain in your ear, in which case it may be a different cranial nerve affected.