The bristles on my toothbrush touched the inside of a very dirty never been cleaned inside of a bathroom faucet. house built in 1988. later realized it is beyond dirty under there. i used the toothbrush w/o realizing it. should i be worried?

I really wouldn't worry too much. Water that passes through all faucets touch whatever debris is in those faucets, yet we drink the water and use it to brush our teeth without incident.

I suppose you feel ok, which should answer your question. How many people disassemble and sterilize b'room or kitchen sink after each use. Don't worry, especially if your water supply is chlorinated. Make sure to rinse t'brush thoroughly after each use and then stand-up to air dry. Brush 2x/day for 2 full minutes by the cock. Floss. See Dentist 2x/year religiously.