Tiny dark spot on the wharton duct below my tongue. no pain. no swelling. what could it be?

Get it checked: It could be normal pigmentation, an amalgam tattoo, or something that requires treatment. Get it looked at and biopsied if your doctor feels that is appropriate to be sure!

See a dentist first: Some conditions like small dark spot on the Wharton duct may require further assessment; tests and your dentist may schedule a follow-up appointment or refer you to a specialist to determine a diagnosis. See your dentist first for evaluation.