For years, an elaborately displayed tooth at the Art Institute of Chicago has been thought to belong to the major Christian religious figure John the Baptist. As it turns out, that claim has no teeth.

St. Brigid has given Ireland one of its most iconic religious and cultural images — the cross that carries her name.

Researchers took samples from the tooth in 2016. The results, not widely disseminated, showed it was from someone in the 5th ...