Complex sentence: Robert Tanner Freeman (18461873) was the first African-American to graduate from the Harvard School of Dental Medicine, and is thoughht to be the first African America to receive a dental degree in the United States.
Split into simpler sentences: Robert Tanner Freeman (18461873) was the first African-American to graduate from the Harvard School of Dental Medicine. He is thought to be the first African America to receive a dental degree in the United States.