Complex sentence: The fluoridation of water is known to prevent tooth decay and is considered by the U.S. Centers for Disease Control and Prevention as "one of 10 great public health achievements of the 20th century".
Split into simpler sentences: The fluoridation of water is known to prevent tooth decay. It is considered by the U.S. Centers for Disease Control and Prevention as "one of 10 great public health achievements of the 20th century".