Dr. Johnson joined the College of Dentistry in 1991 after eight years at the University of Nebraska Medical Center College of Dentistry where he served as chair of the Department of Endodontics from 1989 to 1991. He served as chair of the Endodontic Section of the American Association of Dental Schools in 1992 and subsequently served as counselor to the Endodontic Section of the American Dental Education Association. He was chair of the Educational Affairs Committee of the American Association of Endodontists in 1994 and served on the Association's Ad Hoc Committee to Address Endodontic Nomenclature. Dr. Johnson also served on the American Association of Endodontists Task Force to Revise the Standards for Advanced Education. In 1994, he was elected by the American Association of Endodontists to serve six years as a director of the American Board of Endodontics. He served as secretary of the board for two terms in 1997 and 1998. He was also president of the board for two terms in 1999 and 2000. In 2001, Dr. Johnson was elected to a three-year term on the Board of Directors of the American Association of Endodontist representing 21 Midwestern and Western states. He served as board liaison to the Research and Scientific Affairs Committee and the Committee to Address Endodontic Nomenclature. In addition, Dr. Johnson served as the vice- program chair for the American Association of Endodontists Annual Session Committee in 2003, program chair in 2004, and general chair in 2005. Dr. Johnson served on numerous AAE committees, chairing the AAE Educational Affairs Committee as well as the AAE Continuing Education Committee. Dr. Johnson served as an endodontic consultant to the ADA's Council on Materials, Instruments and Equipment from 1991 to 1995. He was an endodontic consultant to the Commission on Dental Accreditation of the ADA from 1994-2000. In 2004, he was appointed to serve a three-year term on the Endodontic Advisory Committee for the Commission. Dr. Johnson is editor of the endodontic textbook, Color Atlas of Endodontics; senior author of the obturation chapter in Pathways of the Pulp; the isolation and endodontic access chapter as well as the cleaning and shaping chapter in Principles and Practice of Endodontics. Dr. Johnson was also the endodontic editor for the Mosby Yearbook.
Dr. Johnson directs the preclinical sophomore endodontics courses laboratory and teaches in the junior endodontic clerkship, in the senior Family Dentistry curriculum, and the Advanced Education Program in Endodontics.
He participates in the intramural dental practice in the Department of Endodontics and is a consultant to the Veterans Administration Hospital in Iowa City.
Dr. Johnson has served as chair and councilor of the Endodontic Section of the American Dental Education Association (ADEA). He completed four years of service to the American Association of Endodontists (AAE) as a representative on the Council of Hospitals and Advanced Education Programs of ADEA. Dr. Johnson served as a member of the Endodontic Review Commission of ADEA's Commission on Dental Accreditation and completed his term in 2008. Dr. Johnson has served as vice president and president-elect of the American Association of Endodontists and in April 2011, Dr. Johnson was elected president of the American Associatiion of Endodontists. He currently serves as the immediate past president.