Dr. Callen is a published author and lecturer with a practice in Mansfield, Ohio. His books include three used nationwide, "The Cutting Edge I, II and III". Dr. Callen is Associate Editor at Excellence in Dentistry and author of numerous articles in national dental publications. He is a guest lecturer at dental schools and has traveled throughout the US and Canada lecturing on High Tech Dentistry. He is also on the advisory board of Advanced Learning Technologies, Inc.