Dr. Nielsen is a Board Certified Orthodontist and a Clinical Professor (Emeritus) at the University of California, San Francisco. He received his dental education at the Royal Dental college of Århus, Denmark and his Orthodontic education at the Royal Dental College of Copenhagen, Denmark under Professor Arne Bjőrk (MSc). After graduation Dr. Nielsen continued as instructor at the Post Graduate Program of Orthodontics in Copenhagen until 1982 when he came to UCSF as Clinical Assistant Professor under Professor Dr. Robert Isaacson. He has remained at UCSF until the present as Clinical Professor and also holds a Certificate of Orthodontics from UCSF. In 1991 he opened a part-time private practice in Vacaville while still teaching half-time at UCSF. Dr. Nielsen has lectured worldwide, most recently in India, Iran and Taiwan and published more than 50 articles in orthodontic journals on normal and abnormal facial growth and many other topics including cephalometric analysis of growth and treatment, etiology and development of malocclusion, functional appliance treatment, muscle function and jaw movement in TMD patients and long-term stability of orthodontic treatment. Currently he is Director of Preceptorships and Fellowships in Orthodontics at UCSF and teaches part-time.