A. Monsour, for his ongoing support and encouragement not only during this research project, but throughout my entire Dento-maxillofacial Radiology training program. He is a constant source of inspiration and I enormously value his high calibre of supervision, advice and mentoring. The research paper which makes up Chapter 2 of this thesis was prepared partially in collaboration with co-author Mr. Simon Critchley. Mr. Critchley sourced valuable information and contacts essentially required from Australian radiation regulators, to all of whom I am indebted for the information and/or raw data about extraoral radiography machines to date that they have provided. The research paper which makes up Chapter 3 of this thesis was prepared partially in collaboration with co-author Honorary Associate Professor Louise F. Brown, who provided valuable insight and suggestions. I wish to thank both co-authors for their enthusiasm, technical support and academic contributions. My sincerest thanks go to Dr. Alannah Freer and the Dent8 Dental team who have provided me with unwavering support during the course of my postgraduate studies. Words cannot express how much appreciation I have for their understanding and constant encouragement while I was juggling both full-time postgraduate studies and part-time clinical dental work. Additionally, I would also like to thank my friends and fellow postgraduate registrars, colleagues, and clinical and academic staff with the University of Queensland's School of Dentistry and Queensland Health Metro-North who have rendered me with assistance, support and motivation. Last but not least, I would like to express my deepest gratitude to my parents Dr. Xianguang Zhang and Mrs. Xiaolan Li, my younger sister Sophia Zhang, my partner Mr. Seva Shorin, and my extended family, for their love, patience, support and encouragement throughout my postgraduate studies. I am especially grateful that Xianguang and Seva made available their valuable time to read preliminary versions of my research papers, participating in the exchange of ideas and in editorial work.