ACKNOWLEDGEMENTS In the name of ALLAH, most Gracious, most Merciful, the first Who deserves all thanks and appreciation for everything and for providing me with willingness and strength to finish this work. I wish to express my sincere gratitude and admiration to my supervisor Professor Dr. Khidair Adaay Salman, for his guidance, helpful advice and suggestions that have been of great value in the accomplishment of this research. I would like to express my appreciation to Prof. Hussein A. Al-Obaidi, (The past Head of Pedodontics, Orthodontics and Preventive Dentistry Department), and Dr. Fadhil Y. Jasim for their valuable remarks, suggestions, and guidance during the courses of the study. My deep respect and gratitude go to my husband, Nazar Gh. Jameel and my daughters for theirhelp and patience during the last two years. I wish to express my sincere appreciation to University of Mosul, College of Dentistry.