This study was carried out at the Institute of Dentistry, University of Helsinki, and the Department of Oral and Maxillofacial Diseases, Helsinki University Central Hospital, Helsinki. I wish to thank Professor Jukka Ainamo, DDS, PhD, and Professor Heikki Murtomaa, DDS, PhD, the former Deans of the Institute of Dentistry, and Professor Jukka H. Meurman, DDS, PhD, the present Dean of the Institute of Dentistry for placing facilities at my disposal.
I am indebted to my supervisor, Professor Satu Alaluusua, DDS, PhD, for persuading me into scientific writing, and thereby introducing me to the pluralistic, fascinating world of science.
I wish to express heartfelt gratitude towards my official referees, Docent Kaisu Pienihäkkinen, DDS, PhD, and Docent Jaana Vuopio-Varkila, MD, PhD, for their valuable comments and constructive criticism of this thesis. Their sound scientific advice and positive attitude have been reviving.
I owe my warm thanks to all my collaborators at the Espoo City Health Centre, Espoo, the Anaerobe Reference Laboratory and the Laboratory Animal Unit of the National Public Health Institute, Helsinki, the School of Dentistry at Matsudo, Nihon University, Japan, the former Department of Preventive Dentistry and Cariology, University of Kuopio, and the Institute of Dentistry, University of Helsinki; Professor emeritus Heikki Luoma, DDS, PhD, Professor Kazuo Fukushima, DDS, PhD, Docent Hannele Jousimies-Somer, PhD, Docent Sirkka Asikainen, DDS, PhD, Docent Maria Saarela, PhD, Dr Eija Kleemola-Kujala, DDS, PhD, Dr Anja-Riitta Luoma, DDS, PhD, Jaana Mättö, PhD, Liisa Pyhälä, MSc, Heini Torkko, MSc, Dr Xia Zhu, Dr Ulla Tanner-Salo, Dr Sini Innilä and Dr Aura Vuorela. It has been an honour and a privilege to share a piece of your vast knowledge. All researchers and assisting personnel participating in the studies are warmly acknowledged for their generous contribution. Especially the researchers engaged in the longitudinal study, initiated at the Department of Pedodontics and Orthodontics by the late Professor Johannes Haataja, deserve recognition for their positive research interest.
I am grateful for having had the opportunity to attend the basic courses in microbiology and genetics at the Faculty of Science as part of my basic training towards a doctoral thesis in the Faculty of Medicine.
I also wish to thank Carol Pelli, HonBSc, for kindly revising my English in this thesis, Riitta Auvinen, IT-professional, for helping me with computers, and all the mothers, children and adolescents attending the studies who made this thesis possible.
Finally, I thank my family, relatives, colleagues and friends for patience, support, friendship and love.
The study was supported by grants from the Academy of Finland, the Finnish Dental Society, the Finnish Woman Dentists´ Association, the University of Helsinki, and Odontologiska Samfundet i Finland.
Helsinki - Helsingfors, June 2000
Munksgaard International Publishers Ltd (Oral Microbiology and Immunology), Elsevier Science (Archives of Oral Biology), American Society of Microbiology (Antimicrobial Agents and Chemotherapy; Infection and Immunity) and S. Karger AG, Basel (Caries Research) are acknowledged for their kind permission to reprint articles upon which this thesis is based.