1. Division of Orthodontics and Dentofacial Orthopedics, Department of Oral Growth and Development, School of Dentistry, Health Sciences University of Hokkaido, Kanazawa 1757, Ishikari-Tobetsu, Hokkaido 061-0293, Japan
2. Department of Statistics, North Carolina State University, Raleigh, NC 27606, USA
3. Department of Oral Anatomy, Seoul National University, School of Dentistry, 28 Yeongun-Dong, Chongro-Gu, Seoul 110-749, Republic of Korea