1. Department of Pediatric Dentistry, Nihon University School of Dentistry at Matsudo, 2-870-1 Sakaecho-Nishi, Matsudo, Chiba 271-8587, Japan; and
2. Department of Pediatric Dentistry, Tsurumi University School of Dentistry, 2-1-3 Tsurumi, Tsurumi-ku, Yokohama 230-8501, Japan;