1. Igarashi Dental Clinic, Utsunomiya, Tochigi 329-1104, Japan
2. Department of Histology, Nihon University School of Dentistry at Matsudo, Matsudo, Chiba 271-8587, Japan
3. Department of Oral Implant, Nihon University Hospital at Matsudo, Matsudo, Chiba 271-8587, Japan
4. Department of Microbiology and Immunology, Nihon University School of Dentistry at Matsudo, Matsudo, Chiba 271-8587, Japan