1. Department of Fixed Prosthodontics and Oral Implantology, Nihon University School of Dentistry at Matsudo, Matsudo, Chiba 271-8587, Japan
2. Sukegawa Dental Clinic, Mito, Ibaraki 310-0041, Japan
3. Department of Histology, Nihon University School of Dentistry at Matsudo, Matsudo, Chiba 271-8587, Japan
4. Department of Maxillofacial Surgery, Nihon University School of Dentistry at Matsudo, Matsudo, Chiba 271-8587, Japan
5. Department of Removable Prosthodontics, Nihon University School of Dentistry at Matsudo, Matsudo, Chiba 271-8587, Japan