1. Department of Oral and Maxillofacial Surgery, Graduate School of Medicine, School of Medicine, Yokohama City University, Yokohama, Japan
2. Department of Oral Surgery, Graduate School of Medicine, School of Medicine, Sapporo Medical University, Sapporo, Japan
3. Department of Hygiene, Graduate School of Medicine, School of Medicine, Sapporo Medical University, Sapporo, Japan