1. Department of Preventive and Social Dentistry; Graduate School; Kyung Hee University; Hoegi-dong, Dongdaemoon-gu; Seoul South Korea
2. Department of Oral and maxillofacial Radiology; Graduate School; Kyung Hee University; Hoegi-dong, Dongdaemoon-gu; Seoul South Korea
3. Department of Pediatric Dentistry; School of Dentistry; Kyung Hee University; Seoul Korea