1. Department of Preventive Medicine, The Graduate School of Yonsei University, Seoul, Korea.
2. Department of Preventive Medicine and Institute of Occupational and Environmental Medicine, Wonju College of Medicine, Yonsei University, Wonju, Korea.
3. Department of Dental Hygiene, Wonkwang Health Science University, Iksan, Korea.
4. Department of Dental Hygiene, Wonju College of Medicine, Yonsei University, Wonju, Korea.
5. Department of Preventive Medicine and Institute of Occupational Medicine, College of Medicine, Yonsei University, Seoul, Korea.
6. Department of Biostatistics and Computing, The Graduate School of Yonsei University, Seoul, Korea.