1. Department of Preventive Dentistry, School of Dentistry, Kyungpook National University, Daegu 41940, Korea
2. Department of Dental Hygiene, Daegu Health College, Daegu 41453, Korea
3. Department of Dental Hygiene, Ulsan College, Ulsan 44022, Korea
4. Department of Dental Hygiene, College of Science & Technology, Kyungpook National University, Sangju 37224, Korea