1. Department of Dentistry and Periodontology, National Health Insurance Service Ilsan Hospital, Goyang, Korea.
2. Department of Periodontology, Daejeon Dental Hospital, Institute of Wonkwang Dental Research, Wonkwang University College of Dentistry, Daejeon, Korea.
3. Department of Health Insurance Research, National Health Insurance Service Ilsan Hospital, Goyang, Korea.