1. Assistant Professor, Clinic for Persons with Disabilities, Seoul National University Dental Hospital, Dental Research Institute, School of Dentistry, Seoul National University; Seoul 110-768 Korea
2. Graduate Student, Department of Conservative Dentistry and Dental Research Institute, School of Dentistry, Seoul National University; Seoul 110-749 Korea
3. Professor, Department of Conservative Dentistry and Dental Research Institute, School of Dentistry, Seoul National University; Seoul 110-749 Korea
4. Associate Professor, Department of Dental Laboratory Science and Engineering, College of Health Science, Korea University; Seoul 136-703 Korea