[1] Korea Univ, Anam Hosp, Dept Oral & Maxillofacial Surg, Seoul 02841, South Korea
[2] Catholic Univ Korea, Coll Med, Dept Biostat, Seoul 06591, South Korea
[3] NIEHS, Epidemiol Branch, NIH, Res Triangle Pk, NC 27709 USA
[4] Ajou Univ Hosp, Dept Periodontol, Suwon 16499, South Korea
[5] Korea Univ, Anam Hosp, Dept Prosthodont, 73 Inchon Ro, Seoul 02841, South Korea
[6] Catholic Univ Korea, Coll Med, Dept Periodont, Seoul 06591, South Korea