1. Department of Preventive Medicine, Keck School of Medicine of the University of Southern California, Los Angeles, California.
2. Public Health and Community Dentistry, School of Dentistry, University of California, Los Angeles, California.
3. Department of Biomathematics, University of California, Los Angeles, California.
4. Departments of Family Medicine and Orthopaedic Surgery, David Geffen School of Medicine, University of California, Los Angeles, California.
5. Oral and Maxillofacial Radiology, School of Dentistry, University of California, Los Angeles, California.