1. University of Minnesota School of Dentistry, Department of Diagnostic and Biological Sciences,
2. Department of Developmental and Surgical Sciences, 6-320 Moos Tower, 515 Delaware Street SE, Minneapolis, MN 55455, USA;
3. University of Minnesota School of Public Health, Division of Biostatistics, Minneapolis, MN, USA; and
4. Veterans Administration Hospital Dental Clinic, Minneapolis, MN, USA