1. Department of Preventive Dentistry; Faculty of Dentistry; Prince of Songkla University; Hadyai, Songkhla Thailand
2. Department of Preventive and Community Dentistry; College of Dentistry; University of Iowa; Iowa City IA USA
3. Department of Epidemiology; College of Public Health; University of Iowa; Iowa City IA USA
4. Department of Biostatistics; College of Public Health; University of Iowa; Iowa City IA USA
5. Department of Operative Dentistry; College of Dentistry; University of Iowa; Iowa City IA USA