1. King Faisal Specialist Hospital & Research Centre, Riyadh, Saudi Arabia;
2. current address, Department of Periodontics, Loma Linda University, 24860 Taylor Street, Loma Linda, CA 92354, USA;
3. University of Kristianstad, Kristianstad, Sweden; and
4. Section of Periodontology, College of Dentistry, The Ohio State University, Columbus, OH, USA;