1. Dept. of Oral Anatomy and Physiology and TMD,
2. Dept. of Prosthetic Dentistry, School of Stomatology, Fourth Military Medical University, 145 West Changle Road, Xi’an, P.R. China 710032;
3. Dept. of Health Statistics, Faculty of Military Preventive Medicine, Fourth Military Medical University, 17 West Changle Road, Xi’an, P.R. China 710032; and
4. Dept. of Prosthetic Dentistry and Stomatognathic Physiology, Institute of Dentistry, University of Oulu, and Dept. of Oral and Maxillofacial Surgery, Oulu University Hospital, P.O. Box 5281, FIN-90014, Oulu, Finland