1. Department of Biologic and Materials Sciences University of Michigan School of Dentistry 1210 Eisenhower Place Ann Arbor Michigan 48108
2. Facility for Electron Microscopy Research Department of Anatomy and Cell Biology Faculty of Dentistry McGill University Montreal Quebec H3A 2B2 Canada
3. Advanced Photon Source Argonne National Laboratory 9700 S. Cass Ave Building 431‐B005 Argonne Illinois 60439
4. Department of Pediatric Dentistry School and Hospital of Stomatology Peking University 22 South Avenue Zhongguancun Haidian District Beijing 100081 China