1. Department of Dentistry—Biomaterials, Radboud University Medical Center, Philips van Leydenlaan 25, Nijmegen 6525 EX, The Netherlands
2. Department of Preventive Dentistry, Academic Center for Dentistry Amsterdam, University of Amsterdam and Vrije Universiteit Amsterdam, Amsterdam 1081 LA, The Netherlands
3. Department of Stomatology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430022, P. R. China