1. Bas Loomans, DDS, PhD, Radboud Institute for Molecular Life Sciences, Department of Dentistry, Radboud university medical center, Nijmegen, PO Box 9101, Nijmegen 6500 HB, The Netherlands
2. Thomas Hilton, DMD, MS, Department of Restorative Dentistry, Oregon Health and Science University, 2730 S.W. Moody Ave. Portland, OR 97201-0007, USA