1. Department of Cariology, Restorative Sciences and Endodontics, University of Michigan School of Dentistry, 1011 N. University, Rm. 2309, Ann Arbor, MI 48109-1078, USA;
2. Department of Orthodontics and Pediatric Dentistry, University of Michigan School of Dentistry, Ann Arbor, Michigan 48109-1078, USA; and
3. Department of Biomedical Engineering, College of Engineering, University of Michigan, Ann Arbor, MI 48109, USA