1. Department of Operative Dentistry, The University of Coimbra Medical and Dental School, Coimbra, Portugal
2. Department of Operative Dentistry, The University of North Carolina, CB 7450, Brauer Hall, Chapel Hill, North Carolina 27599-7450
3. Department of Operative Dentistry, The University of Iowa, Iowa City, Iowa 52242
4. Department of Pediatric Dentistry and Dows Institute for Dental Research, The University of Iowa, Iowa City, Iowa