1. Department of Periodontology; Catholic University Leuven; Kapucijnenvoer; 33, 3000; Leuven; Belgium
2. Department of Quality of Medical Laboratories; Scientific Institute of Public Health; J. Wytsmanstraat 14; 1050; Brussel; Belgium
3. Oral Imaging Center; Catholic University Leuven; Kapucijnenvoer; 33, 3000; Leuven; Belgium