1. Histology and Embryology Laboratory, Department of Medicine and Surgery, University of Parma, Via Volturno 39, 43126 Parma, Italy
2. Centre for Oral Clinical Research, Institute of Dentistry, Faculty of Medicine and Dentistry, Queen Mary University of London, London E1 2AD, UK
3. Dental School, Department of Medicine and Dentistry, University of Parma, 43126 Parma, Italy