1. Department of Orthodontics, Faculty of Dental Medicine, Medical University Sofia, Sofia, Bulgaria
2. Department of Liquid Crystals and Biomolecular Layers, G. Nadjakov Institute of Solid State Physics, Bulgarian Academy of Sciences, Sofia, Bulgaria
3. Department of Solid Mechanics, Institute of Mechanics, Bulgarian Academy of Sciences, Sofia, Bulgaria
4. Department of Laser, Atomic, Molecular and Plasma Physics, G. Nadjakov Institute of Solid State Physics, Bulgarian Academy of Sciences, Sofia, Bulgaria
5. H. H. Wills Physics Laboratory, Department of Physics, University of Bristol, Bristol, UK
6. Department of Material and Environmental Technology, Institute of Materials and Environmental Technology, Tallinn University of Technology, Tallinn, Estonia