1. Clínica Dental Carolina Barletta del Campo, 33209 Gijón, Spain
2. Department of Construction and Manufacturing Engineering, University of Oviedo, 33004 Oviedo, Spain
3. Department of Business Administration, University of Oviedo, 33004 Oviedo, Spain
4. Department of Mathematics, University of Oviedo, 33007 Oviedo, Spain