Study subjects
Twenty volunteers were recruited from the Department of Operative and Prosthetic Dentistry, Medical University of Innsbruck (Austria). Inclusion criteria were (1) age ≥ 18 years, (2) contractual capability, and (3) the presence of ≥ 5 teeth per quadrant. Exclusion criteria were (1) dental students or professionals, (2) oral hygiene instructions prior to the study, (3) community periodontal index of treatment needs (CPITN) grade 3 or 4 [