The clinical periodontal parameters and the plaque index of each patient will be recorded at baseline (pre-intervention), as well as +30 and +90 days after the non-surgical periodontal therapy. The Kappa index will be used to evaluate the examiner calibration on clinical periodontal parameters collection in order to calculate the intra-examiner agreement. According to the World Health Organization (WHO) criteria for diagnosis, the acceptable Kappa index of agreement must be greater than or equal to 0.85 (WHO, 1997). This level of agreement will be used for calibration of the examiner in this project. Ten patients, each one showing at least two pairs of contralateral single-rooted teeth with PD ≥ 5 mm on interproximal sites, will be selected to calibrate the examiner. Each patient will be evaluated on two separate occasions 48 hours apart in order to obtain the intra-examiner reliability through the Kappa index.