Perio-Ortho treatment needs a specific and continuous evaluation / reevaluation of the clinical parameters to gain and maintain periodontal health during the entire course of therapy. Conventional periodontal measurements (PPD - Probing Pocket Depth, CAL -Clinical Attachment Level, BOP - Bleeding On Probing, GR - Gingival Recession, KTW - Keratinized Tissue Width) are the most relevant clinical indices to continuously assess an healthy periodontal condition. During orthodontic therapy periodontally treated patients need a constant and thorough reevaluation of all these parameters, in order for detecting any single relapse and for treating it consequently ( with a surgical or non-surgical approach ) , sometimes stopping orthodontic movement until a new healthy status is re-established . The lecture will focus on such parameters, on the way and timing of monitoring the periodontal status, on the therapeutic strategies to achieve clinical success, with a common vision shared between periodontist and orthodontist.