The dental implants are considered as successful treatments with high predictability and survival rate for patients. By current increasing use of dental implants, arising more complications are inevitable. One of the growing problem with controversial treatment is, peri-implant diseases (PID). Different types of treatment including surgical and non-surgical methods for management of PID have been described. It seems, in patients with PID that have indication for non-surgical treatment, the mechanical debridement alone is not sufficient and in the most of time adjunctive therapy is recommended. Photodynamic therapy (PDT) is a novel therapeutic method for removal of infectious pathogens with the use of photosensitizer and specific wavelength of light. This study will be launched from mid-October 2016. In this study 25 patients will be assessed in test and control groups. The control group will receive mechanical debridement (MD) alone and the test group will receive MD with PDT. Probing depth, Clinical attachment level, Bleeding on probing, Pain on probing, Plaque index, IL-1β, IL-6, TNF-α and MMP8 will be assessed at baseline, 2 weeks and 3 month post-operatively. A Linear Mixed Model analytic test, Chi-square and Mantle Haenszel test will be used. P≤ 0.05 will be considered to represent a statistically significant differences among tested parameters. The present study will evaluate the post treatment clinical parameters and peri-implant mucosal crevicular fluid cytokine profiles in patients with PIMI, treated by either mechanical debridement alone or mechanical debridement in addition to PDT.