Laila Gadalla*, Samah H. Elmeadawy*, Azza A. Elbaiomy* Oral Medicine & Periodontology and Clinical PathologyDepartments, Faculty of Dentistry, Mansoura University Abstract: Objective: The aim of this study to evaluate the level of osteoprotegerin (OPG) on the gingival crevicular fluid (GCF) in chronic gingivitis and chronic periodontitis patients, to evaluate the efficiency of OPG as a biomarker. And to determine effect of phase l therapy on the level of OPG in GCF. Subjects and Methods: Thirty subjects were included in the study and ten subjects as healthy control, ten patients with chronic gingivitis and ten patients with chronic periodontitis as study groups. Full-mouth clinical periodontal parameters, including periodontal probing depth, plaque index, gingival index and Papillary bleeding index) were recorded at baseline in all groups and after treatment in both study groups. GCF sample was collected at baseline and four, six and eight weeks after therapy for study groups and at baseline for the control group. GCF level of OPG was measured using assay ELISA kits and data were statistically analyzed using SPSS. Result: The results of the present study, showed a significant reduction in all clinical parameters (GI, PI, PPD, PBI and CAL) after phase I periodontal therapy in chronic gingivitis and chronic periodontitis groups. At the baseline the level of OPG in GCF was significantly lower in chronic gingivitis and chronic periodontitis patients than in healthy subjects. After a phase I periodontal therapy, there was an increase in GCF-OPG level in chronic gingivitis patients and chronic periodontitis patients was found versus its level at baseline. Conclusions: Level of OPG in GCF could be considered as novel biomarker in chronic periodontitis, also it was negatively correlated with the progression of periodontal disease. Recommendations: Additional longitudinal studies are needed to evaluate the concentration of OPG in GCF, and periodontal disease tissue will be clarifying its role in pathogenesis of periodontitis and to validate OPG as novel biomarker of periodontal disease progression.