Introduction: Recent studies reported additional clinical improvement  when moderate chronic periodontitis was treated by means of a one stage full mouth disinfection instead of standard treatment .The one stage full mouth disinfection procedure involves periodontal debridement of all pockets within 24 hours with application of an irrigation to all intraoral niches such as periodontal pockets and tongue dorsum. 
Aim : The aim of this randomized clinical trial was to assess the clinical improvement of chronic moderate periodontitis after full mouth disinfection compared to periodontal debridement alone .
Subjects and methods: Thirty patients ( 18 males and 12 females ) suffering from moderate chronic periodontitis, free from any systemic disorders were recruited from the outpatient clinic, Faculty of Dentistry - Assiut University and presented at the department of Periodontology for assessment and treatment. Patients were assigned to the following groups:
Group I: patients  received scaling and root planing. Group II: patients received a full mouth disinfection including a full mouth scaling and root planing in combination with a disinfection of all intraoral niches by means of chlorhexidine. Group III: patients received a full mouth disinfection including a full mouth scaling and root planing in combination with a disinfection of all intraoral niches by means of tetracycline. Randomization of the patients and blinding of assessment were performed to avoid bias. Statistical analysis was performed with IBM SPSS statistics version 20 for windows.
Results: Pocket reduction mean of group I was (+-1.8mm), gain of attachment mean for group I was (+-2.7mm) , Pocket reduction mean of group II was (+-1.2mm), gain of attachment mean for group II was (+-2.5mm), Pocket reduction mean of group III was (+-1.1mm), gain of attachment mean for group III was (+-2.3mm)
Conclusion : All three treatment modalities showed clinical improvement.  Full mouth disinfection either by chlorhexidine or tetracycline gave better clinical results than regular periodontal debridement but there were no statistically significant differences.