Abstract: Objective： To evaluate the feasibility of full-mouth debridement (subgingival scaling and root planning, SRP) by 2 times within 1 week and compare the clinical effects of different sequences of debridement-antibiotic usage in patients with severe chronic periodontitis (CP). Methods: A doubleblinded, placebo-controlled, randomized clinical trial was conducted in 30 severe CP patients (14 males and 16 females, 40.5±8.4 years old on average from 35 to 60) receiving 3 different sequences of debridement-antibiotictherapy: Group A, antibiotic usage (metronidazole, MTZ, 0.2 g, tid, 7 d; amoxicillin, AMX 0.5 g, tid, 7 d) was started together with SRP (completed by 2 times in 7 d); Group B, antibiotic usage (MTZ 0.2 g, tid, 7 d; AMX 0.5 g, tid, 7 d) was started 1 d after SRP(completed by 2 times in 7 d); Group C, SRP alone［probing depth (PD), bleeding index (BI) and tooth mobility］ was examined. The average full-mouth probing depth, the average fullmouth proximal probing depth (pPD), the percentage of sites with PD＞5 mm (PD＞5 mm%), the percentage of sites with proximal PD＞5 mm (pPD＞5 mm%), the average bleeding index (BI) and the percentage of sites with bleeding on probing (BOP%) were calculated. Clinical examinations were performed at baseline and 2 months post therapy. Results: (1) Compared with baseline conditions, all the subjects showed clinical improvements in all the parameters evaluated 2 months post therapy, P＜0.05. (2) Significant difference were observed in the average PD changes between Group A ［(2.15±0.42) mm］, Group B ［(1.76±0.29) mm］ and Group C ［(1.57±0.33) mm］, P＜0.05. No significant difference was observed in the average PD changes between Group B and Group C, P=0.354. Significant differences were observed in the average pPD changes between Group A ［(2.45±0.43)mm］ and Group C［(1.90±0.48) mm］, P＜0.05. No significant difference was observed in BI and BOP% changes between Group A，Group B and Group C. Conclusion: For patients with severe chronic periodontitis, it is safe and feasible to receive full-mouth SRP by 2 times within 1 week. The shortterm (2 months) advantages in PD changes are observed in patients receiving SRP and antibiotic usage at the same time comparing with patients using antibiotics after SRP or SRP alone.

Key words: Periodontitis, Dental scaling, Amoxicillin, Metronidazole