Abstract: Objective　To observe the repeated non-surgical therapeutic effects on mild, moderate and severe peri-implantitis. Methods 29 patients with 31 peri-implantitis implants that were repaired for over 2 years were chosen. According to the severity, there were 12 peri-implantitis implants in mild group, 10 in moderate group and 9 in severe group. The 31 peri-implantitis implants were treated twice with non-surgical combination scheme, ultrasonic mechanical debridement + air-polishing with amino acid glycine powder + minocycline ointment injection + chlorhexidine rinse. One month later, the treatment was repeated again. The PD, BOP positive site numbers, suppuration positive site numbers at the three time points were recorded respectively (the time before therapy denoted as T0, 1month after 1st therapy as T1, 1month after 2st therapy as T2). The changes of clinical parameters were compared at different time points. Results After two treatments, in mild peri-implantitis group, although the mean PD had no statistical difference (P >0.05) between T0 and T1, the difference between T0 and T2 became more obvious (P <0.05), and BOP positive site numbers decreased (T0 vs.T1, P <0.05; T0 vs.T2， P <0.01), ,at T0 none suppuration site was detected. In moderate group, PD, BOP positive site numbers, suppuration positive site numbers decreased continuously through repeated non-surgical therapy (T0 vs.T1, P <0.05; T0 vs.T2， P <0.01). In sever group, there were obvious differences in PD, suppuration positive site numbers (T0 vs.T1, P <0.05; T0 vs.T2 ，P <0.01), while there were no statistical differences in BOP among the three time points. At the time of T2, there were still deep PD sites, BOP sites, suppuration sites in both moderate and sever groups. Conclusions The non-surgical therapy can improve the clinical parameters but cannot cure the peri-implantitis thoroughly. Repeated therapy procedure is needed. Mild peri-implantitis can be basically controlled after two repeated non-surgical therapies while moderate and severe peri-implantitis cannot be controlled thoroughly.

Key words: peri-implantitis, non-surgical therapy, PD, BOP, suppuration