Abstract: Abstract Objective: To investigate the changes of bacterial flora in gingival sulcus and oral cavity before and after orthodontic treatment. Methods: 130 orthodontic patients from July 2013 to September 2014 in the people's Hospital of Bozhou were selected as orthodontic group and 60 healthy?individuals were selected as control group. The gingival sulcus fluids of orthodontic group and control group before and in 1 month, 3 months after operation were collected, and they were used for bacterial culture. The difference of plaque index, gingival sulcus bleeding index and probing depth between two groups were compared. Results: The plaque index, gingival sulcus bleeding index and probing depth of orthodontic group in 1 month and 3 months after operation were significantly higher than that of preoperative and control group, and the difference was statistically significant (P<0.05). Compared with the preoperative, the proportion of cocci, bacilli and campylobacteria of orthodontic group in 1 month and 3 months after operation were significantly reduced, the proportion of fusiforms, spiral bacteria, hyphomycete were significantly increased, and the detection?ratio of porphyromonas gingivalis, nucleic acid bacillus, bacteroides forsythus and actinobacillus were significantly increased, the difference was statistically significant (P<0.05). Conclusion: Oral bacteria reproduction after orthodontic treatment increases, should pay attention to keep oral health and avoid inducing inflammation.

Key words: Keywords: orthodontic treatment, bacterial micro-ecology, gingival sulcus