Abstract: Objective To investigate the effects of invisible orthodontic appliance on the oral microenvironment, teeth and periodontal tissue. Methods Ten orthodontic patients（randomly numbered 1-10）who were treated in our hospital during October 2017 to October 2018 were selected as subjects. The Plaque index（PLI）and Gingival index（GI）were collected before treatment（T0）, 4 months after treatment（T1） and 8 months after treatment（T2）. The changes of bacterial diversity in saliva and the amount of bacteria related to dental caries and periodontal diseases were measured by 16S rDNA sequencing. Results There was no significant change in PLI and GI before and after treatment（P＞0.05）. The bacterial diversity in saliva increased during the treatment. The abundance of main bacteria changed, but the composition was relatively stable at phylum level（P > 0.05）. The abundance of Streptococcu, Actinobacillus and Neisseria increased significantly at genus level（P < 0.05）. Conclusion The wearing of the invisible orthodontic appliance has a certain effect on the oral microenvironment and causes changes in the bacterial community. However, no obvious clinical damage has been observed in the short term. It remains to be further studied whether the longer treatment time will cause other changes.

Key words: invisible orthodontic appliance, 16S rDNA, bacterial diversity, bacterial abundance, oral microenvironment