The goal of the present revision is to systematically investigate the background and statistically summarize the found evidence investigating the impact of thermoplastic clear aligners as well as fixed orthodontic appliances on oral microbiota and salivary parameters. The present systematic study was done according to PRISMA guidelines and the Cochrane Handbook. Five Electronic databases were used to search for relevant articles. A total of 5345 articles were relevant to this topic. Duplicates were removed which caused 4636 articles included in the initial screening after duplicates. 7 studies met the eligibility criteria. Out of 4 studies classified as low risk of bias, 2 of them were regarded as moderate bias hazard and only one research as high bias risk. All of them were included in the systematic review. Overall changes of oral microbiota are higher in patients with fixed appliances than removable appliances. No significant change was observed in salivary flow rate nor salivary buffering power for clear aligner, while there were variations in the results of the fixed orthodontic appliances group in previous studies. However, there were changes in other salivary parameters for fixed orthodontic groups.