This review aimed to conduct a comprehensive review of the literature and statistically synthesize the data discovered about the effect of thermoplastic clear aligners and fixed orthodontic equipment on oral flora and salivary markers. The current systematic review followed the PRISMA criteria and the Cochrane Handbook. Five electronic databases were searched to find relevant articles. There were a total of 5345 articles on this topic. Due to the removal of duplicates, 4636 articles were included in the initial screening. Seven studies satisfied the requirements for qualifying. Of the four studies that were categorized as having a low risk of bias, two were considered to have a moderate risk of bias, and just one was considered to have a high risk of bias. The systematic review included each of them. Patients with permanent appliances had greater overall changes in their oral microbiota than patients with detachable equipment. Although the results of the fixed orthodontic appliances group differed in previous research, neither the salivary flow rate nor the salivary buffering capacity changed significantly for clear aligners. However, other salivary characteristics changed for the fixed orthodontic groups.
