In the process of orthodontic treatment, some indicators of the oral fluid and the composition of the microbiota of the oral cavity are changing. These changes occur in the treatment of both removable and nonremovable orthodontic appliances. At the beginning of orthodontic treatment, the number of colonies of microorganisms increases and reaches a maximum after 2 weeks. At the same time, there is a deterioration in oral hygiene, the rate of secretion of oral fluid and its pH changes too. It was also established that some microorganisms have different degrees of adhesion to the details of the orthodontic appliances. An increase of number of colonies of microorganisms causes additional foci of negative effects on periodontal tissues, which contributes to the occurrence of inflammatory processes. This generally negatively affects the quality of orthodontic treatment. Thus, at the beginning of orthodontic treatment, the physicochemical and microbiological parameters of the oral fluid deteriorate and adhesion of microorganism colonies to the surface of the apparatus is observed. Caring for a high level of oral hygiene in the initial stages of orthodontic treatment is a prerequisite for maintaining oral fluid levels at the proper level and the absence of soft plaque helps to reduce the time of orthodontic treatment and it is one of the important factors in the prevention of periodontal disease.