Qualitative and quantitative changes in the oral bacterial flora occur shortly after implementation of fixed orthodontic appliances

Introduction: In this pilot study, we aimed to determine qualitative and quantitative microbiological changes after the implementation of orthodontic appliances. Methods: A total of 10 healthy patients aged 12-15 years were recruited who needed to undergo orthodontic treatment with buccal fixed appliances. Gingival conditions were assessed by the Gingival Index, Periodontal Screening Index, and Sulcus Bleeding Index. Microbiological samples were collected before and 1 week after the start of therapy at premolars and molars of the right upper quadrant. Bacterial species were identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Results: The total number of bacteria increased. Six bacterial species were identified that are involved in the development of caries and other infectious processes. The bacteria selectively adapted more efficiently to the new oral milieu compared with the general oral microbial background. There was a significant increase in Streptococcus spp at the premolars and molars. In all individuals, symptoms of inflammation and gingivitis were detected as a response to the bacterial challenge. Conclusion: Orthodontic treatment induces significant changes in the oral microbial flora associated with gingivitis and an enhanced risk for cariogenic reactions within the first days of orthodontic treatment. To prevent or reduce infectious side effects, oral hygiene instructions and control of patients are necessary before and during the beginning of the therapy.