Background: The placement of orthodontic apparatus in the oral cavity, according to the literature, should influence the alteration of oral flora, especially the subgingival one. The purpose of the study is to evaluate the subgingival flora of patients with fixed orthodontic appliances, regardless of placement time. In 3 cases of patients with fixed orthodontic appliances, a bacterial sample of the gingival sulcus was taken for laboratory examination. Patients were clinically evaluated for the presence or tendency, of having gingival hypertrophy.Results: Results from the 3 cases included in the study, 1 of them came up with Streptococcus Anginosus positive, Doxycilin-sensitive. The tendency for gingival hypertrophy was maximal 3% to 1.5% respectively in each patient. In the patient with different oral flora, daily topical treatment with tetracycline, placed in the gingival sulcus, was applied.Conclusions: Alteration of the oral flora with the placement of fixed orthodontic appliances is not a fully verifiable fact, as it indicates the patient's follow-up, at the time of placement of the apparatus and until removal after orthodontic treatment, depending on the 2-3-year period of treatment. The tendency for gingival hypertrophy is apparently high, versus the presence of fixed orthodontic apparatus.