Microbial and periodontal shifts induced by orthodontic appliances: a comparative clinical study

This study aimed to evaluate the periodontal and microbiological alterations in oral flora associated with using removable appliances and fixed orthodontic treatments.  Methods: The study materials consist of subgingival-supragingival plaque samples and periodontal measurements from 48 patients. The groups include fixed appliance users, removable appliance users, and a nontreatment control group. Periodontal measurements, including gingival index, plaque index, bleeding on probing, mobility, furcation, probing depth, and attachment level, were recorded at baseline (before treatment) and 6 months after treatment initiation. Plaque samples were collected at T0 and T1. Dental plaque samples were cultured on selective media for qualitative and quantitative microbial analysis, followed by qualitative evaluation using the VITEK 2 (Biomerieux) system. Data were analyzed using one-way one-way analysis of variance one-way analysis of variance (ANOVA), paired sample-T test, and Duncan's multiple range test to identify and compare statistically significant differences within and between groups, while intraobserver reliability was assessed using the Kappa statistic.  Results: Mobility or furcation involvement was not detected in any of the groups at either time point. At the T1 stage, a slight improvement in attachment level was observed in both the fixed and removable appliance groups compared with baseline measurements. However, during the same period, a significant increase in mean probing depth was detected only in the fixed appliance group (p = 0.003). Plaque index levels increased in both the removable appliance group (p = 0.019) and the fixed appliance group (p = 0.023). Furthermore, the bleeding on probing index also showed an increase in both groups, with p = 0.020 in the removable appliance group and p = 0.012 in the fixed appliance group. At the T1 stage, an increase in yeast counts was observed in the removable appliance group (p = 0.008), whereas decreases were detected in Lactobacillus (p = 0.004) and mutans streptococci (p = 0.026) levels. In contrast, the fixed appliance group demonstrated significant increases in Lactococcus (p = 0.042) and mutans streptococci (p = 0.037) counts. The identified microorganisms included a diverse range of bacterial species, such as Actinomyces spp., Fusobacterium spp., Lactobacillus spp., Streptococcus spp., Veillonella spp., and other clinically significant genera.  Conclusions: It may be inferred that fixed orthodontic treatments create a biological environment that is more susceptible to adverse periodontal alterations and increased colonization by specific microbial species. Conversely, the potential suppressive effects of removable appliances on certain microbial groups emphasize the need to consider patients' oral hygiene compliance, periodontal risk profile, and microbial sensitivity during treatment planning.