Retrospective Assessment of Palatal Biofilm and Mucosal Inflammation Under Orthodontic Appliances in Young Adults (2022–2025): A Single-Center Cohort with Microbiologic Sub-Sampling

<b>Background and Objectives:</b> Orthodontic auxiliaries create plaque-retentive niches that may amplify biofilm accumulation and inflame adjacent soft tissues. While cross-sectional comparisons suggest higher palatal burden beneath acrylic elements, less is known about real-world patterns accumulated across years of routine care. We retrospectively evaluated periodontal and palatal outcomes, and, in a microbiology sub-sample, site-specific colonization, across three device types: molar bands, Nance buttons, and removable acrylic plates. <b>Methods:</b> We reviewed 2022-2025 records from a university orthodontic service, including consecutive patients aged 18-30 years with documented pre-placement and 6-month follow-up indices. Groups were bands (<i>n</i> = 92), Nance (<i>n</i> = 78), acrylic (<i>n</i> = 76). Standardized charted measures were abstracted: Plaque Index (PI), Gingival Index (GI), bleeding on probing (BOP%), probing depth (PD), and palatal erythema grade (0-3). A laboratory sub-sample (<i>n</i> = 174 visits) had archived swabs cultured for total aerobic counts (log₁₀ CFU/cm²) at the device, adjacent enamel, and palatal mucosa; <i>Streptococcus mutans</i> burden was available from qPCR (log₁₀ copies/mL). <b>Results:</b> Baseline characteristics were similar, except for longer wear at follow-up in Nance (10.1 ± 4.0 months) vs. bands (8.7 ± 3.2) and acrylic (6.9 ± 3.0; <i>p</i> < 0.001). At 6 months, device type was associated with greater worsening of PI and GI (both <i>p</i> < 0.001) and with higher palatal erythema (bands 0.7 ± 0.5; Nance 1.6 ± 0.8; acrylic 1.9 ± 0.7; <i>p</i> < 0.001). Microbiologically, palatal mucosal colonization was lowest with bands (3.3 ± 0.5), higher with Nance (4.9 ± 0.6), and highest with acrylic (5.0 ± 0.7; <i>p</i> < 0.001); <i>S. mutans</i> mirrored this gradient (<i>p</i> < 0.001). Palatal CFU correlated with erythema (ρ = 0.6, <i>p</i> < 0.001) and ΔGI (ρ = 0.5, <i>p</i> < 0.001). In adjusted models, acrylic (OR 6.7, 95% CI 3.5-12.8) and Nance (OR 4.9, 2.5-9.3) independently predicted erythema ≥2; recent prophylaxis reduced odds (OR 0.6, 0.3-0.9). <b>Conclusions:</b> In this single-center cohort, palate-contacting designs were associated with higher palatal biomass and erythema than bands. These associations support device-tailored hygiene considerations and proactive palatal surveillance, particularly for acrylic components.