Purpose: To compare adhesive flash-free (FF) and adhesive pre-coated (APC) brackets in terms of plaque retention and constituents, gingival biomarkers and enamel demineralisation. Materials and Methods: Fifty adolescents (mean age ± SD; 14.23 ± 0.15 years, age range: 13-18 years) were randomly distributed to receive FF or APC ceramic brackets in the maxillary right or left quadrant. Plaque and gingival indices, quantitative light-induced fluorescence (QLF) imaging, gingival crevicular fluid (GCF) and plaque sampling were performed at baseline and at 1, 2 and 3 months (T0, T1, T2, T3) after bracket placement. QLF was repeated following debonding. GCF samples were analysed for biomarkers by immunoassay and plaque by real-time PCR for bacterial content. Data were analysed using the Wilcoxon test on dependent samples and 2-tailed ANOVA. Results: Plaque index, gingival index and fluorescence changes were similar for the two adhesive-bracket systems. GCF volumes and interleukin (IL)-1ß levels increased compared to baseline (p 0.05). IL-17A levels and RANKL:OPG ratios were similar in both groups. In dental plaque, Aggregatibacter actinomycetemcomitans numbers were higher in the APC group at T3. Fusobacterium nucleatum (Fn) counts statistically significantly decreased at T1 and T3 as compared to T0 in the FF group (p 0.05 and p 0.01, respectively), whereas Fn counts increased in the APC group at T3 (p 0.01). Porphyromonas gingivalis, Streptococcus oralis and total bacterial counts were significantly higher in the APC group than in the FF group at T3 (p 0.01). Conclusion: In orthodontic patients with good oral hygiene, the quantity of plaque on adhesive flash-free brackets and conventional brackets did not differ, but the constituents of plaque differed, with less pathogenic bacteria detected around adhesive flash-free brackets. Further studies also including a group of individuals with poor oral hygiene and longer follow-up periods may better clarify the issue. Keywords: adhesive flash, biomarkers, cytokines, demineralisation