Objective: To assess gingival health and predictors of relapse related to braided-wire bonded retainers after the active phase of comprehensive orthodontic treatment.Materials and methods: Fifty-one subjects were recruited in a prospective study of whom 42 were available for analysis after 2 years of retention (pre-therapeutic ages 11-18 years; 66% female). A rectangular wire retainer (0.027 x 0.011 '') was bonded to the mandibular incisors. Little's index of incisor irregularity; intercanine width; the accumulation of biofilm, calculus and gingivitis; and the incidence of retainer detachment, were recorded. Subjects were examined before orthodontic therapy, upon therapy completion, and after 2 years of retention.Results: The incidence of retainer detachment over the 2 years was 27%. The post-treatment incidence of irregularity was 17%, and intercanine width reduction was 24%. Calculus accumulation increased significantly during retention (p < 0.001) but not the extent of gingivitis. A multiple logistic regression demonstrated that an increase of mandibular intercanine width by >= 3 mm correspondingly increased the odds of relapse 14.3 times (95% confidence interval [CI], 1.1-196.1; p = 0.046). Patients presenting with retainer failure were 10 times (95% CI 1.6-62.8; p = 0.014) more likely to experience relapse. Subjects who experienced relapse had retainer failure earlier than those without relapse (19 vs. 23 months; p = 0.003). The occurence of relapse was not related to a treatment change in incisor irregularity, the duration of treatment, the age of the patient, gender nor to a change of intercanine width during retention.Conclusion: Post-treatment changes in the mandibular arch incorporating bonded retainers were not large, but were common. An increase in mandibular incisor irregularity during retention is mostly related to treatment-induced intercanine width expansion. The bonded retainer often detached and increased calculus accumulation.