This study aimed to compare the survival rates and periodontal health outcomes of two types of mandibular fixed retainers—3-strand round twisted (RT) and 8-strand rectangular braided (RB)—each bonded to all six anterior teeth. A total of 133 orthodontic patients (median age: 24.6 years; interquartile range: 17.2–32.4 years; range: 15.1–49.8 years) were randomly assigned in a 1:1 ratio to receive either an RT or RB fixed retainer. Inclusion criteria included the presence of all permanent mandibular incisors and canines, absence of caries, restorations, fractures, or periodontal disease. Individuals with inadequate oral hygiene prior to debonding were excluded. The primary endpoint was the occurrence of the first retainer failure, while secondary measures included periodontal index, bleeding on probing, plaque index, gingival index, and probing depth. Randomization was achieved using permuted blocks of 4, 6, or 8 with allocation concealment via sealed, opaque envelopes. Due to the nature of the intervention, blinding was not feasible. Follow-up evaluations were conducted at baseline, 3, 6, 12, 18, and 24 months post-placement. Retainer survival was analyzed through Cox regression, while periodontal outcomes were evaluated using generalized estimating equations to assess the effects of treatment, time, tooth, and treatment-time interaction. Baseline characteristics were comparable across groups; one participant withdrew from the trial. Over the 2-year period, retainer failure occurred in 37 of 66 (56.1%) patients in the RT group and 32 of 66 (48.5%) in the RB group (log-rank test, P = 0.55). The adjusted hazard ratio for failure was 0.69 (95% CI: 0.42–1.12; P = 0.13), with neither age nor gender influencing the results. All periodontal measures remained similar between groups and stable across time points. Both retainer types demonstrated high failure rates (overall 52.3%), with no significant difference in survival or periodontal health between the RT and RB designs.
