A comparative assessment of stability and satisfaction between two mandibular lingual retainers in orthodontic patients. A 2-year follow-up, single practice-based randomized trial.

OBJECTIVE: This study aimed to evaluate and compare the stability of mandibular dental arch dimensions and patient satisfaction between two types of fixed retainers-3-strand round twisted (RT) and 8-strand rectangular braided (RB)-both of which are bonded to all six anterior mandibular teeth. TRIAL DESIGN: 2-arm parallel, two-center prospective randomized controlled trial. METHODS: PARTICIPANTS: 133 orthodontic patients (median age 24.6 years, 25th percentile = 17.2 years, 75th percentile = 32.4 years) were recruited. INTERVENTIONS: These patients were randomly assigned to receive either an RT or RB wire retainer at a 1:1 ratio. RANDOMIZATION: It was achieved using random permuted blocks of sizes 4, 6, or 8, which were concealed in sequentially numbered, opaque, sealed envelopes. OUTCOMES: The primary outcome was the change in the irregularity index, with secondary outcomes including arch length; intercanine, interpremolar, and intermolar widths; and patient satisfaction. Evaluations were performed at baseline and at 3, 6, 12, 18, and 24 months after retainer placement. Dental cast measurements were analyzed using random effects linear regression, and satisfaction was assessed at each time point. BLINDING: Blinding of patients was not feasible. Only blinding the assessor for patient satisfaction was achieved. RESULTS: Cast measurements remained relatively stable from T1 to T6, with no significant difference attributed to the retainer type (RT or RB). Time significantly affected all cast measurements except for the irregularity index. There was no significant correlation between retainer type or time and satisfaction questionnaire responses, although the responses varied by question. No harms were observed. CONCLUSIONS: Both RT and RB wire retainers effectively maintain mandibular arch alignment and are equally well tolerated by patients in the medium term.