Węgrodzka 2021.

Study characteristics
Methods	2‐arm parallel RCT
Participants	Number recruited: 133 (65 in round twisted (RT) group and 66 in rectangular braided (RB) group) Sex (M:F): 42:91 Median age (years): 24.6 (IQR 17.2‐32.4) Inclusion criteria: age 15‐50 years at debonding; all mandibular permanent incisors and canines present; no active caries, no restorations, no fractures on the mandibular incisors and canines, no periodontal disease; and retention plan including only retainers bonded from 3‐3 Exclusion criteria: inadequate hygiene, need for restorative or surgical treatment, active periodontal disease, or removable retainer as an adjunct to a bonded retainer Setting: orthodontic private practice, Krakow, Poland
Interventions	2 types of fixed retainers Group 1: 3‐strand round twisted (RT)  Group 2: 8‐strand rectangular braided (RB) fixed retainers bonded to all 6 anterior teeth in the mandible
Outcomes	Survival time of retainers. failure rates (first‐time failure of retainer) and failure risk (hazard ratio) Oral health: periodontal indices (periodontal index, bleeding on probing, plaque and gingival indices, pocket depth) Time points: baseline, at debonding and retainer placement, 3, 6, 12, 18 and 24 months
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Randomisation is very well reported: software‐generated, block‐randomised and equal‐distributed
Allocation concealment (selection bias)	Low risk	Allocation concealment was achieved with sequentially numbered, opaque, sealed envelopes prepared before the study. The study co‐ordinator (practice manager) was responsible for opening  envelopes in sequence and implementing the randomisation process.
Blinding of outcome assessment (detection bias) All outcomes	High risk	Blinding was not possible because the retainers could not be masked during clinical assessments. It is likely to be influenced by lack of blinding.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Few missing outcome data and balanced in numbers between intervention groups, with similar reasons for missing data between groups
Selective reporting (reporting bias)	Unclear risk	This study did not have a published protocol prior to the initiation of the study. Insufficient information to allow judgements, although the publication reports all the outcomes indicated in the material and methods section.
Other bias	Low risk	The study appears to be free of other sources of bias.