Summary of findings 4. Fixed retainer (fibre‐reinforced composite) versus fixed retainer (multistrand/spiral wire) to stabilise tooth position.

Population: people who had received fixed appliance treatment Setting: specialised orthodontic practice and hospital or university orthodontic department Intervention: fibre‐reinforced composite retainer  Comparison: multistrand/spiral wire fixed retainer Follow‐up: 12 months Arch: lower
Outcome	Outcome measure	Illustrative comparative risks* (95% CI)		Relative effect (95% CI)	No of participants (studies)	Certainty of evidence (GRADE)	Comments
		Assumed risk	Corresponding risk
		Multistrand/spiral wire fixed retainers	Fibre‐reinforced composite retainer
Stability  Follow‐up: 12 months	Little's Irregularity Index(LII) in lower arch (ideally 0 mm)	Mean LII was 0.97 mm	MD 0.70 mm lower (1.17 lower to 0.23 lower)	‐	52 (1 RCT)	⊕⊝⊝⊝ Very lowa,b,c	1 RCT at high risk of detection bias and unclear risk of selection bias suggested that there was better stability with the fibre‐reinforced composite retainer, but the mean difference was less than 1 mm, which is not clinically significant.
Survival  Follow‐up: 12 months	Failure of retainer in lower arch	247 per 1000	2 more per 1000 (39 less to 52 more)	RR 1.01  (0.84 to 1.21)	1337 (7 RCTs)	⊕⊕⊝⊝ Lowa,d	4 RCTs at high risk of detection, attrition, and reporting bias and 3 RCTs at unclear selection, detection, and attrition bias suggested that there was no difference between the retainer types.
	Mean survival time in lower arch (months)	‐	‐	‐	0 (0 RCTs)	‐	No studies measured or reported this outcome at 12‐month follow‐up. 1 RCT at high risk of detection and reporting bias and 1 RCT at unclear risk of selection and detection bias suggested that failures occurred earlier when a fibre‐reinforced composite retainer was used at 24‐month follow‐up (MD −1.48, 95% CI −1.88 to −1.08; 103 participants; very low‐certainty evidence).
Patient satisfaction Follow‐up: 12 months	Aesthetic in lower arch VAS 0–10 cm (10 cm is very satisfied)	Mean VAS score was 8.24 cm	MD 1.49 cm higher (0.76 higher to 2.22 higher)	‐	32 (1 RCT)	⊕⊝⊝⊝ Very lowa,b,c	1 RCT at unclear selection, detection and attrition bias suggested that satisfaction with aesthetics was higher with the fibre‐reinforced composite fixed retainer.
Adverse effects on oral health Follow‐up:  12 months	Bleeding on probing in lower arch (ideally < 0.10)	‐	‐	‐	0 (0 RCTs)	‐	No studies measured or reported this outcome at 12‐month follow‐up. 1 RCT at high risk of detection and attrition bias suggested that there was no difference between retainers at 6‐monthfollow‐up (40 participants; very low‐certainty evidence).
	Gingival Index (GI) in lower arch (ideally 0)	‐	‐	‐	0 (0 RCTs)	‐	No studies measured or reported this outcome at 12‐month follow‐up. 1 RCT at high risk of detection and attrition bias suggested that there washigher gingival inflammation of moderate clinical relevance with the fibre‐reinforced composite fixed retainer at 6‐month follow‐up (MD 0.59, 95% CI 0.13 to 1.05; 1 RCT, 40 participants; very low‐certainty evidence).
*The basis for the assumed risk (e.g. the median control group risk across studies) is provided in footnotes. The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: confidence interval; GI: Gingival Index; LII: Little's Irregularity Index; MD: mean difference; RCT: randomised controlled trial; RR: risk ratio; VAS: visual analogue scale
GRADE Working Group grades of evidence  High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of effect.

^aDowngraded one level due to study limitations (serious/unclear risk of bias).
^bDowngraded two levels for imprecision due to the small sample size.
^cOne study ‐ difficult to ascertain the likelihood of publication bias.
^dDowngraded one level for inconsistency due to the presence of unexplained heterogeneity.