Which orthodontic retainer provides the best stabilization? : Systematic review and network meta-analysis

Purpose: The objective of the present systematic review (SR) was to compare available retainers to determine which one has the highest probability of maintaining a stable post-orthodontic outcome. Methods: Electronic platforms were searched up to 20 January 2024 to identify randomized controlled trials (RCTs) comparing the efficacy of different retainers in stabilizing post-orthodontic tooth position (PROSPERO no. CRD42023399604). The Cochrane checklist was used for risk of bias assessment. Network meta-analyses (NMA) were conducted for the Little irregularity index (LII), intercanine width (ICW), and intermolar width (IMW) to identify metric ranking markers (highest probability of being the best [PBB], surface under the cumulative ranking curves [SUCRA], and mean ranking [MR]) for the different retention protocols. Results: Eighteen RCTs were included in the SR, and 15 in the NMA. Seven studies were at high risk of bias, 7 at moderate, and 4 at low risk of bias. The retainers were categorized into 14 groups for analyzing LII, 13 for ICW, and 8 for IMW. The NMA on LII indicated that computer-aided design/computer-aided manufacturing (CAD/CAM) multistrand stainless steel (SS), followed by laboratory round multistrand SS and rectangular flex SS retainers had the highest PBB in maintaining a low LII. The NMA on ICW suggested that CAD/CAM multistrand SS followed by CAD/CAM NiTi and spring hard SS retainers have the highest PBB in maintaining ICW. Very limited evidence showed a low PBB for removable retainers related to LII and ICW. No difference between groups was observed for IMW. Conclusion: There is moderate-to-low quality evidence that CAD/CAM and laboratory-bent multistrand SS followed by rectangular flex SS retainers might be the most effective retention protocol for maintaining a low LII over a short-to-mid-term follow-up, whereas CAD/CAM multistrand SS, CAD/CAM NiTi, and spring-hard wire retainers might be most effective in maintaining ICW. Intermolar width tends to decrease, but this does not seem to be influenced by the type of retention.