Orthodontic retainers and retention strategies

After a phase of active orthodontic treatment there follows a period of retention which aims to hold the teeth in their corrected positions. Without retention there is a tendency for the teeth to return to their original positions. This potential for relapse is a lifetime risk the causes of which are not fully understood. Fixed and removable retainers have been used together with adjunctive procedures and strategies to improve compliance. The Cochrane review on this topic was last updated in 2016 (Dental Elf – 1^st Feb 2016).

The aim of this Cochrane review update was to evaluate the effects of different retention strategies used to stabilise tooth position after orthodontic braces.

Methods

Searches were conducted in the Cochrane Oral Health Trials Register, CENTRAL, MEDLINE, Embase and OpenGrey databases. This was supplemented by searches of US National Institutes of Health Ongoing Trials Register ClinicalTrials.gov (clinicaltrials.gov) and the World Health Organization International Clinical Trials Registry Platform and handsearching of conference proceedings and abstracts from the British Orthodontic Conference, the European Orthodontic Conference and the International Association for Dental Research (IADR) and the journals, British Journal of Orthodontics, European Journals of Orthodontics, American Journal of Orthodontics and Dentofacial Orthopedics, the Orthodontics and Craniofacial Research; The Angle Orthodontist and Progress in Orthodontics from 2016 to 2022.

Randomised controlled trials (RCTs) involving children and adults who had retainers fitted or adjunctive procedures undertaken to prevent relapse following orthodontic treatment with braces were considered. Studies involving aligners were excluded. Two reviewers independently screened studies assessed risk of bias and extracted data. Outcomes included stability or relapse of tooth position, retainer failure adverse effects on teeth and gums and participant satisfaction. Mean differences (MD) were calculated for continuous data, risk ratios (RR) or risk differences (RD) for dichotomous data, and hazard ratios (HR) for survival data, all with 95% confidence intervals (CI). Standard Cochrane approaches to analyses were followed. Little’s Irregularity Index was prioritised as a measure of relapse with 1mm being considered as the minimum important difference. A focus was placed on 12 months follow up.

Results

47 RCTS involving a total of 4377 patients were included.
8 studies assessed removable versus fixed retainers, 22 studies assessed different types of fixed retainers or bonding materials (3 studies), and 16 studies different types of removable retainers. More than one comparison was evaluated in 4 studies.
28 studies were considered to have high risk of bias, 11 a low risk, and 8 studies an unclear risk.
Certainty of the evidence is low to very low.

Removable versus fixed retainers

Removable (part-time) versus fixed
- One study (56 patients) reported that patients wearing clear plastic retainers part-time in the lower arch had more relapse than those with multistrand fixed retainers, but this was not clinically significant (Little’s Irregularity Index (LII) MD= 0.92 mm (95%CI; 0.23 to 1.61).
- Removable retainers were more likely to cause discomfort (RR =12.22 [95%CI; 1.69 to 88.52],57 patients) but were associated with less retainer failure (RR= 0.44 [95%CI; 0.20 to 0.98],57 patients) and better periodontal health (Gingival Index (GI) MD =−0.34 [95%CI; −0.66 to −0.02], 59 patients).
Removable (full-time) versus fixed
- One study (84 patients) reported that removable clear plastic retainers worn full-time in the lower arch did not provide any clinically significant benefit for tooth stability over fixed retainers (LII MD= 0.60 mm [95%CI; 0.17 to 1.03].
- Patients with clear plastic retainers had better periodontal health (gingival bleeding RR= 0.53 [95%CI 0.31 to 0.88], 84 patients), but higher risk of retainer failure (RR= 3.42 [95% CI; 1.38 to 8.47], 77 patients). No difference between retainers was seen for caries.

Different types of fixed retainers

Computer-aided design/computer-aided manufacturing (CAD/CAM) nitinol versus conventional/analogue multistrand
- One study (66 patients) reported that CAD/CAM nitinol fixed retainers were better for tooth stability, but the difference was not clinically significant.
- There was no evidence of a difference between retainers for periodontal health (GI MD= 0.00 [95%CI -0.16 to 0.16], 2 studies, 107 patients), or retainer survival (RR= 1.29, 95%CI; 0.67 to 2.49] 1 study, 41 patients).
Fibre-reinforced composite versus conventional multistrand/spiral wire
- One study reported that fibre-reinforced composite fixed retainers provided better stability than multistrand retainers, but this was not of a clinically significant amount.
- Fibre-reinforced retainers had better patient satisfaction with aesthetics (MD= 1.49 cm on a visual analogue scale, [95%CI; 0.76 to 2.22] 1 study, 32 patients), and similar retainer survival rates (RR= 1.01 [95%CI; 0.84 to 1.21], 7 studies; 1337 patients) at 12 months. However, failures occurred earlier (MD= −1.48 months [95%CI; −1.88 to −1.08] 2 studies, 103 patients; 24-month follow-up) and more gingival inflammation at six months, though bleeding on probing (BoP) was similar (GI MD= 0.59 [95%CI; 0.13 to 1.05], BoP MD= 0.33 [95%CI; −0.13 to 0.79], 1 study, 40 patients).

Different types of removable retainers

Clear plastic versus Hawley
- When worn in the lower arch for six months full-time and six months part-time, clear plastic provided similar stability to Hawley retainers (LII MD= 0.01 mm [95%CI; −0.65 to 0.67],1 study, 30 patients).
- Hawley retainers had lower risk of failure (RR= 0.60 [95%CI; 0.43 to 0.83] 1 study, 111 patients), but were less comfortable at six months (VAS MD= -1.86 cm [95%CI; -2.19 to -1.53] 1 study, 86 patients).
Part-time versus full-time wear of Hawley
- There was no evidence of a difference in stability between part-time and full-time use of Hawley retainers (MD= 0.20 mm [95%CI; −0.28 to 0.68], 1 study, 52 patients).

Conclusions

The authors concluded: –

The evidence is low to very low certainty, so we cannot draw firm conclusions about any one approach to retention over another. More high-quality studies are needed that measure tooth stability over at least two years, and measure how long retainers last, patient satisfaction and negative side effects from wearing retainers, such as tooth decay and gum disease.

Comments

This Cochrane review provides an update to the 2016 version of the review (Dental Elf – 1^st Feb 2016). This update has seen the number of included studies rise from 18 to 47. However only 11 of the included studies were considered to be at low risk of bias and the overall assessment of the certainty of the evidence was assessed as being low to very low which means that firm recommendations on orthodontic retention strategies cannot be made.

While recognising the challenges in undertaking retention studies the review authors outline a number of features future studies should include to minimise bias including: –

Adequate allocation concealment and appropriate generation of randomisation;
Blinding of outcome assessors;
full and accurate reporting and analysis of withdrawals and dropouts;
reporting of all data collected;
a priori sample size calculations;
clear inclusion and exclusion criteria;
follow-up for at least two years, given the long-term nature of the problem of relapse.

They also highlight a number of area where research is needed and a range of appropriate outcomes.

Links

Primary Paper.

Martin C, Littlewood SJ, Millett DT, Doubleday B, Bearn D, Worthington HV, Limones A. Retention procedures for stabilising tooth position after treatment with orthodontic braces. Cochrane Database Syst Rev. 2023 May 22;5(5):CD002283. doi: 10.1002/14651858.CD002283.pub5. PMID: 37219527; PMCID: PMC10202160.

Other references

Dental Elf – 1^st Feb 2016

Orthodontic retention – little high quality evidence to recommend any one approach to over another

The Dental Elf