Following active orthodontic treatment unwanted tooth movement or relapse may occur where the dentition, partly or completely returns to its pre-treatment state. In order to prevent or reduce relapse a number of retention strategies are employed including the use of fixed and removable retainers discussed in a recent Cochrane review by Martin et al (Dental Elf – 6th Jun 2023). This review focusses on the failure rates of fixed orthodontic bonded retainers.
The main aim of this review was to assess the prevalence of failure of both maxillary and mandibular fixed orthodontic bonded retainers (FOBRs).
Methods
A protocol was registered with PROSPERO. Searches were conducted in the Cochrane Central Register of Controlled Trials (CENTRAL); The Cochrane Library Medline, Embase, Clinical Trials.gov (https://www. clinicaltrials.gov), the National Research Register (https://dis- covery.nationalarchives.gov.uk), and Pro-Quest Dissertation Abstracts and Thesis database (http://pqdtopen.proquest. com) with no language restrictions. Randomised clinical trials (RCTs) and prospective controlled clinical trials (CCTs) in patients of any age who completed a course of orthodontic treatment and were retained using FOBRs were considered.
Three reviewers independently selected studies with data being extracted by two reviewers. Three reviewers assessed Risk of bias for using the Cochrane risk of bias 2.0 tool for RCTs and the Newcastle Ottawa tool being used for non-randomised studies. The primary outcome was failure rate related to loosening, breakage, and bond failure. Factors influencing failure e.g., type retainer wire, adhesive, and bonding technique were secondary outcomes. For continuous data mean differences (MD) and 95% confidence intervals (CIs) were calculated along with risk ratio (RR) with 95% CI for dichotomous data. The GRADE (Grading of Recommendations Assessment, Development, and Evaluation) criteria were used to report certainty of the evidence.
Results
- 34 studies (25 RCTs, 9 prospective clinical trials) involving a total of 3,484 patients (4,540 FOBRs) were included.
- 6 studies were conducted in Switzerland, 5 in Turkey, 3 studies in Italy. Iran and the USA, 2 studies in Germany, Norway, Saudi Arabia, Sweden, and the UK and one study in Belgium, Canada, China, and Pakistan.
- 26 studies were conducted in a university hospital setting and 8 studies in an orthodontic practice setting.
- A range of criteria were used to assess failure rate including, retainer failure, debonding rate, fracture in either the wire or composite with or without partial or total loosening of the retainer from the teeth and incidence of retainer loss or breakage.
- Failure rate for mandibular retainers was reported by all 34 studies with just 9 studies reporting failure rate of both maxillary and mandibular retainers.
- 9 studies reported a follow-up period of 6 months, 22 studies a medium-term follow-up period of between 1 and 4 years and 3 studies a long-term follow-up period of 5–6 years.
- None of the included studies were at low risk of bias. 13 RCTs were at high risk of bias with 12 RCTs having some concerns. One of the non-RCT prospective studies rated as high quality, 6 were considered fair and two as poor-quality studies.
- The failure rate of FOBR for both arches and individual maxillary and mandibular arches are shown in the table below together with sensitivity analyses excluding non-RCTs and high risk of bias RCTs.
| No of studies | Failure rate (95%CI) | |
| Maxillary and mandibular arches | 31 | 28.17% (23.19 to 33.15%) |
| maxillary and mandibular arches (sensitivity analysis) | 22 | 35.22% (27.46–42.98%) |
| Maxillary arch | 9 | 35.59% (24.44–46.73%) |
| Maxillary arch (sensitivity analysis) | 6 | 37.53% [27.73–47.32%) |
| Mandibular arch | 31 | 27.94% (23.03–32.85%) |
| Mandibular arch (sensitivity analysis) | 22 | 38.67% (31.00–46.34%) |
- The table below shows failure rates at different follow up times together with sensitivity analyses excluding non-RCTs and high risk of bias RCTs.
| No of studies | Failure rate (95%CI) | |
| Up to 12 months follow up | ||
| Both arches | 9 | 21.44% (15.69 to 27.20%) |
| Both arches -sensitivity analysis | 4 | 24.18% (20.16 to 29.21%) |
| Maxillary arch | 3 | 21.10% (10.98 to 31.22%) |
| Maxillary arch – sensitivity analysis | 1 | 21.91% (15.83 to 27.99%) |
| Mandibular arch | 8 | 21.77% (15.68 to 27.87%) |
| Mandibular arch-sensitivity analysis | 4 | 25.02% (19.10 to 30.94%) |
| 1 to 4 years follow up | ||
| Both arches | 19 | 29.26% (21.97 to 36.55%) |
| Both arches -sensitivity analysis | 6 | 40.09% (30.92 to 49.26%) |
| Maxillary arch | 5 | 44.84% (28.95 to 60.73%) |
| Maxillary arch -sensitivity analysis | 2 | 41.07% (35.63 to 46.50%) |
| Mandibular arch | 19 | 28.91% (21.92 to 35.89%) |
| Mandibular arch-sensitivity analysis | 6 | 45.60% (40.83 to 50.37%) |
| 5 to 6 years follow up | ||
| Both arches | 3 | 41.78% (25.41 to 58.14%) |
| Maxillary arch | 1 | 34.38% (17.92 to 50.84%) |
| Mandibular arch | 3 | 41.05% (23.18 to 58.93%) |
| Mandibular arch-sensitivity analysis | 1 | 53.85% (40.31 to 67.39%) |
- No statistically significant difference in retainer failure was found between direct and indirect bonding with a RR = 0.84 (95%CI: 0.57 to 1.25) [6 studies].
- No statistically significant difference in retainer failure between resin and non-resin composites was evident (RR = 0.44 (95%CI: 0.06 to 2.95) [2 studies].
- Pooled estimates for five studies (898 FOBR) using the whole retainer as the unit of assessment indicated no statistically significant difference between multi-stranded wire and fibre-reinforced composite, RR = 1.76 (95%CI: 0.86 to 3.58)
Conclusions
The authors concluded: –
- The failure rate of fixed bonded retainers is relatively high, 38.67% in the mandible and 37.53% in the maxilla. Almost 25% of FOBR failed in the first 12 months with the risk of failure increasing over time to almost 50% at 6 years follow up.
- Indirect bonding, FRC, and the use of liquid resin with composite do not have a significant influence on the failure rate of fixed bonded retainers.
- There is a need for high-quality, well-reported clinical studies to assess factors that influence the failure rate of fixed-bonded retainers.
Comments
The recent Cochrane review (Dental Elf – 6th Jun 2023) only found vey low to low certainty evidence for different retention strategies. This review focuses on failure rates for fixed orthodontically bonded retainers. The author registered their protocol and searches a broad range of relevant databases including 34 studies of which 25 were RCTs. None of the RCTS were considered to be at low risk of bias, 13 being assessed at being at high risk and 12 having some concerns. A number of meta-analyses were performed and for many of the outcomes assessed sensitivity analysis were undertaken where high risk studies were excluded.
An overall failure rate for FOBR of 28.17% (23.19 to 33.15%) based on 31 studies was found. Failure rates were higher in the maxilla 35.59% (24.44–46.73%) than the mandible 21.77% (15.68 to 27.87%) with failure rates increasing with length of follow up. Higher failure rates were seen for outcomes where sensitivity analysis was undertaken. The overall certainty of the evidence was rated as very low to low so the findings should be considered carefully as new evidence is likely to change these estimates. The Cochrane reviewers (Dental Elf – 6th Jun 2023) outlined a number of recommendations for future retention studies that are needed to improve the quality of evidence relating to orthodontic retention.
Links
Primary Paper
Aye ST, Liu S, Byrne E, El-Angbawi A. The prevalence of the failure of fixed orthodontic bonded retainers: a systematic review and meta-analysis. Eur J Orthod. 2023 Oct 12:cjad047. doi: 10.1093/ejo/cjad047. Epub ahead of print. PMID: 37824794.
Other references
Dental Elf – 6th Jun 2023
Dental Elf – Orthodontic retainer blogs
