Following active orthodontic treatment, the wearing of orthodontic retainers is required to enable adaptive muscle and soft tissues to reach a stable state. Typically, orthodontic retainers are worn for 2 or more years and longer for some patients. The use of orthodontic retainers encourages plaque retention which may have adverse effects on the periodontal tissues without adequate oral hygiene. The Hawley retainer and vacuum-formed retainers are currently the most widely used orthodontic retainers.

The aim of this review was to compare the effects of vacuum-formed retainers (VFR) and Hawley retainers (HR) on periodontal health.

Methods

Searches were conducted in the China Academic Journals full-text database (CNKI), Cochrane Library Databases, Embase, Medline/PubMed, Scopus, Web of Science, Grey Literature in Europe, Google Scholar, ClinicalTrials.gov (www.clinicaltrials.gov) and the National Research Register. Randomized controlled trials (RCTs) comparing the periodontal health of patients undergoing orthodontic maintenance using Hawley retainer or vacuum-formed retainer published in Chinese or English were considered. Two reviewers independently selected studies, extracted data and assessed risk of bias using the Cochrane tool. Outcomes considered included plaque index (PI), gingival index (GI) and sulcus probing depth (PD). Mean difference (MD) and 95% confidence intervals (CI) were used to estimate the results using a random effects model.

Results

• 6 RCTs involving a total of 304 patients (152 in VFR group, 152 in HR group) were included.
• 5 studies were considered to have a high risk of bias and one an unclear risk.
• Meta-analysis showed a significant difference for gingival index between the VFR and HR groups at 1 and 3 months but not six months.
  • 1 month MD = 0.12 (95%CI: 0.06 to 0.19) [5 studies].
  • 3 months MD = 11 (95%CI: 0.06 to 0.17) [4 studies].
  • 6 months MD = 10 (95% CI: -0.07 to 0.27) [4 studies].
• Meta-analysis showed a significant difference for plaque index between the VFR and HR groups at 1, 3 and 6 months.
  • 1 month MD = 06 (95% CI: 0.01 to 0.12) [4 studies].
  • 3 months MD = 12 (95%CI: 0.08 to 0.16) [4 studies].
  • 6 months MD = 0.19 (95%CI: 0.09 to 0.29) [4 studies].
• Meta-analysis showed no significant difference in probing depth between the VFR group and the HR groups at 1,3 or 6 months
  • 1 month MD = 07 (95% CI: -0.01 to 0.16) [3 studies].
  • 3 months MD = -0.04 (95% CI: -0.25 to 0.18) [3 studies].
  • 6 months MD = -0.10 (95% CI: -0.42 to 0.23) [2 studies].

Conclusions

The authors concluded: –

….patients using Hawley retainers showed advantages in terms of periodontal health. Hawley retainers also showed a lower adverse effect on periodontal tissue compared with vacuum-formed retainers. However, due to the limited number and quality of studies on this topic, this conclusion needs to be confirmed by more high-quality studies.

Comments

Two previous reviews of the impact of orthodontic retainers on periodontal health (Dental Elf – 17^th Apr 2020 and Dental Elf – 14^th Oct 2016) included a broader range of studies than this new review. For this new review the authors have searched a broad range of databases restricting their inclusion to RCTs written in Chinese and English. This may have had an impact and they indicated that they had excluded one study as it was published in French. The review findings indicated statistically significant differences in favour of the Hawley retainer for plaque and gingival indices at up to 3 months. However, none of the included studies were at low risk of bias with all but one of the studies being considered at high risk because of a lack of blinding the outcome assessment. We also need to consider if this statistically significant difference is clinically important. With orthodontic retainers being worn for periods of two years or longer it is also worth noting that the included studies only reported data at 6 months. Future studies need to be well-conducted and well reported with an appropriate sample size and  longer follow up periods.

Links

Primary Paper

Li B, Xu Y, Lu C, Wei Z, Li Y, Zhang J. Assessment of the effect of vacuum-formed retainers and Hawley retainers on periodontal health: A systematic review and meta-analysis. PLoS One. 2021 Jul 9;16(7):e0253968. doi: 10.1371/journal.pone.0253968. PMID: 34242289.

Review protocol on PROSPERO

Other references

Dental Elf – 17^th Apr 2020

Orthodontic retainers: Effects on periodontal health

Dental Elf – 14^th Oct 2016

Orthodontic retainers: impact on periodontal health