Original article
The effectiveness of Hawley and vacuum-formed retainers: A single-center randomized controlled trial

https://doi.org/10.1016/j.ajodo.2006.06.019Get rights and content

Introduction: Vacuum-formed retainers (VFRs) are often prescribed by orthodontists in the British National Health Service (NHS). There is no good evidence that VFRs are more effective than Hawley retainers. The aim of this study was to compare the clinical effectiveness of Hawley and VFRs over a 6-month period of retention. The study design was a randomized clinical trial, performed in a single orthodontic practice. Methods: Eligible patients treated by a specialist orthodontist were randomly allocated to either Hawley retainers (n = 196) or VFRs (n = 201). Two technicians fabricated the retainers to standardized designs. A blinded, dentally qualified examiner analyzed the records. Maxillary and mandibular dental casts at debond and 6 months into retention were assessed for tooth rotations mesial to the first permanent molars, intercanine and intermolar widths, and Little’s index of irregularity. Results: The results showed significantly greater changes in irregularity of the incisors in the Hawley group than in the VFR group at 6 months. There were otherwise no statistically significant differences. Conclusions: VFRs are more effective than Hawley retainers at holding the correction of the maxillary and mandibular labial segments. The median differences were 0.56 mm in the mandibular arch and 0.25 mm in the maxillary arch. Although this difference is unlikely to be clinically significant in the maxillary arch, it could be considered clinically significant in the mandibular arch if located to a single tooth displacement.

Section snippets

Material and methods

This clinical trial was set in an orthodontic practice; this allowed for the recruitment of a large sample of patients treated by 1 orthodontist.5 The study was approved by the Local Research and Ethics Committee at the United Bristol Healthcare Trust (approval number E5421). Patients who were due to have their fixed orthodontic appliances removed were assessed by the orthodontist for inclusion in the trial according to the following criteria: treated under the NHS by the same orthodontist;

Results

Three hundred fifty-five subjects (172 Hawley, 183 VFR) attended for the 6-month review appointment, giving a completion rate of 89%. One hundred fifty-five models were analyzed in the Hawley group and 155 in the VFR group (Fig 8).

Both groups had a median change in overjet between T1 and T2 of 0.5 mm (P = .24). In 54 subjects (32%) in the Hawley group and 49 subjects (27%) in the VFR group, a change in overbite was observed at T2 (P = .32). Overall, there was no statistically significant

Discussion

Conducting this study in a practice setting enabled the research team to recruit and randomize 397 patients treated by 1 operator over a relatively short time period (18 months). To date, this is the largest such clinical trial on the effectiveness of the Hawley and the VFR.

In this study, the retainer groups matched favorably for baseline characteristics, and it is therefore likely that the 2 groups were equally matched and that the randomization process worked well.

No statistically significant

Conclusions

The results of this study suggest that VFRs are more effective than Hawley retainers at holding corrections of the maxillary and mandibular labial segments. This is likely to be clinically significant only in the mandibular arch if located to a single tooth displacement. In addition, this trial supports the need for further research in primary care.

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Funded by the Special Trustees of the United Bristol Healthcare Trust (grant reference number: DE/2202/1331).

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