Performance of Hawley-type appliances: a systematic review of randomized clinical trials

Abstract

BACKGROUND: Although post-treatment changes are almost inevitable, and retention has long been recognized as one of the most critical and routine problems faced by orthodontists, there remains a lack of certainty regarding the parameters of any definitive retention protocol following orthodontic treatment. AIM: To compare the performance of the Hawely-type appliances to that of the other removable appliances (clear thermoplastic appliances, tooth positioners and modifications, etc.) immediately used after completion of orthodontic treatment, together with a comparison of the effectiveness of different wearing schedules.

MATERIALS AND METHODS: An electronic search without restrictions for published and unpublished literature, together with hand searching, was carried out. We reviewed randomized clinical trials (RCTs) investigating the performance of the Hawley-type appliances. The risk of bias was assessed using the Cochrane Collaboration‘s Risk of Bias ii assessment tool for RCTs and the quality of evidence assessed according the Grades of Recommendation, Assessment, Development and Evaluation (GRADE) approach.

RESULTS: The initially identified 1174 records were finally reduced to 10 full-text reports analyzing various outcomes in 854 patients who had been followed for a maximum period of one year after the removal of the fixed orthodontic appliances. Eight of the eligible publications investigated groups of subjects using Hawley removable appliances and clear thermoplastic retainers, another study compared the Hawley appliance to positioner use during the retention period and, finally, one study involved patients allocated to groups using different wearing schedules for Hawley retention appliances. Three studies were considered as being of low risk of bias, four of unclear and three of high risk of bias. In general, few differences were observed between the comparative performance of the Hawely-type appliances and the other removable appliances (clear thermoplastic appliances, tooth positioners and modifications, etc.) used after the completion of orthodontic treatment regarding outcomes relevant to maxillary and mandibular dental arch measurements, dental arch relationships and occlusal contacts, speech evaluation, patient reported outcomes, adverse effects and problems related to the appliances, in addition to economic evaluation related outcomes. Moreover, no differences were found between different appliance wearing schedules and protocols. Overall, the quality of the available evidence was considered low.

CONCLUSIONS: Based on the available data there are few differences were observed between the comparative performance of the Hawley-type appliances to the other removable appliances (clear thermoplastic appliances, tooth positioners and modifications, etc.) used after the completion of orthodontic treatment. Moreover, no differences were found between different appliance wearing schedules and protocols.