Comparing the effects of Essix and Hawley retainers on the acoustics of speech.

Objective: The aim of this study was to compare the effects of two retainer types (Essix and Hawley) on speech performance.

Subjects and methods: The speech articulation of 30 patients was evaluated prospectively. Five patients did not appear during the follow-up periods. The patients were randomly divided into retention groups by treatment allocation cards as Essix and Hawley. The Essix group included 13 participants with a mean age of 15.3±2.4 years; the Hawley group included 12 participants with a mean age of 16.3±2.56 years. Speech sound assessments were performed on the first day and 1 week, 4 weeks, and 3 months later. On the first day, the assessments were conducted prior to inserting the retainers, immediately after maxillary and mandibular retainer application, individually, and with both retainers applied. The acoustic analyses were obtained using spectral and temporal parameters.

Results: Statistical analyses were performed with IBM SPSS for Windows, version 20. A P value less than 0.05 was considered statistically significant. The most apparent changes were found in the [a] vowel in the Hawley group, the [e] vowel in the Essix group, and the [u] vowel in both groups (P < 0.05). While the number of affected consonant-vowel couples in the Essix group was low, alterations were common in the Hawley group. There was a statistically significant difference (P < 0.05) in voice onset time of the [d] sound between the groups.

Limitations: The trial had a small sample size and a short follow-up period.

Conclusions: The Hawley retainer affected articulatory movements in consonant-vowel combinations more prominently than the Essix retainer did. Voice onset time of the consonant [d] in the Hawley group was shorter than normal, indicating rapid articulatory movement in the alveolar region.