Impact of a rapid palatal expander on speech articulation.

INTRODUCTION Rapid palatal expanders (RPEs) have attachments cemented to the teeth and a screw that covers the palate. Because of their position and relative size, RPEs can affect speech. Our objective was to assess speech perturbation and adaptation related to RPE appliances over time. METHODS RPEs were planned for the treatment of 22 patients in the orthodontic clinic at the University of Toronto in Canada. Speech recordings were made at 6 time points: before RPE placement, after placement, during expansion, during retention, after removal, and 4 weeks after removal. The speech recordings consisted of 35 sentences, from which 3 sentences were chosen for analysis. Speech acceptability was assessed perceptually by 10 listeners who rated each sentence on an equal-appearing interval scale. The vowel formants for /i/ and the fricative spectra for /s/ and /∫/ were measured with speech analysis software. Repeated-measures analysis of variance with post-hoc paired t tests was used for statistical analysis. RESULTS When the appliance was placed, speech acceptability deteriorated. Over time, the ratings improved and returned to baseline when the appliance was removed. For the vowel /i/, the first formant increased, and the second formant decreased in frequency, indicating centralization of the vowel. The formants returned to the pretreatment levels during treatment. For the fricatives (/s/ and /∫/), low-to-high frequency ratios indicated that the fricatives were distorted when the appliance was placed. The ratios returned to baseline levels once the appliance was removed. The results for the spectral moments indicated that spectral mean decreased and skewness became more positive. Repeated-measures analysis of variance showed significant effects for time for all acoustic measures. CONCLUSIONS Speech was altered and distorted when the appliance was first placed. The patients' speech gradually improved over time and returned to baseline once the appliance was removed. The results from the study will be useful for pretreatment counseling of patients and their families.