Effects of maxillary protraction with an orthopedic facemask on fricatives

This prospective cohort study aimed to investigate the effect of rapid maxillary expansion (RME) and orthopedic facemask (FM) treatment on the acoustic properties of fricative sounds (/s/ and /ʃ/) through objective and subjective (perceptual) assessments.

Twenty-two patients (7 females and 15 males; mean age: 11.27 ± 1.38 years) underwent speech recordings at 4 time points: immediately before RME (T0), 2 weeks later (immediately before FM application, T1), 3 months later (T2), and 1 week after treatment (T3). Speech therapists recorded the data and conducted acoustic analyses using Praat software. Acoustic parameters-duration, spectral peak, center of gravity, and second formant transition-were analyzed for /s/ and /ʃ/ in monosyllabic words with /a/, /u/, and /ı/ vowels in both word-initial and word-final positions. Data were statistically analyzed using repeated measures analysis of variance and the Friedman test. Cephalometric radiographs were taken at T0 and T3.

After RME and FM therapy, duration decreased significantly in the word-initial positions of /s/ and /ʃ/ (P = 0.002). Spectral peaks decreased significantly in the word-initial and word-final positions during treatment for both /s/ (P <0.001) and /ʃ/ (P = 0.007), returning to baseline by T3. However, a significant overall decrease persisted (P <0.001). Center of gravity also decreased significantly during treatment (P <0.05), whereas second formant transition values did not change. A perceptual evaluation revealed high articulation accuracy (2.00) at T0 for all evaluations, a significant decrease at T2 with increased scores (3.65 for /s/ and /ʃ/ total, 4.00 for overall intelligibility, P <0.001), and a subsequent improvement at T3 (1.33 for all evaluations, P <0.001), with scores significantly lower than at T0 (P <0.001).

RME and FM therapy led to favorable structural and phonetic changes. Improvements in acoustic properties and perceptual scores suggest effective adaptation and enhanced articulation after treatment.