Evaluation of acoustic and perceptual speech changes following class II correction with Forsus fixed functional appliance therapy: A prospective clinical study

Objectives: The aim of this study was to evaluate acoustic and perceptual speech changes following correction of Class II Division 1 malocclusion using a Forsus fixed functional appliance in late adolescent patients. Material and Methods: This prospective clinical study included 13 late adolescent patients (7 females and 6 males; mean age, 16.2 ± 2.1 years) diagnosed with Class II Division 1 malocclusion requiring sagittal correction with a Forsus fixed functional appliance. Speech recordings were obtained before treatment (T0) and after completion of the functional phase of treatment (T1). Acoustic analysis was performed using PRAAT software and included spectral moments (M1–M4), fundamental frequency (F0), intensity, and phoneme duration. Perceptual speech assessment was performed using the Ali Yavur Jung National Institute of Hearing Handicapped speech intelligibility grading scale. Overjet, ANB (A point - Nasion - B point) angle, and Wits appraisal were recorded to evaluate orthodontic treatment changes. The primary acoustic outcomes were changes in spectral moments (M1–M4) between T0 and T1. Fundamental frequency (F0), intensity, and phoneme duration were considered secondary acoustic outcomes, while speech intelligibility was assessed as the principal perceptual outcome. Because multiple acoustic parameters and phonemes were evaluated, the secondary acoustic findings were interpreted cautiously with consideration of the potential for type I error due to multiple comparisons. Results: A significant reduction in overjet was observed following treatment (8.15 ± 1.47 mm to 2.08 ± 0.69 mm; p < 0.001). ANB angle and Wits appraisal also demonstrated significant improvement. Speech intelligibility scores improved significantly from 2.62 ± 0.65 to 0.85 ± 0.55 ( p < 0.001; d = 2.8). Fundamental frequency did not demonstrate a statistically significant change ( p = 0.21). Intensity increased significantly after treatment (63.2 ± 7.4 dB to 69.1 ± 6.8 dB; p < 0.01), while/r/duration demonstrated a significant reduction ( p = 0.004). Spectral moment analysis demonstrated significant changes in M1, M2, M3, and M4. The changes in F0, intensity, and duration were considered secondary findings, while the spectral moment findings were considered the primary acoustic outcomes. Conclusion: Within the limitations of this prospective pre-post study, correction of Class II malocclusion with a Forsus fixed functional appliance was associated with changes in selected spectral characteristics and improved speech intelligibility. Spectral moment changes represented the primary acoustic findings, whereas changes in F0, intensity, and duration were considered secondary. These findings should be interpreted cautiously and do not establish that Forsus therapy directly caused the observed speech changes.