Summary Introduction Patients with dentofacial disharmonies (DFDs) seek orthodontic care and orthognathic surgery to address issues with mastication, esthetics, and speech. Speech distortions are seen 18 times more frequently in Class III DFD patients than the general population, with unclear causality. We hypothesize there are significant differences in spectral properties of stop (/t/ or /k/), fricative (/s/ or /ʃ/), and affricate (/tʃ/) consonants and that severity of Class III disharmony correlates with the degree of speech abnormality. Methods To understand how jaw disharmonies influence speech, orthodontic records and audio recordings were collected from Class III surgical candidates and reference subjects (n = 102 Class III, 62 controls). A speech pathologist evaluated subjects and recordings were quantitatively analysed by Spectral Moment Analysis for frequency distortions. Results A majority of Class III subjects exhibit speech distortions. A significant increase in the centroid frequency (M1) and spectral spread (M2) was seen in several consonants of Class III subjects compared to controls. Using regression analysis, correlations between Class III skeletal severity (assessed by cephalometric measures) and spectral distortion were found for /t/ and /k/ phones. Conclusions Class III DFD patients have a higher prevalence of articulation errors and significant spectral distortions in consonants relative to controls. This is the first demonstration that severity of malocclusion is quantitatively correlated with the degree of speech distortion for consonants, suggesting causation. These findings offer insight into the complex relationship between craniofacial structures and speech distortions.

Introduction: Articulation problems are seen in 80% to 90% of dentofacial deformity (DFD) subjects compared with 5% of the general population, impacting communication and quality of life, but the causal link is unclear. We hypothesize there are both qualitative (perceptual) and quantitative (spectral) differences in properties of stop (/t/ or /k/), fricative (/s/ or /ʃ/), and affricate (/tʃ/) consonant sounds and that severity of anterior open bite (AOB) jaw disharmonies correlates with degree of speech abnormality. Methods: To test our hypotheses, surgical orthodontic records and audio recordings were collected from DFD patients (n = 39 AOB, 62 controls). A speech pathologist evaluated subjects, and recordings were analyzed using spectral moment analysis (SMA) to measure sound frequency distortions. Results: Perceptually, there is a higher prevalence of auditory and visual speech distortions in AOB DFD patients when compared to controls. Quantitatively, a significant ( P < .01) increase in the centroid frequency (M1) was seen in the /k/, /t/, /tʃ/, and /s/ sounds of AOB subjects compared to the controls. Using linear regression, correlations between AOB skeletal severity and spectral distortion were found for /k/ and /t/ sounds. Conclusions: A higher prevalence of qualitative distortions and significant quantitative spectral distortions in consonant sounds were seen in AOB patients compared to controls. Additionally, severity of skeletal AOB is correlated with degree of distortion for consonant sounds. These findings provide insight into how the surgical and/or orthodontic treatment of AOB may impact speech.

Summary Background/Objectives Articulation problems impact communication, development, and quality of life, and are diagnosed in 73–87% of patients with Class II Dentofacial Disharmony (DFD). We evaluated whether differences exist in stop (/t/ or/k/), fricative (/s/ or/ʃ/), and affricate (/tʃ/) consonant sounds of Class II DFD subjects, and whether extent of malocclusion correlates with severity of speech distortion. We hypothesized that Class II patients display milder distortions than Class III and anterior open bite (AOB), as Class II patients can posture into a Class I occlusion. Materials/Methods Audio and orthodontic records were collected from DFD patients (N = 53-Class II, 102-Class III, 72-Controls) who were pursuing orthodontics and orthognathic surgery. A speech pathologist perceptually scored speech. Acoustic differences in recordings were measured using Spectral Moment Analysis. Results When Class II subjects were compared to controls, significant differences were found for the centroid frequency (M1) of the /s/ sound and the spectral spread (M2) of /t/, /tʃ/, and /s/ sounds, with pairwise significance for controls relative to Class II AOB and all Class II subjects. Class II AOB subjects had higher M1 and M2 values than patients with Class II closed bites and Class I controls for most sounds. When comparing across anterior-posterior (AP) groups, differences exist between controls, Class II and III DFD subjects for M1 of /t/, /tʃ/, and/ʃ/ and M2 for /t/, /tʃ/, /s/, and /ʃ/ sounds. Using linear regression, correlations between Class II and III severity and spectral measures were found for /t/ and /tʃ/ sounds. Conclusions/Implications Class II and III patients have a higher prevalence of qualitative distortions and spectral changes in consonants compared to controls, but Class II spectral shifts are smaller and affect fewer sounds than in Class III and AOB cohorts. Linear correlations between AP discrepancy and spectral change suggest causation and that treatment may improve articulation problems.

Purpose: This study examined the relationship between judged speech sound distortions and spectral moment metrics in speakers with Class III malocclusion. Method: A quantitative online survey was distributed to 30 speech specialists (clinicians and/or students) and 100 lay listeners to judge the clarity of the sounds /s/, /ʃ/, /t/, and /k/ using a visual analog scale (VAS) from recordings of 11 Class III (underbite) dentofacial disharmony (DFD) patients and eight Class I controls. Patients and controls were grouped according to high, moderate, and low /s/−/ʃ/ first spectral moment differences. A linear mixed model was used to analyze the data. Results: VAS scale ratings increased as a function of decreasing spectral contrast for both groups of listeners. VAS ratings of speech specialists were more homogenous than lay listeners, and speech specialists rated distortions as less severe than lay listeners. Conclusions: Recordings of Class III DFD patients with low /s/−/ʃ/ first spectral moment differences were scored by listeners as having increased VAS scale ratings, indicative of more significant perceived speech-sound distortions. Spectral moment analysis appears to be a promising approach for characterizing speech of DFD patients and other craniofacial disorders. Supplemental Material: https://doi.org/10.23641/asha.19686510

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