## 3 Effects of Malocclusion on Speech
### Anterior-Posterior Discrepancies  
_Class III_: Speech distortions are well-documented in the Class III population [44; 50]. A study of 451 Finnish students found that those with Class III malocclusions were 4.5 times more likely to produce consonants more anteriorly [66]. In our study of 102 patients with Class III malocclusions, we observed perceptual distortions of /sa/, /si/, and /ssi/ in 63.73%, 61.11%, and 55.56% of Class III patients compared with 1.61%, 2.50%, and 2.50% of controls, respectively [26]. The severity of Class III malocclusion is also linearly correlated with the degree of speech distortion, specifically for sounds [t] and [k] [26]. Fricatives such as [f], [s], and [z] are frequently affected in Class III patients due to either a prognathic \begin{table}
\begin{tabular}{c c c} \hline \hline
**Analysis Type** & **Analysis** & **Description** \\ \hline Perceptual & Live perceptual evaluation & Real time visual/perceptual evaluation by a speech pathologist at scheduled time intervals. \\ \hline Perceptual & Perceptual evaluation of recordings & Visual/perceptual evaluation from a video/audio recording by a speech pathologist at scheduled time intervals. \\ \hline Acoustic & Cephalometric analysis & Utilizing lateral cephalometric radiographs to analyze bony and soft tissue landmarks to relate the cranial base, maxilla, and mandible to the teeth. \\ \hline Acoustic & Electropalatopraphy & Utilization of a palatal stent with electrodes to record tongue and palate contacts during speech. \\ \hline Acoustic & Formant analysis of vowels & A method used to analyze vowel pronunciation. The first formant (F1) and the second formant (F2) are typically extracted from a speech recording. An F1 xF2 vowel plot is then used to display vowel sound distribution. \\ \hline Acoustic & Spectral moment analysis & A type of spectral analysis typically used to describe consonants. The power spectrum is treated as if it is a probability distribution. \\ \hline Acoustic & Spectral peak analysis & A type of spectral analysis typically used to describe consonants. Spectral peaks are measured. \\ \hline Acoustic & Tongue thrust evaluation & Visual analysis of tongue position during different actions. \\ \hline Acoustic & Tongue position is ranked on a subjective, predetermined scale. \\ \hline Acoustic & Velopharyngealevaluation & Estimation of the size of velopharyngealpost area using pressure–flow measurements while participants are asked to repeat pressure sounds, such as [p]. \\ \hline \hline \end{tabular}  
* Includes speech analysis methods used in DFD studies. This is not an exhaustive list of all available speech analyses.  
\end{table} 
Table 2: Speech analyses used in DFD studies *. mandible, a retrognathic maxilla or a combination of both; SSDs are found 20 times more often in the Class III population than in the general population [49; 75]. The Class III skeletal discrepancy may lead to speech distortions due to alterations in the structure of the anterior oral cavity, where many consonant sounds are articulated [3; 4; 20; 26; 76]. Class III underbites are characterized by mandibular incisors being positioned anteriorly of their maxillary incisors, influencing the articulation of alveolar siblant fricatives ([s] and [z]), where the tongue normally interacts with the maxillary alveolus, and labiodental fricatives ([f] and [v]), where the lower lip typically meets the maxillary incisors. To adjust for an underbite, Class III patients produce sounds with compensatory articulation gestures, such as the upper lip contacting the mandibular incisors to produce fricatives [f] and [v], and the tongue contacting the incisors instead of the alveolar ridge for sibilants [s] and [z] [75]. However, this compensation is often inadequate, leading to increased incidence of speech distortions [48; 57].