## 4 Effects of Orthongathic Surgery on Speech
### Anterior-Posterior Discrepancies  
Class III: Studies have indicated Class III patients have variable speech outcomes following orthognathic surgery, with most studies using perceptual evaluations of recordings (Table 2). [PERSON] et al. (N = 10) found no significant changes in speech patterns at 2 months postoperation, when patients are still quite swollen; others noted that some patients had reduced frequencies of speech errors postoperatively at 2-, 3-, and 6-month time points [52; 53; 54; 55; 68]. One study of Class III patients (N = 20) that underwent two-jaw surgery found a decrease in speech errors of consonants [s], [j], [z], and [z] with complete elimination of errors by 6 months postsurgery in all subjects [54]. Similarly, [PERSON] al. (N = 20) found 41.7% of Class III subjects experienced correction of speech errors at 6-months postoperation [68]. A small, underpowered study (N = 4), by [PERSON] and [PERSON], showed improved articulation in two of their participants [53]. Most studies have indicated qualitative improvement in speech in 41-100% of Class III patients. Similar to AOB studies, manuscripts on Class III DFD subjects have small sample sizes and lack comparison with Class I control groups, preventing definitive conclusions.  
Class II: In a study by [PERSON] et al., Class II DFD patients (N = 5) with no significant speech distortions were evaluated up to 30 weeks postoperatively [60]. Postoperative changes were highly variable across individuals. For example, one patient demonstrated a decrease in F1 values for vowels /ae, a/, and another patient exhibited decreases in F1 for all vowels, except mid front vowels /e, o/. Vowel sounds can be produced without articulation with skeletal structures (such as the tongue with the palate), making interpretation challenging; vowel sound production in Class II patients can be varied due to compensations in tongue or jaw positions and possible differences in vocal tract anatomy [60].  
Literature focused on Class II DFD patients' postoperative outcomes is quite sparse. Instead, most studies evaluating speech outcomes have utilized an unstratified mix of DFD patients with markedly different occlusions: this is a methodological issue in need of careful consideration. In a study of 12 DFD patients who produced preoperative articulation errors, 5 subjects (n = 2 Class II, 3 Class III) exhibited complete correction of their speech errors after surgery and another 5 had a decrease in the number of errors (n = 1 Class II; 3 Class III; 1 facial asymmetry) [68]. [PERSON] et al. noted modest changes in some DFD patients' speech after surgery (n = 5, one Class III, three Class II and one Class III/AOB); these slight changes in a small, heterogeneous sample are encouraging but make it difficult to draw definitive conclusions [71]. Another study of 41 patients with varying preoperative malocclusions (n = 29 Class II, 11 Class III, and 25 AOB) found a significant improvement in speech on 70 test sounds, 6 months after surgery. While some DFD groups improved less than others, all experienced a reduction in speech errors [57]. The variability in results likely stems from small sample sizes, heterogenous DFD cohorts (Classes II, Class III and AOB), and use of qualitative methods (i.e., perceptual visual and auditory analysis), exemplifying the need for additional research, with data stratified by DFD group and sufficient power.