Effects of Orthognathic Surgery on Perioral Muscle Function: A Comparative Analysis Between Class II and Class III Female Patients

Effects of Orthognathic Surgery on Perioral Muscle Function: A Comparative Analysis Between Class II and Class III Female Patients | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Effects of Orthognathic Surgery on Perioral Muscle Function: A Comparative Analysis Between Class II and Class III Female Patients Jing Yuan, Taishi Ohtani, Manabu Habu, Izumi Yoshioka This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6888612/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 15 Oct, 2025 Read the published version in Oral and Maxillofacial Surgery → Version 1 posted 9 You are reading this latest preprint version Abstract Purpose The purpose of this study was to investigate changes in lip-closing force, tongue pressure, and buccinator pressure before and after orthognathic surgery, and to compare these changes between skeletal Class II and Class III female patients. Materials and Methods Thirty-six female patients who underwent orthognathic surgery at Kyushu Dental University Hospital were enrolled. Patients were divided into two groups (Group A: skeletal Class II; Group B: skeletal Class III), and ten females with normal occlusion served as the control group. Lip-closing force, tongue pressure, and buccinator pressure were measured one day before surgery, and at three months and one year postoperatively. Maximum values were analyzed using the Mann–Whitney U test and Wilcoxon signed-rank sum test. Results Lip-closing force, tongue pressure, and buccinator pressure significantly increased one year after surgery in both groups (p < 0.05), although a temporary decline was observed at three months postoperatively, except for lip-closing force in Group A. The change rates for lip-closing force and buccinator pressure were higher in Group A, whereas tongue pressure increased more in Group B. However, a statistically significant difference was observed only in lip-closing force (p < 0.05). Conclusion Orthognathic surgery significantly improves perioral muscle function as well as facial aesthetics. Enhancements in lip-closing force and buccinator pressure were more pronounced in Class II patients compared to Class III patients. Lip-closing force Tongue pressure Buccinator pressure Orthognathic surgery Skeletal classification Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 1. Introduction Orthognathic surgery is well known not only for correcting malocclusion, but also for enhancing facial esthetics [ 1 , 2 , 3 ]. In addition, postoperative improvements can be achieved in perioral muscle function. The lips, cheeks and tongue are located on the outside and inside of the dentition and their forms and functions therefore affect the maxillofacial structure and dentition. In previous studies, lip-closing force was seen to temporarily decrease following orthognathic surgery and subsequently increase after skeletal stabilization [ 4 , 5 , 6 , 7 , 8 ]. Profitt reported that tongue pressure increased after maxillary setback surgery using anterior alveolar osteotomy [ 9 ]. In contrast, Przygonski reported that tongue pressure decreased after mandibular setback surgery using intra vertical ramus osteotomy [ 10 ]. However, no reports have clarified functional changes in the perioral muscles, including the buccinator muscle, at the same time. Further, the relationship between functional changes to the perioral musculature and the skeletal type of jaw deformity is unclear. Ueki reported that lip-closing force in patients with mandibular prognathism is lower compared to that in controls [ 5 ]. Profitt demonstrated that tongue pressure is low in patients with maxillary protrusion [ 9 ]. Few reports have examined the effects of differences in skeletal type of jaw deformity on functional changes in the perioral muscles [ 7 ]. The purpose of this study was to investigate changes in lip-closing force, tongue pressure, and buccinator pressure before and after orthognathic surgery, and to compare these changes between skeletal Class II and Class III female patients. We hypothesized that all perioral muscle functions would be decreased at 3 months postoperatively, but would be improved compared to the preoperative baseline by 1 year postoperatively in both skeletal Class II and Class III groups. Further, we expected that the rate of improvement would differ between groups, with skeletal Class II patients demonstrating a greater rate of increase across all perioral muscle function parameters. The specific aims of this study were to: 1) analyze changes in lip-closing force, tongue pressure, and buccinator pressure in skeletal Class II and Class III patients; 2) compare these changes between groups; 3) compare pre- and postoperative perioral muscle functions between skeletal Class II patients, skeletal Class III patients and controls with normal occlusion; and 4) compare rates of change in lip-closing force, tongue pressure, and buccinator pressure between skeletal Class II and Class III patients. 2. Materials and methods 2.1. Study design and sample This was a prospective cohort study. Participants comprised 36 females who underwent orthognathic surgery between 2021 and 2024 at Kyushu Dental University Hospital, Japan. Bilateral sagittal split ramus osteotomy (BSSRO) alone was performed in 12 patients, Le Fort I osteotomy alone in 4 patients, and both in 20 patients. Participants were divided into groups based on the preoperative skeletal classification: Group A, skeletal class II; and Group B, skeletal class III. Inclusion criteria were: 1) complete medical records; 2) diagnosis of jaw deformity; and 3) history of orthognathic surgery. Exclusion criteria were: 1) incomplete medical records; 2) intellectual disabilities that impaired full understanding of the study; 3) presence of neuromuscular disorders; or 4) history of oral myofunctional therapy. The control group comprised 10 females with normal occlusion without jaw deformity. The research protocol was approved by the research Ethics Committee of Kyushu Dental University (approval no. 24 − 6). All procedures were performed in accordance with the ethical standards of the committee responsible for human experimentation and the 2013 Declaration of Helsinki. All the participants provided written informed consent. 2.2. Variables The primary predictor variable was skeletal classification (skeletal Class II or III). The primary outcome variables were changes in perioral muscle function, including lip-closing force, tongue pressure and buccinator pressure. The secondary outcome variable was the rate of change in each perioral muscle function, as a percentage. Covariates included age, type of surgical treatment (Le Fort I osteotomy, BSSRO, or Le Fort I osteotomy and BSSRO), overbite, overjet and direction of movement. 2.3. Data collection methods Lip-closing force was measured using Lipple-kun (Shofu Inc., Kyoto, Japan) (Fig. 1 ) preoperatively (1 day before surgery) and at 3 months and 1 year postoperatively. The device consists of a disposable plastic button, a simple pressure-recording manometer, and a 15-cm length of dental floss connecting the two components. Participants were instructed to sit upright with the head in a natural position. The plastic button was placed between the upper and lower lips at the level of the central incisors. Participants were then asked to press the lips together with maximal voluntary effort to hold the button in place. The force exerted during lip closure was recorded. Each measurement was performed three times with 60-second rest intervals, and the highest value was recorded for analysis. Tongue pressure and buccinator pressure were measured using a pressure-measuring device (TPM-02E; JMS Co., Tokyo, Japan) (Fig. 2 ) preoperatively (1 day before surgery) and at 3 months and 1 year postoperatively. The device comprised a disposable probe and a simple pressure-recording manometer. For tongue pressure measurement, participants were instructed to sit upright in a relaxed position with the lips lightly closed. The balloon probe was placed on the anterior part of the hard palate, and participants were instructed to compress the balloon against the palate using the tongue with maximal voluntary effort for approximately 5 seconds. For buccinator pressure measurement, the balloon probe was positioned in the oral vestibule, specifically between the buccal mucosa and the teeth in the region of the first molar, where the buccinator muscle is anatomically prominent. Participants were asked to compress the balloon laterally using the buccinator muscle by contracting the cheek inward against the teeth for approximately 5 seconds. Each measurement was performed three times with a 60-second rest between trials, and the highest value was recorded for further analysis. Buccinator pressure was calculated as the average of values from the left and right sides. In addition, the rate of change in each perioral muscle function at 3 months postoperatively was calculated using the following formula: (value at 3 months postoperatively - preoperative value) / preoperative value × 100 (%). Similarly, the rate of change at 1 year postoperatively was calculated as: (value at 1 year postoperatively - preoperative value) / preoperative value × 100 (%). Furthermore, lateral cephalometric radiographs taken 1 month before surgery were traced, and the ANB angle was measured. Patients with an ANB angle greater than 4° were classified as skeletal Class II, while those with an ANB angle less than or equal to 0° were classified as skeletal Class III. To maintain impartiality, all cephalometric evaluations were performed by one of the authors, who was unaware of the cephalometric radiographs being examined. Type of surgical treatment, overbite, overjet and direction of movement were obtained from the medical records. 2.4. Data analysis All statistical analyses were performed using Microsoft Excel (version 2505; Microsoft, Redmond, WA, USA). The Wilcoxon signed-rank sum test was used to compare pre- and postoperative measurements (3 months after surgery and 1 year after surgery) of lip-closing force, tongue pressure, and buccinator pressure. In addition, the Mann–Whitney U test was used to assess differences in maximum perioral muscle functions among Group A, Group B, and the Control Group, as well as to evaluate rates of change in each perioral muscle function at 3 months and 1 year postoperatively between Groups A and B. Continuous variables are reported as mean ± standard deviation and 95% confidence interval. The level of significance was set at P < 0.05. Categorical data are presented as frequencies and percentages. 3. Results A total of 36 females met the inclusion criteria, with a mean age of 24.22 ± 7.92 years (range, 17–46 years). Patients were divided into two groups based on preoperative facial skeletal classification: Group A (Class II) and Group B (Class III). Group A included 14 females (mean age, 25.21 ± 8.41 years; range, 17–45 years). Among them, 4 patients underwent BSSRO alone, 4 underwent Le Fort I osteotomy alone, and 6 underwent both Le Fort I osteotomy and BSSRO. Mean overbite in Group A was − 0.44 ± 2.26 mm and mean overjet was 5.35 ± 1.76 mm. Group B included 22 females (mean age, 23.59 ± 7.72 years; range, 17–46 years). Among them, 8 patients underwent BSSRO alone, and 14 underwent both Le Fort I osteotomy and BSSRO. Mean overbite in Group B was 0.03 ± 2.13 mm and mean overjet was − 4.65 ± 3.71 mm. The Control group comprised 10 females (mean age, 29.31 ± 4.02 years; range, 24–37 years). Mean lip-closing force in the Control Group was 9.12 ± 1.48 N, mean tongue pressure was 34.87 ± 4.22 kPa, and mean buccinator pressure was 17.39 ± 1.18 kPa. The direction of skeletal movement and participant characteristics are summarized in Table 1 . Table 1 Characteristics of study participants Group A (skeletal Class II) Group B (skeletal Class III) Total n = 14 n = 22 Age, yr 25.21 ± 8.41 23.59 ± 7.72 Treatment BSSRO only 4 (28.6%) Le Fort Ⅰ only 4 (28.6%) Le Fort Ⅰ and BSSRO 6 (42.8%) BSSRO only 8 (36.4%) Le Fort Ⅰ only 0 (0%) Le Fort Ⅰ and BSSRO 14 (63.6%) Overbite, mm -0.44 ± 2.26 0.03 ± 2.13 Overjet, mm 5.35 ± 1.76 * -4.65 ± 3.71 * Direction of movement Maxilla Mandible n Maxilla Mandible n Posterosuperior - 4 (28.6%) - Setback 8 (36.4%) - Advance 4 (28.6%) Anterosuperior Setback 10 (45.5%) Posterosuperior Advance 5 (35.7%) Superior Setback 1 (4.5%) Superior Advance 1 (7.1%) Anterior Setback 1 (4.5%) Posterosuperior Setback 2 (9.1%) Data are given as number (%). 3.1. Group A (Skeletal Class II) In the Class II group, mean preoperative lip-closing force was 7.35 ± 1.53 N, increasing to 8.08 ± 1.81 N at 3 months postoperatively and 9.72 ± 2.14 N at 1 year. Tongue pressure and buccinator pressure exhibited a different trend, with mean tongue pressure decreasing slightly from 30.83 ± 8.85 kPa preoperatively to 29.76 ± 9.07 kPa at 3 months, then increasing to 33.70 ± 8.01 kPa at 1 year. Similarly, buccinator pressure decreased from 18.33 ± 5.17 kPa to 17.67 ± 4.22 kPa at 3 months, then increased to 20.76 ± 3.73 kPa at 1 year. Overall, functions of all three perioral muscles were improved at 1 year postoperatively compared with preoperatively, despite temporary reductions in tongue and buccinator pressure at 3 months. No significant differences were observed between preoperative and 3-month postoperative values for any of the perioral muscle functions. However, significant increases were found between preoperatively and 1 year postoperatively for all functions (lip-closing force, p < 0.001; tongue pressure, p = 0.026; and buccinator pressure, p = 0.028) (Figs. 3 – 5 ). 3.2. Group B (Skeletal Class III) In the Class III group, all perioral muscle functions exhibited a similar pattern. Mean lip-closing force decreased from 7.92 ± 2.00 N preoperatively to 7.52 ± 2.29 N at 3 months postoperatively, then increased to 9.00 ± 2.14 N at 1 year. Tongue pressure decreased slightly from 30.86 ± 8.19 kPa preoperatively to 30.49 ± 5.83 kPa at 3 months, then rose to 34.40 ± 6.81 kPa at 1 year. Buccinator pressure also declined from 18.75 ± 3.42 kPa to 17.85 ± 2.59 kPa at 3 months, followed by an increase to 20.22 ± 4.40 kPa at 1 year. All muscle function values at 1 year postoperatively exceeded the respective preoperative values. Unlike the Class II group, significant decreases at 3 months postoperatively were observed for lip-closing force (p = 0.020) and buccinator pressure (p = 0.044) compared to preoperatively. Similar to Group A, significant increases at 1 year postoperatively compared to preoperatively were noted for lip-closing force (p = 0.010), tongue pressure (p = 0.023), and buccinator pressure (p = 0.028) (Figs. 3 – 5 ). 3.3. Comparisons between Group A, Group B, and the Control Group Lip-closing force increased in order of Class II preoperative to Class III preoperative to Control. After 1 year, the order changed to Class III 1-year to Control to Class II 1-year. Significant differences were observed between Class II preoperative and Control (p = 0.020), and between Class III preoperative and Control (p = 0.043) (Fig. 3 ). For tongue pressure, the preoperative trend was the same as for lip-closing force, increasing from Class II preoperative to Class III preoperative to Control. However, after 1 year, the order changed to Class II 1-year to Class III 1-year to Control. No significant differences were observed (Fig. 4 ). Buccinator pressure at baseline increased from Control to Class II preoperative to Class III preoperative. After 1 year, the order changed from Control to Class III 1-year to Class II 1-year. A significant difference was observed between Class II 1-year and Control (p = 0.028) (Fig. 5 ). In addition, mean preoperative lip-closing force (7.70 ± 1.81 N) and tongue pressure (30.85 ± 8.21 kPa) were lower in the jaw deformity group (Group A + Group B) than in the Control group, whereas mean preoperative buccinator pressure (18.58 ± 4.06 kPa) was higher. A significant difference was observed in preoperative lip-closing force (P = 0.017). At 1 year postoperatively, mean lip-closing force (9.28 ± 2.11 N) and buccinator pressure (20.43 ± 4.04 kPa) were higher in the jaw deformity group than in the Control group. In contrast, mean tongue pressure (34.13 ± 7.09 kPa) remained slightly lower. A significant difference in 1-year postoperative buccinator pressure was observed between groups (P = 0.033). 3.4. Comparison of postoperative rates of change in perioral muscle function At 3 months postoperatively, the Class II group showed rates of change of 11.34 ± 21.43% for lip-closing force, -1.51 ± 18.70% for tongue pressure, and 0.29 ± 23.31% for buccinator pressure, while the Class III group showed − 3.39 ± 27.95%, 1.62 ± 17.13%, and − 1.71 ± 26.90%, respectively. At 1 year postoperatively, rates of change in the Class II group were 33.99 ± 25.19% for lip-closing force, 11.79 ± 15.15% for tongue pressure, and 18.38 ± 24.54% for buccinator pressure, compared to 16.00 ± 24.70%, 14.67 ± 21.99%, and 8.19 ± 15.63% in the Class III group. In both periods, lip-closing force and buccinator pressure increased more in the Class II group than in the Class III group, whereas tongue pressure increased more in the Class III group. However, only the difference in lip-closing force reached the level of significance at both 3 months (p = 0.004) and 1 year (p = 0.024) postoperatively (Fig. 6 ). 4. Discussion This study evaluated the recovery of perioral muscle functions following orthognathic surgery in skeletal Class II and Class III female patients. While previous studies have investigated changes in lip-closing force and tongue pressure before and after surgery [ 4 , 5 , 6 , 7 , 8 , 11 ], the present study additionally evaluated buccinator pressure. These three key muscle functions were assessed preoperatively and at 3 months and 1 year postoperatively. In both groups, all muscle functions showed improvement at 1 year postoperatively compared to preoperatively. However, different recovery patterns were observed between the two skeletal classes. First, in Class II patients, all perioral muscle functions showed significant improvements at 1 year after orthognathic surgery. This enhancement was attributed to improved skeletal balance, which creates a favorable environment for perioral muscles to function more efficiently [ 12 ]. Notably, tongue pressure and buccinator pressure demonstrated a tendency to be decreased at 3 months postoperatively. This transient reduction may be attributed to rapid skeletal changes following surgery, to which the surrounding soft tissues may not immediately adapt, likely due to temporary disruptions in neuromuscular coordination associated with extensive mandibular advancement [ 13 ]. Interestingly, lip-closing force exhibited a slight increasing trend even within the early postoperative period. Despite the potential early-phase maladaptation to the new skeletal configuration, lip-closing force did not decline and instead showed early improvement. This may be particularly evident in Class II patients, in whom mandibular advancement facilitates easier lip closure, reducing excessive effort by the orbicularis oris and allowing the muscle to function more efficiently and recover from an earlier stage [ 8 , 14 ]. As a result, improvements in lip-closing force were observed as early as 3 months postoperatively in this group. These findings align with previous reports. For instance, Ueki et al. [ 8 ] found that maximum lip-closing force was increased at 6 months and 1 year postoperatively. Similarly, Gomi et al. [ 4 ] reported an increase in maximum lip-closing force, but no significant change in tongue pressure at 1 year. In contrast, Tsutsui et al. [ 7 ] found no change in maximum lip-closing force among Class II female patients. Second, in Class III patients, all perioral muscle functions also showed significant improvements 1 year after orthognathic surgery. However, unlike Class II patients, all functions were decreased at 3 months postoperatively, with significant decreases observed in lip-closing force and buccinator pressure. Previous studies have demonstrated improvements in maximum lip-closing force in Class III patients after surgery [ 5 , 6 , 7 ], and our findings are consistent with these observations. Temporary postoperative decreases may also be explained by the rapid skeletal changes that soft tissues are not able to immediately accommodate, leading to transient suppression of muscle function [ 13 ]. To further contextualize these findings, comparisons with a control group were made. Previous studies have demonstrated that preoperative lip-closing force and tongue pressure in both Class II and Class III patients are lower than those observed in individuals with normal occlusion [ 11 ], and our results were consistent with those reports. Such reductions may be attributed to impaired lip closure caused by skeletal discrepancies, as well as to abnormal resting and functional positioning of the tongue, leading to decreased functional use and disuse atrophy of the orbicularis oris and tongue muscles [ 15 ]. In contrast to lip-closing force and tongue pressure, buccinator pressure exhibited the opposite trend. Specifically, preoperative buccinator pressure was higher in both Class II and Class III patients than in control subjects, which may reflect compensatory activation of the buccinator muscle to assist with lip closure when lip-closing force is insufficient [ 16 ]. Interestingly, mean 1-year postoperative lip-closing force and buccinator pressure were higher in the jaw deformity group (Group A + Group B) than in the control group. Since orthognathic surgery aims to establish optimal skeletal relationships, patients who undergo the procedure may exhibit higher perioral muscle function postoperatively, despite achieving a skeletal Class I relationship. However, mean tongue pressure at 1 year postoperatively remained slightly lower than that in the control group. This may be explained by the fact that tongue pressure is influenced not only by skeletal positioning, but also by central neural control and intrinsic tongue muscle activation. Furthermore, persistent factors such as low tongue posture or habitual mouth breathing may have hindered full recovery of tongue pressure [ 16 ]. Given that perioral muscle function varies significantly between individuals, direct cross-subject comparisons are difficult [ 17 ]. We therefore also evaluated the rate of change within each participant to provide a more accurate and reliable assessment of the effects of orthognathic surgery. Rates of change for lip-closing force and buccinator pressure were higher in the Class II group than in the Class III group at both 3 months and 1 year postoperatively. However, only the difference in lip-closing force reached the level of significance (P = 0.004 at 3 months; P = 0.024 at 1 year). Several factors may explain this finding: Effect of mandibular advancement on lip-closing force : Mandibular advancement facilitates lip closure, reducing excessive effort by the perioral muscles, particularly the orbicularis oris. This promotes more efficient muscle function and supports more rapid recovery [ 18 ]. Improvement in tension of the lower lip and chin : In Class II patients, mandibular retrusion causes chronic strain on the chin muscles, often resulting in muscular overactivity. Surgical advancement repositions these muscles into a more functional alignment, alleviating tension and enhancing neuromuscular coordination [ 19 ]. Differences in preoperative muscle effort and potential for improvement : Class II patients typically need to exert more muscular effort to achieve lip closure preoperatively [ 20 ]. Following surgery, this effort is redirected into more efficient functional activity, resulting in greater improvement. By contrast, Class III patients usually do not require as much muscular effort for lip closure before surgery [ 5 ], leaving less room for postoperative functional gain. On the other hand, the rate of change in tongue pressure was higher in the Class III group compared to the Class II group. This may be attributed to the fact that mandibular prognathism complicates the generation of adequate tongue pressure against the hard palate. Following mandibular setback surgery, the skeletal relationship is corrected, allowing the tongue to position itself more optimally and enabling better functional recovery of tongue pressure. Finally, this study has several limitations. These include the relatively small sample size, which restricted scope of analyses to the available clinical data. In addition, skeletal Class II patients are relatively uncommon in clinical practice in Japan [ 21 ], potentially contributing to the imbalance in group sizes. Moreover, only female patients were included in this study, as male patients undergoing orthognathic surgery were rare at Kyushu Dental University Hospital. 5. Conclusion Orthognathic surgery not only improves facial aesthetics, but also significantly enhances perioral muscle function at 1 year postoperatively. These functional improvements were more pronounced in Class II patients than in Class III patients with respect to lip-closing force and buccinator pressure. Such findings highlight the importance of developing targeted postoperative rehabilitation programs based on skeletal classification to optimize functional recovery following orthognathic surgery. Declarations Funding No funding was received in association with this study. Conflict of interest The authors have no conflicts of interest to declare. Author Contributions All authors contributed to the study conception and design. Material preparation, data collection was performed by [ Jing Yuan]. Analysis and interpretation of data collected were performed by [Jing Yuan] and [Taishi Ohtani]. Final approval and guarantor of manuscript were [Manabu Habu] and [Izumi Yoshioka]. The first draft of the manuscript was written by [ Jing Yuan] and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript. Human Ethics and Consent to Participate declarations This study was performed in line with the principles of the Declaration of Helsinki. This study was approved by the Ethics Committee of Kyushu Dental University (Approval Number: 24-6). Written informed consent was obtained from all participants prior to their inclusion in the study. Consent to Participate declaration Written informed consent was obtained from all individual participants included in the study. Clinical trial number Approval Number: 24-6 Clinical trial registration This study was registered at the Ethics Committee of Kyushu Dental University (Trial Registration Number: 24-6, Date of registration: November 24th, 2020). References Weiss RO, Ong II, Reddy AA, Bahmanyar LV, VincentAG S, Ducic Y (2021) Orthognathic surgery—LeFort I osteotomy. Fac Plast Surg 37(06):703–708 Olivares HG, Pérez AG, Saucedo FL, Medina FÁ (2019) Electromyographic changes in the masseter and temporalis muscles before and after orthognathic surgery in patients with mandibular prognathism. 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Cite Share Download PDF Status: Published Journal Publication published 15 Oct, 2025 Read the published version in Oral and Maxillofacial Surgery → Version 1 posted Editorial decision: Revision requested 19 Aug, 2025 Reviews received at journal 14 Aug, 2025 Reviewers agreed at journal 09 Jul, 2025 Reviews received at journal 25 Jun, 2025 Reviewers agreed at journal 25 Jun, 2025 Reviewers invited by journal 24 Jun, 2025 Editor assigned by journal 17 Jun, 2025 Submission checks completed at journal 17 Jun, 2025 First submitted to journal 13 Jun, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6888612","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":476371425,"identity":"48039c71-26ee-498e-a311-6a58dc2f139e","order_by":0,"name":"Jing Yuan","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABCklEQVRIiWNgGAWjYDAC9uYDDAwVcgwMPCAeG0yYB48WnmMJDAxnjBFaeAhqkcgxYGBsw9CCB5g3JBg+LpxnIM/Ac8ZMgqHMJs+egfnhBwaZOzi1yBw4kGw8c5uBYQNvD1DLubRiHgY2YwkGnme43cXYcEyad9sfxgZ+HjPpv22HE3sYGMyAzjuMWwszY/tv3jkG9iAtEoxt/4Fa2L/h18LGzMbM22CQCHYYY9sBoBYeArbwsDFL8xwzSG7jOVZswXAuObHnME+xRAI+v8i///iZp8bAtp8neeMNhjK7xPb29o0fPvbgDjE4YGPgMICwmIE4secAYS3ApPMAifODKC2jYBSMglEwMgAAY8ZHYKVgtxAAAAAASUVORK5CYII=","orcid":"","institution":"Kyushu Dental University","correspondingAuthor":true,"prefix":"","firstName":"Jing","middleName":"","lastName":"Yuan","suffix":""},{"id":476371426,"identity":"9168f304-6682-4dad-954a-5a330c39c51a","order_by":1,"name":"Taishi Ohtani","email":"","orcid":"","institution":"Kyushu Dental University","correspondingAuthor":false,"prefix":"","firstName":"Taishi","middleName":"","lastName":"Ohtani","suffix":""},{"id":476371427,"identity":"8da0a547-b9bb-460c-9efa-19d3f24f7cc8","order_by":2,"name":"Manabu Habu","email":"","orcid":"","institution":"Kyushu Dental University","correspondingAuthor":false,"prefix":"","firstName":"Manabu","middleName":"","lastName":"Habu","suffix":""},{"id":476371428,"identity":"0acf1f13-6ca5-4481-ab72-f35662b200c0","order_by":3,"name":"Izumi Yoshioka","email":"","orcid":"","institution":"Kyushu Dental University","correspondingAuthor":false,"prefix":"","firstName":"Izumi","middleName":"","lastName":"Yoshioka","suffix":""}],"badges":[],"createdAt":"2025-06-13 13:23:25","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6888612/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6888612/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s10006-025-01474-9","type":"published","date":"2025-10-15T15:57:08+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":85648395,"identity":"3c64e2ad-2d4a-42d7-bcdc-57831dff44a3","added_by":"auto","created_at":"2025-06-30 08:53:32","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":313888,"visible":true,"origin":"","legend":"\u003cp\u003eJMS tongue pressure and buccinator pressure-measuring device.\u003c/p\u003e","description":"","filename":"Fig15.png","url":"https://assets-eu.researchsquare.com/files/rs-6888612/v1/41c631e0b19275d06a3a3b81.png"},{"id":85647004,"identity":"c227f67c-cda0-42c2-8f9b-4fdb46519c0d","added_by":"auto","created_at":"2025-06-30 08:45:34","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1349638,"visible":true,"origin":"","legend":"\u003cp\u003eLip-closing force measurement device.\u003c/p\u003e","description":"","filename":"Fig23.png","url":"https://assets-eu.researchsquare.com/files/rs-6888612/v1/76ac0ba16d23a6ae8ccbda34.png"},{"id":85647002,"identity":"01f95173-4690-4244-a249-a5a9f617204b","added_by":"auto","created_at":"2025-06-30 08:45:33","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":72046,"visible":true,"origin":"","legend":"\u003cp\u003eMaximum lip-closing force (N) measured in Class II(n=14), Class III(n=22), and control groups(n=10)\u003c/p\u003e\n\u003cp\u003eError bars represent standard deviation. *Significant difference at p \u0026lt; 0.05; **p \u0026lt; 0.01.\u003c/p\u003e","description":"","filename":"OnlineFig3.png","url":"https://assets-eu.researchsquare.com/files/rs-6888612/v1/cb596cbcdeb07d92fb2cb85b.png"},{"id":85648406,"identity":"bc8f9295-f48f-4502-9f6b-a93e026f155e","added_by":"auto","created_at":"2025-06-30 08:53:33","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":78842,"visible":true,"origin":"","legend":"\u003cp\u003eMaximum tongue pressure (kPa) measured in Class II(n=14), Class III(n=22), and control groups(n=10)\u003c/p\u003e\n\u003cp\u003eError bars represent standard deviation. *Significant difference at p \u0026lt; 0.05.\u003c/p\u003e","description":"","filename":"OnlineFig4.png","url":"https://assets-eu.researchsquare.com/files/rs-6888612/v1/cc9f254ba2f78e5243f14776.png"},{"id":85646985,"identity":"32fe2891-0b16-4687-9465-7252952c50b8","added_by":"auto","created_at":"2025-06-30 08:45:32","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":71953,"visible":true,"origin":"","legend":"\u003cp\u003eMaximum buccinator pressure (kPa) measured in Class II(n=14), Class III(n=22), and control groups(n=10)\u003c/p\u003e\n\u003cp\u003eError bars represent standard deviation. *Significant difference at p \u0026lt; 0.05.\u003c/p\u003e","description":"","filename":"OnlineFig5.png","url":"https://assets-eu.researchsquare.com/files/rs-6888612/v1/6204331a225c7c6e50e33150.png"},{"id":85646984,"identity":"2273dbce-5a48-4e75-873f-6bc88c1d7dc0","added_by":"auto","created_at":"2025-06-30 08:45:32","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":66641,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of postoperative rates of change in lip-closing force, tongue pressure, and buccinator pressure between Class II and Class III patients at 3 months and 1 year after surgery\u003c/p\u003e\n\u003cp\u003eError bars represent standard deviation. *Significant difference at p \u0026lt; 0.05; **p \u0026lt; 0.01.\u003c/p\u003e","description":"","filename":"OnlineFig6.png","url":"https://assets-eu.researchsquare.com/files/rs-6888612/v1/80e4cf6362d2b0aae9edee30.png"},{"id":93956024,"identity":"72df77f6-3a50-45a3-ab50-4c0445f7976a","added_by":"auto","created_at":"2025-10-20 16:09:21","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2798325,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6888612/v1/0558023f-1f96-45a2-a7d9-4c12ae115d22.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Effects of Orthognathic Surgery on Perioral Muscle Function: A Comparative Analysis Between Class II and Class III Female Patients","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eOrthognathic surgery is well known not only for correcting malocclusion, but also for enhancing facial esthetics [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. In addition, postoperative improvements can be achieved in perioral muscle function. The lips, cheeks and tongue are located on the outside and inside of the dentition and their forms and functions therefore affect the maxillofacial structure and dentition.\u003c/p\u003e \u003cp\u003eIn previous studies, lip-closing force was seen to temporarily decrease following orthognathic surgery and subsequently increase after skeletal stabilization [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Profitt reported that tongue pressure increased after maxillary setback surgery using anterior alveolar osteotomy [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. In contrast, Przygonski reported that tongue pressure decreased after mandibular setback surgery using intra vertical ramus osteotomy [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. However, no reports have clarified functional changes in the perioral muscles, including the buccinator muscle, at the same time. Further, the relationship between functional changes to the perioral musculature and the skeletal type of jaw deformity is unclear.\u003c/p\u003e \u003cp\u003eUeki reported that lip-closing force in patients with mandibular prognathism is lower compared to that in controls [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Profitt demonstrated that tongue pressure is low in patients with maxillary protrusion [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Few reports have examined the effects of differences in skeletal type of jaw deformity on functional changes in the perioral muscles [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe purpose of this study was to investigate changes in lip-closing force, tongue pressure, and buccinator pressure before and after orthognathic surgery, and to compare these changes between skeletal Class II and Class III female patients. We hypothesized that all perioral muscle functions would be decreased at 3 months postoperatively, but would be improved compared to the preoperative baseline by 1 year postoperatively in both skeletal Class II and Class III groups. Further, we expected that the rate of improvement would differ between groups, with skeletal Class II patients demonstrating a greater rate of increase across all perioral muscle function parameters. The specific aims of this study were to: 1) analyze changes in lip-closing force, tongue pressure, and buccinator pressure in skeletal Class II and Class III patients; 2) compare these changes between groups; 3) compare pre- and postoperative perioral muscle functions between skeletal Class II patients, skeletal Class III patients and controls with normal occlusion; and 4) compare rates of change in lip-closing force, tongue pressure, and buccinator pressure between skeletal Class II and Class III patients.\u003c/p\u003e"},{"header":"2. Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Study design and sample\u003c/h2\u003e \u003cp\u003eThis was a prospective cohort study. Participants comprised 36 females who underwent orthognathic surgery between 2021 and 2024 at Kyushu Dental University Hospital, Japan. Bilateral sagittal split ramus osteotomy (BSSRO) alone was performed in 12 patients, Le Fort I osteotomy alone in 4 patients, and both in 20 patients. Participants were divided into groups based on the preoperative skeletal classification: Group A, skeletal class II; and Group B, skeletal class III.\u003c/p\u003e \u003cp\u003eInclusion criteria were: 1) complete medical records; 2) diagnosis of jaw deformity; and 3) history of orthognathic surgery. Exclusion criteria were: 1) incomplete medical records; 2) intellectual disabilities that impaired full understanding of the study; 3) presence of neuromuscular disorders; or 4) history of oral myofunctional therapy. The control group comprised 10 females with normal occlusion without jaw deformity. The research protocol was approved by the research Ethics Committee of Kyushu Dental University (approval no. 24\u0026thinsp;\u0026minus;\u0026thinsp;6). All procedures were performed in accordance with the ethical standards of the committee responsible for human experimentation and the 2013 Declaration of Helsinki. All the participants provided written informed consent.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2. Variables\u003c/h2\u003e \u003cp\u003eThe primary predictor variable was skeletal classification (skeletal Class II or III). The primary outcome variables were changes in perioral muscle function, including lip-closing force, tongue pressure and buccinator pressure. The secondary outcome variable was the rate of change in each perioral muscle function, as a percentage.\u003c/p\u003e \u003cp\u003eCovariates included age, type of surgical treatment (Le Fort I osteotomy, BSSRO, or Le Fort I osteotomy and BSSRO), overbite, overjet and direction of movement.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3. Data collection methods\u003c/h2\u003e \u003cp\u003eLip-closing force was measured using Lipple-kun (Shofu Inc., Kyoto, Japan) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) preoperatively (1 day before surgery) and at 3 months and 1 year postoperatively. The device consists of a disposable plastic button, a simple pressure-recording manometer, and a 15-cm length of dental floss connecting the two components. Participants were instructed to sit upright with the head in a natural position. The plastic button was placed between the upper and lower lips at the level of the central incisors. Participants were then asked to press the lips together with maximal voluntary effort to hold the button in place. The force exerted during lip closure was recorded. Each measurement was performed three times with 60-second rest intervals, and the highest value was recorded for analysis.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTongue pressure and buccinator pressure were measured using a pressure-measuring device (TPM-02E; JMS Co., Tokyo, Japan) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) preoperatively (1 day before surgery) and at 3 months and 1 year postoperatively. The device comprised a disposable probe and a simple pressure-recording manometer. For tongue pressure measurement, participants were instructed to sit upright in a relaxed position with the lips lightly closed. The balloon probe was placed on the anterior part of the hard palate, and participants were instructed to compress the balloon against the palate using the tongue with maximal voluntary effort for approximately 5 seconds. For buccinator pressure measurement, the balloon probe was positioned in the oral vestibule, specifically between the buccal mucosa and the teeth in the region of the first molar, where the buccinator muscle is anatomically prominent. Participants were asked to compress the balloon laterally using the buccinator muscle by contracting the cheek inward against the teeth for approximately 5 seconds. Each measurement was performed three times with a 60-second rest between trials, and the highest value was recorded for further analysis. Buccinator pressure was calculated as the average of values from the left and right sides.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn addition, the rate of change in each perioral muscle function at 3 months postoperatively was calculated using the following formula: (value at 3 months postoperatively - preoperative value) / preoperative value \u0026times; 100 (%). Similarly, the rate of change at 1 year postoperatively was calculated as: (value at 1 year postoperatively - preoperative value) / preoperative value \u0026times; 100 (%).\u003c/p\u003e \u003cp\u003eFurthermore, lateral cephalometric radiographs taken 1 month before surgery were traced, and the ANB angle was measured. Patients with an ANB angle greater than 4\u0026deg; were classified as skeletal Class II, while those with an ANB angle less than or equal to 0\u0026deg; were classified as skeletal Class III.\u003c/p\u003e \u003cp\u003eTo maintain impartiality, all cephalometric evaluations were performed by one of the authors, who was unaware of the cephalometric radiographs being examined.\u003c/p\u003e \u003cp\u003eType of surgical treatment, overbite, overjet and direction of movement were obtained from the medical records.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4. Data analysis\u003c/h2\u003e \u003cp\u003eAll statistical analyses were performed using Microsoft Excel (version 2505; Microsoft, Redmond, WA, USA). The Wilcoxon signed-rank sum test was used to compare pre- and postoperative measurements (3 months after surgery and 1 year after surgery) of lip-closing force, tongue pressure, and buccinator pressure.\u003c/p\u003e \u003cp\u003eIn addition, the Mann\u0026ndash;Whitney U test was used to assess differences in maximum perioral muscle functions among Group A, Group B, and the Control Group, as well as to evaluate rates of change in each perioral muscle function at 3 months and 1 year postoperatively between Groups A and B. Continuous variables are reported as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation and 95% confidence interval. The level of significance was set at P\u0026thinsp;\u0026lt;\u0026thinsp;0.05. Categorical data are presented as frequencies and percentages.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results","content":"\u003cp\u003eA total of 36 females met the inclusion criteria, with a mean age of 24.22\u0026thinsp;\u0026plusmn;\u0026thinsp;7.92 years (range, 17\u0026ndash;46 years). Patients were divided into two groups based on preoperative facial skeletal classification: Group A (Class II) and Group B (Class III).\u003c/p\u003e \u003cp\u003eGroup A included 14 females (mean age, 25.21\u0026thinsp;\u0026plusmn;\u0026thinsp;8.41 years; range, 17\u0026ndash;45 years). Among them, 4 patients underwent BSSRO alone, 4 underwent Le Fort I osteotomy alone, and 6 underwent both Le Fort I osteotomy and BSSRO. Mean overbite in Group A was \u0026minus;\u0026thinsp;0.44\u0026thinsp;\u0026plusmn;\u0026thinsp;2.26 mm and mean overjet was 5.35\u0026thinsp;\u0026plusmn;\u0026thinsp;1.76 mm.\u003c/p\u003e \u003cp\u003eGroup B included 22 females (mean age, 23.59\u0026thinsp;\u0026plusmn;\u0026thinsp;7.72 years; range, 17\u0026ndash;46 years). Among them, 8 patients underwent BSSRO alone, and 14 underwent both Le Fort I osteotomy and BSSRO. Mean overbite in Group B was 0.03\u0026thinsp;\u0026plusmn;\u0026thinsp;2.13 mm and mean overjet was \u0026minus;\u0026thinsp;4.65\u0026thinsp;\u0026plusmn;\u0026thinsp;3.71 mm.\u003c/p\u003e \u003cp\u003eThe Control group comprised 10 females (mean age, 29.31\u0026thinsp;\u0026plusmn;\u0026thinsp;4.02 years; range, 24\u0026ndash;37 years). Mean lip-closing force in the Control Group was 9.12\u0026thinsp;\u0026plusmn;\u0026thinsp;1.48 N, mean tongue pressure was 34.87\u0026thinsp;\u0026plusmn;\u0026thinsp;4.22 kPa, and mean buccinator pressure was 17.39\u0026thinsp;\u0026plusmn;\u0026thinsp;1.18 kPa. The direction of skeletal movement and participant characteristics are summarized in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eCharacteristics of study participants\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c4\" namest=\"c2\"\u003e \u003cp\u003eGroup A (skeletal Class II)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c7\" namest=\"c5\"\u003e \u003cp\u003eGroup B (skeletal Class III)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTotal\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"3\" nameend=\"c4\" namest=\"c2\"\u003e \u003cp\u003en\u0026thinsp;=\u0026thinsp;14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"3\" nameend=\"c7\" namest=\"c5\"\u003e \u003cp\u003en\u0026thinsp;=\u0026thinsp;22\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAge, yr\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"3\" nameend=\"c4\" namest=\"c2\"\u003e \u003cp\u003e25.21\u0026thinsp;\u0026plusmn;\u0026thinsp;8.41\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"3\" nameend=\"c7\" namest=\"c5\"\u003e \u003cp\u003e23.59\u0026thinsp;\u0026plusmn;\u0026thinsp;7.72\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTreatment\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"3\" nameend=\"c4\" namest=\"c2\"\u003e \u003cp\u003eBSSRO only 4 (28.6%)\u003c/p\u003e \u003cp\u003eLe Fort Ⅰ only 4 (28.6%)\u003c/p\u003e \u003cp\u003eLe Fort Ⅰ and BSSRO 6 (42.8%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"3\" nameend=\"c7\" namest=\"c5\"\u003e \u003cp\u003eBSSRO only 8 (36.4%)\u003c/p\u003e \u003cp\u003eLe Fort Ⅰ only 0 (0%)\u003c/p\u003e \u003cp\u003eLe Fort Ⅰ and BSSRO 14 (63.6%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOverbite, mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"3\" nameend=\"c4\" namest=\"c2\"\u003e \u003cp\u003e-0.44\u0026thinsp;\u0026plusmn;\u0026thinsp;2.26\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"3\" nameend=\"c7\" namest=\"c5\"\u003e \u003cp\u003e0.03\u0026thinsp;\u0026plusmn;\u0026thinsp;2.13\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOverjet, mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"3\" nameend=\"c4\" namest=\"c2\"\u003e \u003cp\u003e5.35\u0026thinsp;\u0026plusmn;\u0026thinsp;1.76 *\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"3\" nameend=\"c7\" namest=\"c5\"\u003e \u003cp\u003e-4.65\u0026thinsp;\u0026plusmn;\u0026thinsp;3.71 *\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"5\" rowspan=\"6\"\u003e \u003cp\u003eDirection of movement\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003eMaxilla\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003eMandible\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003en\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003eMaxilla\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003eMandible\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e\u003cb\u003en\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePosterosuperior\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4 (28.6%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eSetback\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e8 (36.4%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAdvance\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4 (28.6%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eAnterosuperior\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eSetback\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e10 (45.5%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePosterosuperior\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAdvance\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5 (35.7%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eSuperior\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eSetback\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e1 (4.5%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSuperior\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAdvance\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1 (7.1%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eAnterior\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eSetback\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e1 (4.5%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003ePosterosuperior\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eSetback\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e2 (9.1%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"7\"\u003eData are given as number (%).\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.1. Group A (Skeletal Class II)\u003c/h2\u003e \u003cp\u003eIn the Class II group, mean preoperative lip-closing force was 7.35\u0026thinsp;\u0026plusmn;\u0026thinsp;1.53 N, increasing to 8.08\u0026thinsp;\u0026plusmn;\u0026thinsp;1.81 N at 3 months postoperatively and 9.72\u0026thinsp;\u0026plusmn;\u0026thinsp;2.14 N at 1 year. Tongue pressure and buccinator pressure exhibited a different trend, with mean tongue pressure decreasing slightly from 30.83\u0026thinsp;\u0026plusmn;\u0026thinsp;8.85 kPa preoperatively to 29.76\u0026thinsp;\u0026plusmn;\u0026thinsp;9.07 kPa at 3 months, then increasing to 33.70\u0026thinsp;\u0026plusmn;\u0026thinsp;8.01 kPa at 1 year. Similarly, buccinator pressure decreased from 18.33\u0026thinsp;\u0026plusmn;\u0026thinsp;5.17 kPa to 17.67\u0026thinsp;\u0026plusmn;\u0026thinsp;4.22 kPa at 3 months, then increased to 20.76\u0026thinsp;\u0026plusmn;\u0026thinsp;3.73 kPa at 1 year. Overall, functions of all three perioral muscles were improved at 1 year postoperatively compared with preoperatively, despite temporary reductions in tongue and buccinator pressure at 3 months.\u003c/p\u003e \u003cp\u003eNo significant differences were observed between preoperative and 3-month postoperative values for any of the perioral muscle functions. However, significant increases were found between preoperatively and 1 year postoperatively for all functions (lip-closing force, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001; tongue pressure, p\u0026thinsp;=\u0026thinsp;0.026; and buccinator pressure, p\u0026thinsp;=\u0026thinsp;0.028) (Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e5\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.2. Group B (Skeletal Class III)\u003c/h2\u003e \u003cp\u003eIn the Class III group, all perioral muscle functions exhibited a similar pattern. Mean lip-closing force decreased from 7.92\u0026thinsp;\u0026plusmn;\u0026thinsp;2.00 N preoperatively to 7.52\u0026thinsp;\u0026plusmn;\u0026thinsp;2.29 N at 3 months postoperatively, then increased to 9.00\u0026thinsp;\u0026plusmn;\u0026thinsp;2.14 N at 1 year. Tongue pressure decreased slightly from 30.86\u0026thinsp;\u0026plusmn;\u0026thinsp;8.19 kPa preoperatively to 30.49\u0026thinsp;\u0026plusmn;\u0026thinsp;5.83 kPa at 3 months, then rose to 34.40\u0026thinsp;\u0026plusmn;\u0026thinsp;6.81 kPa at 1 year. Buccinator pressure also declined from 18.75\u0026thinsp;\u0026plusmn;\u0026thinsp;3.42 kPa to 17.85\u0026thinsp;\u0026plusmn;\u0026thinsp;2.59 kPa at 3 months, followed by an increase to 20.22\u0026thinsp;\u0026plusmn;\u0026thinsp;4.40 kPa at 1 year. All muscle function values at 1 year postoperatively exceeded the respective preoperative values.\u003c/p\u003e \u003cp\u003eUnlike the Class II group, significant decreases at 3 months postoperatively were observed for lip-closing force (p\u0026thinsp;=\u0026thinsp;0.020) and buccinator pressure (p\u0026thinsp;=\u0026thinsp;0.044) compared to preoperatively. Similar to Group A, significant increases at 1 year postoperatively compared to preoperatively were noted for lip-closing force (p\u0026thinsp;=\u0026thinsp;0.010), tongue pressure (p\u0026thinsp;=\u0026thinsp;0.023), and buccinator pressure (p\u0026thinsp;=\u0026thinsp;0.028) (Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e5\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.3. Comparisons between Group A, Group B, and the Control Group\u003c/h2\u003e \u003cp\u003eLip-closing force increased in order of Class II preoperative to Class III preoperative to Control. After 1 year, the order changed to Class III 1-year to Control to Class II 1-year. Significant differences were observed between Class II preoperative and Control (p\u0026thinsp;=\u0026thinsp;0.020), and between Class III preoperative and Control (p\u0026thinsp;=\u0026thinsp;0.043) (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eFor tongue pressure, the preoperative trend was the same as for lip-closing force, increasing from Class II preoperative to Class III preoperative to Control. However, after 1 year, the order changed to Class II 1-year to Class III 1-year to Control. No significant differences were observed (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eBuccinator pressure at baseline increased from Control to Class II preoperative to Class III preoperative. After 1 year, the order changed from Control to Class III 1-year to Class II 1-year. A significant difference was observed between Class II 1-year and Control (p\u0026thinsp;=\u0026thinsp;0.028) (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e5\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn addition, mean preoperative lip-closing force (7.70\u0026thinsp;\u0026plusmn;\u0026thinsp;1.81 N) and tongue pressure (30.85\u0026thinsp;\u0026plusmn;\u0026thinsp;8.21 kPa) were lower in the jaw deformity group (Group A\u0026thinsp;+\u0026thinsp;Group B) than in the Control group, whereas mean preoperative buccinator pressure (18.58\u0026thinsp;\u0026plusmn;\u0026thinsp;4.06 kPa) was higher. A significant difference was observed in preoperative lip-closing force (P\u0026thinsp;=\u0026thinsp;0.017). At 1 year postoperatively, mean lip-closing force (9.28\u0026thinsp;\u0026plusmn;\u0026thinsp;2.11 N) and buccinator pressure (20.43\u0026thinsp;\u0026plusmn;\u0026thinsp;4.04 kPa) were higher in the jaw deformity group than in the Control group. In contrast, mean tongue pressure (34.13\u0026thinsp;\u0026plusmn;\u0026thinsp;7.09 kPa) remained slightly lower. A significant difference in 1-year postoperative buccinator pressure was observed between groups (P\u0026thinsp;=\u0026thinsp;0.033).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.4. Comparison of postoperative rates of change in perioral muscle function\u003c/h2\u003e \u003cp\u003eAt 3 months postoperatively, the Class II group showed rates of change of 11.34\u0026thinsp;\u0026plusmn;\u0026thinsp;21.43% for lip-closing force, -1.51\u0026thinsp;\u0026plusmn;\u0026thinsp;18.70% for tongue pressure, and 0.29\u0026thinsp;\u0026plusmn;\u0026thinsp;23.31% for buccinator pressure, while the Class III group showed \u0026minus;\u0026thinsp;3.39\u0026thinsp;\u0026plusmn;\u0026thinsp;27.95%, 1.62\u0026thinsp;\u0026plusmn;\u0026thinsp;17.13%, and \u0026minus;\u0026thinsp;1.71\u0026thinsp;\u0026plusmn;\u0026thinsp;26.90%, respectively. At 1 year postoperatively, rates of change in the Class II group were 33.99\u0026thinsp;\u0026plusmn;\u0026thinsp;25.19% for lip-closing force, 11.79\u0026thinsp;\u0026plusmn;\u0026thinsp;15.15% for tongue pressure, and 18.38\u0026thinsp;\u0026plusmn;\u0026thinsp;24.54% for buccinator pressure, compared to 16.00\u0026thinsp;\u0026plusmn;\u0026thinsp;24.70%, 14.67\u0026thinsp;\u0026plusmn;\u0026thinsp;21.99%, and 8.19\u0026thinsp;\u0026plusmn;\u0026thinsp;15.63% in the Class III group. In both periods, lip-closing force and buccinator pressure increased more in the Class II group than in the Class III group, whereas tongue pressure increased more in the Class III group. However, only the difference in lip-closing force reached the level of significance at both 3 months (p\u0026thinsp;=\u0026thinsp;0.004) and 1 year (p\u0026thinsp;=\u0026thinsp;0.024) postoperatively (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"4. Discussion","content":"\u003cp\u003eThis study evaluated the recovery of perioral muscle functions following orthognathic surgery in skeletal Class II and Class III female patients. While previous studies have investigated changes in lip-closing force and tongue pressure before and after surgery [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e], the present study additionally evaluated buccinator pressure. These three key muscle functions were assessed preoperatively and at 3 months and 1 year postoperatively.\u003c/p\u003e \u003cp\u003eIn both groups, all muscle functions showed improvement at 1 year postoperatively compared to preoperatively. However, different recovery patterns were observed between the two skeletal classes.\u003c/p\u003e \u003cp\u003eFirst, in Class II patients, all perioral muscle functions showed significant improvements at 1 year after orthognathic surgery. This enhancement was attributed to improved skeletal balance, which creates a favorable environment for perioral muscles to function more efficiently [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Notably, tongue pressure and buccinator pressure demonstrated a tendency to be decreased at 3 months postoperatively. This transient reduction may be attributed to rapid skeletal changes following surgery, to which the surrounding soft tissues may not immediately adapt, likely due to temporary disruptions in neuromuscular coordination associated with extensive mandibular advancement [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eInterestingly, lip-closing force exhibited a slight increasing trend even within the early postoperative period. Despite the potential early-phase maladaptation to the new skeletal configuration, lip-closing force did not decline and instead showed early improvement. This may be particularly evident in Class II patients, in whom mandibular advancement facilitates easier lip closure, reducing excessive effort by the orbicularis oris and allowing the muscle to function more efficiently and recover from an earlier stage [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. As a result, improvements in lip-closing force were observed as early as 3 months postoperatively in this group. These findings align with previous reports. For instance, Ueki et al. [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e] found that maximum lip-closing force was increased at 6 months and 1 year postoperatively. Similarly, Gomi et al. [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e] reported an increase in maximum lip-closing force, but no significant change in tongue pressure at 1 year. In contrast, Tsutsui et al. [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e] found no change in maximum lip-closing force among Class II female patients.\u003c/p\u003e \u003cp\u003eSecond, in Class III patients, all perioral muscle functions also showed significant improvements 1 year after orthognathic surgery. However, unlike Class II patients, all functions were decreased at 3 months postoperatively, with significant decreases observed in lip-closing force and buccinator pressure. Previous studies have demonstrated improvements in maximum lip-closing force in Class III patients after surgery [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e], and our findings are consistent with these observations. Temporary postoperative decreases may also be explained by the rapid skeletal changes that soft tissues are not able to immediately accommodate, leading to transient suppression of muscle function [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eTo further contextualize these findings, comparisons with a control group were made. Previous studies have demonstrated that preoperative lip-closing force and tongue pressure in both Class II and Class III patients are lower than those observed in individuals with normal occlusion [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e], and our results were consistent with those reports. Such reductions may be attributed to impaired lip closure caused by skeletal discrepancies, as well as to abnormal resting and functional positioning of the tongue, leading to decreased functional use and disuse atrophy of the orbicularis oris and tongue muscles [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn contrast to lip-closing force and tongue pressure, buccinator pressure exhibited the opposite trend. Specifically, preoperative buccinator pressure was higher in both Class II and Class III patients than in control subjects, which may reflect compensatory activation of the buccinator muscle to assist with lip closure when lip-closing force is insufficient [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eInterestingly, mean 1-year postoperative lip-closing force and buccinator pressure were higher in the jaw deformity group (Group A\u0026thinsp;+\u0026thinsp;Group B) than in the control group. Since orthognathic surgery aims to establish optimal skeletal relationships, patients who undergo the procedure may exhibit higher perioral muscle function postoperatively, despite achieving a skeletal Class I relationship. However, mean tongue pressure at 1 year postoperatively remained slightly lower than that in the control group. This may be explained by the fact that tongue pressure is influenced not only by skeletal positioning, but also by central neural control and intrinsic tongue muscle activation. Furthermore, persistent factors such as low tongue posture or habitual mouth breathing may have hindered full recovery of tongue pressure [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eGiven that perioral muscle function varies significantly between individuals, direct cross-subject comparisons are difficult [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. We therefore also evaluated the rate of change within each participant to provide a more accurate and reliable assessment of the effects of orthognathic surgery. Rates of change for lip-closing force and buccinator pressure were higher in the Class II group than in the Class III group at both 3 months and 1 year postoperatively. However, only the difference in lip-closing force reached the level of significance (P\u0026thinsp;=\u0026thinsp;0.004 at 3 months; P\u0026thinsp;=\u0026thinsp;0.024 at 1 year). Several factors may explain this finding:\u003c/p\u003e \u003cp\u003e \u003col\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eEffect of mandibular advancement on lip-closing force\u003c/b\u003e: Mandibular advancement facilitates lip closure, reducing excessive effort by the perioral muscles, particularly the orbicularis oris. This promotes more efficient muscle function and supports more rapid recovery [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e].\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eImprovement in tension of the lower lip and chin\u003c/b\u003e: In Class II patients, mandibular retrusion causes chronic strain on the chin muscles, often resulting in muscular overactivity. Surgical advancement repositions these muscles into a more functional alignment, alleviating tension and enhancing neuromuscular coordination [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e].\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eDifferences in preoperative muscle effort and potential for improvement\u003c/b\u003e: Class II patients typically need to exert more muscular effort to achieve lip closure preoperatively [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Following surgery, this effort is redirected into more efficient functional activity, resulting in greater improvement. By contrast, Class III patients usually do not require as much muscular effort for lip closure before surgery [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e], leaving less room for postoperative functional gain.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \u003c/p\u003e \u003cp\u003eOn the other hand, the rate of change in tongue pressure was higher in the Class III group compared to the Class II group. This may be attributed to the fact that mandibular prognathism complicates the generation of adequate tongue pressure against the hard palate. Following mandibular setback surgery, the skeletal relationship is corrected, allowing the tongue to position itself more optimally and enabling better functional recovery of tongue pressure.\u003c/p\u003e \u003cp\u003eFinally, this study has several limitations. These include the relatively small sample size, which restricted scope of analyses to the available clinical data. In addition, skeletal Class II patients are relatively uncommon in clinical practice in Japan [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e], potentially contributing to the imbalance in group sizes. Moreover, only female patients were included in this study, as male patients undergoing orthognathic surgery were rare at Kyushu Dental University Hospital.\u003c/p\u003e"},{"header":"5. Conclusion","content":"\u003cp\u003eOrthognathic surgery not only improves facial aesthetics, but also significantly enhances perioral muscle function at 1 year postoperatively. These functional improvements were more pronounced in Class II patients than in Class III patients with respect to lip-closing force and buccinator pressure. Such findings highlight the importance of developing targeted postoperative rehabilitation programs based on skeletal classification to optimize functional recovery following orthognathic surgery.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNo funding was received in association with this study.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors have no conflicts of interest to declare.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e\u003cstrong\u003eAuthor Contributions\u003c/strong\u003e\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eAll authors contributed to the study conception and design. Material preparation, data collection was performed by [\u003c/em\u003e\u003cem\u003eJing Yuan].\u003c/em\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eAnalysis and interpretation of data collected were performed by [Jing Yuan] and [Taishi Ohtani].\u003cem\u003e\u0026nbsp;\u003c/em\u003eFinal approval and guarantor of manuscript were [Manabu Habu] and [Izumi Yoshioka]. \u003cem\u003eThe first draft of the manuscript was written by [\u003c/em\u003e\u003cem\u003eJing Yuan] and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eHuman Ethics and Consent to Participate declarations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eThis study was performed in line with the principles of the Declaration of Helsinki.\u003c/em\u003e This study was approved by the Ethics Committee of Kyushu Dental University (Approval Number: 24-6). Written informed consent was obtained from all participants prior to their inclusion in the study.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to Participate\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;declaration\u003c/strong\u003e\u003cbr\u003e\u0026nbsp;Written informed consent was obtained from all individual participants included in the study.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eClinical trial number\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eApproval Number: 24-6\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eClinical trial registration\u003c/strong\u003e\u003cbr\u003e\u0026nbsp;This study was registered at the Ethics Committee of Kyushu Dental University (Trial Registration Number: 24-6, Date of registration: November 24th, 2020).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eWeiss RO, Ong II, Reddy AA, Bahmanyar LV, VincentAG S, Ducic Y (2021) Orthognathic surgery\u0026mdash;LeFort I osteotomy. Fac Plast Surg 37(06):703\u0026ndash;708\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eOlivares HG, P\u0026eacute;rez AG, Saucedo FL, Medina F\u0026Aacute; (2019) Electromyographic changes in the masseter and temporalis muscles before and after orthognathic surgery in patients with mandibular prognathism. J Craniofac Surg 30(5):1539\u0026ndash;1543\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTomaz AFG, Marinho LCN, de Aquino ARL et al (2020) Impact of orthognathic surgery on the treatment of gummy smile: an integrative review. Oral Maxillofac Surg 24:283\u0026ndash;288\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGomi K, Moroi A, Yoshizawa K et al (2023) Evaluation of tongue pressure and lip closing force in bimaxillary orthognathic surgery: A retrospective study. Surg 51(11):696\u0026ndash;701\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eUeki K, Mukozawa A, Okabe K et al (2012 Jul) Changes in the lip closing force of patients with class III malocclusion before and after orthognathic surgery. Int J Oral Maxillofac Surg 41(7):835\u0026ndash;838\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eUeki K, Marukawa K, Moroi A et al (2014) The time-course change in the lip closing force in Class III malocclusion after orthognathic surgery. J Craniomaxillofac Surg 42(6):896\u0026ndash;900\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTsutsui T, Yoshizawa K, Moroi A et al (2017) Change in lip closing force in Class II and III malocclusion before and after sagittal split ramus osteotomy with Le Fort I osteotomy. J Craniomaxillofac Surg 45(9):1415\u0026ndash;1418\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eUeki K, Moroi A, Sotobori M et al (2014) Evaluation of recovery in lip closing pressure and occlusal force and contact area after orthognathic surgery. Craniomaxillofac Surg 42(7):1148\u0026ndash;1153\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eProffit WR, Knight JM Tongue pressures and tooth stability after anterior maxillary osteotomy. J Oral Surg 35: 798\u0026ndash;801, 1977.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePrzygonski A, Arkuszewski P (2006) Evaluation of tongue pressure on the inferior dental arch in patients with mandibular prognathism. Ann Acad Med Stetin 52(Suppl 3):131\u0026ndash;133\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKoizumi K, Shintani T, Yoshimi Y et al (2022) Impact of Maximum Tongue Pressure in Patients with Jaw Deformities Who Underwent Orthognathic Surgery. Diagnostics (Basel) 12(2):404\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSahu GR, Kaur A, Rattan V et al (2022) Effect of Orthognathic Surgery on Temporomandibular Disorders: A Prospective Study. J Maxillofac Oral Surg 21(1):277\u0026ndash;282\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRen M, Bai Y, Wang M et al (2025) Impact of the orofacial muscular rehabilitation exercise on facial expression recovery post-orthognathic surgery. J Stomatol Oral maxillofac Surg 126(2):102038\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTakeuchi G, Kobayashi T, Hasebe D et al Changes in maximum lip closing force following orthognathic surgery in patients with jaw deformities. June 2014. J Oral Maxillofacial Surg Med Pathol 27(4)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWilliam R, Proffit H, Fields B, Larson et al (2018) Contemporary Orthodontics 6th Edition-August 6\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHori K, Ono T, Iwata H et al (2005) Tongue pressure against hard palate during swallowing in post-stroke patients. Gerodontology 22(4):227\u0026ndash;233\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eE D\u0026rsquo;Andrea Ebarbaix Anatomic research on the perioral muscles, functional matrix of the maxillary and mandibular bones. 2006 July Surg radiologic Anat 28(3):261\u0026ndash;266\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCarlos Nicolet D, Munoz A, Marino (2012) Lip Competence in Class III patients Undergoing Orthognathic Surgery: An Electromyographic Study. Maxillofac Surg 70(5):e331\u0026ndash;e336\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePintavirooj P, Sumetcherngpratya R, Chaiwat A et al (December 2014) Relationship between mentalis muscle hyperactivity and mandibular symphysis morphology in skeletal Class I and II patients. Orthodontic Waves Volume 73(4):30\u0026ndash;135\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTosello DO, Vitti M, Berzin F (1998) EMG activity of the orbicularis oris and mentalis muscles in children with malocclusion, incompetent lips and atypical swallowing\u0026ndash;part I. J Oral Rehabil 25(11):838\u0026ndash;846\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiliana M, Otero LA, Morford, Gabriel Falc\u0026atilde;o-Alencar (2014) Family History and Genetics of Mandibular Prognathism. Orthodontic Treatment of Class III\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"oral-and-maxillofacial-surgery","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"omfs","sideBox":"Learn more about [Oral and Maxillofacial Surgery](http://link.springer.com/journal/10006)","snPcode":"10006","submissionUrl":"https://submission.nature.com/new-submission/10006/3","title":"Oral and Maxillofacial Surgery","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Lip-closing force, Tongue pressure, Buccinator pressure, Orthognathic surgery, Skeletal classification","lastPublishedDoi":"10.21203/rs.3.rs-6888612/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6888612/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003ePurpose\u003c/h2\u003e \u003cp\u003eThe purpose of this study was to investigate changes in lip-closing force, tongue pressure, and buccinator pressure before and after orthognathic surgery, and to compare these changes between skeletal Class II and Class III female patients.\u003c/p\u003e\u003ch2\u003eMaterials and Methods\u003c/h2\u003e \u003cp\u003eThirty-six female patients who underwent orthognathic surgery at Kyushu Dental University Hospital were enrolled. Patients were divided into two groups (Group A: skeletal Class II; Group B: skeletal Class III), and ten females with normal occlusion served as the control group. Lip-closing force, tongue pressure, and buccinator pressure were measured one day before surgery, and at three months and one year postoperatively. Maximum values were analyzed using the Mann\u0026ndash;Whitney U test and Wilcoxon signed-rank sum test.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eLip-closing force, tongue pressure, and buccinator pressure significantly increased one year after surgery in both groups (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05), although a temporary decline was observed at three months postoperatively, except for lip-closing force in Group A. The change rates for lip-closing force and buccinator pressure were higher in Group A, whereas tongue pressure increased more in Group B. However, a statistically significant difference was observed only in lip-closing force (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05).\u003c/p\u003e\u003ch2\u003eConclusion\u003c/h2\u003e \u003cp\u003eOrthognathic surgery significantly improves perioral muscle function as well as facial aesthetics. Enhancements in lip-closing force and buccinator pressure were more pronounced in Class II patients compared to Class III patients.\u003c/p\u003e","manuscriptTitle":"Effects of Orthognathic Surgery on Perioral Muscle Function: A Comparative Analysis Between Class II and Class III Female Patients","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-06-30 08:45:27","doi":"10.21203/rs.3.rs-6888612/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-08-19T12:20:59+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-08-14T09:14:21+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"183382933056625536219315934074044631005","date":"2025-07-09T15:32:52+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-06-25T13:57:59+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"268961755357624358100781630401610197545","date":"2025-06-25T08:28:01+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-06-24T09:33:17+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-06-17T09:57:00+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-06-17T09:54:17+00:00","index":"","fulltext":""},{"type":"submitted","content":"Oral and Maxillofacial Surgery","date":"2025-06-13T13:20:15+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"oral-and-maxillofacial-surgery","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"omfs","sideBox":"Learn more about [Oral and Maxillofacial Surgery](http://link.springer.com/journal/10006)","snPcode":"10006","submissionUrl":"https://submission.nature.com/new-submission/10006/3","title":"Oral and Maxillofacial Surgery","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"b2640de4-9160-4a56-b314-2b991101812c","owner":[],"postedDate":"June 30th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-10-20T16:02:10+00:00","versionOfRecord":{"articleIdentity":"rs-6888612","link":"https://doi.org/10.1007/s10006-025-01474-9","journal":{"identity":"oral-and-maxillofacial-surgery","isVorOnly":false,"title":"Oral and Maxillofacial Surgery"},"publishedOn":"2025-10-15 15:57:08","publishedOnDateReadable":"October 15th, 2025"},"versionCreatedAt":"2025-06-30 08:45:27","video":"","vorDoi":"10.1007/s10006-025-01474-9","vorDoiUrl":"https://doi.org/10.1007/s10006-025-01474-9","workflowStages":[]},"version":"v1","identity":"rs-6888612","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6888612","identity":"rs-6888612","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}