Three-dimensional soft tissue and cephalometric analysis for Class II malocclusion with Twin-Block appliance treatment

Three-dimensional soft tissue and cephalometric analysis for Class II malocclusion with Twin-Block appliance treatment | 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 Three-dimensional soft tissue and cephalometric analysis for Class II malocclusion with Twin-Block appliance treatment Yue Sun, Ying Zhang, Chengjing Xu, Yuting He, Huan Jiang, Min Hu This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8692897/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Background To evaluate the dentoskeletal and 3D soft tissue changes induced by Twin-Block appliances in adolescents with Class II Division 1 malocclusion, and to assess short-term treatment stability via 3D facial scanning. Materials and Methods Fifty-six patients with Class II division 1 malocclusion (mean age: 9.60 ± 1.16 years) undergoing Twin-Block treatment at University Stomatological Hospital from November 2023 to March 2025. After diagnosis and analysis, patients who needed Twin-Block orthopedic treatment underwent three-dimensional facial scanning (Artec Space Spider) and cephalometric lateral radiography. Pre-treatment (T0), post-treatment (T1), 3-month (T2), and 6-month (T3) data were collected using 3D facial scanning (Artec Space Spider) and lateral cephalography. Soft tissue and skeletal parameters were measured, with statistical analysis performed via paired t-tests and Wilcoxon tests. Results Cephalometric analysis revealed significant post-treatment changes: SNB angle increased ( P < 0.01), ANB angle decreased ( P < 0.01), mandibular ramus/body lengths (Ar-Go, Go-Pog) and facial heights (ANS-Me, N-Me) increased (P < 0.01). Overjet reduced by 3.18 mm ( P < 0.01), and upper incisor inclination (U1-SN) decreased by 3.9° ( P < 0.01). 3D facial analysis showed statistically significant soft tissue changes at T1: alae nasi width (+ 0.43 mm, P < 0.01), upper/lower lip lengths (+ 0.50 mm, + 0.93 mm, P < 0.01), mentolabial angle (+ 9.89°, P < 0.01), and reduced upper lip-chin convexity ( P 0.05). At the 6-month follow-up, significant differences were observed in the upper/lower lip to chin convex angle (P < 0.01). Statistically significant differences were also found in the width of the nasal alar, the width of the nasal base, the width of the philtrum, and the mentolabial angle (P < 0.05). Overlap analysis of the three-dimensional model showed that the corresponding landmarks produced different degrees of displacement in the vertical and sagittal directions, respectively. Conclusions Twin-Block treatment effectively improves occlusal relationships, promotes mandibular growth, and enhances soft tissue aesthetics by reducing lip protrusion and optimizing chin-lip-nose harmony. 3D scanning demonstrates high reliability in quantifying soft tissue remodeling. Short-term stability (3 months and 6 months) highlight Twin-Block’s efficacy in adolescent Class II correction, with implications for early orthopedic intervention. Trial registration: This study was registered at the Chinese Clinical Trial Registry (ChiCTR2300077826) on November 21, 2023. Angle II Twin Block Facial 3D scanning Cephalometric analysis Soft tissue Figures Figure 1 Figure 2 Figure 3 Introduction Class II malocclusion often presents distinct facial characteristics. Typically, it shows a protruding maxilla, open lips, exposed teeth, and a retruded mandible. Among these, the retrusion of the posterior mandible is regarded as the primary contributing factor [1]. Mandibular retrognathia has far-reaching consequences. It not only mars the aesthetic appearance but also causes dental crowding and may even lead to a reduction in airway size [2]. Clinically, for children with Class II malocclusion who meet the treatment criteria during their growth spurt, early intervention with functional appliances is highly beneficial. This treatment approach can effectively stimulate mandibular development, balance the sagittal growth of the maxilla and mandible, facilitate the reconstruction of facial soft tissues, and ultimately contribute to a more harmonious and attractive facial profile [3]. The Twin-Block appliance is a classic functional appliance. For adolescent patients with mandibular hypoplasia before the peak of growth and development, the Twin Block functional orthopedic therapy is widely used both domestically and internationally to coordinate the development of the maxilla and mandible and improve facial aesthetics [4]. It consists of two occlusal blocks designed to mesh with each other to position the mandible forward [5]. The upper block includes a lip arch extending from canine to canine. The mandibular occlusal block features an acrylic cap for the mandibular incisors. Its design forces the mandible forward, causing neuromuscular functional changes, which result in the advancement of the mandibular position, accelerate mandibular growth, reduce overjet, and improve molar relationships [6]. Previous evidence has described the effectiveness of the Twin-Block appliance in promoting orthodontic and orthopedic changes and correcting Class II malocclusion [7-9]. Twin-Block can cause changes in the morphology, structure, and position of hard tissues such as the mandible, while also altering the morphology of soft tissues attached to the surface of hard tissues. Previous studies have mostly investigated changes in soft tissue or hard tissue separately, which is relatively single and cannot reflect the correlation between soft and hard tissue. Moreover, soft tissues are mostly measured using two-dimensional X-ray cephalometric radiography [10-12]. Due to inaccurate positioning of two-dimensional planes, differences in projection angles, and changes in image magnification, measurement accuracy is limited, especially in the horizontal direction, where a significant amount of data is lost, which is important for facial soft tissue morphology analysis. The systematic review by Flores et al. also suggests that three-dimensional quantification of soft tissue changes is needed to overcome the current limitations in our understanding of the soft tissue changes observed after using Twin-Block appliances in patients with Class II malocclusion [13]. In recent years, three-dimensional measurement methods have gradually been applied to studies evaluating soft tissue changes, allowing for more accurate and detailed morphological analysis. Flores-Mir et al. believe that three-dimensional facial scanning may be the best tool for studying the impact of Twin-Block orthodontics on soft tissues [13]. The changes in soft tissue after Twin-Block orthodontic treatment can be influenced by numerous factors, such as alterations in hard tissues like teeth and bones, as well as occlusal factors, condylar remodeling, muscle tension, and individual growth and development [6,14]. The stability of orthodontic treatment outcomes is crucial. Currently, there is limited research on the stability of Twin-Block treatment efficacy. This study aims to comprehensively analyze the changes in soft and hard tissues of the maxillofacial region in adolescents with mandibular retraction treated with Twin-Block appliances, utilizing a structured light 3D scanner and cephalometric lateral radiographs. Furthermore, through the measurement and overlap of 3D facial models, we explore the changes in soft tissues during the follow-up period after treatment to observe the stability of the Twin-Block appliances. Material And Methods In this study, patients who visited the Department of Orthodontics at the Stomatological Hospital of University from November 2023 to March 2025 were recruited. Only patients who met the following criteria were included in the study. Before treatment, the patients were informed about the role, course of treatment, and precautions associated with Twin-Block orthopedic treatment, and they signed the informed consent after understanding and agreeing to the terms. Inclusion criteria: 1) Angle Class II division 1, both male and female; 2) In the mixed dentition stage or early permanent dentition stage, the cervical spine stage of cephalometric lateral radiograph was before or at the peak of growth (CVMs Ⅱ - CVMs Ⅲ); 3) The molar is distally related, skeletal Class II, MP-FH ≤ 34°, and the profile shows that the mandible is significantly retracted, and the profile was significantly improved after the jaw was extended; 4) Coben analysis[ 15 ] showed mandibular hypoplasia or mandibular relative to maxillary hypoplasia; 5) Good oral hygiene; 6) The BMI of patients before and after treatment was within the normal range. Exclusion criteria: 1) Obvious symptoms of temporomandibular joint disease; 2) Significant facial deviation; 3) History of facial syndrome; 4) Systemic congenital diseases; 5) Previous orthodontic treatment; 6) Poor oral hygiene. All patients used alginate impression material and super anhydrite to create upper and lower dentition models. The mandible was extended forward, and occlusion was recorded using occlusal wax when the upper and lower incisors were in opposition. It is important to note that there should be a 3–4 mm occlusion between the upper and lower incisors at this time [ 16 – 18 ]. The Twin-Block appliance was made by using dentition model and matching wax bite record. All patients used the Twin-Block appliance shown in Fig. 1 for orthopedic treatment. A labial arch is incorporated in the anterior region of the appliance to facilitate the retraction of proclined anterior teeth in patients. Prior to treatment, the labial arch is adjusted away from the teeth to relieve restrictions on arch expansion. They were instructed to wear the appliance every day, except when it needed to be removed and cleaned while brushing their teeth. Patients should wear it all day, for at least 22 hours each day. During the wearing process, they should avoid strenuous exercise to prevent accidental injury. In the initial stage of wearing the appliance, patients underwent simultaneous arch expansion. The method of arch expansion involved widening the spiral arch expander by 0.25 mm horizontally every day for 2 weeks. A follow-up appointment was scheduled two weeks after the appliance was placed to adjust the retention mechanism and labial arch of the appliance, with the efficacy of rapid maxillary expansion evaluated concurrently. The height and weight of patients were routinely recorded before each data collection session. Cephalometric lateral films were taken before treatment and at the end of treatment, and the data were imported into Dolphin Imaging cephalometric software for measurement. The marked points on the cephalometric lateral radiographs are shown in Fig. 2 . The cephalometric items are listed in Table I. The Artec Space Spider 3D scanner (Artec 3D, Luxembourg) was used before Twin-Block treatment (T0), at the end of treatment (T1), 3 months after the end, and 6 months after the end of treatment. During facial scanning, patients were required to remove all glasses, facial/auricular accessories, as well as any obstructive items including collars and scarves; intraoral orthodontic appliances, if worn, must be detached prior to the scanning procedure. For data acquisition, patients were positioned in a strict upright sitting posture with their heads held in a neutral, erect alignment, gazing horizontally at a white wall in front without any external visual or auditory distractions. The operator then provided standardized verbal guidance to ensure that the patients’ median sagittal plane was perpendicular to the ground, their tongues were maintained in a resting position, their mandibles were fully relaxed, their maxillary and mandibular teeth were naturally spaced apart, and their upper and lower lips were in a gentle, natural closure [ 18 ]. After maintaining this stable, relaxed posture for 20 seconds, three-dimensional facial data acquisition was initiated. Throughout the entire scanning process, patients were instructed to maintain calm, regular breathing while refraining from any chewing or swallowing movements. To mitigate potential discomfort caused by the blue light and flash emitted by the scanner, patients were asked to close their eyes naturally with a relaxed facial expression following head position adjustment, after which the formal three-dimensional facial data collection was performed. The data were saved in STL format (Stereolithography format). The selected data are shown in Table II and Fig. 3. The soft tissue measurement index from the facial scanning is displayed in Table III. The digital model data in STL format were imported into Geomagic Control X 2018 software for fixed-point measurement and data collection. The model in STL format was then exported to Geomagic Wrap 2021 (3D Systems, USA), where a Cartesian coordinate system (X, Y, Z) was established. The coordinate axes were defined that the front, left, and upper directions of the subject were considered positive, while the rear, right, and lower directions were considered negative. Referring to the 3D facial data of the T0 point, the 3D facial data of the T1 point was overlapped to observe the changes before and after orthodontic treatment. T1 data were used as a reference, and T2 and T3 three-dimensional facial data were overlaid with them to observe the changes in soft tissues during the follow-up period. The three-dimensional directional changes of the corresponding facial landmarks were measured using the "Create Annotation" command. Taking the superimposition of the T0 and T1 models as an example, the specific superimposition steps are detailed as follows: The T0 and T1 models were imported into Geomagic Wrap 2021 software separately. First, the T0 model was reoriented. Subsequently, a Cartesian coordinate system (X, Y, Z axes) was established: the soft tissue Frankfort horizontal plane was defined as the X-axis (anterior direction as positive); the Y-axis was set parallel to the line connecting the bilateral medial canthi (left direction as positive); the plane formed by the X-axis and Y-axis was parallel to the ground; and the Z-axis was perpendicular to the ground (superior direction as positive). The "Pin" command was executed on the T0 model to fix its position. Thereafter, the "Align - Manual Registration" command was applied to both the T0 and T1 models. Upon completion of the above operations, the superimposition of the T0 and T1 models was accomplished. S: Sella、N: Nasion、P: Porion、Or: Orbitale、Ptm: Pterygomaxillary fissure、Ba: Basion、A: Subspinale、B: Supramental、ANS: Anterior nasal spine UL: Upper lip、LL༚Lower lip、Prn༚Pronasale、Pog༚Pogonion、Me༚Menton、Co༚Condylion 、Go༚Gonion、Ar༚Articulare、UI: Upper incisor、 LI: Lower incisor Pog'༚Pogonion of soft tissue Statistical methods In this study, G*Power 3.1 software was used to calculate the sample size by paired-sample t-test and the n-sn-pog angle (convexity angle) as the reference index. On the basis of previous studies [ 16 ], the α (test level) was set at 0.05 and the 1-β (test efficiency) was set at 80%. Therefore, the minimum sample size is 16. In this study, the cephalometric data and the 3D model data of the face were measured three times by the person. After the first measurement, repeated measurements were performed 15 days and 30 days later, and the average value was taken for statistical analysis. The data were imported into SPSS 25.0 software for statistical analysis, the data were normally tested, the paired t-test was used for the data conforming to the normal distribution, and the Wilcoxon test was used for statistical analysis for the data that did not conform to the normal distribution. Statistical significance was defined as P < 0.05 and highly significant as P < 0.01. Descriptive statistics were applied to analyze the displacement of three-dimensional facial landmarks, with a 95% confidence interval preset for accuracy, and interval estimation was performed on the mean displacement values. Results A total of 56 patients who met the criteria were included in this study. All patients cooperated well throughout the process. Cephalometric analysis and three-dimensional facial scanning were performed at the beginning of treatment (T0) and at the end (T1). The average age of patients before treatment was 9.60 ± 1.16 years. The average duration of treatment was 311.04 ± 90.72 days. In this study, a total of 28 patients were collected for facial scan data at the end of treatment (T1) and 3 months after orthodontic treatment (T2). Facial scan data were collected at the end of treatment (T1) and at 6 months after treatment (T2) in 17 patients. For the above data that conform to the normal distribution, the mean and standard deviation are expressed, and the data that do not conform to the normal distribution are expressed by the media and quartile. In the analysis of all facial scan models and lateral radiographs, 20 cases were randomly selected. A single measurer conducted measurements every two weeks, with each model assessed three times. Test-retest reliability was analyzed using the intraclass correlation coefficient (ICC). The results indicated that the ICC for all measurement items was greater than 0.80, demonstrating high test-retest reliability and confirming the reliability of the model measurement results. The Cronbach's alpha reliability coefficients for the measured items are presented in Table IV. The research results obtained from the measurement and analysis of 56 patients’ lateral radiographs before and after treatment included in this study are shown in Table V, Table VI. The statistical analysis indicated that SNA showed no significant differences ( p > 0.05), suggesting that Twin-Block orthopedic treatment had no notable effect on the maxilla. Post-treatment, the SNB angle increased significantly ( p < 0.01), while the ANB decreased markedly ( p < 0.01). Additionally, the mandibular ramus length (Ar-Go) and mandibular body length (Go-Pog) both increased significantly ( p < 0.01). Coben analysis revealed that mandibular length (MaL) and MaL% also increased significantly, indicating that Twin-Block orthopedic treatment may promote sagittal growth of the mandible. Although FMA increased by the end of treatment ( p > 0.05), there was no significant difference in the amount of change. ANS-Me、N-Me and ANS-Me/N-Me increased significantly ( p < 0.01). The U1-SN angle decreased significantly ( p < 0.01) by an average of 3.9°, reflecting a recovery of the upper anterior teeth. IMPA increased by 2.08° ( p < 0.01), and Overjet decreased significantly by approximately 3.18 mm. The upper lip convexity (UL-E) decreased after correction ( p 0.05). Table VII presents the research results regarding three-dimensional facial dimension changes at the conclusion of Twin-Block correction, derived from the measurement and analysis of 56 patients’ facial three-dimensional scanning models included in this study. The statistical analysis revealed significant differences in several measurements: Ral-Lal、sn-stom、stom-B’、gor-gol、ls-n- pg’、n-me’、sn- me’、li-B’-pg’、ls-n-li ( p < 0.01). Post-treatment, there was an increase in nasal width, with the alae nasi widening by 0.43 mm ( p < 0.01) and the base of the nose expanding by 0.24 mm ( p < 0.01). Both the upper and lower lip lengths increased significantly ( p < 0.01), with the upper lip lengthening by approximately 0.50 mm and the lower lip by about 0.93 mm. In terms of face size, the total height of the face and the height of the lower part of the face increased, similar to the changes of hard tissue. The width of zygoma and the width between mandibular angles increased. In terms of angle measurements, the nasolabial angle and the chin convex angle of the lower lip showed no significant changes, but the mentolabial angle increased significantly ( p < 0.01), with an increase of 9.89°. Additionally, the angle between the upper and lower lips decreased ( p < 0.01), as did the upper lip chin convex angle ( p < 0.01), decreasing by 0.91° and 0.80°, respectively. The face shape angle also increased ( p < 0.05). These angular changes indicate an improved relationship among the nose, lip, and chin, a reduction in facial convexity, and a more coordinated profile. The three-dimensional soft tissue changes between the end of treatment and the 3-month follow-up are presented in Tables IX and X. The statistical results indicated that there was no statistical difference between the soft tissue measurement items at 3 months of follow-up and the end of orthodontic treatment. After 6 months of follow-up after orthodontic treatment, the three-dimensional soft tissue changes of patients were shown in Table XI and Table XII. The statistical results showed that there were significant differences in ls-n- pg and li-n- pg (P < 0.01), and the upper lip and lower lip chin convex angles were smaller. There were statistically significant differences in Ral-Lal, Rulp-Lulp, Rnb-Lnb, and li-B-pg’, The nasal width increased and the mentolabial angle became smaller (p < 0.05). The face model at 3 months after Twin-Block treatment and the face model at 6 months after orthodontic treatment overlapped with the model at the end of orthodontic treatment, respectively, and the results are shown in Table XIII and Table XIV. The displacement of each landmark point was small at 3 months after Twin-Block orthodontic treatment. The soft tissue points B', Pg', and Me moved forward and downward 6 months after Twin-Block orthodontic treatment. Discussion This study employed cephalometric and three-dimensional facial scanning technologies to comprehensively investigate the changes in facial soft and hard tissues before and after Twin-Block treatment, providing a holistic assessment of the facial alterations induced by this treatment. In this study, lateral cephalometric analysis revealed that the SNA angle showed no significant change after Twin-Block orthopedic treatment. This aligns with the results of Ajami, Khoja, and Jaiswal et al., indicating that the appliance has no notable inhibitory effect on maxillary growth [ 7 , 19 , 20 ]. However, there are discrepancies among different studies. For example, Illing, Khan, and others reported a slight reduction in the mean SNA angle [ 21 , 22 ]. In Bastiani's study, the SNA angle decreased by 0.64°, suggesting a mild restriction of maxillary growth due to the appliance, while Baysal and others argued that Twin-Block treatment does not have this promoting effect [ 23 , 24 ]. Jamilian et al. proposed that Twin-Block appliance activates the retractor muscles, influencing the positioning of maxillary and promoting changes in its growth [ 25 ]. These differences may stem from variations in the ethnicity and growth stages of the research samples, as well as differences in measurement methods and research designs. Meanwhile, in this study, the SNB angle increased significantly, with this investigation showing an increase of 1.05°, and the ANB angle decreased remarkably. This indicates that the Twin-Block appliance is highly effective in advancing the mandible and improving the sagittal relationship between the maxilla and mandible, which is consistent with most previous research findings [ 7 , 10 , 20 , 22 ]. Baysal et al. observed a decrease in the ANB angle by 2.85 degrees, and prior research indicated a similar reduction of approximately 2.0-2.3 degrees compared to the control group [ 21 , 26 ]. Ajami et al. found an average decrease in the ANB angle of 1.76°, which closely resembles the 1.73° reduction observed in this study [ 19 ]. These results indicate that Twin-Block has a notable effect in advancing the mandible and improving the sagittal relationship between the maxilla and mandible. Many scholars have found that the length of the mandible increases significantly after Twin-Block treatment [ 3 , 22 , 27 ]. Our study also observed an increase in the lengths of the mandibular ramus and mandibular body. The increase in mandibular length varies among different studies. For instance, in Kirtane's research, Ar-Go increased by 2.38 mm compared with the control group, while in our study, the mandibular body increased by approximately 2.58 mm, which is not much different from the research by Toth and McNamara [ 27 , 28 ]. Such differences might be attributed to the ethnic diversity and distinct growth and development conditions of the patients [ 7 , 20 ]. In addition, Coben's analysis showed that the length and depth of the mandible increased, indicating that Twin-Block orthopedic treatment can promote mandibular growth. Both the lower facial height and total facial height increased in our study, yet there are differences in the magnitude of increase among various studies [ 18 , 21 – 23 , 27 – 29 ]. In our study, the increase was 2.49 mm, and the total face height increased by 4.51 mm. This could be related to the "posterior bite - block effect" of the Twin-Block appliance, which has different impacts on vertical development inhibition and molar eruption promotion in different individuals [ 27 ]. In contrast, this study observed no significant change in FMA, and no additional clockwise rotation of the mandible was detected in the Twin-Block group. This may be attributed to Twin-Block promoting mandibular remodeling through upward and forward growth of the condyle, with less impact on the mandibular angle [ 30 , 31 ]. Apart from the changes in the maxilla and mandible, Twin-Block also affects the teeth. In this study, the U1-SN angle decreased by an average of 3.9°, which may be related to the lip arch of the maxillary appliance, consistent with the conclusion in other studies that the inclination of the upper teeth decreases [ 12 , 20 – 22 ]. O'Brien et al. demonstrated that maxillary incisor retraction significantly contributed to the reduction in overjet [ 32 ]. In our study, the overjet was also reduced, suggesting that maxillary incisor retraction played a role in this outcome. At the same time, the IMPA increased by 2.08°, which may be attributed to the acrylic capping of the lower incisors with the Twin-Block appliance [ 27 ]. However, different studies have reported varying effects on the mandibular incisors. Some studies found no significant change in the inclination of the mandibular incisors, while in Khoja's research, the inclination of the mandibular incisors increased significantly [ 10 , 20 , 21 , 27 , 28 , 33 ]. These differences may be due to the forward force generated by mandibular prognathism, as well as variations in appliance design and individual patient characteristics. Excessive lower incisor lip inclination may weaken the skeletal effects of the appliances, suggesting that control of lower incisors should be emphasized when applying Twin-Block appliances [ 3 ]. These compensations may need correction in the second stage of orthodontic treatment, potentially involving the extraction of premolars to achieve upright lower incisors and enhance stability [ 34 ]. The changes in hard tissues form the structural basis for the morphology of maxillofacial soft tissues. In this study, with the reconstruction of the jaw relationship, the retraction of the upper incisors led to the backward movement of the upper lip, resulting in a decrease in upper lip convexity (UL-E). Most scholars agree that this reduction aligns with our findings [ 8 , 10 , 11 , 19 , 23 , 27 , 28 , 35 ]. Regarding the lower lip convexity, there are controversial conclusions in different studies. Our study results are consistent with some studies, showing no significant change in the lower lip convexity after treatment, which may be related to the maintained inclination of the mandibular incisors after treatment [ 8 , 10 , 11 , 28 ]. Ajami noted a decrease in lower lip convexity of about 1.37 mm, while other studies reported an increase, with Jaiswal, Bastiani, and Morris observing more than 1 mm of protrusion [ 7 , 9 , 19 , 23 , 35 ]. This prominence may reflect the adaptability of soft tissue to changes in hard tissue following orthodontic treatment. When exploring the impact of the Twin-Block appliance on soft tissue morphology, the differences in patient compliance and individual variations during appliance wear are important factors that cannot be ignored. Patient compliance directly affects the treatment outcome of the appliance. In this study, the changes in three-dimensional facial morphology were categorized into nasal morphology, lip morphology, chin morphology, and the relationship between the nose-lip and chin-lip. Previous studies have explored these aspects in detail. The horizontal changes in facial soft tissue are rarely reported. After treatment, patients showed an average increase of 0.43 mm in alae nasi width and 0.24 mm in nasal base width. The increase in nasal base width was about 87.73% of that in alare width, smaller than Badreddine’s CBCT findings (1.0 mm increase in alare width with Hyrax expander) [ 36 ]. This discrepancy may result from different soft tissue responses to various arch expansion devices and methods. In our study, we combined Twin-Block with a maxillary detachable expander instead of an adhesive Hyrax expander, which may have led to smaller soft tissue changes. The lengths of the upper and lower lips changed significantly during Twin-Block correction, with the upper lip length increasing by 0.50 mm and the lower lip length by 0.93 mm. et al. also reported increases in both lip lengths after Twin-Block treatment, with a greater increase in the lower lip, consistent with Lee’s findings [ 18 , 29 ]. Güler et al. found no significant change in upper lip length, although the lower lip length increased significantly [ 16 ]. While studies agree on the increase in lower lip length, the significance of upper lip length changes remains controversial. In our study, mechanistically, Twin-Block’s continuous mandibular forward-downward force increases intermaxillary distance via lower incisors sliding along upper incisors, reducing lip extrusion and elongating both lips. Additionally, soft tissue B point forward movement stretches the lower lip from a "curled" to "extended" position, augmenting its length. In terms of the nasolabial relationship, previous studies and our findings show a trend of backward displacement at the convex point of the upper lip [ 8 , 37 ]. However, nasolabial angle remained unchanged at all treatment time points, as corroborated by Güler’s 3D analysis [ 16 ] and McDonagh’s observation [ 38 , 39 ]. Additionally, some studies suggest that the impedance center of the craniomaxillary complex is positioned behind the dental arch. As a result, the bony effects produced by arch expansion exhibit a cone-like effect in both sagittal and vertical directions meaning that expansion diminishes from front to back and from bottom to top. When the hard palate expands laterally, this may simultaneously decrease the height of the palatal cover and the nasal base [ 40 – 42 ]. Consequently, the vertical movements of the columella and subnasale, together with the displacement of the upper lip's convex point, contribute to maintaining a relatively unchanged nasolabial angle. The lip-chin relationship is a key part of the aesthetic and functional evaluation of facial profile analysis. This study highlights the lip-chin relationship’s role in facial aesthetics by analyzing three angles: the upper lip-chin convex angle, lower lip-chin convex angle, and mentolabial angle. Post-treatment, the upper lip-chin convex angle decreased, reflecting greater forward chin movement than upper lip retraction, enhancing chin prominence. The lower lip-chin convex angle showed no significant change, likely due to opposing effects of chin advancement and compensatory mandibular anterior tooth proclination. Notably, the mentolabial angle increased by 9.89°, attributed to overjet reduction and alleviation of upper incisor pressure on the lower lip. In Angle II Division 1 cases, mandibular retraction typically forces the lower lip into a "rolled-back" position, deepening the mentolabial sulcus and sharpening the angle, which compromises aesthetics. Orthodontic correction stretches the lower lip, softening the mentolabial transition and improving profiles—a finding consistent with Baysal et al.’s work on soft-tissue adaptations [ 10 , 29 ]. These changes underscore the interplay between skeletal repositioning, dental compensation, and soft tissue remodeling in optimizing facial harmony. This study evaluated 3D soft tissue changes post-treatment, revealing distinct displacement patterns: the upper lip convex point retruded downward, while the lower lip convex point, soft tissue B point, and pogonion advanced downward, with mandibular landmarks exhibiting greater movement than maxillary counterparts. The most pronounced forward displacement occurred at soft tissue B point (> pogonion > lower lip convex point), consistent with cephalometric studies by Salloum & McDonagh [ 17 , 38 ]. Yıldırım's findings indicated an average backward movement of the upper lip convex point (0.44 mm), though this change was not statistically significant ( p = 0.084). In contrast, the pogonion of soft tissue showed a significant forward displacement (2.14 mm, p < 0.01), corroborating this study's findings. The smaller anterior displacement of the menton may be attributed to individual patient variations and the chosen coordinate system [ 37 ]. Menton displacement was minimal, potentially due to anatomical variability or coordinate system selection. Its downward shift correlated with increased total and lower facial height [ 29 , 38 ]. However, an increased lower facial height could exacerbate vertical bone patterns in patients with a high mandibular plane angle (FMA), prompting their exclusion from this study's design phase. For low/average FMA cases, increased anterior height enhances aesthetics [ 18 ]. Overall, Twin-Block correction improved soft tissue morphology in these patients, supporting Sattarzadeh et al.’s vertical skeletal-soft tissue linkage theory [ 43 ]. Moreover, the growth and remodeling of soft tissues are also regulated at the cellular and molecular levels. Growth factors and cytokines are involved in the process of soft - tissue adaptation to the forces exerted by the appliance. For instance, certain growth factors may promote the proliferation and differentiation of fibroblasts in the soft tissues, leading to changes in the extracellular matrix and ultimately resulting in soft - tissue remodeling. However, the specific regulatory mechanisms and interactions among these factors in the context of Twin Block treatment remain to be further explored. There are still deficiencies in this study: This study lacked a parallel control group. Patients with skeletal Class II mandibular hypoplasia without intervention during growth may risk needing orthognathic surgery later and could face increased airway stenosis and obstructive sleep apnea [ 44 , 45 ]. Establishing a control group solely to assess the appliance's therapeutic effect conflicts with medical ethics and prioritizing patient interests. Using a general population with normal jaw development as a control is debatable due to differing growth trends between the groups. Due to medical ethics, similar studies often do not include a control group, instead referencing previous research [ 10 , 43 ]. Kamínková and colleagues conducted regression analysis on the three-dimensional shape of facial soft tissue in 113 children aged 6–13, finding that changes in facial soft tissue shape were stable and unrelated to changes in height, weight, or age [ 46 ]. Morris et al. established a control group in a 9-month study, showing no significant changes in facial soft tissue morphology in the control group, providing a useful reference for this study [ 9 ]. In addition, the average treatment duration was only 296 days. Although this reduces the influence of confounding factors such as growth and development to a certain extent, it may still be insufficient to observe the long - term effects of the treatment. Future research could consider extending the follow - up period to further observe the changes in soft and hard tissues. Meanwhile, efforts should be made to better control research variables under ethical circumstances to improve the accuracy and reliability of research results. Additionally, ensuring patients' BMI was within the normal range for children reduced the impact of weight changes on the results [ 47 ]. Patients should be followed up after treatment to assess the long-term stability of facial changes. Sharma et al. found that the soft tissue pogonion retracted by about 1.0 mm within 3 months post-treatment, representing 25%-33% of the anterior displacement [ 35 ]. Lee reported a 1.0 mm relapse in overjet within 3 months after a 9-month treatment period [ 29 ]. Given the differences among ethnic groups and individuals, longer-term follow-up is necessary, and this research group plans to conduct further studies in the future. In conclusion, Twin-Block orthopedic treatment has a significant impact on the soft and hard tissues of patients with Class II malocclusion. In clinical applications, it is necessary to fully consider patient compliance and individual differences to improve the treatment effect. Conclusion Based on this study’s findings, the following can be concluded: Twin-Block functional orthodontic treatment can alter the maxillomandibular relationship in children with Class II malocclusion, reduce overjet, and improve skeletal discrepancies. Twin-Block orthodontic treatment induces three-dimensional changes in the soft tissue of the nose, upper lip, lower lip, and chin, positively improving deformities in the lower lip and chin, thereby enhancing facial aesthetics. No significant differences were noted in the morphological changes of facial soft tissues at 3 months following Twin-Block treatment relative to those at treatment completion, demonstrating a relatively stable short-term therapeutic outcome. At 6 months post-treatment, the soft tissue facial profile of patients exhibited further improvements, and such alterations are likely attributable to skeletal growth and development. Abbreviations CVMs Cervical Vertebrae Maturation Staging BMI Body Mass Index CBCT Cone-Beam Computed Tomography Declarations Authors’ contributions Yue Sun contributed to conceptualization, formal analysis, manuscript review and editing, and original draft preparation; Ying Zhang contributed to conceptualization, visualization, manuscript review and editing, and original draft preparation; Chengjing Xu contributed to manuscript review and editing; Yuting He contributed to manuscript review and editing and visualization; Min Hu contributed to resources, manuscript review and editing, and supervision. Huan Jiang contributed to original draft preparation, manuscript review and editing, and supervision. Funding The authors received no specific funding for this work. Data Availability All relevant data are within the manuscript. The data in this article is available. Ethics approval and consent to participate This study was approved by the medical ethics committee of Jilin University Stomatological Hospital on October 25, 2023, with the approval number JDKQ2023(48). In this study, informed consent to participate was obtained from the parents or legal guardians of any participant under the age of 16. Consent for publication Not applicable. Competing interests The authors declare no competing interests. References McNamara JA Jr. Components of class II malocclusion in children 8-10 years of age. Angle Orthod. 1981;51(3):177-202. doi:10.1043/0003-3219(1981)0512.0.CO;2. Campbell C, Millett D, Kelly N, Cooke M, Cronin M. Frankel 2 appliance versus the Modified Twin Block appliance for Phase 1 treatment of Class II division 1 malocclusion in children and adolescents: A randomized clinical trial. Angle Orthod. 2020;90(2):202-208. doi:10.2319/042419-290.1. Mills CM, McCulloch KJ. Treatment effects of the twin block appliance: a cephalometric study. Am J Orthod Dentofacial Orthop. 1998;114(1):15-24. doi:10.1016/s0889-5406(98)70232-x. O'Brien K. Is early treatment for Class II malocclusion effective? Results from a randomized controlled trial. Am J Orthod Dentofacial Orthop. 2006;129(4 Suppl):S64-S65. doi:10.1016/j.ajodo.2005.09.016. Clark WJ. The twin block technique. A functional orthopedic appliance system. Am J Orthod Dentofacial Orthop. 1988;93(1):1-18. doi:10.1016/0889-5406(88)90188-6. Shen G, Condylar adaptation triggered by SGTwin-Block orthopedic therapy-Biological mechanism and clinical significance[J].Shanghai J of Stoma,2018, 27(3): 225-229. DOI:10.19439/j.sjos.2018.03.001. Jaiswal K, Saha S, Dhinsa K, Kapoor S, Singh G, Jaiswal RK. Evaluation of Hard Tissue, Soft Tissue and Airway Changes Post Twin Block Therapy: An In-vitro Study. Journal of Clinical and Diagnostic Research. 2023 Mar, Vol-17(3): ZC06-ZC11.DOI: 10.7860/JCDR/2023/59327.17554. Quintão C, Helena I, Brunharo VP, Menezes RC, Almeida MA. Soft tissue facial profile changes following functional appliance therapy. Eur J Orthod. 2006;28(1):35-41. doi:10.1093/ejo/cji067. Morris DO, Illing HM, Lee RT. A prospective evaluation of Bass, Bionator and Twin Block appliances. Part II--The soft tissues. Eur J Orthod. 1998;20(6):663-684. doi:10.1093/ejo/20.6.663. Baysal A, Uysal T. Soft tissue effects of Twin Block and Herbst appliances in patients with Class II division 1 mandibular retrognathy. Eur J Orthod. 2013;35(1):71-81. doi:10.1093/ejo/cjq187. Varlik SK, Gültan A, Tümer N. Comparison of the effects of Twin Block and activator treatment on the soft tissue profile. Eur J Orthod. 2008;30(2):128-134. doi:10.1093/ejo/cjm121. Schaefer AT, McNamara JA Jr, Franchi L, Baccetti T. A cephalometric comparison of treatment with the Twin-block and stainless steel crown Herbst appliances followed by fixed appliance therapy. Am J Orthod Dentofacial Orthop. 2004;126(1):7-15. doi:10.1016/j.ajodo.2003.06.017. Flores-Mir C, Major PW. Cephalometric facial soft tissue changes with the twin block appliance in Class II division 1 malocclusion patients. A systematic review. Angle Orthod. 2006;76(5):876-881. doi:10.1043/0003-3219(2006)076[0876:CFSTCW]2.0.CO;2. Moro A, Mattos CFP, Borges SW. Stability of Class II corrections with removable and fixed functional appliances: a literature review[J]. J World Fed Orthod. 2020, 9(2): 56-67. DOI: 10.1016/j.ejwf.2020.04.003. COBEN S E. The intergration of facial skeletal variation. A serial cephalometric roentgenographic analysis of craniofacial form and growth. Am J orthod, 1955, 41: 407.doi:10.1016/0002-9416(55)90153-6. Güler ÖÇ, Malkoç S. Comparison of facial soft tissue changes after treatment with 3 different functional appliances. Am J Orthod Dentofacial Orthop. 2020;158(4):518-526. doi:10.1016/j.ajodo.2019.06.020. Salloum E, Millett DT, Kelly N, McIntyre GT, Cronin MS. Soft tissue changes: a comparison between changes caused by the construction bite and by successful treatment with a modified Twin-block appliance. Eur J Orthod. 2018;40(5):512-518. doi:10.1093/ejo/cjx098. Lee RT, Barnes E, DiBiase A, Govender R, Qureshi U. An extended period of functional appliance therapy: a controlled clinical trial comparing the Twin Block and Dynamax appliances. Eur J Orthod. 2014;36(5):512-521. doi:10.1093/ejo/cjs076. Ajami S, Morovvat A, Khademi B, Jafarpour D, Babanouri N. Dentoskeletal effects of class II malocclusion treatment with the modified Twin Block appliance. J Clin Exp Dent. 2019;11(12):e1093-e1098. Published 2019 Dec 1. doi:10.4317/jced.56241. Khoja A, Fida M, Shaikh A. Cephalometric evaluation of the effects of the Twin Block appliance in subjects with Class II, Division 1 malocclusion amongst different cervical vertebral maturation stages. Dental Press J Orthod. 2016;21(3):73-84. doi:10.1590/2177-6709.21.3.073-084.oar. Illing HM, Morris DO, Lee RT. A prospective evaluation of Bass, Bionator and Twin Block appliances. Part I--The hard tissues. Eur J Orthod. 1998;20(5):501-516. doi:10.1093/ejo/20.5.501. Khan MI, Neela PK, Unnisa N, Jaiswal AK, Ahmed N, Purkayastha A. Dentoskeletal effects of Twin Block appliance in patients with Class II malocclusion. Med Pharm Rep. 2022;95(2):191-196. doi:10.15386/mpr-1989. Bastiani C, Bellini-Pereira SA, Aliaga-Del Castillo A, Chiqueto K, Castanha Henriques JF, Janson G. Twin-block and mandibular anterior repositioning appliances effects in Class II malocclusion correction. Am J Orthod Dentofacial Orthop. 2023;163(2):181-190. doi:10.1016/j.ajodo.2021.09.021. Baysal A, Uysal T. Dentoskeletal effects of Twin Block and Herbst appliances in patients with Class II division 1 mandibular retrognathy. Eur J Orthod. 2014;36(2):164-172. doi:10.1093/ejo/cjt013. Jamilian A, Showkatbakhsh R, Amiri SS. Treatment effects of the R-appliance and twin block in Class II division 1 malocclusion. Eur J Orthod. 2011;33(4):354-358. doi:10.1093/ejo/cjq082. Gazzani F, Franchi L, Lione R, Cozza P, Pavoni C. Soft tissue evaluation of functional therapy in growing patients with Class II malocclusion: a long-term study. Eur J Orthod. 2022;44(1):37-42. doi:10.1093/ejo/cjab008. Toth LR, McNamara JA Jr. Treatment effects produced by the twin-block appliance and the FR-2 appliance of Fränkel compared with an untreated Class II sample. Am J Orthod Dentofacial Orthop. 1999;116(6):597-609. doi:10.1016/s0889-5406(99)70193-9. Kirtane RS, Wiltshire WA, Thiruvenkatachari B, Shah A, Bittencourt Dutra Dos Santos P, Henrique de Sa Leitao Pinheiro F. Cephalometric effects of Twin-block and van Beek Headgear-Activator in the correction of Class II malocclusion. Am J Orthod Dentofacial Orthop. 2023;163(5):677-689. doi:10.1016/j.ajodo.2022.05.020. Lee RT, Kyi CS, Mack GJ. A controlled clinical trial of the effects of the Twin Block and Dynamax appliances on the hard and soft tissues. Eur J Orthod. 2007;29(3):272-282. doi:10.1093/ejo/cjm004. Jiang YY, Sun L, Wang H, Zhao CY, Zhang WB. Three-dimensional cone beam computed tomography analysis of temporomandibular joint response to the Twin-block functional appliance. Korean J Orthod. 2020;50(2):86-97. doi:10.4041/kjod.2020.50.2.86. Ivorra-Carbonell L, Montiel-Company JM, Almerich-Silla JM, Paredes-Gallardo V, Bellot-Arcís C. Impact of functional mandibular advancement appliances on the temporomandibular joint - a systematic review. Med Oral Patol Oral Cir Bucal. 2016;21(5):e565-e572. Published 2016 Sep 1. doi:10.4317/medoral.21180. O'Brien K, Wright J, Conboy F, et al. Effectiveness of early orthodontic treatment with the Twin-block appliance: a multicenter, randomized, controlled trial. Part 1: Dental and skeletal effects. Am J Orthod Dentofacial Orthop. 2003;124(3):234-339. doi:10.1016/S0889540603003524. van der Plas MC, Janssen KI, Pandis N, Livas C. Twin Block appliance with acrylic capping does not have a significant inhibitory effect on lower incisor proclination. Angle Orthod. 2017;87(4):513-518. doi:10.2319/102916-779.1. Tulloch JF, Phillips C, Proffit WR. Benefit of early Class II treatment: progress report of a two-phase randomized clinical trial. Am J Orthod Dentofacial Orthop. 1998;113(1):62-74. doi:10.1016/S0889-5406(98)70277-X. Sharma AA, Lee RT. Prospective clinical trial comparing the effects of conventional Twin-block and mini-block appliances: Part 2. Soft tissue changes. Am J Orthod Dentofacial Orthop. 2005;127(4):473-482. doi:10.1016/j.ajodo.2004.03.027. Badreddine FR, Fujita RR, Alves FEMM, Cappellette M Jr. Rapid maxillary expansion in mouth breathers: a short-term skeletal and soft-tissue effect on the nose. Braz J Otorhinolaryngol. 2018;84(2):196-205. doi:10.1016/j.bjorl.2017.01.009. Yıldırım E, Karaçay Ş, Tekin D. Three-Dimensional Evaluation of Soft Tissue Changes after Functional Therapy. Scanning. 2021;2021:9928101. Published 2021 Apr 24. doi:10.1155/2021/9928101. McDonagh S, Moss JP, Goodwin P, Lee RT. A prospective optical surface scanning and cephalometric assessment of the effect of functional appliances on the soft tissues. Eur J Orthod. 2001;23(2):115-126. doi:10.1093/ejo/23.2.115. Har Zion G, Katzhendler E, Bader Farraj A, et al. Evaluating the Effects of Carriere Motion Appliance and Twin Block Appliances in Class II Correction-A Retrospective Study. Dent J (Basel). 2024;12(5):119. Ong SC, Khambay BS, McDonald JP, Cross DL, Brocklebank LM, Ju X. The novel use of three-dimensional surface models to quantify and visualise the immediate changes of the mid-facial skeleton following rapid maxillary expansion. Surgeon. 2015;13(3):132-138. doi: 10.1016/j.surge.2013.10.012. Cantarella D, Dominguez-Mompell R, Moschik C, et al. Zygomaticomaxillary modifications in the horizontal plane induced by micro-implant-supported skeletal expander, analyzed with CBCT images. Prog Orthod. 2018;19(1):41. Published 2018 Oct 22. doi:10.1186/s40510-018-0240-2. Ok U, Kayalar E, Sadry S. Three-dimensional zygomatic changes after rapid maxillary expansion in growing patients. Dreidimensionale Jochbeinveränderungen nach schneller Gaumennahterweiterung bei heranwachsenden Patienten. J Orofac Orthop. 2023;84(3):147-156. doi:10.1007/s00056-021-00348-5. Sattarzadeh AP, Lee RT. Assessed facial normality after Twin Block therapy. Eur J Orthod. 2010;32(4):363-370. doi:10.1093/ejo/cjp141. Battagel JM, L'Estrange PR. The cephalometric morphology of patients with obstructive sleep apnoea (OSA). Eur J Orthod. 1996;18(6):557-569. doi:10.1093/ejo/18.6.557. Lowe AA, Ono T, Ferguson KA, Pae EK, Ryan CF, Fleetham JA. Cephalometric comparisons of craniofacial and upper airway structure by skeletal subtype and gender in patients with obstructive sleep apnea. Am J Orthod Dentofacial Orthop. 1996;110(6):653-664. doi:10.1016/s0889-5406(96)80043-6. Kamínková P, Dírer P, Fudalej P. Association of 3-dimensional facial changes and height and weight increase in children: A 2-year follow-up. Am J Orthod Dentofacial Orthop. 2022;161(3):e199-e214. doi:10.1016/j.ajodo.2021.01.025. Hongyun,Fang Liyun,Zhao Qiya,Guo et al. Trends in height, weight, and BMI of children and adolescents aged 6-17 in China. Food and Nutrition in China.2021,27(04):16-20. doi:10.19870/j.cnki.11-3716/ts.20210413.001. Tables Tables I to XIV are available in the supplementary files section Additional Declarations No competing interests reported. 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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-8692897","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":585885573,"identity":"379aeb55-bbc4-4b2a-87d3-e26e1401d702","order_by":0,"name":"Yue Sun","email":"","orcid":"","institution":"School and Hospital of Stomatology, Jilin University, Changchun","correspondingAuthor":false,"prefix":"","firstName":"Yue","middleName":"","lastName":"Sun","suffix":""},{"id":585885574,"identity":"889c79a2-8635-4ad6-aa9a-d1d83e4834d9","order_by":1,"name":"Ying Zhang","email":"","orcid":"","institution":"School and Hospital of Stomatology, Jilin 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14:08:14","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8692897/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8692897/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":102297214,"identity":"0d3c8a81-4d6a-4f1b-8fec-532a317da90f","added_by":"auto","created_at":"2026-02-10 10:26:31","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":223427,"visible":true,"origin":"","legend":"\u003cp\u003eTwin-Block appliance\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-8692897/v1/28fba48d240ea29f13c31392.png"},{"id":102209995,"identity":"5888eff7-870d-4c4d-995b-7d281ebc6c59","added_by":"auto","created_at":"2026-02-09 12:15:38","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":64660,"visible":true,"origin":"","legend":"\u003cp\u003eMarking points on lateral cephalogram radiographs\u003c/p\u003e\n\u003cp\u003eS: Sella、N: Nasion、P: Porion、Or: Orbitale、Ptm: Pterygomaxillary fissure、Ba: Basion、A: Subspinale、B: Supramental、ANS: Anterior nasal spine UL：Upper lip、LL：Lower lip、Prn：Pronasale、Pog：Pogonion、Me：Menton、Co：Condylion 、Go：Gonion、Ar：Articulare、UI: Upper incisor、 LI: Lower incisor Pog'：Pogonion of soft tissue\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-8692897/v1/a8310ee3b11c6e702f559e82.png"},{"id":102209998,"identity":"21c82acb-1f82-48e4-a3ed-f0511382566a","added_by":"auto","created_at":"2026-02-09 12:15:38","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":171522,"visible":true,"origin":"","legend":"\u003cp\u003e3D Facial Scanning Landmarks\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-8692897/v1/448145bb5af0152dd44517f9.png"},{"id":102936921,"identity":"188718f7-15e3-434d-8378-c070d1a7b0b2","added_by":"auto","created_at":"2026-02-18 16:27:00","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1027272,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8692897/v1/2ca62f24-1b3a-4ceb-b06e-d70e369e3a2e.pdf"},{"id":102209997,"identity":"6834dc51-b585-4f01-be34-fff56d432705","added_by":"auto","created_at":"2026-02-09 12:15:38","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":41423,"visible":true,"origin":"","legend":"","description":"","filename":"Tables.docx","url":"https://assets-eu.researchsquare.com/files/rs-8692897/v1/713c14b10cf3ff6acbb85dd2.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Three-dimensional soft tissue and cephalometric analysis for Class II malocclusion with Twin-Block appliance treatment","fulltext":[{"header":"Introduction","content":"\u003cp\u003eClass II malocclusion often presents distinct facial characteristics. Typically, it shows a protruding maxilla, open lips, exposed teeth, and a retruded mandible. Among these, the retrusion of the posterior mandible is regarded as the primary contributing factor [1]. Mandibular retrognathia has far-reaching consequences. It not only mars the aesthetic appearance but also causes dental crowding and may even lead to a reduction in airway size [2]. Clinically, for children with Class II malocclusion who meet the treatment criteria during their growth spurt, early intervention with functional appliances is highly beneficial. This treatment approach can effectively stimulate mandibular development, balance the sagittal growth of the maxilla and mandible, facilitate the reconstruction of facial soft tissues, and ultimately contribute to a more harmonious and attractive facial profile [3].\u003c/p\u003e\n\u003cp\u003eThe Twin-Block appliance is a classic functional appliance. For adolescent patients with mandibular hypoplasia before the peak of growth and development, the Twin Block functional orthopedic therapy is widely used both domestically and internationally to coordinate the development of the maxilla and mandible and improve facial aesthetics [4]. It consists of two occlusal blocks designed to mesh with each other to position the mandible forward [5]. The upper block includes a lip arch extending from canine to canine. The mandibular occlusal block features an acrylic cap for the mandibular incisors. Its design forces the mandible forward, causing neuromuscular functional changes, which result in the advancement of the mandibular position, accelerate mandibular growth, reduce overjet, and improve molar relationships [6]. Previous evidence has described the effectiveness of the Twin-Block appliance in promoting orthodontic and orthopedic changes and correcting Class II malocclusion [7-9].\u003c/p\u003e\n\u003cp\u003eTwin-Block can cause changes in the morphology, structure, and position of hard tissues such as the mandible, while also altering the morphology of soft tissues attached to the surface of hard tissues. Previous studies have mostly investigated changes in soft tissue or hard tissue separately, which is relatively single and cannot reflect the correlation between soft and hard tissue. Moreover, soft tissues are mostly measured using two-dimensional X-ray cephalometric radiography [10-12]. Due to inaccurate positioning of two-dimensional planes, differences in projection angles, and changes in image magnification, measurement accuracy is limited, especially in the horizontal direction, where a significant amount of data is lost, which is important for facial soft tissue morphology analysis. The systematic review by Flores et al. also suggests that three-dimensional quantification of soft tissue changes is needed to overcome the current limitations in our understanding of the soft tissue changes observed after using Twin-Block appliances in patients with Class II malocclusion [13]. In recent years, three-dimensional measurement methods have gradually been applied to studies evaluating soft tissue changes, allowing for more accurate and detailed morphological analysis. Flores-Mir et al. believe that three-dimensional facial scanning may be the best tool for studying the impact of Twin-Block orthodontics on soft tissues [13].\u003c/p\u003e\n\u003cp\u003eThe changes in soft tissue after Twin-Block orthodontic treatment can be influenced by numerous factors, such as alterations in hard tissues like teeth and bones, as well as occlusal factors, condylar remodeling, muscle tension, and individual growth and development [6,14]. The stability of orthodontic treatment outcomes is crucial. Currently, there is limited research on the stability of Twin-Block treatment efficacy.\u003c/p\u003e\n\u003cp\u003eThis study aims to comprehensively analyze the changes in soft and hard tissues of the maxillofacial region in adolescents with mandibular retraction treated with Twin-Block appliances, utilizing a structured light 3D scanner and cephalometric lateral radiographs. Furthermore, through the measurement and overlap of 3D facial models, we explore the changes in soft tissues during the follow-up period after treatment to observe the stability of the Twin-Block appliances.\u003c/p\u003e"},{"header":"Material And Methods","content":"\u003cp\u003eIn this study, patients who visited the Department of Orthodontics at the Stomatological Hospital of University from November 2023 to March 2025 were recruited. Only patients who met the following criteria were included in the study. Before treatment, the patients were informed about the role, course of treatment, and precautions associated with Twin-Block orthopedic treatment, and they signed the informed consent after understanding and agreeing to the terms. Inclusion criteria: 1) Angle Class II division 1, both male and female; 2) In the mixed dentition stage or early permanent dentition stage, the cervical spine stage of cephalometric lateral radiograph was before or at the peak of growth (CVMs Ⅱ - CVMs Ⅲ); 3) The molar is distally related, skeletal Class II, MP-FH\u0026thinsp;\u0026le;\u0026thinsp;34\u0026deg;, and the profile shows that the mandible is significantly retracted, and the profile was significantly improved after the jaw was extended; 4) Coben analysis[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e] showed mandibular hypoplasia or mandibular relative to maxillary hypoplasia; 5) Good oral hygiene; 6) The BMI of patients before and after treatment was within the normal range. Exclusion criteria: 1) Obvious symptoms of temporomandibular joint disease; 2) Significant facial deviation; 3) History of facial syndrome; 4) Systemic congenital diseases; 5) Previous orthodontic treatment; 6) Poor oral hygiene.\u003c/p\u003e \u003cp\u003eAll patients used alginate impression material and super anhydrite to create upper and lower dentition models. The mandible was extended forward, and occlusion was recorded using occlusal wax when the upper and lower incisors were in opposition. It is important to note that there should be a 3\u0026ndash;4 mm occlusion between the upper and lower incisors at this time [\u003cspan additionalcitationids=\"CR17\" citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. The Twin-Block appliance was made by using dentition model and matching wax bite record. All patients used the Twin-Block appliance shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e for orthopedic treatment. A labial arch is incorporated in the anterior region of the appliance to facilitate the retraction of proclined anterior teeth in patients. Prior to treatment, the labial arch is adjusted away from the teeth to relieve restrictions on arch expansion. They were instructed to wear the appliance every day, except when it needed to be removed and cleaned while brushing their teeth. Patients should wear it all day, for at least 22 hours each day. During the wearing process, they should avoid strenuous exercise to prevent accidental injury. In the initial stage of wearing the appliance, patients underwent simultaneous arch expansion. The method of arch expansion involved widening the spiral arch expander by 0.25 mm horizontally every day for 2 weeks. A follow-up appointment was scheduled two weeks after the appliance was placed to adjust the retention mechanism and labial arch of the appliance, with the efficacy of rapid maxillary expansion evaluated concurrently.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe height and weight of patients were routinely recorded before each data collection session. Cephalometric lateral films were taken before treatment and at the end of treatment, and the data were imported into Dolphin Imaging cephalometric software for measurement. The marked points on the cephalometric lateral radiographs are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The cephalometric items are listed in Table I. The Artec Space Spider 3D scanner (Artec 3D, Luxembourg) was used before Twin-Block treatment (T0), at the end of treatment (T1), 3 months after the end, and 6 months after the end of treatment. During facial scanning, patients were required to remove all glasses, facial/auricular accessories, as well as any obstructive items including collars and scarves; intraoral orthodontic appliances, if worn, must be detached prior to the scanning procedure. For data acquisition, patients were positioned in a strict upright sitting posture with their heads held in a neutral, erect alignment, gazing horizontally at a white wall in front without any external visual or auditory distractions. The operator then provided standardized verbal guidance to ensure that the patients\u0026rsquo; median sagittal plane was perpendicular to the ground, their tongues were maintained in a resting position, their mandibles were fully relaxed, their maxillary and mandibular teeth were naturally spaced apart, and their upper and lower lips were in a gentle, natural closure [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. After maintaining this stable, relaxed posture for 20 seconds, three-dimensional facial data acquisition was initiated. Throughout the entire scanning process, patients were instructed to maintain calm, regular breathing while refraining from any chewing or swallowing movements. To mitigate potential discomfort caused by the blue light and flash emitted by the scanner, patients were asked to close their eyes naturally with a relaxed facial expression following head position adjustment, after which the formal three-dimensional facial data collection was performed. The data were saved in STL format (Stereolithography format). The selected data are shown in Table II and Fig.\u0026nbsp;3. The soft tissue measurement index from the facial scanning is displayed in Table III. The digital model data in STL format were imported into Geomagic Control X 2018 software for fixed-point measurement and data collection. The model in STL format was then exported to Geomagic Wrap 2021 (3D Systems, USA), where a Cartesian coordinate system (X, Y, Z) was established. The coordinate axes were defined that the front, left, and upper directions of the subject were considered positive, while the rear, right, and lower directions were considered negative. Referring to the 3D facial data of the T0 point, the 3D facial data of the T1 point was overlapped to observe the changes before and after orthodontic treatment. T1 data were used as a reference, and T2 and T3 three-dimensional facial data were overlaid with them to observe the changes in soft tissues during the follow-up period. The three-dimensional directional changes of the corresponding facial landmarks were measured using the \"Create Annotation\" command. Taking the superimposition of the T0 and T1 models as an example, the specific superimposition steps are detailed as follows: The T0 and T1 models were imported into Geomagic Wrap 2021 software separately. First, the T0 model was reoriented. Subsequently, a Cartesian coordinate system (X, Y, Z axes) was established: the soft tissue Frankfort horizontal plane was defined as the X-axis (anterior direction as positive); the Y-axis was set parallel to the line connecting the bilateral medial canthi (left direction as positive); the plane formed by the X-axis and Y-axis was parallel to the ground; and the Z-axis was perpendicular to the ground (superior direction as positive). The \"Pin\" command was executed on the T0 model to fix its position. Thereafter, the \"Align - Manual Registration\" command was applied to both the T0 and T1 models. Upon completion of the above operations, the superimposition of the T0 and T1 models was accomplished.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eS: Sella、N: Nasion、P: Porion、Or: Orbitale、Ptm: Pterygomaxillary fissure、Ba: Basion、A: Subspinale、B: Supramental、ANS: Anterior nasal spine UL: Upper lip、LL༚Lower lip、Prn༚Pronasale、Pog༚Pogonion、Me༚Menton、Co༚Condylion 、Go༚Gonion、Ar༚Articulare、UI: Upper incisor、 LI: Lower incisor Pog'༚Pogonion of soft tissue\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eStatistical methods\u003c/h3\u003e\n\u003cp\u003eIn this study, G*Power 3.1 software was used to calculate the sample size by paired-sample t-test and the n-sn-pog angle (convexity angle) as the reference index. On the basis of previous studies [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e], the α (test level) was set at 0.05 and the 1-β (test efficiency) was set at 80%. Therefore, the minimum sample size is 16. In this study, the cephalometric data and the 3D model data of the face were measured three times by the person. After the first measurement, repeated measurements were performed 15 days and 30 days later, and the average value was taken for statistical analysis. The data were imported into SPSS 25.0 software for statistical analysis, the data were normally tested, the paired t-test was used for the data conforming to the normal distribution, and the Wilcoxon test was used for statistical analysis for the data that did not conform to the normal distribution. Statistical significance was defined as \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05 and highly significant as \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01. Descriptive statistics were applied to analyze the displacement of three-dimensional facial landmarks, with a 95% confidence interval preset for accuracy, and interval estimation was performed on the mean displacement values.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eA total of 56 patients who met the criteria were included in this study. All patients cooperated well throughout the process. Cephalometric analysis and three-dimensional facial scanning were performed at the beginning of treatment (T0) and at the end (T1). The average age of patients before treatment was 9.60\u0026thinsp;\u0026plusmn;\u0026thinsp;1.16 years. The average duration of treatment was 311.04\u0026thinsp;\u0026plusmn;\u0026thinsp;90.72 days. In this study, a total of 28 patients were collected for facial scan data at the end of treatment (T1) and 3 months after orthodontic treatment (T2). Facial scan data were collected at the end of treatment (T1) and at 6 months after treatment (T2) in 17 patients. For the above data that conform to the normal distribution, the mean and standard deviation are expressed, and the data that do not conform to the normal distribution are expressed by the media and quartile.\u003c/p\u003e \u003cp\u003eIn the analysis of all facial scan models and lateral radiographs, 20 cases were randomly selected. A single measurer conducted measurements every two weeks, with each model assessed three times. Test-retest reliability was analyzed using the intraclass correlation coefficient (ICC). The results indicated that the ICC for all measurement items was greater than 0.80, demonstrating high test-retest reliability and confirming the reliability of the model measurement results. The Cronbach's alpha reliability coefficients for the measured items are presented in Table IV.\u003c/p\u003e \u003cp\u003eThe research results obtained from the measurement and analysis of 56 patients\u0026rsquo; lateral radiographs before and after treatment included in this study are shown in Table V, Table VI. The statistical analysis indicated that SNA showed no significant differences (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05), suggesting that Twin-Block orthopedic treatment had no notable effect on the maxilla. Post-treatment, the SNB angle increased significantly (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01), while the ANB decreased markedly (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01). Additionally, the mandibular ramus length (Ar-Go) and mandibular body length (Go-Pog) both increased significantly (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01). Coben analysis revealed that mandibular length (MaL) and MaL% also increased significantly, indicating that Twin-Block orthopedic treatment may promote sagittal growth of the mandible. Although FMA increased by the end of treatment (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05), there was no significant difference in the amount of change. ANS-Me、N-Me and ANS-Me/N-Me increased significantly (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01). The U1-SN angle decreased significantly (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01) by an average of 3.9\u0026deg;, reflecting a recovery of the upper anterior teeth. IMPA increased by 2.08\u0026deg; (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01), and Overjet decreased significantly by approximately 3.18 mm. The upper lip convexity (UL-E) decreased after correction (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01), while the lower lip convexity (LL-E) showed no significant change (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05).\u003c/p\u003e \u003cp\u003eTable VII presents the research results regarding three-dimensional facial dimension changes at the conclusion of Twin-Block correction, derived from the measurement and analysis of 56 patients\u0026rsquo; facial three-dimensional scanning models included in this study. The statistical analysis revealed significant differences in several measurements: Ral-Lal、sn-stom、stom-B\u0026rsquo;、gor-gol、ls-n- pg\u0026rsquo;、n-me\u0026rsquo;、sn- me\u0026rsquo;、li-B\u0026rsquo;-pg\u0026rsquo;、ls-n-li (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01). Post-treatment, there was an increase in nasal width, with the alae nasi widening by 0.43 mm (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01) and the base of the nose expanding by 0.24 mm (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01). Both the upper and lower lip lengths increased significantly (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01), with the upper lip lengthening by approximately 0.50 mm and the lower lip by about 0.93 mm.\u003c/p\u003e \u003cp\u003eIn terms of face size, the total height of the face and the height of the lower part of the face increased, similar to the changes of hard tissue. The width of zygoma and the width between mandibular angles increased. In terms of angle measurements, the nasolabial angle and the chin convex angle of the lower lip showed no significant changes, but the mentolabial angle increased significantly (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01), with an increase of 9.89\u0026deg;. Additionally, the angle between the upper and lower lips decreased (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01), as did the upper lip chin convex angle (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01), decreasing by 0.91\u0026deg; and 0.80\u0026deg;, respectively. The face shape angle also increased (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05). These angular changes indicate an improved relationship among the nose, lip, and chin, a reduction in facial convexity, and a more coordinated profile.\u003c/p\u003e \u003cp\u003eThe three-dimensional soft tissue changes between the end of treatment and the 3-month follow-up are presented in Tables IX and X. The statistical results indicated that there was no statistical difference between the soft tissue measurement items at 3 months of follow-up and the end of orthodontic treatment. After 6 months of follow-up after orthodontic treatment, the three-dimensional soft tissue changes of patients were shown in Table XI and Table XII. The statistical results showed that there were significant differences in ls-n- pg and li-n- pg (P\u0026thinsp;\u0026lt;\u0026thinsp;0.01), and the upper lip and lower lip chin convex angles were smaller. There were statistically significant differences in Ral-Lal, Rulp-Lulp, Rnb-Lnb, and li-B-pg\u0026rsquo;, The nasal width increased and the mentolabial angle became smaller (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). The face model at 3 months after Twin-Block treatment and the face model at 6 months after orthodontic treatment overlapped with the model at the end of orthodontic treatment, respectively, and the results are shown in Table XIII and Table XIV. The displacement of each landmark point was small at 3 months after Twin-Block orthodontic treatment. The soft tissue points B', Pg', and Me moved forward and downward 6 months after Twin-Block orthodontic treatment.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eThis study employed cephalometric and three-dimensional facial scanning technologies to comprehensively investigate the changes in facial soft and hard tissues before and after Twin-Block treatment, providing a holistic assessment of the facial alterations induced by this treatment.\u003c/p\u003e \u003cp\u003eIn this study, lateral cephalometric analysis revealed that the SNA angle showed no significant change after Twin-Block orthopedic treatment. This aligns with the results of Ajami, Khoja, and Jaiswal et al., indicating that the appliance has no notable inhibitory effect on maxillary growth [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. However, there are discrepancies among different studies. For example, Illing, Khan, and others reported a slight reduction in the mean SNA angle [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. In Bastiani's study, the SNA angle decreased by 0.64\u0026deg;, suggesting a mild restriction of maxillary growth due to the appliance, while Baysal and others argued that Twin-Block treatment does not have this promoting effect [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. Jamilian et al. proposed that Twin-Block appliance activates the retractor muscles, influencing the positioning of maxillary and promoting changes in its growth [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. These differences may stem from variations in the ethnicity and growth stages of the research samples, as well as differences in measurement methods and research designs.\u003c/p\u003e \u003cp\u003eMeanwhile, in this study, the SNB angle increased significantly, with this investigation showing an increase of 1.05\u0026deg;, and the ANB angle decreased remarkably. This indicates that the Twin-Block appliance is highly effective in advancing the mandible and improving the sagittal relationship between the maxilla and mandible, which is consistent with most previous research findings [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. Baysal et al. observed a decrease in the ANB angle by 2.85 degrees, and prior research indicated a similar reduction of approximately 2.0-2.3 degrees compared to the control group [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. Ajami et al. found an average decrease in the ANB angle of 1.76\u0026deg;, which closely resembles the 1.73\u0026deg; reduction observed in this study [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. These results indicate that Twin-Block has a notable effect in advancing the mandible and improving the sagittal relationship between the maxilla and mandible.\u003c/p\u003e \u003cp\u003eMany scholars have found that the length of the mandible increases significantly after Twin-Block treatment [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. Our study also observed an increase in the lengths of the mandibular ramus and mandibular body. The increase in mandibular length varies among different studies. For instance, in Kirtane's research, Ar-Go increased by 2.38 mm compared with the control group, while in our study, the mandibular body increased by approximately 2.58 mm, which is not much different from the research by Toth and McNamara [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. Such differences might be attributed to the ethnic diversity and distinct growth and development conditions of the patients [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. In addition, Coben's analysis showed that the length and depth of the mandible increased, indicating that Twin-Block orthopedic treatment can promote mandibular growth. Both the lower facial height and total facial height increased in our study, yet there are differences in the magnitude of increase among various studies [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan additionalcitationids=\"CR22\" citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan additionalcitationids=\"CR28\" citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. In our study, the increase was 2.49 mm, and the total face height increased by 4.51 mm. This could be related to the \"posterior bite - block effect\" of the Twin-Block appliance, which has different impacts on vertical development inhibition and molar eruption promotion in different individuals [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. In contrast, this study observed no significant change in FMA, and no additional clockwise rotation of the mandible was detected in the Twin-Block group. This may be attributed to Twin-Block promoting mandibular remodeling through upward and forward growth of the condyle, with less impact on the mandibular angle [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eApart from the changes in the maxilla and mandible, Twin-Block also affects the teeth. In this study, the U1-SN angle decreased by an average of 3.9\u0026deg;, which may be related to the lip arch of the maxillary appliance, consistent with the conclusion in other studies that the inclination of the upper teeth decreases [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan additionalcitationids=\"CR21\" citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. O'Brien et al. demonstrated that maxillary incisor retraction significantly contributed to the reduction in overjet [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. In our study, the overjet was also reduced, suggesting that maxillary incisor retraction played a role in this outcome. At the same time, the IMPA increased by 2.08\u0026deg;, which may be attributed to the acrylic capping of the lower incisors with the Twin-Block appliance [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. However, different studies have reported varying effects on the mandibular incisors. Some studies found no significant change in the inclination of the mandibular incisors, while in Khoja's research, the inclination of the mandibular incisors increased significantly [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. These differences may be due to the forward force generated by mandibular prognathism, as well as variations in appliance design and individual patient characteristics. Excessive lower incisor lip inclination may weaken the skeletal effects of the appliances, suggesting that control of lower incisors should be emphasized when applying Twin-Block appliances [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. These compensations may need correction in the second stage of orthodontic treatment, potentially involving the extraction of premolars to achieve upright lower incisors and enhance stability [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe changes in hard tissues form the structural basis for the morphology of maxillofacial soft tissues. In this study, with the reconstruction of the jaw relationship, the retraction of the upper incisors led to the backward movement of the upper lip, resulting in a decrease in upper lip convexity (UL-E). Most scholars agree that this reduction aligns with our findings [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. Regarding the lower lip convexity, there are controversial conclusions in different studies. Our study results are consistent with some studies, showing no significant change in the lower lip convexity after treatment, which may be related to the maintained inclination of the mandibular incisors after treatment [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. Ajami noted a decrease in lower lip convexity of about 1.37 mm, while other studies reported an increase, with Jaiswal, Bastiani, and Morris observing more than 1 mm of protrusion [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. This prominence may reflect the adaptability of soft tissue to changes in hard tissue following orthodontic treatment.\u003c/p\u003e \u003cp\u003eWhen exploring the impact of the Twin-Block appliance on soft tissue morphology, the differences in patient compliance and individual variations during appliance wear are important factors that cannot be ignored. Patient compliance directly affects the treatment outcome of the appliance. In this study, the changes in three-dimensional facial morphology were categorized into nasal morphology, lip morphology, chin morphology, and the relationship between the nose-lip and chin-lip. Previous studies have explored these aspects in detail.\u003c/p\u003e \u003cp\u003eThe horizontal changes in facial soft tissue are rarely reported. After treatment, patients showed an average increase of 0.43 mm in alae nasi width and 0.24 mm in nasal base width. The increase in nasal base width was about 87.73% of that in alare width, smaller than Badreddine\u0026rsquo;s CBCT findings (1.0 mm increase in alare width with Hyrax expander) [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. This discrepancy may result from different soft tissue responses to various arch expansion devices and methods. In our study, we combined Twin-Block with a maxillary detachable expander instead of an adhesive Hyrax expander, which may have led to smaller soft tissue changes.\u003c/p\u003e \u003cp\u003eThe lengths of the upper and lower lips changed significantly during Twin-Block correction, with the upper lip length increasing by 0.50 mm and the lower lip length by 0.93 mm. et al. also reported increases in both lip lengths after Twin-Block treatment, with a greater increase in the lower lip, consistent with Lee\u0026rsquo;s findings [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. G\u0026uuml;ler et al. found no significant change in upper lip length, although the lower lip length increased significantly [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. While studies agree on the increase in lower lip length, the significance of upper lip length changes remains controversial. In our study, mechanistically, Twin-Block\u0026rsquo;s continuous mandibular forward-downward force increases intermaxillary distance via lower incisors sliding along upper incisors, reducing lip extrusion and elongating both lips. Additionally, soft tissue B point forward movement stretches the lower lip from a \"curled\" to \"extended\" position, augmenting its length.\u003c/p\u003e \u003cp\u003eIn terms of the nasolabial relationship, previous studies and our findings show a trend of backward displacement at the convex point of the upper lip [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. However, nasolabial angle remained unchanged at all treatment time points, as corroborated by G\u0026uuml;ler\u0026rsquo;s 3D analysis [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e] and McDonagh\u0026rsquo;s observation [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]. Additionally, some studies suggest that the impedance center of the craniomaxillary complex is positioned behind the dental arch. As a result, the bony effects produced by arch expansion exhibit a cone-like effect in both sagittal and vertical directions meaning that expansion diminishes from front to back and from bottom to top. When the hard palate expands laterally, this may simultaneously decrease the height of the palatal cover and the nasal base [\u003cspan additionalcitationids=\"CR41\" citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e]. Consequently, the vertical movements of the columella and subnasale, together with the displacement of the upper lip's convex point, contribute to maintaining a relatively unchanged nasolabial angle.\u003c/p\u003e \u003cp\u003eThe lip-chin relationship is a key part of the aesthetic and functional evaluation of facial profile analysis. This study highlights the lip-chin relationship\u0026rsquo;s role in facial aesthetics by analyzing three angles: the upper lip-chin convex angle, lower lip-chin convex angle, and mentolabial angle. Post-treatment, the upper lip-chin convex angle decreased, reflecting greater forward chin movement than upper lip retraction, enhancing chin prominence. The lower lip-chin convex angle showed no significant change, likely due to opposing effects of chin advancement and compensatory mandibular anterior tooth proclination. Notably, the mentolabial angle increased by 9.89\u0026deg;, attributed to overjet reduction and alleviation of upper incisor pressure on the lower lip. In Angle II Division 1 cases, mandibular retraction typically forces the lower lip into a \"rolled-back\" position, deepening the mentolabial sulcus and sharpening the angle, which compromises aesthetics. Orthodontic correction stretches the lower lip, softening the mentolabial transition and improving profiles\u0026mdash;a finding consistent with Baysal et al.\u0026rsquo;s work on soft-tissue adaptations [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. These changes underscore the interplay between skeletal repositioning, dental compensation, and soft tissue remodeling in optimizing facial harmony.\u003c/p\u003e \u003cp\u003eThis study evaluated 3D soft tissue changes post-treatment, revealing distinct displacement patterns: the upper lip convex point retruded downward, while the lower lip convex point, soft tissue B point, and pogonion advanced downward, with mandibular landmarks exhibiting greater movement than maxillary counterparts. The most pronounced forward displacement occurred at soft tissue B point (\u0026gt;\u0026thinsp;pogonion\u0026thinsp;\u0026gt;\u0026thinsp;lower lip convex point), consistent with cephalometric studies by Salloum \u0026amp; McDonagh [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]. Yıldırım's findings indicated an average backward movement of the upper lip convex point (0.44 mm), though this change was not statistically significant (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.084). In contrast, the pogonion of soft tissue showed a significant forward displacement (2.14 mm, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01), corroborating this study's findings. The smaller anterior displacement of the menton may be attributed to individual patient variations and the chosen coordinate system [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. Menton displacement was minimal, potentially due to anatomical variability or coordinate system selection. Its downward shift correlated with increased total and lower facial height [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]. However, an increased lower facial height could exacerbate vertical bone patterns in patients with a high mandibular plane angle (FMA), prompting their exclusion from this study's design phase. For low/average FMA cases, increased anterior height enhances aesthetics [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Overall, Twin-Block correction improved soft tissue morphology in these patients, supporting Sattarzadeh et al.\u0026rsquo;s vertical skeletal-soft tissue linkage theory [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eMoreover, the growth and remodeling of soft tissues are also regulated at the cellular and molecular levels. Growth factors and cytokines are involved in the process of soft - tissue adaptation to the forces exerted by the appliance. For instance, certain growth factors may promote the proliferation and differentiation of fibroblasts in the soft tissues, leading to changes in the extracellular matrix and ultimately resulting in soft - tissue remodeling. However, the specific regulatory mechanisms and interactions among these factors in the context of Twin Block treatment remain to be further explored.\u003c/p\u003e \u003cp\u003eThere are still deficiencies in this study: This study lacked a parallel control group. Patients with skeletal Class II mandibular hypoplasia without intervention during growth may risk needing orthognathic surgery later and could face increased airway stenosis and obstructive sleep apnea [\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e, \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e]. Establishing a control group solely to assess the appliance's therapeutic effect conflicts with medical ethics and prioritizing patient interests. Using a general population with normal jaw development as a control is debatable due to differing growth trends between the groups.\u003c/p\u003e \u003cp\u003eDue to medical ethics, similar studies often do not include a control group, instead referencing previous research [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e]. Kam\u0026iacute;nkov\u0026aacute; and colleagues conducted regression analysis on the three-dimensional shape of facial soft tissue in 113 children aged 6\u0026ndash;13, finding that changes in facial soft tissue shape were stable and unrelated to changes in height, weight, or age [\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e]. Morris et al. established a control group in a 9-month study, showing no significant changes in facial soft tissue morphology in the control group, providing a useful reference for this study [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. In addition, the average treatment duration was only 296 days. Although this reduces the influence of confounding factors such as growth and development to a certain extent, it may still be insufficient to observe the long - term effects of the treatment. Future research could consider extending the follow - up period to further observe the changes in soft and hard tissues. Meanwhile, efforts should be made to better control research variables under ethical circumstances to improve the accuracy and reliability of research results. Additionally, ensuring patients' BMI was within the normal range for children reduced the impact of weight changes on the results [\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e].\u003c/p\u003e \u003cp\u003ePatients should be followed up after treatment to assess the long-term stability of facial changes. Sharma et al. found that the soft tissue pogonion retracted by about 1.0 mm within 3 months post-treatment, representing 25%-33% of the anterior displacement [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. Lee reported a 1.0 mm relapse in overjet within 3 months after a 9-month treatment period [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. Given the differences among ethnic groups and individuals, longer-term follow-up is necessary, and this research group plans to conduct further studies in the future.\u003c/p\u003e \u003cp\u003eIn conclusion, Twin-Block orthopedic treatment has a significant impact on the soft and hard tissues of patients with Class II malocclusion. In clinical applications, it is necessary to fully consider patient compliance and individual differences to improve the treatment effect.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eBased on this study\u0026rsquo;s findings, the following can be concluded:\u003c/p\u003e \u003cp\u003e \u003col\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eTwin-Block functional orthodontic treatment can alter the maxillomandibular relationship in children with Class II malocclusion, reduce overjet, and improve skeletal discrepancies.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eTwin-Block orthodontic treatment induces three-dimensional changes in the soft tissue of the nose, upper lip, lower lip, and chin, positively improving deformities in the lower lip and chin, thereby enhancing facial aesthetics.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eNo significant differences were noted in the morphological changes of facial soft tissues at 3 months following Twin-Block treatment relative to those at treatment completion, demonstrating a relatively stable short-term therapeutic outcome. At 6 months post-treatment, the soft tissue facial profile of patients exhibited further improvements, and such alterations are likely attributable to skeletal growth and development.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003eCVMs \u0026nbsp; Cervical Vertebrae Maturation Staging\u003c/p\u003e\n\u003cp\u003eBMI \u0026nbsp; \u0026nbsp; Body Mass Index\u003c/p\u003e\n\u003cp\u003eCBCT \u0026nbsp; Cone-Beam Computed Tomography\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAuthors\u0026rsquo; contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eYue Sun contributed to conceptualization, formal analysis, manuscript review and editing, and original draft preparation; Ying Zhang contributed to conceptualization, visualization, manuscript review and editing, and original draft preparation; Chengjing Xu contributed to manuscript review and editing; Yuting He contributed to manuscript review and editing and visualization; Min Hu contributed to resources, manuscript review and editing, and supervision. Huan Jiang contributed to original draft preparation, manuscript review and editing, and supervision.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors received no specific funding for this work.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll relevant data are within the manuscript. The data in this article is available.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study was approved by the medical ethics committee of Jilin University Stomatological Hospital on October 25, 2023, with the approval number JDKQ2023(48). In this study, informed consent to participate was obtained from the parents or legal guardians of any participant under the age of 16.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eMcNamara JA Jr. Components of class II malocclusion in children 8-10 years of age. Angle Orthod. 1981;51(3):177-202. doi:10.1043/0003-3219(1981)051\u0026lt;0177:COCIMI\u0026gt;2.0.CO;2.\u003c/li\u003e\n \u003cli\u003eCampbell C, Millett D, Kelly N, Cooke M, Cronin M. Frankel 2 appliance versus the Modified Twin Block appliance for Phase 1 treatment of Class II division 1 malocclusion in children and adolescents: A randomized clinical trial. 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A prospective evaluation of Bass, Bionator and Twin Block appliances. Part I--The hard tissues.\u0026nbsp;Eur J Orthod. 1998;20(5):501-516. doi:10.1093/ejo/20.5.501.\u003c/li\u003e\n \u003cli\u003eKhan MI, Neela PK, Unnisa N, Jaiswal AK, Ahmed N, Purkayastha A. Dentoskeletal effects of Twin Block appliance in patients with Class II malocclusion.\u0026nbsp;Med Pharm Rep. 2022;95(2):191-196. doi:10.15386/mpr-1989.\u003c/li\u003e\n \u003cli\u003eBastiani C, Bellini-Pereira SA, Aliaga-Del Castillo A, Chiqueto K, Castanha Henriques JF, Janson G. Twin-block and mandibular anterior repositioning appliances effects in Class II malocclusion correction. Am J Orthod Dentofacial Orthop. 2023;163(2):181-190. doi:10.1016/j.ajodo.2021.09.021.\u003c/li\u003e\n \u003cli\u003eBaysal A, Uysal T. Dentoskeletal effects of Twin Block and Herbst appliances in patients with Class II division 1 mandibular retrognathy. 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A prospective optical surface scanning and cephalometric assessment of the effect of functional appliances on the soft tissues.\u0026nbsp;Eur J Orthod. 2001;23(2):115-126. doi:10.1093/ejo/23.2.115.\u003c/li\u003e\n \u003cli\u003eHar Zion G, Katzhendler E, Bader Farraj A, et al. Evaluating the Effects of Carriere Motion Appliance and Twin Block Appliances in Class II Correction-A Retrospective Study. Dent J (Basel). 2024;12(5):119.\u003c/li\u003e\n \u003cli\u003eOng SC, Khambay BS, McDonald JP, Cross DL, Brocklebank LM, Ju X. The novel use of three-dimensional surface models to quantify and visualise the immediate changes of the mid-facial skeleton following rapid maxillary expansion. Surgeon. 2015;13(3):132-138. doi: 10.1016/j.surge.2013.10.012.\u003c/li\u003e\n \u003cli\u003eCantarella D, Dominguez-Mompell R, Moschik C, et al. Zygomaticomaxillary modifications in the horizontal plane induced by micro-implant-supported skeletal expander, analyzed with CBCT images.\u0026nbsp;Prog Orthod. 2018;19(1):41. Published 2018 Oct 22. doi:10.1186/s40510-018-0240-2.\u003c/li\u003e\n \u003cli\u003eOk U, Kayalar E, Sadry S. Three-dimensional zygomatic changes after rapid maxillary expansion in growing patients. Dreidimensionale Jochbeinver\u0026auml;nderungen nach schneller Gaumennahterweiterung bei heranwachsenden Patienten. J Orofac Orthop. 2023;84(3):147-156. doi:10.1007/s00056-021-00348-5.\u003c/li\u003e\n \u003cli\u003eSattarzadeh AP, Lee RT. Assessed facial normality after Twin Block therapy. Eur J Orthod. 2010;32(4):363-370. doi:10.1093/ejo/cjp141.\u003c/li\u003e\n \u003cli\u003eBattagel JM, L\u0026apos;Estrange PR. The cephalometric morphology of patients with obstructive sleep apnoea (OSA). Eur J Orthod. 1996;18(6):557-569. doi:10.1093/ejo/18.6.557.\u003c/li\u003e\n \u003cli\u003eLowe AA, Ono T, Ferguson KA, Pae EK, Ryan CF, Fleetham JA. Cephalometric comparisons of craniofacial and upper airway structure by skeletal subtype and gender in patients with obstructive sleep apnea. Am J Orthod Dentofacial Orthop. 1996;110(6):653-664. doi:10.1016/s0889-5406(96)80043-6.\u003c/li\u003e\n \u003cli\u003eKam\u0026iacute;nkov\u0026aacute; P, D\u0026iacute;rer P, Fudalej P. Association of 3-dimensional facial changes and height and weight increase in children: A 2-year follow-up.\u0026nbsp;Am J Orthod Dentofacial Orthop. 2022;161(3):e199-e214. doi:10.1016/j.ajodo.2021.01.025.\u003c/li\u003e\n \u003cli\u003eHongyun,Fang Liyun,Zhao Qiya,Guo et al. Trends in height, weight, and BMI of children and adolescents aged 6-17 in China. Food and Nutrition in China.2021,27(04):16-20. doi:10.19870/j.cnki.11-3716/ts.20210413.001.\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003eTables I to XIV are available in the supplementary files section\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Angle II, Twin Block, Facial 3D scanning, Cephalometric analysis, Soft tissue","lastPublishedDoi":"10.21203/rs.3.rs-8692897/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8692897/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e \u003cp\u003eTo evaluate the dentoskeletal and 3D soft tissue changes induced by Twin-Block appliances in adolescents with Class II Division 1 malocclusion, and to assess short-term treatment stability via 3D facial scanning.\u003c/p\u003e\u003ch2\u003eMaterials and Methods\u003c/h2\u003e \u003cp\u003eFifty-six patients with Class II division 1 malocclusion (mean age: 9.60\u0026thinsp;\u0026plusmn;\u0026thinsp;1.16 years) undergoing Twin-Block treatment at University Stomatological Hospital from November 2023 to March 2025. After diagnosis and analysis, patients who needed Twin-Block orthopedic treatment underwent three-dimensional facial scanning (Artec Space Spider) and cephalometric lateral radiography. Pre-treatment (T0), post-treatment (T1), 3-month (T2), and 6-month (T3) data were collected using 3D facial scanning (Artec Space Spider) and lateral cephalography. Soft tissue and skeletal parameters were measured, with statistical analysis performed via paired t-tests and Wilcoxon tests.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eCephalometric analysis revealed significant post-treatment changes: SNB angle increased (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01), ANB angle decreased (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01), mandibular ramus/body lengths (Ar-Go, Go-Pog) and facial heights (ANS-Me, N-Me) increased (P\u0026thinsp;\u0026lt;\u0026thinsp;0.01). Overjet reduced by 3.18 mm (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01), and upper incisor inclination (U1-SN) decreased by 3.9\u0026deg; (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01). 3D facial analysis showed statistically significant soft tissue changes at T1: alae nasi width (+\u0026thinsp;0.43 mm, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01), upper/lower lip lengths (+\u0026thinsp;0.50 mm, +\u0026thinsp;0.93 mm, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01), mentolabial angle (+\u0026thinsp;9.89\u0026deg;, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01), and reduced upper lip-chin convexity (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01). At 3-month follow-up, no significant soft tissue regression was observed (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05). At the 6-month follow-up, significant differences were observed in the upper/lower lip to chin convex angle (P\u0026thinsp;\u0026lt;\u0026thinsp;0.01). Statistically significant differences were also found in the width of the nasal alar, the width of the nasal base, the width of the philtrum, and the mentolabial angle (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05). Overlap analysis of the three-dimensional model showed that the corresponding landmarks produced different degrees of displacement in the vertical and sagittal directions, respectively.\u003c/p\u003e\u003ch2\u003eConclusions\u003c/h2\u003e \u003cp\u003eTwin-Block treatment effectively improves occlusal relationships, promotes mandibular growth, and enhances soft tissue aesthetics by reducing lip protrusion and optimizing chin-lip-nose harmony. 3D scanning demonstrates high reliability in quantifying soft tissue remodeling. Short-term stability (3 months and 6 months) highlight Twin-Block\u0026rsquo;s efficacy in adolescent Class II correction, with implications for early orthopedic intervention.\u003c/p\u003e\u003ch2\u003eTrial registration:\u003c/h2\u003e \u003cp\u003eThis study was registered at the Chinese Clinical Trial Registry (ChiCTR2300077826) on November 21, 2023.\u003c/p\u003e","manuscriptTitle":"Three-dimensional soft tissue and cephalometric analysis for Class II malocclusion with Twin-Block appliance treatment","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-02-09 12:15:17","doi":"10.21203/rs.3.rs-8692897/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"f5520c0e-f0e5-45fc-a7bc-88d21dcd62ad","owner":[],"postedDate":"February 9th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-02-18T16:25:45+00:00","versionOfRecord":[],"versionCreatedAt":"2026-02-09 12:15:17","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8692897","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8692897","identity":"rs-8692897","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}