Injury Risk Estimation in Mandible-Related Surgical Procedures: A CBCT Study Based on Vital Interforaminal Anatomical Structures.

The mandibular interforaminal region has been considered safe for surgical procedures; nevertheless, the risk of injury to neurovascular structures, such as the mental foramen (MF) and its related structures (anterior loop [AL] and lingual foramina [LF]) should not be overlooked. The study aimed to evaluate the relative risk of injury to these structures during surgical procedures in the anterior region of the mandible based on cone-beam computed tomography (CBCT) scans. A retrospective cross-sectional and observational study was performed on 250 CBCTs from adults (18-69 years) with dentate jaws. Linear measurements of the MF, AL, and LF were evaluated to estimate the risk of injury to these structures during chin-related surgical procedures. The most frequent distance between the base of the mandible (BM) and MF was 8 mm (30.2%). In addition, 20.4% of the CTs had 6 mm from the vestibular cortical bone to the LF. The commonly found measurement from LF to the apex of the nearest tooth was 7 mm (24.0%); 64.2% of the CTs showed a 2-mm distance between the most distal point of the dental implant site to the most anterior point of the AL. Safety distances for genioplasty techniques (MF to mandible base > 6 mm, 96.6% [CI 95%, 95.0%-98.2%]) were observed. Considering the 5-mm cut-off point between the lower limit of a hypothetical bone graft and the chin, 65.4% (CI 95%, 58.9%-71.9%) of CTs were within this distance. Regarding the safety margin of 8 mm, 85.6% (CI 95%, 80.8%-90.4%) were up to this value. This study found safety margins for genioplasty and chin bone grafting surgical techniques that adopt a 5-mm cut-off point. Further similar studies assessing other surgical methods and employing larger samples from different geographical origins may contribute to this field of investigation.

Facial Asymmetry Caused by Mandibular Condylar Hyperplasia: A Two Center Study.

BACKGROUND: Condylar hyperplasia is a non-neoplastic overgrowth of the mandibular condyle. The disorder is progressive and causes gradual jaw deviation, facial asymmetry, and dental malocclusion. The only treatment capable of stopping hyperplastic growth is surgical condylectomy to remove the upper portion of the condyle containing the deranged growth center. When this procedure is conducted in proportion to the length of the healthy side it may also correct the jaw deviation and facial asymmetry. OBJECTIVES: To assess the degree to which condylectomy corrects the asymmetry and to determine the proportion of patients after condylectomy who were satisfied with the esthetic result and did not desire further corrective surgery. METHODS: We conducted a retrospective analysis of medical records of patients who underwent condylectomy that was not followed by corrective orthognathic surgery for at least 1 year to determine the degree of correction of chin deviation and lip cant. Patient satisfaction from treatment or desire and undergo further corrective surgery was reported. RESULTS: Chin deviation decreased after condylectomy from a mean of 4.8° to a mean of 1.8° (P < 0.001). Lip cant decreased after condylectomy from a mean of 3.5° to a mean of 1.5° (P < 0.001). Most patients (72%) were satisfied with the results and did not consider further corrective orthognathic surgery. CONCLUSIONS: Proportional condylectomy could be a viable treatment to both arrest the condylar overgrowth and achieve some correction of the facial asymmetry.

Optimizing Esthetic Outcomes and Bone Stability: Chin Advancement Through Inverted V Osteotomy.

Traditional horizontal osteotomies for small and short chins often yield suboptimal results due to limited bone advancement, resulting in deep labiomental folds and heightened bone resorption risks. This study investigates the effectiveness of an innovative inverted V-shaped osteotomy technique in enhancing esthetic outcomes for patients with such chin concerns. Thirty-eight patients who underwent inverted V-shaped osteotomy for recessed chins between January 2018 and June 2022 were included. Excluding cases involving simultaneous mandibular contouring surgery, patients were followed up for a median duration of 1.2±0.5 years. Preoperation and postoperation soft tissue pogonion (Pg') and labiomental fold depth (LMF) changes were measured. IBM SPSS (version 27.0) was used for statistical analysis, with significance defined as P <0.05. Patient satisfaction was assessed using a visual analog scale. Successful advancement genioplasty was performed on all patients without any severe complications. The average change in soft tissue pogonion (Pg') measured 6.2 (1.9) mm, and the mean alteration in labiomental depth was 0.42 (0.4) mm. The procedure achieved a bone to soft tissue movement ratio of 1:0.96. Patient satisfaction was notably high, with a mean VAS score of 8.7. An inverted V-shaped osteotomy enables greater bone advancement for small and short chins, leading to improved esthetic outcomes and offering a mechanically advantageous condition for bone segments.

Clinical application of V-shaped folded submental flap in the repair of oral defect. / Våž‹æŠ˜å é¢ä¸‹çš®ç“£ä¿®å¤å£è ”ç¼ºæŸçš„ä¸´åºŠåº”ç”¨.

OBJECTIVES: The repair of small and medium-sized defects in the oral has always been a challenge, free skin flap and distal pedicled tissue flaps are difficult to meet clinical needs, and the traditional under-chin flap has the risk of donor-area injury. This study aims to investigate the efficacy of V-shaped folded submental flap in the repair of small-sized and medium-sized oral defects. METHODS: The clinical data of 28 patients with oral defect lesions, who were hospitalized in the Department of Stomatology, Third Xiangya Hospital of Central South University from March 2019 to December 2022, were retrospectively analyzed. Patients were divided into a V-shaped folded group (17 cases) and a conventional group (11 cases) according to different surgical methods. The V-shaped folded group was treated with a V-shaped folded submental flap for postoperative soft tissue repair, while the conventional group was treated with a conventional submental flap for repair. The postoperative follow-up time was 6-48 months. The survival status, repair time, and repair effect of the 2 groups were compared. RESULTS: There was no significant difference in flap survival rate, flap size, flap preparation time, repair surgery time, and postoperative hospital stay between the 2 groups (all P>0.05). At 6 months after the surgery, the V-shaped folded group had no difficulty in raising the head or everting the lower lip, no "cat ear" deformity in the submental skin. Scars in the V-shaped folding group were hidden at the lower edge of the mandible. The wound aesthetics and functional scores in the V-shaped folded group were significantly higher than those in the conventional group (both P<0.05). CONCLUSIONS: The V-shaped foldable submental flap has the advantages of flexible design, simple preparation, reliable blood supply, and protection of the donor area, which can effectively protect the appearance of the chin and avoid functional disorders.

A New Distal Pharyngeal Airway Device Associated with a Reduced Need for Chin-Lift and Jaw-Thrust Maneuvers in Sedated Patients.

Oropharyngeal airways (OPA) or nasopharyngeal airways (NPA) sometimes require chin-lift or jaw-thrust (CLJT) maneuvers to relieve airway obstruction which creates the burden of continuous hands-on care by the anesthesia provider. A new distal pharyngeal airway device (DPA) was used on 63 successive ambulatory surgery patients to assess the frequency of patients requiring manual CLJT maneuvers to prevent airway obstruction. Results were then compared with a contemporaneous group of patients who had used OPA or NPA devices for similar procedures. Patients using the DPA had a 38.5% lower rate of CLJT maneuvers compared with the combined OPA/NPA groups (22.2% of 63 vs. 60.7% of 163, P ≤ .001). Moreover, the results for the DPA group were close to those of the natural airway group (22.2% of 62 vs. 24.8% of 233, P = .66) Results were similar for a sub-set of the above groups who required deep sedation or deep extubation. CLJT maneuvers were common in this ambulatory surgery setting. The new DPA device was associated with a reduced need for such manual maneuvers when compared with similar patients who received OPA or NPA devices and is comparable with the rate for natural airways.

Effectiveness and Safety of a New Hyaluronic Acid Injectable for Augmentation and Correction of Chin Retrusion.

BACKGROUND: A hyaluronic acid (HA) filler intended for non-surgical improvement of chin appearance should ideally be of high strength/firmness (high G') to allow for deep injections on the bone. HASHA (Restylane Shaype) is a new hyaluronic acid (HA) injectable with high G' and high HA concentration (25 mg/mL), engineered by the new NASHA-HD (High Definition) technology. HASHA is suitable to be placed periosteally, aiming to mimic the natural shape of the bony chin. This pivotal clinical investigation evaluated effectiveness and safety of HASHA for augmentation and correction of chin retrusion.  Methods: Subjects 18 years or older with mild or moderate chin retrusion by the Galderma Chin Retrusion Scale (GCRS), were randomized 3:1 to HASHA (n=103) or no treatment (n=37). Assessments included GCRS (blinded evaluator), aesthetic improvement (Global Aesthetic Improvement Scale [GAIS]), subject satisfaction, and safety.  Results: GCRS responder rate (1-grade or greater improvement from baseline) was significantly higher for HASHA (83.3%) versus controls (10.8%) at month 3 (P<0.001) and maintained through month 12 (P<0.001). Aesthetic improvement was high throughout the study in the HASHA group, according to investigators (97% or greater) and subjects (89% or greater). Overall, subject satisfaction was high at month 3 and maintained at month 12. Product- or injection-related adverse events were mostly mild or moderate and transient. No product- or injection-related serious adverse events were reported. CONCLUSIONS: HASHA, a new NASHA-HD injectable with extra strength/firmness, was safe and effective for chin augmentation and correction of chin retrusion, with high aesthetic improvement and subject satisfaction throughout 12 months. J Drugs Dermatol. 2024;23(4):255-261.     doi:10.36849/JDD.8145.

The TSAR-osteotomy, a total subapical and ramus osteotomy: A technical note.

There are several treatment options to treat a class II dentofacial deformity with a pronounced chin. A total subapical osteotomy is one of these options. This type of osteotomy was refined to total subapical and ramus (TSAR) osteotomy. In this technical note, a detailed and schematic presentation of the TSAR osteotomy is presented step by step. The surgical approach to the TSAR osteotomy is divided into three parts. The first part consists of the horizontal osteotomy at the level of the ramus, the second part approaches the corticotomy to release and protect the mental nerve and the third part consists of connecting the horizontal ramus osteotomy and the local corticotomy around the mental nerve. In this third part, it is important that the inferior alveolar nerve (IAN) is actively sought and protected.

Abordagem cirúrgica em fratura de sínfise e côndilo mandibular bilateral em paciente pediátrico: um relato de caso / Surgical approach for syphysis and bilateral mandibular condyle fracture in a pediatric patient: a case report

As indicações de tratamento das fraturas mandibulares em paciente pediátrico variam em conservador, fixação não rígida e interna rígida. Alterações no crescimento ósseo, disfunções na articulação temporomandibular e assimetrias faciais podem ser decorrentes ao insucesso do tratamento. O objetivo deste trabalho consiste em relatar abordagem cirúrgica em fratura de sínfise e côndilo mandibular bilateral em paciente pediátrico. Paciente gênero feminino, 09 anos de idade, foi encaminhada ao Hospital Geral do Estado - Bahia vítima de queda de nível, cursando com trauma em face. Apresentou queixa principal, referida pela progenitora, de dificuldades em fechar a boca. Ao exame físico, a paciente apresentou mobilidade atípica à manipulação da mandíbula, mordida aberta anterior, equimose sublingual, ausência das unidades dentárias 74 e 75, com abertura bucal regular e suturas em posição em região de mento. Ao exame de imagem de tomografia computadorizada da face, pôde-se notar sinais sugestivos de fratura em região de sínfise e côndilos mandibulares bilateral. Após diagnóstico das fraturas, a paciente foi submetida à cirurgia sob anestesia geral para redução e fixação das mesmas. Realizou-se acessos em ferimento na região mentual e retromandibular bilateral com posterior síntese das fraturas utilizando fixação interna rígida com placas do sistema 2.0mm, associada a odontossíntese na fratura de sínfise. Ao acompanhamento periódico, a eleição do tratamento cirúrgico para fraturas mandibulares em pacientes pediátricos, pode permitir segurança no crescimento ósseo mandibular e facial(AU)

The indications for treatment of mandibular fractures in pediatric patients vary from conservative, non-rigid fixation and rigid internal fixation. Changes in bone growth, temporomandibular joint disorders and facial asymmetries may be due to treatment failure. The objective of this work is to report a surgical approach to bilateral symphysis and mandibular condyle fractures in a pediatric patient. Female patient, 9 years old, was sent to the State General Hospital - Bahia, victim of a fall in level, suffering from trauma to the face. She presented a main complaint, mentioned by her mother, of difficulties in closing her mouth. On physical examination, the patient presented atypical mobility when manipulating the jaw, anterior open bite, sublingual ecchymosis, absence of dental units 74 and 75, with regular mouth opening and sutures in position in the chin region. When examining the computed tomography image of the face, signs suggestive of fracture in the region of the symphysis and bilateral mandibular condyles were noted. After diagnosis of the fractures, the patient underwent surgery under general anesthesia to reduce and fix them. Access was performed on a wound in the mental and bilateral retromandibular region with subsequent synthesis of the fractures using rigid internal fixation with 2.0mm system plates, associated with odontosynthesis in the symphysis fracture. With periodic monitoring, the choice of surgical treatment for mandibular fractures in pediatric patients can allow for safe mandibular and facial bone growth(AU)

Different methods of determining centric relation - comparison with a digital mandibular motion analyser.

BACKGROUND: Finding and registering the maxillary-mandibular jaw relation is crucial in dental practice. Several comparative studies have been conducted to investigate the reproducibility and accuracy of techniques for determining the centric relation (CR) position of the mandible. The aim of our study was to determine which of seven different CR determination methods had the smallest deviation from the theoretical zero with the help of a digital mandibular motion analyser. The chosen theoretical zero position, the maximal intercuspal position (MIP), is the most reproducible and widely used position. METHODS: Thirty-four volunteers (24 females and 10 males) with a mean (SD) age of 29.1 (± 7.3) years with a negative history of temporomandibular disorder (TMD) participated in the study. A digital mandibular motion analyser was used to register the condylar position after the use of each technique for the determination of CR. The calibration was performed to the maximal intercuspal position (MIP) for each volunteer. The investigated techniques were (A) the gothic arch tracer, (B) the adduction field method, (C) Dawson's bimanual manipulation, (D) the patient placing the tongue tip on the palatal rugae, (E) the patient placing the tongue tip to the border of the hard and soft palate, (F) the patient actively pulling the chin backwards, and (G) the examiner pushing the patient's chin back. RESULTS: The position of the mandibular condyle was illustrated in a three-dimensional coordinate system, where the origin represented the MIP. Among the seven methods examined, five showed significant deviations compared to the MIP. Among these, two methods resulted in posterior deviation of the condyles. Methods C and E coincided with the MIP in all directions. CONCLUSIONS: Within the limitations of our study, we found that the smallest deviations from our theoretical zero (MIP) among the investigated centric relation determining methods were obtained with the bimanual mandibular manipulation technique derived from Dawson and the placement of the tongue tip on the border of the hard and soft palate (linguomandibular homotrophy theory).

What is a trait? Lessons from the human chin.

The chin, a distinguishing feature of Homo sapiens, has sparked ongoing debates regarding its evolutionary origins and adaptive significance. We contend that these controversies stem from a fundamental disagreement about what constitutes a well-defined biological trait, a problem that has received insufficient attention despite its recognized importance in biology. In this paper, we leverage paleoanthropological research on the human chin to investigate the general issue of character or trait identification. First, we examine four accounts of the human chin from the existing literature: the mandibular differential growth byproduct, the bony prominence, the inverted T-relief, and the symphyseal angle. We then generalize from these accounts and propose a three-stage framework for the process of character identification: description, detection, and justification. We use this framework to reinterpret the four accounts, elucidating key points of contention surrounding the chin as well as other morphological characters. We show that debates over the chin carry broad and important biological implications that extend beyond this trait and that are not mere semantic issues of definition.

Double Chin Concerns after En Bloc Mandibular U-Shaped Osteotomy: Submental-Cervical Soft Tissue Changes and Anterior Belly of Digastric Muscle Assessment.

OBJECTIVE: To assess submental-cervical soft tissue changes after en bloc mandibular U-shaped osteotomy and examine alterations in the anterior belly of digastric muscle (ABDM). METHODS: A retrospective study analyzed 20 patients who underwent en bloc mandibular U-shaped osteotomy from 2018 to 2023. Preoperative (Tp) and long-term follow-up (Tf) CT data were collected for analysis, measuring mandibular volume, soft tissue thickness at menton (Mes) and cervicale (C), and ABDM parameters (length, cross-sectional area (CSA), volume, distance from centroid point to the mandibular margin). Correlation analyses were performed to investigate the connection between soft tissue thickness changes, ABDM changes, and mandibular osteotomy volume. RESULTS: Long-term follow-up revealed a significant increase in soft tissue thickness at the Mes and C points after U-shaped mandibular osteotomy, especially at the C point. The adaptive length of ABDM decreased, CSA increased, and volume decreased, but the ABDM centroid point shifted downward relative to the mandibular margin, indicating drooping protrusion. The increment of soft tissue thickness was moderately positively correlated with the amount of osteotomy, and the decrement of ABDM length and volume were slightly positively correlated with the amount of osteotomy. CONCLUSION: The degree of soft tissue relaxation after U-shaped osteotomy is related to the extent of osteotomy. Notably, the protrusion of ABDM relative to the mandibular margin affects submental-cervical contour aesthetics. Prior to U-shaped osteotomy, it is crucial to assess the soft tissue condition of the patient's lower face, and the individualized design of the osteotomy volume should be carried out cautiously and safely. LEVEL OF EVIDENCE IV: This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

F-Chin/Feminizing the Chin: A Genioplasty Technique with Virtual Planning for Male-to-Female Transgender Patients.

The chin is an essential structure in facial harmony and an important gender marker. Advancing a receding chin is fundamental to improve the facial appearance, particularly in male-to-female transgender patients. However, in patients with microgenia and/or retrognathia, desiring a more feminine appearance, a chin advancement can result in a wider, square shape; an undesirable effect. Genioplasty is a versatile procedure used in facial feminization surgery that allows modifying the natural anatomy of the chin in all three spatial dimensions. The technique herein described proposes a simple genioplasty procedure for feminizing the chin (F-chin genioplasty) in transgender patients where anteroposterior advance is required. Virtual planning was used to establish the landmarks for an anteroposterior advancement with transverse reduction in the chin. A perpendicular line to the Frankfurt plane passing through the incisal edge of the upper central incisor was used to plan the anteroposterior movement, and two vertical lines on the outer wall of the nasal cavity  for the chin transverse measurement. The authors present three case reports with the F-chin genioplasty transgender technique with satisfactory results, ensuring a more feminine facial appearance.Level of Evidence V This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Accuracy of Dolphin Imaging software in predicting soft tissue changes of Class II Division 1 incisor relationship treated by all first premolar extraction compared with post-treatment lateral cephalogram.

BACKGROUND: To quantify the accuracy of Dolphin Imaging software in predicting soft tissue changes of Class II Division 1 incisor relationship treated by all first premolar extraction compared with actual changes. METHODS: Pretreatment and post-treatment lateral cephalograms of 30 young adult subjects (25 females and 5 males; age range of 16 to 21 years) were imported and traced in Dolphin Imaging software (version 11.95). Tracings of actual treatment results and the Dolphin predicted treatment outcome were superimposed to calculate the prediction errors. The mean difference for the Holdaway soft tissue analysis and at each landmark was measured in both the X and Y axes. Paired t test was used to compare the statistical differences in Holdaway soft tissue analysis parameters. RESULTS: There were significant differences between the predicted and actual values in three parameters of the Holdaway soft tissue analysis (P < 0.05). The overall accuracy of estimation was better in vertical direction than horizontal. Prediction of upper and lower lip landmarks was overestimated horizontally and underestimated vertically, whereas that belonging to chin was underestimated horizontally and overestimated vertically. Soft tissue nasion and soft tissue A-point were most accurately predicted, whereas the least accuracy was found in soft tissue chin region. CONCLUSIONS: Dolphin Imaging Software (version 11.95) can be accurate enough for use in patient communication and education but should be used with caution. It is most accurate in predicting soft tissue changes in the nasion and A-point regions, but least accurate in chin region.

Custom-Made Implant Fabrication for Chin Augmentation Using Piled-Up Expanded Polytetrafluoroethylene Sheets: An Innovative Surgical Technique and Literature Review.

BACKGROUND: Alloplastic chin augmentation is the most common esthetic surgical treatment to reshape the chin. However, factory-made chin implants are typically standardized rather than custom-made and have potential to cause complications. Although the fabrication of custom-made implants by using computer-assisted planning and 3D-printing technology has become widespread, the process has several disadvantages, including long preoperative prosthesis preparation times, high costs, and unsuitability for patients with asymmetric chins or those who undergo combined mandibuloplasty before implant placement. The present study developed an innovative chin augmentation technique involving stacked expanded polytetrafluoroethylene (e-PTFE) sheets that is suitable for most patients and has minimal side effects. MATERIALS AND METHODS: A retrospective review of a single surgeon's experience was performed over a 2 year period for patients who underwent a procedure involving piled-up e-PTFE sheets for alloplastic chin augmentation. This study analyzed the outcomes, complications (temporary nerve numbness, wound infection, hematoma formation, and implant displacement), and patient satisfaction during follow-up. RESULTS: Between January 2018 and December 2020, 38 patients underwent the procedure involving piled-up e-PTFE sheets for alloplastic chin augmentation. Six patients (15.8%) experienced nerve-related temporary numbness, and one (2.6%) experienced wound infection. None had developed major complications such as implant displacement or wound infection at follow-up. Moreover, the patients demonstrated a high level of satisfaction with the surgical results. CONCLUSION: Piled-up e-PTFE sheets can be used to produce custom-fit porous polyethylene chin implants that result in minimal complications and a very high satisfaction rate. LEVEL OF EVIDENCE IV: This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Preoperative Radiology and Virtual Surgical Planning.

Virtual surgical planning enables precise surgical planning and translation of this planning into the operating room. Preoperative maxillofacial computed tomography scans are compared to a reference skull to identify desired surgical changes. In facial feminization surgery, these include forehead recontouring/frontal table setback, gonial angle reduction, and possible chin repositioning/reshaping, while in facial masculinization surgery, this includes forehead augmentation and gonial angle/chin augmentation. Cutting and recontouring guides as well as custom implants are then custom manufactured. Common guides include osteotomy guides, depth drilling guides, ostectomy guides, and guides for one/two-piece genioplasty or chin burring. Common implants include mandibular and chin implants.

Chin Augmentation and Treatment of Chin Retrusion with a Flexible Hyaluronic Acid Filler in Asian Subjects: A Randomized, Controlled, Evaluator-Blinded Study.

BACKGROUND: Aesthetic improvement of the chin is increasingly requested by patients, including those of Chinese origin. METHODS: A randomized, evaluator-blinded, no-treatment controlled study evaluated the effectiveness and safety of a flexible hyaluronic acid (HA) filler, Restylane® DefyneTM (HADEF), in the correction of chin retrusion in a Chinese adult population over 12 months after treatment. On Day 1, subjects were randomized 3:1 into two groups, HADEF or delayed-treatment controls, and those in the HADEF group were administered treatment. An optional touch-up treatment was administered 1 month after treatment to obtain optimal chin augmentation. The initially untreated control group was offered delayed-treatment after 6 months (including 1-month touch-up). RESULTS: HADEF was superior to no-treatment in improving chin retrusion according to the blinded evaluator at 6 months [Galderma Chin Retrusion Scale (GCRS) responder rate (≥ 1-point improvement from baseline) of 81% vs. 5% for untreated controls; p < 0.001, meeting the primary effectiveness objective. A majority of subjects maintained improvement at 12 months (61% in the HADEF group). All subjects reported satisfaction with results at 6 months after treatment with HADEF and aesthetic improvement rates per the global aesthetic improvement scale (GAIS) were high for 12 months following treatment, with an acceptable safety profile. CONCLUSIONS: These results demonstrated HADEF to be effective and safe for the correction of mild-to-moderate chin retrusion in Chinese subjects, confirming findings previously observed in a western population. LEVEL OF EVIDENCE I: This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Injectable Fillers for Lower Face Rejuvenation.

The lower face is an integral component of a beautiful face. Age-related changes in this region are so significant that they are often easily appreciated by patients. The aging process not only includes volume loss or downward fat repositioning, but also soft tissue laxity, skin changes, and even bony resorption. In the lower face, this results in sagging of the soft tissue leading to the formation of jowling, loss of an attractive well-defined jaw line, and a retruded chin. Both surgical and non-surgical options are available to reverse the aging signs; however, the popularity of non-surgical treatment has dramatically increased in last 2 decades.

[Preliminary evaluation of chin symmetry with three dimentional soft tissue spatial angle wireframe template].

OBJECTIVE: To develop an efficient and robust method based on three dimensional facial landmarks for evaluating chin region asymmetry at the soft tissue level and to compare it with the traditional mirror-overlap analysis method in order to test its availability. METHODS: Standard symmetrical face was used for mental tubercle coordinate transformation so as to filter soft tissue three dimensional spatial angle and construct corresponding three dimensional spatial angle wireframe template. Ten patients aged 12-32 years with clinical chin region asymmetry diagnosis at the Department of Orthodontics of Peking University Hospital of Stomatology from November 2020 to November 2021 were randomly selected. Three dimensional soft tissue face scan data of the patients were collected by three dimensional face scanner and the landmark points were automatically determined by the Meshmonk non-rigid registration algorithm program, and in this way, the asymmetric three dimensional spatial angle wireframe template and corresponding spatial angle parameters were generated. Mirror-overlap analysis of face scan data was also performed in Geomagic Studio 2015 software and deviation color maps were generated. This study took mirror-overlap analysis as the gold standard method, the response rate of chin region asymmetry was eva-luated by the outcomes of the mirror-overlap analysis and three dimensional spatial angle wireframe template analysis. RESULTS: Nine three dimensional spatial angle indicators were selected through coordinate transformation, and the response rate was calculated using mirror-overlap analysis as the gold standard method. Among these ten selected patients, the response rate of the total chin region asymmetry was 90% (9/10). Using the deviation value of mirror-overlap analysis as a reference, the response rate of chin region asymmetry in the X dimension was 86%, the response rate of chin region asymmetry in the Y dimension was 89%, and the response rate of chin region asymmetry in the Z dimension was 100%. CONCLUSION: The three dimensional soft tissue spatial angle wireframe template proposed in this study has some feasibility in evaluating chin region asymmetry at the soft tissue level, and its ability to recognize asymmetry separately in the three dimensional direction is better than the mirror-overlap analysis method, and the indicators recognition rate still needs to be further improved.