Genioplasty - A Review.

Genioplasty, a key technique for dentofacial abnormalities, is essential for establishing facial harmony. This surgical procedure entails an osteotomy of the chin, which alters its three-dimensional location to restore overall face equilibrium. Modern genioplasty, which is frequently performed alone or in combination with rhinoplasty, facelifts, and orthognathic surgery, employs a variety of materials for chin augmentation, ranging from autologous to alloplastic. Recent improvements include porous graft materials such as high-density polyethylene. Despite the need for secure osteotomy segments, soft tissues around the mandible have a natural propensity to return to their original anatomical position. In the discipline of genioplasty, face esthetics and facial evaluation have been a prominent emphasis, with historical evidence emphasizing the relevance of the chin in harmony, balance, and character perception. Customized implants provide a single therapy for rare anatomical defects, generally with lower morbidity, making them critical for patients undergoing many procedures or suffering from syndromic disorders. Virtual surgical planning advances will continue to give dependable solutions for small and complex chin position issues. Modern surgeons will continue to combine history, anatomy, rigorous evaluation, excellent execution, and technological breakthroughs to achieve the best possible outcomes for their patients, raising their social standing.

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.

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)

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 .

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 .

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.

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.

Esthetic Surgery of the Chin in Cis- and Transgender Patients-Application of T-Genioplasty vs. Single-Piece Segment Lateralization.

Background and Objectives: Correction of lower face asymmetry still remains challenging in maxillofacial surgery. This report describes techniques for the lateral transposition of the symphyseal segment to restore lower face symmetry while maintaining gender-related features in cis- and transgender patients. Materials and Methods: A retrospective review of medical records of 31 patients who attended for esthetic corrective surgery after orthodontic camouflage or orthognathic treatment, or during facial feminization of the lower face between June 2021 and June 2023 was performed. Result: All patients underwent lateralization genioplasty (with or without advancement or setback), either with or without narrowing T-osteotomy supplemented with necessary procedures in order to obtain proper facial balance and desired esthetical effects, such as bichectomy, liposuction, and face and neck lift. The mean asymmetry of the chin was 5.15 mm and was surgically corrected either by single segment lateralization or T-shape narrowing genioplasty depending on the gender and esthetical requirements. No complications were reported. Conclusions: Lateral shift genioplasty serves as a powerful tool in primary and secondary corrective surgery for lower face asymmetry that maintains gender-specific facial features. It may serve either as an additive to orthodontic camouflage or a way to correct previous orthognathic surgery pitfalls. The surgeon performing esthetic genioplasty associated with gender-specific expectations must be trained in facelift and facial liposculpting techniques in order to provide the best results and properly choose the right procedures for the right patients.

Chin Dysmorphology in the Primary Rhinoplasty Population: Prevalence, Objective Analysis, and Implications.

BACKGROUND: Chin flaws are far more common than recognized. Denial of genioplasty by parents or adult patients can present a surgical planning enigma, especially in patients with microgenia and chin deviation. This study aims to investigate the frequency of chin imperfections on patients seeking rhinoplasty, review the conundrum they generate, and offer management suggestions based on over 40 years of the senior author's experience. METHODS: This review included 108 consecutive patients presenting for primary rhinoplasty. Demographics, soft tissue cephalometrics, and surgical details were obtained. Exclusion criteria included prior orthognathic or isolated chin surgery, mandiblular trauma, or congenital craniofacial deformities. RESULTS: Of the 108 patients, 92 (85.2%) were female. Mean age was 30.8 years (SD±13, range 14-72). Ninety-seven (89.8%) patients exhibited some degree of objective chin dysmorphology. Fifteen (13.9%) had Class I deformities (macrogenia), 63 (58.3%) Class II (microgenia), and 14 (12.9%) Class III (combined macro and microgenia in the horizontal or vertical vectors). Forty-one (38%) patients had Class IV deformities (asymmetry). While all patients were offered the opportunity to correct chin flaws, only 11 (10.1%) underwent such procedures. Five (4.6%) patients had simultaneous osseous genioplasty (mean advancement 7.8mm, range 5-9mm); 7 (6.5%) received fat grafting to the chin (mean volume 4.4cc, range 1-9cc). CONCLUSIONS: A considerable proportion of primary rhinoplasty patients possess quantifiable chin dysmorphology on circumspect examination, high-resolution photographs and cephalometric analysis. Only a small number agree to surgical interventions that pursue full facial harmony. Potential reasons for these findings, patient aversion, and mitigation strategies will be discussed. LEVEL OF EVIDENCE III: 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 .

Soft-Tissue Response following Genioplasty Combined with Anterior Segmental Osteotomy.

BACKGROUND: The authors' main aim was to analyze soft-tissue response of the chin following genioplasty with anterior segmental osteotomy, which enables optimal surgical planning of genioplasty. METHODS: Sixty-two patients who underwent genioplasty with concomitant anterior segmental osteotomy were divided into three groups depending on the direction of pogonion (Pog) movement: G1 (without sagittal change), G2 (advancement genioplasty), and G3 (setback genioplasty). All genioplasties included height reduction. Hard- and soft-tissue measurements with cephalometry were performed at T1 (before surgery), T2 (after surgery), and T3 (after orthodontic treatment) for the analysis of sagittal and vertical changes. Correlation and regression analyses were conducted to analyze soft- to hard -tissue movement and soft-tissue thickness changes. RESULTS: During the T1 to T2 period, the horizontal soft- to hard-tissue ratio at Pog was 0.85 in G2 and 0.80 in G3, and the vertical ratio at menton (Me) was 0.9 for all groups. The correlation coefficients were 0.64 (G2) and 0.83 (G3) at Pog and 0.9 (all), 0.85 (G1), 0.95 (G3) at Me. There was no significant correlation between initial soft-tissue thickness and soft-tissue response ratio. During the T2 to T3 period, no significant relapses were observed, which demonstrates the stability of anterior segmental osteotomy combined genioplasty. CONCLUSIONS: Clinically and statistically significant soft-tissue responses were demonstrated at Pog and Me. The higher values in G3 in particular suggest that setback genioplasty with anterior segmental osteotomy is an effective treatment alternative to conventional two-jaw surgery in some patients with bimaxillary prognathism with macrogenia. CLINICAL QUESTION/LEVEL OF EVIDENCE: Therapeutic, IV.

Osseous genioplasty versus chin implants: early complications and patient satisfaction.

Osseous genioplasty and chin augmentation with implants are the two main treatment options for retrognathia. This retrospective cohort study was performed to compare the prevalence of complications and patient satisfaction following osseous genioplasty and chin augmentation by implant. Eighty patients were included: 38 underwent advancement osseous genioplasty and 42 received chin implants (alloplastic, either Medpor or Silastic) intraorally or extraorally. The patients were assessed for complications 12 months after surgery, including neurosensory disturbances, infection or extrusion, wound dehiscence, and the need for reoperation. Patient satisfaction was evaluated using a visual analogue scale. The infection rate was significantly higher in the chin implant group than in the genioplasty group (P = 0.028). Moreover, dehiscence and the need for reoperation appeared to be more common following chin augmentation with implants. However, there was no significant difference in the prevalence of neurosensory disturbances between the two groups (P = 0.137). In the chin implants group, the extraoral approach resulted in a lower dehiscence rate than the intraoral approach. Patients in the genioplasty group had significantly higher satisfaction scores than those in the chin implant group (P = 0.001). Overall, the rates of the complications assessed were lower and patient satisfaction was higher after osseous genioplasty when compared to chin augmentation with implants.

Does Aesthetic Osseous Genioplasty Impact Upper Airway Volume?

BACKGROUND: Although maxillomandibular advancement is the treatment of choice for obstructive sleep apnea syndrome (OSAS) in the presence of underlying maxillomandibular complex hypoplasia, there is still a gap in the literature regarding the impact of genioplasty upon upper airway volume (UAV). OBJECTIVES: The aim of this study was to evaluate the impact of isolated osseous genioplasty upon UAV. METHODS: A retrospective analysis of all patients subjected to isolated osseous genioplasty between July 2015 and July 2022 was conducted. Cone-beam computed tomography was performed preoperatively and postoperatively to assess the chin and hyoid 3-dimensional (3D) spatial position and UAV changes after surgery. RESULTS: A total of 44 patients were included in the study. Regarding surgical movements of the chin, almost all patients received a sagittal movement (n = 42; 39 forward and 3 backward), while in 8 patients a vertical movement (5 upward and 3 downward) was applied, and in 6 patients the chin was centered. Statistically significant increases in total UAV (P = .014) and at the level of the oropharynx (P = .004) were observed. Specifically, chin centering, upward and forward movements enlarged the oropharynx volume (P = .006, .043 and .065, respectively). Chin advancement enlarged the hypopharynx volume (P = .032), as did upward movement of the hyoid bone (P < .001). CONCLUSIONS: Results of the study suggest that aesthetic osseous genioplasty impacts the UAV: each 3D spatial chin movement differently impacts the upper airway by enlarging or narrowing it. However, further studies addressing the apnea-hypopnea index are required to assess its effectiveness in treating OSAS.

Nonsurgical Chin Augmentation Using Hyaluronic Acid: A Systematic Review of Technique, Satisfaction, and Complications.

The article titled "Nonsurgical Chin Augmentation Using Hyaluronic Acid: A Systematic Review of Technique, Satisfaction, and Complications" by Ou et al. in Aesthetic Plastic Surgery presents a systematic review focused on categorizing complications associated with hyaluronic acid (HA) dermal fillers. However, concerns arise regarding the methodologies employed in the reviewed studies. It is essential to have precise knowledge of the properties of the active substance for treatment standardization. Gaining a comprehensive understanding of the key characteristics of the HA used is paramount to determine if there is an association between these properties and the risk of complications.Understanding HA's rheological properties, including viscosity, elasticity, and cohesiveness, is crucial for selecting the most suitable facial filler. While we acknowledge the authors' contributions, we strongly believe that further analysis should incorporate these factors.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 .

[Three-dimensional comparative study on the stability of bimaxillary simultaneous genioplasty and simple genioplasty].

PURPOSE: To establish a three-dimensional method to evaluate whether there is a difference in stability between bimaxillary simultaneous genioplasty and simple genioplasty. METHODS: This study was a retrospective study. Sixty patients who underwent genioplasty were selected. They were divided into bimaxillary simultaneous genioplasty group (n=30) and simple genioplasty group (n=30). The spiral CT data of patients at 2 months before operation (T0), 7 days after operation (T1) and 12 months after operation (T2) were collected, reconstructed and separated, and the three-dimensional model of maxilla and mandible was obtained. A three-dimensional analysis method of stability was established by 3D-matching. Recurrences in three-dimensional space 12 months after surgery were analyzed in two groups of patients. Statistical analysis of the data was performed with SPSS 26.0 software package. RESULTS: In simple genioplasty, the maximum amount of the chin recurrence was sagittal backward recurrence (0.54±0.38) mm, and the sagittal recurrence rate was 12.27%. In bimaxillary simultaneous genioplasty, the maximum amount of the chin recurrence was sagittal backward recurrence (0.60±0.31) mm, and the sagittal recurrence rate was 12.96%. Rotation occurred in both groups 12 months after operation, which was 1.98±2.70° in the simple genioplasty group and 1.01±1.61° in the bimaxillary simultaneous genioplasty group(P＜0.05). There was no significant difference in the sagittal movement of the chin between the two groups, and in the sagittal recurrence(P＞0.05). CONCLUSIONS: The three-dimensional method established in this study can be used to evaluate the stability after genioplasty. The recurrence after genioplasty mainly occurred in the sagittal direction. The rotation trend of chin after genioplasty is worthy of attention. There was no increased risk for bimaxillary simultaneous genioplasty.

The prediction of sagittal chin point relapse following two-jaw surgery using machine learning.

The study aimed to identify critical factors associated with the surgical stability of pogonion (Pog) by applying machine learning (ML) to predict relapse following two-jaw orthognathic surgery (2 J-OGJ). The sample set comprised 227 patients (110 males and 117 females, 207 training and 20 test sets). Using lateral cephalograms taken at the initial evaluation (T0), pretreatment (T1), after (T2) 2 J-OGS, and post treatment (T3), 55 linear and angular skeletal and dental surgical movements (T2-T1) were measured. Six ML modes were utilized, including classification and regression trees (CART), conditional inference tree (CTREE), and random forest (RF). The training samples were classified into three groups; highly significant (HS) (≥ 4), significant (S) (≥ 2 and < 4), and insignificant (N), depending on Pog relapse. RF indicated that the most important variable that affected relapse rank prediction was ramus inclination (RI), CTREE and CART revealed that a clockwise rotation of more than 3.7 and 1.8 degrees of RI was a risk factor for HS and S groups, respectively. RF, CTREE, and CART were practical tools for predicting surgical stability. More than 1.8 degrees of CW rotation of the ramus during surgery would lead to significant Pog relapse.