Bony Chin Research Articles

Effect of Different Treatment Modalities for Condylar Fractures in Childhood on Mandibular Symmetry and Temporomandibular Joint Function: A Retrospective Study.

In a retrospective study of the effects of different treatment modalities of condylar fractures in childhood on mandibular symmetry and temporomandibular function, the cases selected for this article were adult patients who had sustained a condylar fracture in childhood. The aim was to investigate the effects of condylar fractures in children on the development and function of the mandible and their specific manifestations after the completion of mandibular development. According to the different treatment modalities, the patients were divided into the conservative treatment group and the open surgical treatment group, and the effects of the 2 treatment modalities on the patients' condylar healing, the difference in growth ability, and the symmetry of the jaws were evaluated. The effects of different treatment modalities of children's condylar fracture on the growth, development, and function of the mandible were investigated using the Ai and Di, the grading of the imaging results, and the 3-dimensional CT fixation measurements from the aspects of both clinical examination and imaging examination. The 2 groups had condylar malalignment and condylar morphology abnormality, and there was one case of joint ankylosis in the surgical treatment group. There was a statistical difference in the evaluation of condylar reconstruction between the 2 groups, and the condylar reconstruction in the surgical treatment group was better than that in the conservative treatment, and there was a statistical difference between the condylar length, condylar width, condylar height, and depth of TMJ fossa between the healthy side and the affected side in the closed treatment group. There was a statistical difference in the height of the mandibular ascending branch between the healthy side and the affected side, and the unilateral condylar fracture was treated conservatively; the difference in the bony chin point deviation between the 2 groups was not statistically significant. In children, after conservative treatment of condylar fracture, the growth of condylar process is poor, and the condylar shape and position are not as good as surgical repositioning, but through the proliferation of temporomandibular joint fossa, it can make up for the insufficient height of condylar process, which has no effect on the symmetry of the mandible, and the surgical treatment can achieve good anatomical repositioning, which has a greater effect on the symmetry of the mandible than the conservative treatment.

Combined Genioplasty and External Oblique Line Grafting: An Innovative Method to Improve Lower Facial Contour.

Microgenia and the accompanying plump cheeks or hamster-like facial contour are all unattractive appearances among the Asian. Genioplasty with autogenous bone grafting is one of the effective ways to improve microgenia, in which a suitable donor area with less additional damage, lower infection rate, and more excellent effect is crucial. Patients who had undergone genioplasty and autogenous external oblique line grafting (G-EOL) were followed up. The operation-related complications, preoperative, and long-term follow-up 3-dimensional spiral computed tomography (3D-CT) were collected and analyzed. Eight female patients who had received G-EOL and received 1 to 3 years of follow-up were included in this study. There were no short-term or long-term complications. CT data of bone of 8 patients and CT data of soft tissue of 6 patients at the preoperative and long term were compared. Through comparing CT data, the width at the level of the intersection of EOL and mandibular body, and the protrusion of the bony chin had improved significantly; the P values were all <0.001. Through measuring the soft tissue and analyzing the data, the ratio of lower and middle facial width, and the distance from the lower lip to Ricketts' line were all improved, with the P values 0.042 and 0.001, respectively. For patients with microgenia and hamster-like facial contour, the combination of genioplasty and autogenous external oblique line grafting is innovative and effective in improving both the front and side contour of the lower face simultaneously, with excellent stability, bone healing, and low complication rates.

Coronal-splitting Reduction Genioplasty Combined with Bilateral Osteotomies of the Mandibular Inferior Border for Macrogenia

Summary: There are various types of chin deformities, and the least established surgical method for deformity correction may be reduction for anteroposterior macrogenia. Anteroposterior macrogenia is commonly corrected by either setback genioplasty or burring reduction, but these approaches are less likely to produce aesthetically pleasing results. Both procedures have poor reduction effects because of the low response rate of soft tissues to skeletal alterations. There is a high likelihood of chin ptosis and flattening. Setback genioplasty can also yield step deformities at the inferior mandibular border. To overcome these drawbacks of conventional methods, I developed a novel technique of coronal-splitting reduction genioplasty. I have performed more than 83 procedures with a high success rate over the past 10 years. Alloplastic chin implant-shaped bone fragments were resected from the prominent bony chin, in which the average thickness of resected bone was 8.2 mm. Sufficient sagittal reduction effects were then achieved in most cases, although the soft tissue response rate remains 25%–50%, as reported in the literature. The no-degloving technique with cephalic suspension of the mentalis muscle prevents chin ptosis. Combined bilateral oblique osteotomies of the inferior mandibular border contribute to minimizing obvious postoperative chin flattening. Moreover, macrogenia can be large in multiple planes, including anteroposterior, vertical, transverse, or their combinations. This new technique can handle all three planes by combining both bilateral oblique osteotomies of the inferior mandibular border and burr ostectomy. Overall, these findings suggest that the coronal-splitting genioplasty method may replace conventional methods for correcting macrogenia.

Genetic and environmental impact on mandibular growth in mono- and dizygotic twins during adolescence: A retrospective cohort study

This study aimed to discover the genetic and environmental factors that contribute to the mandibular development of untreated monozygotic and dizygotic twins. The sample, taken from the Forsyth Moorrees Twin Study, included 52 untreated monozygotic twins (36 male, 16 female) and 46 untreated dizygotic twins (23 male, 23 female). At the ages of 12 and 17, lateral cephalograms were collected and traced to assess total mandibular length, mandibular ramus length, mandibular corpus length, gonial angle, SNB, and bony chin prominence. The genetic and environmental components of variation were assessed using multilevel mixed-effects structural equation modelling. At 12 years of age, high additive genetic influences were observed for total mandibular length (74%), gonial angle (76%), SNB (41%), and bony chin prominence (64%), whereas strong dominant genetic components were observed for corpus length (72%), and mandibular ramus length was under unique environment influence (54%). At 17 years of age, only total mandibular length (45%), ramus length (53%), gonial angle (76%), and bony chin prominence (68%) were under strong additive genetic control, while the remainder were under strong dominant genetic control. Although monozygotic and dizygotic twins share at least a portion of their DNA, additive, dominant, or environmental components were discovered during adolescence. Nonetheless, by the age of 17, the majority of the mandibular traits are under either additive or dominant genetic impact.

A Novel Cephalometric Approach Aiming to Quantify a Normal Range of Bony Chin Protrusion.

Cephalometric analysis is an essential tool in the diagnostics and planning of orthognathic surgery. No objective criterion exists to facilitate decision making regarding genioplasties. Differing opinions amongst clinicians therefore leads to wide variability amongst treatment options offered to potentially suitable patients. This study has three aims. The first was to quantify the distribution of chin morphology amongst the average population using cephalometric analysis. Secondly, we sought to determine whether cephalometric parameters could be used to predict overlying soft tissue changes. Lastly, we consider the use of a new cephalometric angle, BNPg, for pre- and post-operative assessment of genioplasty patients. This study retrospectively analysed 231 lateral cephalograms. The angle between the landmarks: B point, Nasion and Pogonion was measured to generate 'BNPg' a novel unit to quantify bony chin protrusion. The mean BNPg from all 231 samples was 1.12 degrees with a standard deviation of ± 1.35. Comparison between sexes showed no significant differences between male and females (P = 0.108). Furthermore, bony chin protrusion was found to strongly positively correlate with soft tissue chin appearance (r = 0.731), however, BNPg was found not to correlate with skeletal malocclusion (ANB, r = 0.085). The novel unit BNPg may serve as a useful tool in contributing to the determination of treatment thresholds in osseous genioplasty for desirable aesthetic outcomes and may be used post-operatively to assess outcomes also. As this is a pilot study, further clinical studies would be required to validate this parameter in genioplasty patients, both pre- and post-operatively. The online version contains supplementary material available at 10.1007/s12663-022-01784-5.

The 3D-printed surgical guides used during genioplasty

Genioplasty is a seemingly simple procedure performed to correct the bony chin. The results of the procedure are, however, strongly correlated with the experience of the surgeon. 3D-printed surgical guides could act as a transfer modality to translate the preoperative planning directly into the achieved result. Prospective studies evaluating the usefulness of the 3D-printed surgical guides have not yet been carried out and consensus regarding the best design is lacking. In order to become more familiar with working with surgical guides, a genioplasty using 3D-printed surgical guides was performed. The postoperative analysis of the achieved result showed minor differences compared to preoperative planning. Surgical guides have the potential to improve the accuracy and predictability of genioplasty. The design should be further refined and the added value of the guides should be confirmed by means of prospective research.

Variable negative external pressure-an alternative to continuous positive airway pressure for the treatment of obstructive sleep apnea: a pilot study.

To assess variable negative external pressure (vNEP) therapy using a range of pressures and varying collar sizes and shapes to identify combinations that improve the efficacy and comfort of this emerging therapy for obstructive sleep apnea (OSA). This prospective, open-label pilot study included 28 eligible patients (71% men) having documented moderate OSA (apnea-hypopnea index [AHI] 15 events/h ≤ AHI ≤ 30 events/h) at 1 sleep clinic for an overnight, in-lab sleep trial. Each participant tested at least 2 of 6 available vNEP devices during sleep periods ≥ 2 hours. During the assessment of AHI by polysomnography, negative pressures of -20 cm H2O to -35 cm H2O were adjusted to improve each patient's response. Participants' therapeutic preferences were assessed by a questionnaire and interviews. Twenty (71%) of the participants responded to vNEP therapy: excellent response (AHI ≤ 5 events/h) was observed in 14 (50%); 6 (21%) achieved a partial response (AHI ≤ 50% baseline). For the 20 responders, the therapy reduced the fraction of total sleep time when peripheral oxygen saturation < 90% and improved minimum pulse oximetry oxygen saturation. Six patients experienced a minor, self-limited adverse event. Twenty-six participants (93%) stated that they would use vNEP nightly. In this pilot study, vNEP therapy markedly improved AHI and oxygenation in most patients with moderate OSA. The majority of participants found vNEP comfortable and preferable to prevailing OSA therapies. Further development and studies of vNEP are warranted. Registry: ClinicalTrials.gov; Name: Study of Variable Negative External Pressure (vNEP) in Reducing Respiratory Event in Individuals With OSA; URL: https://clinicaltrials.gov/ct2/show/NCT04718142; Identifier: NCT04718142. Kram JA, Pelayo R. Variable negative external pressure-An alternative to continuous positive airway pressure for the treatment of obstructive sleep apnea: A pilot study. J Clin Sleep Med. 2022;18(1):305-314.

The goniomaxillar length/goniomandibular length ratio in normal newborn infants: A clinical tool for defining chin position abnormalities.

Retrognathia (recessed chin) and prognathism (prominent chin) often present as signs of an underlying condition. Accurate clinical definitions are important. Yet their definitions were according to "clinical impression", or to seldom used X-ray criteria. We propose a statistical and anthropometric definition of retrognathia and prognathism based upon the ratio between the goniomaxillar length (distance between the gonion at the mandible angle and the subnasale and the goniomandibular length (distance between the mandible angle and the most anterior point of the bony chin). We assumed that an increase in the ratio indicates retrognathia and a decrease reflects prognathism. We conducted a prospective, observational, anthropometric study in 204 consecutive healthy term infants. Measurements took place on the second day of life, using sliding calipers. Mean ± SD of goniomandibular length (5.1 ± 0.3 cm), goniomaxillar length (5.4 ± 0.3 cm), were calculated. All measurements correlated significantly with gestational age, and with infant birthweight. The mean ± SD goniomaxillar length/goniomandibular length ratio was 1.06 ± 0.05. We defined a normal ratio as being within 2 SD of the mean, that is, between 0.96 and and 1.16. This ratio correlated with neither gestational age nor with birthweight. We conclude that the goniomaxillar length/goniomandibular length ratio can be calculated whenever retro - or prognathism is suspected. A ratio outside of the 95% confidence interval should help in making this diagnosis. An increase in this ratio beyond 2 SD above the mean (1.16) could be interpreted as retrognathia and a decrease beyond 2 SD below the mean (0.96) as prognathism.

Cephalometric features of Angle class III malocclusion with different dentoalveolar compensation (retrospective study)

Introduction: This study was to investigate dentoalveolar compensation in untreated skeletal Class III patients. Methods:This retrospective study was conducted on 102 untreated Class III malocclusion patients. They were divided into group 1 (overjet<0mm, n=51) and group 2 (overjet ≥ 0mm, n=51). Twenty-six cephlometric readings were compared between the two groups. Correlation analysis was performed between the overjet with skeletal and dental measurements and Regression analysis was performed to determine the overjet. Results: The results showed a significantly higher SNB, S-N-Pg, gonial angle and L1-NB mm in the negative overjet group. While, the ANB angle, angle of convexity, Wits appraisal, bony chin and U1- A-Pg mm were significantly higher in the positive overjet group. However, no statistically significant difference was found in the rest of the readings. Correlational analyses showed that the overjet has significant negative correlation with SNB, S-N-Pg, L1-Frankfort, gonialangles. On the other hand, it had significant positivecorrelation with ANB angle, angle of convexity, Wits appraisal, bony chin, L1-MP angle and U1-A-Pg mm. Nine regression equations for the overjet were calculated with the highest coeffcient of determination of 0.33. Conclusion: Dentoalveolar compensation was seen in Class III cases with less skeletal discrepancy, lower mandibular prominence, larger bony chin, greater angle of convexity and smaller gonial angle. Moreover, the position of the maxillary and mandibular incisors on the basal bone, rather than their inclination, contributed in dentoalveolar compensation

A novel cephalometric approach aiming to quantify a normal range of bony chin protrusion

A novel cephalometric approach aiming to quantify a normal range of bony chin protrusion

Modification of Chin Projection and Aesthetics With OnabotulinumtoxinA Injection.

Because of the soft-tissue envelope and the dimensional complexity of the muscular contraction of the mentalis muscle, the projection and shape of the chin is not determined by only the bony projection. In a subset of patients with a seemingly underprojected chin, a hyperactive, high-riding mentalis muscle contributes to a blunted chin contour. To evaluate the use of onabotulinumtoxinA (botulinum toxin A) for improving chin aesthetics in patients with an underprojected bony chin and a high-riding hyperactive mentalis muscle. This case series and photographic analysis included 11 patients presenting with an underprojected bony chin and a high-riding hyperactive mentalis muscle at a private facial plastic surgery practice from August 25, 2006, to November 10, 2012. Data were analyzed from November 13, 2012, to April 9, 2013. Injection with 12 to 15 U of onabotulinumtoxinA into the mentalis muscle. Photographic analysis of the vertical and horizontal positions of the pogonion relative to fixed facial points before and after injection. A patient satisfaction scale was also used to assess improvement in overall chin aesthetic. Eleven patients (3 men and 8 women; mean [SD] age, 46.3 [16.4] years) participated in the study, including 2 who had undergone prior chin implantation. The vertical position of the pogonion was more inferior after injection in 10 of 11 patients (mean [SD] vertical position, 1.36 [0.18] preinjection and 1.44 [0.18] postinjection; P = .005). Although the horizontal position of the pogonion changed in all patients, this change was not statistically significant (mean [SD] horizontal position, 0.11 [0.13] preinjection and 0.14 [0.13] postinjection; P = .32). All patients experienced improvement in their overall chin aesthetic and a subjective decrease in chin tension. Chin contour was improved, with soft-tissue volume overall displaced more inferiorly with a rounded rather than blunted appearance. No adverse effects were reported after injection. OnabotulinumtoxinA is effective at improving chin aesthetics by altering the position of the pogonion. In this first photographic analysis to date of the influence of onabotulinumtoxinA treatment, patients demonstrated a measurable change in the position of the pogonion, in addition to improvements to the chin contour on profile. This nonsurgical mentoplasty may be used as an independent procedure or as an adjunct to optimize traditional chin augmentation in carefully selected patients. 4.

Automatic repositioning of jaw segments for three-dimensional virtual treatment planning of orthognathic surgery

PurposeTo develop a computer-based method for automating the repositioning of jaw segments in the skull during three-dimensional virtual treatment planning of orthognathic surgery. The method speeds up the planning phase of the orthognathic procedure, releasing surgeons from laborious and time-consuming tasks. Materials and methodsThe method finds the optimal positions for the maxilla, mandibular body, and bony chin in the skull. Minimization of cephalometric differences between measured and standard values is considered. Cone-beam computed tomographic images acquired from four preoperative patients with skeletal malocclusion were used for evaluating the method. ResultsDentofacial problems of the four patients were rectified, including skeletal malocclusion, facial asymmetry, and jaw discrepancies. ConclusionsThe results show that the method is potentially able to be used in routine clinical practice as support for treatment-planning decisions in orthognathic surgery.

Reconstruction of the bony chin using sagittal split osteotomies of the remaining mandible – A new technique for a special indication: Case report

There are several indications for resecting the bony chin, such as squamous cell carcinoma, sarcoma, or benign tumors of the jaw such as ameloblastoma. Several techniques for reconstruction of the bony chin, such as the use of metal plates and also revascularized free bone grafts of the iliac crest, fibula, or scapula, are common. In the case of poor vascular supply, however, alternative techniques may be necessary. In this report, a new technique is described using pedicled bone flaps from both sagittally split mandibular stumps following chin resection. These flaps were pedicled on the mylohyoid muscles and advanced to restore the continuity of the mandible. An advantage of this procedure was minimization of the soft tissue defect, making repair easier. Morbidity of the resection and reconstruction was thus reduced, and recovery of the patient was very quick.

Three-dimensional morphological characterization of malocclusions with mandibular lateral displacement using cone-beam computed tomography

Objective: The purpose of this study was to evaluate the morphologic characteristics of MLD malocclusions using 3D imaging.Materials and methods: MLD characteristics were examined using CBCT data in 40 subjects. A 3D Cephalometric analysis was developed to describe the spatial position of the mandible and temporal bones.Results: Vertical dental heights were shorter and the posterior occlusal plane (POP) presented a steeper sagittal inclination on the shifted side (the side of the laterally displaced bony chin) than on the contralateral side. (p < 0.01). The MLD was related to a superiorly inclined POP Cant in the same direction (r = 0.82; p < 0.01). The shifted side condyle was dislocated medially and was smaller. Temporal bone sagittal inclination showed a more forward and medial inclination on the contralateral side (p < 0.01).Conclusions: A unilateral decrease in the vertical height of the dentition and the subsequent steeper occlusal plane inclinations correlated with (1) mandibular rotational displacement and condylar lateral displacement, (2) mandibular and condylar morphologic changes (3) changes in temporal bone position.

Reliability of Ultrasound in the Identification and Measurement of Blood Supply to the Anterior Part of the Mandible

ABSTRACTObjectiveThe aim of this study is to identifyin vivothe main blood supply to the bony chin and to determine the efficacy of ultrasound Doppler in determining this aspect and then compare it with radiograph.Materials and methodsThe study was carried on 50 subjects divided into two equal groups. In the first group, the lingual foramen was identitifed on intraoral periapical (IOPA) radiograph of the mandibular incisor region. Ultrasound Doppler identification of blood supply to the anterior part of the mandible was carried out. In the second group of 25 subjects, the procedure was reversed. This was done to avoid procedural bias.DiscussionIn our patients, the midline artery entering the lingual foramen was seen by ultrasound and radiograph. Their average diameters and velocities were measured. It was identified in 46 cases by the ultrasound Doppler examination. The IOPA radiographic examination was successful in identifying the foramen in 30 cases. The average diameter of the midline artery entering the lingual foramen was found to be 0.14 cm. The average velocity of blood flow in this artery was found to be 25.5 cm/second.ConclusionThe ultrasound Doppler is a reliable tool to visualize and measure the blood supply to the anterior part of the mandible.How to cite this articleKiran MS, Manjunath M, Shukla AK, Vidya S. Reliability of Ultrasound in the Identification and Measurement of Blood Supply to the Anterior Part of the Mandible. J Med Sci 2017;3(1):20-24.

Orthognathic Surgery for Correction of Patients With Mandibular Excess: Don’t Forget to Assess the Gonial Angle

To evaluate the gonial angle (GA) and associated factors that can contribute to stability after bilateral sagittal split ramus osteotomy setback and Le Fort I advancement osteotomy for the treatment of patients with mandibular excess. This retrospective study included 42 randomly selected, adult patients. Lateral cephalometric radiographs were obtained before and 1 week and 1 year after surgery. Patients in group 1 (n= 18) had a GA smaller than 125° and those in group 2 (n= 24) had a GA larger than 125°. Data were analyzed by analysis of variance and Pearson correlations. Multivariate linear regression analysis was used to identify factors that influenced postsurgical stability. Mean surgical changes were similar in the 2 groups. The mandible was set back an average of 5.4mm in group 1 and 6.4 mm in group 2, whereas the maxilla was advanced 2.5 mm in group 1 and 1.7mm in group 2. Statistically significant postoperative changes were noted for group 1 only. Relapse was found at the innermost point of the contour of the mandible between the incisor tooth and bony chin and the pogonion for the horizontal landmarks; the innermost point of the contour of the maxilla between the anterior nasal spine and incisor tooth and the menton for the vertical landmarks; and the GA, the angle between the sella-nasion line and the innermost point of the contour of the mandible between the incisor tooth and bony chin, and the esthetic plane to the upper lip for the dimensional landmarks. No statistically significant changes were noted for group 2 (GA >125°). Patients with a preoperative GA smaller than 125° have a greater risk of relapse after receiving bilateral sagittal split ramus osteotomy setback and Le Fort I advancement for the treatment of mandibular excess. Patients with a preoperative GA larger than 125° appear to have a more predictable procedure.

Skeletal and Dental Variables Related to the Stability of Orthognathic Surgery in Skeletal Class III Malocclusion With a Surgery-First Approach

The objectives of the study were to identify the parameters related to skeletal stability after orthognathic surgery in skeletal Class III malocclusion using a surgery-first approach and to analyze the factors correlated with surgical relapse. Forty-five consecutive patients were included. Serial cephalometric radiographs were traced and superimposed to investigate surgical stability at the initial examination, 1 week postoperatively, and after orthodontic debonding (12.22 mo after surgery). Patient grouping was based on the amount of horizontal relapse at the innermost point of the contour of the mandible between the incisor tooth and the bony chin, the B point (less stable group, n = 15; highly stable group, n = 18). Parameters, such as presurgical skeletal and dental variables, the amount of surgical setback, and total treatment duration, were compared between groups and analyzed for correlations with surgical stability. The mean setback at the innermost point of the contour of the mandible between the incisor tooth and the bony chin was 11.19 mm, and the mean relapse rate was 12.46%. The amount of surgical setback, overbite (positive values), overjet, depth of the curve of Spee, and lower anterior facial height showed statistically significant differences between groups. The amount of surgical setback, overbite (positive values), overjet, and depth of the curve of Spee showed statistically significant correlations with the amount of relapse. Skeletal relapse of the mandible increased significantly as the overbite increased. The factors for instability in the surgery-first approach include a larger overbite, a deeper curve of Spee, a greater negative overjet, and a greater mandibular setback. The initial overbite may be an indicator to predict possible skeletal relapse of mandibular setback.

Long anterior mandibular tooth roots in Neanderthals are not the result of their large jaws

Tooth root length has been shown to taxonomically distinguish Neanderthals from modern humans. However, this may result from differences in jaw size between both taxa, although most previous studies have revealed a very low or non-existent correlation between tooth size and jaw size in recent modern humans. We therefore investigated, within a broader taxonomical frame, to what extent measurements on the anterior tooth roots and the symphyseal region covary.Our samples comprise permanent mandibular incisors and canines from Mauer, Neanderthals, and extant and fossil modern humans sensu lato. Using micro-computed tomography, we took linear and cross-sectional surface area measurements of the roots and the symphyseal region and calculated the root volume. We also measured 3D landmarks to quantify the overall size of the mandible using centroid size. Furthermore, we analyzed the relationship between root size and symphyseal shape, based on Procrustes shape variables of semi-landmarks along the symphyseal outline.Our results show that Neanderthals have significantly larger anterior tooth roots than recent modern humans in terms of root length, mid-sagittal surface area and volume, even after correction for mandibular size. In contrast, symphyseal height and width do not differ significantly between both taxa, whereas, without scaling, the mid-sagittal symphyseal surface area and the centroid size of the mandible do differ. Importantly, no significant correlation was found between any of the root and symphyseal measurements after correction for overall mandibular size. The shape analyses revealed that Neanderthals have a vertical symphyseal profile with an evenly-thick symphysis, whereas recent modern humans display an unevenly-thick symphysis, comprising a pronounced incurvatio mandibularis and a bony chin. These results suggest a negative evolutionary allometry for the recent modern human anterior root size. Therefore, root length and other root dimensions can be considered taxonomically relevant for distinguishing Neanderthals from modern humans.

Long-term skeletal and dental effects and treatment timing for functional appliances in Class II malocclusion

To analyze the long-term skeletal and dentoalveolar effects and to evaluate treatment timing of Class II treatment with functional appliances followed by fixed appliances. A group of 40 patients (22 females and 18 males) with Class II malocclusion consecutively treated either with a Bionator or an Activator followed by fixed appliances was compared with a control group of 20 subjects (9 females and 11 males) with untreated Class II malocclusion. Lateral cephalograms were available at the start of treatment (mean age 10 years), end of treatment with functional appliances (mean age 12 years), and long-term observation (mean age 18.6 years). The treated sample also was divided into two groups according to skeletal maturity. The early-treatment group was composed of 20 subjects (12 females and 8 males) treated before puberty, while the late-treatment group included 20 subjects (10 females and 10 males) treated at puberty. Statistical comparisons were performed with analysis of variance followed by Tukey's post hoc tests. Significant long-term mandibular changes (Co-Gn) in the treated group (3.6 mm over the controls) were associated with improvements in the skeletal sagittal intermaxillary relationship, overjet, and molar relationship (∼3.0-3.5 mm). Treatment during the pubertal peak was able to produce significantly greater increases in total mandibular length (4.3 mm) and mandibular ramus height (3.1 mm) associated with a significant advancement of the bony chin (3.9 mm) when compared with treatment before puberty. Treatment of Class II malocclusion with functional appliances appears to be more effective at puberty.

Chin development as a result of differential jaw growth

During facial growth, the maxilla and mandible translate downward and forward. Although the forward displacement of the maxilla is less than that of the mandible, the interarch relationship of the teeth in the sagittal view during growth remains essentially unchanged. Interdigitation is thought to provide a compensatory (tooth movement) mechanism for maintaining the pattern of occlusion during growth: the maxillary teeth move anteriorly relative to the maxilla while the mandibular teeth move posteriorly relative to the basilar mandible. The purpose of this study was to investigate the hypothesis that the human chin develops as a result of this process. Twenty-five untreated subjects from the Iowa Facial Growth Study with Class I normal occlusion were randomly selected based on availability of cephalograms at T1 (mean= 8.32 yr) and T2 (mean= 19.90 yr). Measurements of growth (T2 minus T1) parallel to the Frankfort horizontal (FH) for the maxilla, maxillary dentition, mandible, mandibular dentition, and pogonion (Pg) were made. Relative to Pg (a stable bony landmark), B-point moved posteriorly, on average 2.34 mm during growth, and bony chin development (B-point to Pg) increased concomitantly. Similarly, the mandibular and maxillary incisors moved posteriorly relative to Pg 2.53 mm and 2.76 mm, respectively. A-point, relative to Pg, moved posteriorly 4.47 mm during growth. Bony chin development during facial growth occurs, in part, from differential jaw growth and compensatory dentoalveolar movements.