Chin Projection Research Articles

High-efficiency Combination Treatment of Submental Neck Fullness.

Background:Fat accumulation, skin laxity, and muscle contraction cause aging cervical fullness. Combining botulinum toxin to treat muscle contraction, and technique-oriented microfocused ultrasound for skin laxity, can improve cervical fullness without requiring lipolysis. Gel-assisted depth adjustment (GADA) is a depth-targeting, image-guided approach using an appropriate gel volume to precisely heat tissue layers during real-time visualization.Methods:A 41-year-old woman presented with moderate submental neck fullness and saggy cheeks. An appropriate gel volume was applied as determined by the targeted tissue layer’s distance from the skin. The submental and submandibular areas received 112 lines of 0.9 J/cm2 microfocused ultrasound with visualization (MFU-V) from a 4.5-mm transducer and 0.3 J/cm2 from a 3-mm transducer to treat the SMAS and dermosubcutis, respectively. For concomitant jowling, these transducers delivered 111 MFU-V lines to the lower cheek. Six units of incobotulinumtoxinA was injected in 1 point at the mandible to modulate hyperactive mentalis muscles. The platysma received 10U of incobotulinumtoxinA per cheek, whereas downturned mouth corners received 4U of incobotulinumtoxinA.Results:One-month posttreatment, submentum improvements included changes of the vertical pogonion position, more mandible angularity, and a straighter mandibular line. Anterior chin projection was more pronounced and the pogonion had more inferior displacement, creating a younger appearance in the chin-neck complex. Patients followed-up for 3 months also demonstrated these changes.Conclusions:Delivering MFU-V using the GADA technique effectively tightens submental and submandibular soft tissues. When combined with incobotulinumtoxinA, muscles in the chin and perioral area are relaxed. Thus, GADA yields significant clinical improvement and patient satisfaction.

Orthognathic surgery with mandibular osteotomy modified for OSAS treatment in class II patient

Background: Obstructive Sleep Apnea Syndrome (OSAS) is a common underdiagnosed pathology. Its consequences are serious, especially in terms of quality of life and cardiovascular risk. Orthognathic surgery of maxillo-mandibular advancement has increased in popularity due to the increase of the entire velo-oro-hypopharyngeal air system. The advancement of the genioglossus muscle is crucial in maintaining an airborne pharyngeal patent due to the anterior traction of the tongue. Such advancement associated with hyoid suspension are relatively conservative techniques that can enlarge the retrolingual airway without occlusion, facial or dental aesthetic alteration. In cases of patients with natural chin projection, a modified advancement surgery may promote airway augmentation along with an improvement in the patient's facial profile.

Do Unaffected Parents of Children with Orofacial Clefts have Decreased Facial Integration Compared to Controls?

Orofacial clefts are the most common congenital craniofacial anomaly affecting humans. Non‐syndromic clefts may result from decreased integration of the palate during fetal facial growth. This study will investigate whether this pattern is detectable in individuals who do not have a cleft, but do have a child with an orofacial cleft (and therefore carry genetic risk factors for clefting). In order to examine this, we hypothesize that 1) facial shape differences exist between unaffected parents of children with clefts (cases) compared to adults with no history of clefting (controls), and 2) cases will have lower facial integration values compared to controls.For this study, 3D facial scans were obtained from the University of Pittsburgh Center for Craniofacial and Dental Genetics (CCDG). 34 landmarks were placed on n=230 case faces of unaffected parents from the Pitt Orofacial Cleft Study and n=490 control faces from the Pitt 3D Facial Norms Study. Landmarks were aligned using Generalized Procrustes Analysis (GPA) and geometric morphometrics were used for quantifying facial phenotypes. Facial shape differences as a function of age were removed prior to all analyses using linear regression. Canonical Variate Analysis (CVA) was employed to examine shape differences in three different subsets of facial landmarks: a midfacial nose and mouth dataset, a lower facial mouth and jaw dataset and a third dataset consisting of the nose and jaw. Two Block Partial Least Squares analysis (2B PLS) was used to measure the strength of integration by comparing RV coefficients between the case and control populations.Results from the CVA identify significant differences in facial morphology, including jaw width, chin projection, nasal height and mouth width, between cases and controls across all datasets (nose/mouth midfacial set p<0.001, mouth/jaw lower facial set p<0.001, and nose/jaw dataset p=0.028). 2B PLS results, however, showed overall equivalent or higher integration levels in case faces compared to the controls. When comparing levels of integration within the midface (nose and mouth dataset), case samples demonstrate significant (p<0.001) overall higher integration levels (RV=0.352) compared to control samples (RV=0.301). This pattern is also seen within the nose and jaw dataset, with cases (RV=0.614) showing increased integration compared to controls (RV=0.554). Interestingly, integration levels within the lower facial mouth and jaw dataset were nearly identical in both case samples (RV=0.444) and controls (RV=0.447).While facial shape differences exist between unaffected cleft relatives and controls with no family history of clefting, integration values were actually higher in case samples compared to control samples. This indicates that integration in facial soft tissue structures may not serve as a good indicator of cleft risk. Future studies will examine skeletal structures (such as the maxilla and mandible) to test if differences in integration are quantifiable in the facial skeleton only.Support or Funding InformationNIDCR: R01‐DE016148, U01‐DE020078This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Rotational effects of Class II Division 1 treatment with the Herbst appliance and fixed appliances in growing subjects with different vertical patterns

AimThis retrospective study was undertaken to assess the rotational effects of the Herbst appliance and fixed appliances in the treatment of Class II Division 1 subjects with different vertical facial patterns. MethodPretreatment, post-Herbst, and post-fixed appliance lateral cephalograms from 115 growing Class II Division 1 subjects were divided into three groups based on differences in the mandibular plane angle. Changes in dental and skeletal measurements were assessed within these vertical groups and in relation to pretreatment overbite, overjet, and stage of cervical maturity. ResultsDuring the overall treatment period, there were changes as expected in upper and lower incisor angulations, reductions in the incisal overjet, and increases in total mandibular length in all groups. A real increase in horizontal chin projection was, however, seen only in mesofacial and brachyfacial subjects. In general, rotational facial changes during treatment were minimal, so that dolichofacial patterns remained long and brachyfacial patterns remained short. ConclusionThe results support previous reports that combined Herbst and fixed appliance treatment is likely to be associated with considerable Class II dental correction in many cases. Although there is likely to be a wide range of individual response to the use of the Herbst appliance, it is unlikely that such overall treatment will be associated with clinically significant forward mandibular rotation in dolichofacial subjects.

What Is the Most Beautiful Facial Proportion in the 21st Century? Comparative Study among Miss Universe, Miss Universe Thailand, Neoclassical Canons, and Facial Golden Ratios.

Background:An ideal facial proportion has been attempted since the ancient times. However, modern facial proportions of the most beautiful women in the 21st century are unavailable and have never been determined.Methods:A retrospective review of the photographs of Miss Universe Thailand and Miss Universe from 2001 to 2015 was conducted. All photographs were searched from Internet websites. Twenty-six dominant points were identified. Comparisons of the facial proportion among Miss Universe Thailand, Miss Universe, neoclassical canons, and facial golden ratios were performed.Results:Sixteen Miss Universe Thailand and 16 Miss Universe were included. Nine points of facial proportions were found to be statistically significant between Miss Universe Thailand and neoclassical canons. Miss Universe Thailand showed wider nasofrontal angle, thinner lower-upper lip height ratio, and less chin projection. Ten points of facial proportions were found to be statistically significant between Miss Universe and neoclassical canons. Miss Universe showed wider nasofrontal and nasofacial angle, more nasal tip projection, and thinner lower-upper lip height ratio. Seven points of facial analysis were found to be statistically significant between Miss Universe Thailand and Miss Universe groups. Of the 16 facial golden ratios, 12 demonstrated statistical significance in both the Miss Universe Thailand and Miss Universe groups.Conclusions:Modern facial proportions of beauty are different from the past. Photogrammetic analysis demonstrated longer forehead, thinner lower-upper lip height proportion, wider interala-medial canthus width proportion, and wider nasofrontal angle compared with previous references. Furthermore, facial golden ratios were statistically significantly invalid in modern facial proportions of beauty.

Correlation of Craniofacial Measurements between Cephalometric Radiographs and Facial Photographs

Objective: The aim of this study was to correlate the linear and angular measurements between lateral cephalogram and lateral photographs.
 Method: An observational cross-sectional study was carried out at the department of orthodontics, Karachi Medi- cal and Dental College, Karachi, Pakistan. The study was conducted for six months from 30th October 2016 to 30th April 2017. Inclusion criteria included no previous orthodontic or surgical treatment, having all six maxillary anterior teeth present, no craniofacial trauma and no neurologic disturbances. Exclusion criteria includes those patients in whom radiation exposure cannot be given. A sample of 179 patients was selected which included 49 males and 139 females and they were examined by the researcher. A lateral cephalogram and a digital single lens reflex (DSLR) camera was used to obtain the linear and angular craniofacial measurements. A standard lateral cephalogram and standardized lateral photograph of each patient was taken respectively and then their measurements were taken with respect to different variables. Cephalogram measurements taken were as follows: (1) SNA (sella-nasion to A point); (2) SNB (sella-nasion to B point); (3) SNMP (sella-nasion to mandibular plane); (4) total facial height; (5) lower facial height; and (6) mandibular length. Whereas photo- graphic measurements taken were as follows: (1) TN'A' (angle between tragion-soft tissue nasion line and soft tissue nasion-soft tissue A-point line); (2) TN'B' (angle between tragion-soft tissue nasion line and soft tissue nasion-soft tissue B-point line); (3) FH'MP' (angle between soft tissue Frankfort plane and soft tissue mandibular plane); (4) CP'MP' (angle between cranial plane and soft tissue mandibular plane); (5) lower facial height; (6) total facial height; (7) mandibular length; and (8) chin projection. The lateral cephalogram and lateral photo- graphs measurements of patients were compared respectively and the Pearson correlation between them was calculated using SPSS 20.
 Results: The results obtained showed that there was a moderate correlation between SNA and TN'A', SNB and SN'B', SNMP and FH'MP' whereas the correlation between facial heights and lower facial heights was very weak and CP and CP'MP' holds no correlation between them. All the correlations found between were statistically sig- nificant and had linear, positive co-relation between them.
 Conclusion: Photographs can be used in place of lateral cephalogram X-rays for diagnostics and treatment planning.

Temporomandibular Joint Reconstruction in Patients With Autoimmune/Connective Tissue Disease

To evaluate clinical outcomes in patients with autoimmune or connective tissue (CT) disease undergoing temporomandibular joint (TMJ) reconstruction. Patients were divided into 2 groups based on type of TMJ reconstruction. Patients in group 1 (n=9) underwent autogenous reconstruction and had a diagnosis of rheumatoid arthritis (5), lupus arthritis (1), and psoriatic arthritis (3). Patients in group 2 (n=2l) had alloplastic reconstruction with a patient-fitted total joint prosthesis (TMJ Concepts, Ventura, CA) and had a diagnosis of rheumatoid arthritis (15), lupus (3), and psoriatic arthritis (3). Standardized clinical and radiographic examinations were performed before surgery, immediately after surgery, and at longest follow-up after surgery (T3). Group l showed no meaningful improvement in maximal opening without pain, a decrease in lateral excursions, minimal decrease in TMJ pain, and a 32% relapse of chin projection at point B at T3. Average postsurgery follow-up time was 58months. Postsurgical ankylosis was seen in 22% of patients. In contrast, group 2 showed a statistically meaningful decrease in subjective TMJ pain and lateral excursive movements and improvement in jaw function, diet, maximal incisal opening without pain, and only 5% showed a relapse at point B at T3. Average postsurgical follow-up in this group was 78months. Improved treatment outcomes were obtained with alloplastic TMJ total joint reconstruction compared with autogenous TMJ reconstruction in patients with autoimmune or CT disease.

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.

Orthodontic-surgical treatment of a class II division 1 patient. Case report

The objective of this case report was to show the correction of a class II division 1 malocclusion in an adult patient. A female patient of 20 years of age attended the Orthodontics Clinic of the Division of Postgraduate Studies and Research of the Odontology Faculty at the National Autonomous University of Mexico. Her main reason for consultation was: «When I removed the wisdom teeth I was told that I could have orthognathic surgery but fi rst I needed braces»; this in order to correct the dentofacial disharmony. Upon facial clinical examination, the patient presented a mesofacial biotype with competent lips; vertically she presented an increased lower third. Her profile was convex with deficient chin projection. Intraorally, the patient exhibited upper and lower crowding, molar and canine class II, considerably increased overbite and overjet as well as noncoincident dental midlines. The cephalometric diagnosis showed a skeletal class II due to maxillary protrusion. It was suggested an orthodontic-surgical treatment in three phases: presurgical, surgical and postsurgical. In the presurgical phase the patient was decompensated in order to prepare her for surgery. During the surgical phase, mandibular sagittal osteotomies were performed to advance the mandible in combination with an advancement genioplasty. During the post-surgical phase, ideal occlusal relationships were achieved in terms of canine classes, overbite, overjet, dental midlines and fi nal detailing of the case. Through the treatment, the occlusion and facial harmony of the patient were improved.

The effects of surgically assisted rapid maxillary expansion (SARME) on the dental show and chin projection

ObjectiveTo quantify the postoperative changes of the dental show and chin projection following SARME using 3D CBCT imaging. Material and methods78 patients with transversal maxillary hypoplasia and mandibular hypoplasia who underwent SARME were enrolled into the study. A cone beam computed tomography (CBCT) scan was acquired preoperatively and at least 1 year postoperatively. 3D postoperative changes in the dental show and pogonion position were measured based on soft tissue and hard tissue landmarks. Results68 patients (87%) exhibited a postoperative increase in the dental show. The dental show was increased by a mean of 2.2 ± 2.0 mm (p < 0.01). The mean horizontal and vertical displacement of the chin (pogonion) following SARME was 1.6 ± 2.5 mm posteriorly and 1.6 ± 2.0 mm inferiorly (p < 0.01). An inferior displacement of the maxilla and maxillary tooth as well as a consequent clockwise pitch of the mandible seemed to play a role in inducing these postoperative changes. ConclusionAn increase in dental show and a posterior and inferior displacement of the chin should be considered prior to SARME to prevent undesirable postoperative changes of the facial esthetics.

Chin-throat anatomy: Normal relations and changes following orthognathic surgery and growth modification

To determine if a new facial line (T), tangent to the throat, intersects the mandibular border in anterior (ANT) and posterior (POST) parts in proportions varying with facial configuration, and to evaluate the association between chin projection and throat inclination and the potential for the T-line to reflect this association. Measurements on profile photographs and cephalograms of 135 adults (aged 18-50 years)-45 each of Class I, II, and III (CI, CII, CIII) malocclusions-included ANT and POST, chin-throat (CTA), and mento-cervical (MCA) angles. Pre- and posttreatment measurements were compared in two subgroups (n = 25 each) of CII and CIII orthognathic surgery patients and in CII, division 1 early-treatment patients (n = 63). Statistics included analysis of variance and t-test for group differences, and Pearson correlation for associations among variables. ANT was nearly equal to POST in CI (50.99%) and CIII (51.86%) subjects and shorter in CII (36.01%) subjects. CTA and MCA were greater in CII profiles and smaller in CIII profiles. Significant differences (P < .0001) were observed for ANT, POST, CTA, and MCA between Classes I/II and II/III and for MCA between Classes II/III (P = .016). High correlations were noted between ANT and CTA in Classes I (r = -0.83), II (r = -0.73), and III (r = -0.68). In surgically treated patients, posttreatment measurements approached CI values. In the early-treatment group, ANT increased but remained smaller than POST; CTA decreased by nearly 13%. Chin-throat relations and chin extension are associated and require routine assessment in terms of diagnosis and treatment outcome. A practical tool to assess chin-throat relationship, the T-line bisects the mandibular body nearly equally in Class I faces.

Postoperative changes of dental show and chin projection following surgical-assisted rapid maxillary expansion

Postoperative changes of dental show and chin projection following surgical-assisted rapid maxillary expansion

Evaluation of mandibular hard and soft tissues in cleft patients.

The aim of this study was to compare the mandibular hard and soft tissue measurements of unilateral and bilateral cleft lip and palate patients with non-cleft individuals. The study sample comprised of lateral cephalograms of 45 subjects. Sample included 15 non-cleft (NC), 15 unilateral cleft lip and palate (UCLP) and 15 bilateral cleft lip and palate (BCLP) cases whose age were between 15 to 17. 1 angular 13 linear measurements were carried out using Arnett and Gunson soft tissue cephalometric analysis and 4 angular measurements were calculated with Steiner Analysis. Mandibular incisor inclinations relative to the occlusal plane (Md1-Md OP) were significantly greater and mandibular incisor projections (Md1-TVL) were significantly retrusive in cleft subjects (p<0.05). Projection values pertaining to lower lip anterior (LLA-TVL), soft tissue B point (B'-TVL), and soft tissue pogonion (Pog'-TVL) were significantly deficient as well in cleft patients (p<0.05). Sagittal position of the maxilla (SNA) (p<0.001) and intermaxillary relation of the jaws (ANB) were significantly deficient in UCLP subjects (p<0.05) and BCLP individuals (p<0.01). LLA-TVL and B'-TVL correlated with SNB in cleft patients (p<0.05). Decreased lower lip and chin projection values suggest that mandibular region of cleft patients should be taken into account in forming the treatment plan to improve the esthetic outcome of orthodontic and plastic surgery interventions.

Effect of frontal facial type and sex on preferred chin projection.

ObjectiveTo investigate the effects of frontal facial type (FFT) and sex on preferred chin projection (CP) in three-dimensional (3D) facial images.MethodsSix 3D facial images were acquired using a 3D facial scanner (euryprosopic [Eury-FFT], mesoprosopic [Meso-FFT], and leptoprosopic [Lepto-FFT] for each sex). After normal CP in each 3D facial image was set to 10° of the facial profile angle (glabella–subnasale-pogonion), CPs were morphed by gradations of 2° from normal (moderately protrusive [6°], slightly protrusive [8°], slightly retrusive [12°], and moderately retrusive [14°]). Seventy-five dental students (48 men and 27 women) were asked to rate the CPs (6°, 8°, 10°, 12°, and 14°) from the most to least preferred in each 3D image. Statistical analyses included the Kolmogorov-Smirnov test, Kruskal-Wallis test, and Bonferroni correction.ResultsNo significant difference was observed in the distribution of preferred CP in the same FFT between male and female evaluators. In Meso-FFT, the normal CP was the most preferred without any sex difference. However, in Eury-FFT, the slightly protrusive CP was favored in male 3D images, but the normal CP was preferred in female 3D images. In Lepto-FFT, the normal CP was favored in male 3D images, whereas the slightly retrusive CP was favored in female 3D images. The mean preferred CP angle differed significantly according to FFT (Eury-FFT: male, 8.7°, female, 9.9°; Meso-FFT: male, 9.8°, female, 10.7°; Lepto-FFT: male, 10.8°, female, 11.4°; p < 0.001).ConclusionsOur findings might serve as guidelines for setting the preferred CP according to FFT and sex.

Treatment of Micrognathia by Intraoral Distraction Osteogenesis: A Prospective Study.

Purpose:Maxillofacial deformities are always psychologically and physically distressing to the patients and is also challenging to the treating surgeons. The term Micrognathia means a “small jaw”. True micrognathia, where the maxilla or the mandibular skeleton does not grow to the full size can be congenital or acquired. Distraction osteogenesis also called as callus distraction or callostasis or osteodistraction or distraction histogenesis is a biological process of regenerating newly formed bone and adjacent soft tissue by a gradual and controlled traction of surgically separated bone segments. The purpose of this prospective study was to assess the versatility of distraction osteogenesis in the treatment of micrognathia.Materials and Methods:Four patients (three males and one female) with micrognathia of mandible were included in this prospective study. The patients were between the age group of 10-20 years. Facial asymmetry was the chief complaint of all the patients. In all the patients following treatment protocol was carried out, Osteotomy and placement of intraoral distraction device under general anaesthesia, latency phase (5-7 days), activation period-rate 1.5 mm per day, consolidation period of 8 weeks, removal of distraction device under local anaesthesia. The parameters assessed were ramus height, body length, hyo mental distance, posterior pharyngeal airway space, chin projection, facial symmetry occlusion, mid line shift pre and post operatively.Results:The mean increase in ramus height achieved was 9.2 + 2.17 mm and the mandibular body length achieved was 10.4+1.67 mm. There was an average increase in hyo-mental distance of 2.75 cm +0.9 cm postoperatively showing a definitive improvement in the airway. The posterior pharyngeal space measured from the lateral cephalogram preoperatively ranged from 3-6 mm and post operatively from 6-9 mm.Intraorally there was a shift in occlusion to class I molar relation in three patients and there was posterior open bite in one patient. Marked correction of facial asymmetry was noticed in all cases both clinically and in PA cephalogram. There was a restoration of dental as well as lip midline and improved lip competence. There was a significant improvement in chin projection and occlusal cant however further chin correction was needed in one case by means of advancement genioplasty.Conclusion:A definite improvement in all parameters such as body length,ramus height,chin projection,occlusal cant was observed in all patients. Moreover the patients were subjectively satisfied with the outcome of the results. Distraction Osteogenesis is definitely a boon to the oral and maxillofacial surgeons in treating large deficiencies of mandible in terms of stability

The Herbst appliance and the Activator: influence of the vertical facial pattern

Abstract Aim To compare the effects of the Herbst appliance and the Activator at the completion of two-phase treatment, with respect to the vertical facial pattern (VFP) and to identify possible predictors of treatment effect. Materials and methods Pretreatment, post-treatment and overall cephalometric change data were used to assess the dental and skeletal effects. Results for the change in mandibular length were also compared with changes reported for an untreated external control group. Results Clinically significant dental and skeletal changes (including mandibular incisor proclination and overjet reduction) were characteristics of both treatment methods. Any increases in mandibular length and chin prominence were not greater than those expected following natural growth. The pretreatment VFP remained essentially unaltered, while mean changes as a result of treatment were similar for brachyfacial, mesofacial, and dolichofacial subjects. No predictive factors were identified. Conclusions Clinicians are advised to expect significant overjet reduction and mandibular incisor proclination with either treatment method. Significant skeletal change may be observed in growing subjects; however, any increase in mandibular length or chin projection is not likely to be beyond the limit set by nature. While there will be some individual variation, no significant long-term alteration in the pretreatment vertical facial pattern should be expected with either treatment. Long faces will remain long and short faces will remain short.

Growth characteristics underlying the lack of a chin in pigs: a histomorphometric study.

Despite similar mandibular growth to that of humans, pigs lack a chin projection as shown in most humans. To understand whether this divergence is contributed to differences in local symphyseal growth, this project characterized bone modeling activities at the symphyseal surfaces of juvenile pigs. Symphyseal specimens from two age groups (4-and 6-month-old, n=10) were processed into histological sections with and without decalcification, which were assessed for surface mineral apposition and bone resorption, respectively. In a blinded fashion, measurements of four parameters (MAR: mineral apposition rate, MAZ: mineral apposition zone, ES/BS: eroded surface and OC.N/BS: osteoclast number) were obtained and tested by a multivariate two-way mixed-model analyses of variance (manova) for the differences between symphyseal regions and ages. Qualitatively, pig symphyseal labial and lingual surfaces were horizontally oriented and characterized by mineral apposition and bone resorption, respectively. Quantitatively, labial mineral apposition tended to be greater rostrally than caudally at 4months, which became greater caudally than rostrally at 6months (region/age interactions: p=0.127 for MAR, p=0.012 for MAZ). Lingual bone resorption tended to be greater caudally than rostrally, but only ES/BS measurements were significant (p=0.039) regardless of age, while OC.N/BS measurements varied with ages and regions (age/region interaction, p=0.087). Insufficient differential in symphyseal surface modeling between the labial-caudal and labial-rostral regions contributes to the lack of chin projection in the pig.

The ontogeny of the chin: an analysis of allometric and biomechanical scaling.

The presence of a prominent chin in modern humans has been viewed by some researchers as an architectural adaptation to buttress the anterior corpus from bending stresses during mastication. In contrast, ontogenetic studies of mandibular symphyseal form suggest that a prominent chin results from the complex spatial interaction between the symphysis and surrounding soft tissue and skeletal anatomy during development. While variation in chin prominence is clearly influenced by differential growth and spatial constraints, it is unclear to what degree these developmental dynamics influence the mechanical properties of the symphysis. That is, do ontogenetic changes in symphyseal shape result in increased symphyseal bending resistance? We examined ontogenetic changes in the mechanical properties and shape of the symphysis using subjects from a longitudinal cephalometric growth study with ages ranging from 3 to 20+ years. We first examined whether ontogenetic changes in symphyseal shape were correlated with symphyseal vertical bending and wishboning resistance using multivariate regression. Secondly, we examined ontogenetic scaling of bending resistance relative to bending moment arm lengths. An ontogenetic increase in chin prominence was associated with decreased vertical bending resistance, while wishboning resistance was uncorrelated with ontogenetic development of the chin. Relative to bending moment arm lengths, vertical bending resistance scaled with significant negative allometry whereas wishboning resistance scaled isometrically. These results suggest a complex interaction between symphyseal ontogeny and bending resistance, and indicate that ontogenetic increases in chin projection do not provide greater bending resistance to the mandibular symphysis.

A study of Class III treatment: orthodontic camouflage vs orthognathic surgery

Abstract Aim To evaluate the differences in pretreatment and post-treatment characteristics of Class III patients treated with orthodontic camouflage or orthognathic surgery, and to compare the range of skeletal, dental and soft tissue changes that are likely to occur with treatment, with particular reference to the influence of extractions on the resultant incisor angulations. Method Pretreatment and post-treatment cephalograms of 31 Class III orthodontically-camouflaged patients and 36 Class III surgical patients (without genioplasty) were obtained from one specialist practice. From the surgical group, 26 pre-surgical lateral cephalograms were also obtained. Inclusion criteria for the two groups were at least three of the following: (1) an ANB angle of 1 degree or less, (2) a Wits appraisal less than -4 mm, (3) an incisal overjet ≤0 mm, and (4) a Class III molar relationship. All lateral cephalograms were traced and digitised and a number of skeletal, dental and soft tissue variables were measured. The camouflage and surgical groups were also divided into premolar extraction and non-extraction subgroups to allow for a specific analysis of extraction effects. Results Before treatment, the surgical group demonstrated, on average, a more severe skeletal discrepancy and increased dental compensations, compared with the orthodontically camouflaged group. After treatment, the mean SNA angle was greater, the ANB angle was more positive, the Wits appraisal was closer to ideal and the lower incisors were less retroclined in the surgery group. There was a small mean reduction in horizontal chin projection in the surgery group compared with a small increase in the camouflage group. The mentolabial fold and the lower lip curve were deeper, on average, and the lips less retrusive after surgery. There was a mean increase in upper incisor proclination during treatment in both the surgical and camouflage groups with a greater increase in the camouflage group. There was a significant reduction in upper incisor proclination and a subsequent greater increase in the ANB angle associated with upper premolar extractions in the surgical group compared with the non-extraction group. Lower premolar extractions in the camouflage group resulted only in a deeper mentolabial fold compared with those treated without lower extractions. Conclusions Class III patients selected for surgical treatment are likely to have more severe pretreatment dental and skeletal discrepancies than those selected for camouflage treatment. Surgical treatment is associated with significant decompensation of the lower incisors but, ultimately, not the upper incisors. Class III patients treated with either camouflage or surgery treatment are likely to finish with slightly proclined upper incisors. Generally, surgical treatment results in greater skeletal change, involving normalisation of the skeletal base relationship, a reduction in chin prominence, fuller lips, and a more favourable lip and chin contour.

The difficult neck in facelifting.

The management of the neck often presents the most challenging aspect of the facelift procedure. The aesthetic neck has a well-defined jaw line, a pleasing and adequate cervicomental angle, and visible definitions of the deeper lateral and midline structures, such as the sternocleidomastoid muscles and trachea. Several unfavorable anatomic characteristics will present that will compound the challenge. These characteristics are contrasted with ideal features and include the following: an excess of adipose tissue, an excess of either thin or thick inelastic skin, marked relaxation of the suspension structures of the neck with resultant platysma banding and jowling, and unfavorable skeletal features such as microgenia and hyoid malposition. These patients present for rhytidectomy with inadequate chin projection, an obtuse cervicomental angle, sagging skin, and a heavy neck. To maximize rhytidectomy results in these patients with difficult neck anatomy, special attention to the anatomy and application of recognized techniques in an individualized manner is recommended. This article reviews the issues encountered in the management of the difficult neck in facelifting, with special attention given to patients with a heavy neck.