Why do humans have chins? Testing the mechanical significance of modern human symphyseal morphology with finite element analysis

The modern human mandibular symphysis differs from those of all other primates in being vertically orientated and possessing a chin, but the functional significance of this unique morphology is not well understood. Some hypotheses propose that it is an adaptation to specific loads occurring during masticatory function. This study uses finite element analysis to examine these symphyseal loads in a model of a modern human mandible. By modifying the symphyseal cross-sectional form, the mechanical significance of the presence of the chin and symphyseal orientation is tested, and modern human and Neanderthal symphyseal cross-sections are compared with regard to their ability to withstand different loads. The results show that changes in symphyseal form have profound effects on the strains. The presence of a chin leads to lower symphyseal strains overall, whereas a vertical orientation of the symphysis results in higher strains under wishboning, but not under vertical bending in the coronal plane and dorsoventral shear. Compared to Neanderthals, the modern human symphysis shows higher strains during dorsoventral shear and wishboning, but is as effective as the Neanderthal symphysis in resisting vertical bending in the coronal plane and the loads resulting from simulated incision and unilateral molar biting. In general, the results of this study corroborate prior hypotheses about the mechanical effects of the human chin and vertical symphyseal orientation and support the idea that the relative importance of wishboning and vertical bending in the coronal plane might have played a role in the evolution of modern human symphyseal morphology.     

Maxillary advancement for mandibular prognathism: indications and rationale

The surgical correction of mandibular prognathism has traditionally involved posterior repositioning of the mandibular body. This treatment approach corrects the skeletal disproportion at the expense of reducing facial skeletal volume and can unpredictably result in inadequately supported soft tissues with loss of skeletal definition. In an effort to avoid these sequelae of mandibular reduction, 18 patients diagnosed as having mandibular prognathism were treated with maxillary advancement surgery at the Le Fort I level. Mean patient SNB angle was 85.2 degrees, as compared with a normal 79 +/- 3 degrees. Maxillae were documented to be in normal position relative to both cranial base and Frankfort horizontal. The mean maxillary advancement was 6.9 mm, with a range of 4.5 to 8.8 mm. All patients required genioplasty to reduce vertical chin height and/or to laterally shift the chin. At the time of follow-up (mean 16.2 months), all patients retained cephalometric data suggestive of enlarged mandibles and excessive anterior facial divergence. However, maxillomandibular harmony and facial convexity had been restored without sacrificing skeletal volume. Treatment results demonstrated these faces to be skeletally well proportioned despite lower face protrusion that was beyond "normal." Postoperative appearances were characterized by a well-supported soft-tissue envelope and a highlighted skeletal foundation, creating angular, well-defined lower faces. These findings support the credibility of maxillary advancement as the procedure of choice in selected individuals with mandibular prognathism. Indications and an aesthetic rationale for this surgical approach are presented.     

Mandibular stiffness in humans: numerical predictions

The chin is a feature unique to humans. This study evaluates the effect of mandibular symphyseal design on biomechanical masticatory effectiveness as determined by structural stiffness and stress developed under flexural and torsional loading. A simple model of three symphyseal shapes (chin, flat symphysis and lingual buttress), was built to represent human, Neanderthal and higher primate symphyses and these were subjected to wishboning and torsional forces. Additionally, an anatomically detailed reconstruction was made of the CT scan of an actual human mandible, which was then also morphed into a chinless model. The results of a 3-D finite element analysis show firstly, that none of the three different symphyseal shapes is biomechanically more advantageous than the others for the given loading condition. Secondly, we show in a CT-derived model, that the presence of a chin does not confer significantly improved stiffness to torsional or flexural loading. These results indicate that the acquisition of a chin in modern humans is not related to the functional demands placed upon the mandible during mastication, but suggest that it may have developed in response to other biomechanical demands.     

The cleft lip lower-lip deformity

A patient with a repaired upper lip cleft may acquire a deformity in the lower lip. Records of 63 cleft lip patients who exhibited lower-lip abnormalities were analyzed in order to characterize the soft-tissue and skeletal configuration. The typical deformity was a hypertrophied, superiorly displaced, and anteriorly rotated lower lip. Skeletal analysis of the mandible revealed a variable and inconsistent degree of vertical elongation with posterior displacement of the chin. Operative correction of the cleft lip lower-lip deformity required evaluation of both the soft-tissue and skeletal abnormalities. Soft-tissue procedures gave permanent correction, provided there was a normal maxillary-mandibular relationship. Skeletal correction alone did not completely rectify the abnormal lower-lip posture.     

Cross-sectional geometry and morphology of the mandibular symphysis in Middle and Late Pleistocene Homo

Studies of the evolutionary emergence of the human "chin" have been investigated from a phylogenetic perspective during the later Pleistocene or from a biomechanical perspective across extant primates. Since it was during the Middle and Late Pleistocene that the distinctive human mentum osseum emerged, the relationship between mentum osseum form and resistance to mechanical stress at the mandibular symphysis was examined for forty-two Middle and Late Pleistocene human mandibles. Mentum osseum variation was scored on a five-point ordinal scale (mentum osseum rank). Resistance to bending was represented by second moments of area calculated from symphyseal cross-sections. Relative strength in bending was represented by second moments of area divided by estimated moment arm or beam length. Vertical bending resistance in the coronal plane was maintained across the range of mentum osseum variation within and between later Pleistocene human groups. In contrast, resistance to lateral transverse bending (wishboning) was significantly negatively correlated with the emergence of a protruding mentum osseum. However, Neandertals and early modern humans were equivalent in their abilities to resist this bending regime, while both groups were less resistant in wishboning than earlier archaic humans. In addition, symphyseal inclination, which decreased throughout the later Pleistocene, was highly correlated with mentum osseum rank. Although the overall pattern of differential stasis and change in vertical bending and wishboning resistance at the symphysis is consistent with aspects of the current biomechanical model of the "chin," the decoupling of bending resistance and mentum osseum form in the Late Pleistocene suggests that the evolutionary emergence of the modern human "chin" was at least partly independent of the biomechanical demands placed on the symphysis.     

Longitudinal study of craniofacial growth in Macaca fascicularis

This paper is an analysis of normal craniofacial growth in adolescent crab-eating macaques (Macaca fascicularis). Eight female adolescent monkeys were used in this study. Their individual craniofacial growth was studied for a 24-month period utilizing tantalum implants and roentgenographic cephalograms. Throughout the observation period, each monkey consistently showed a class I molar relationship with a good overjet and overbite. The amount of anterior displacement of the maxilla and the mandible was significantly dominant compared to the vertical displacements at every observation period. The midface exhibited a maxillary differential growth pattern in which the premaxilla displaced superiorly and the posterior maxilla moved inferiorly, resulting in a counterclockwise rotation of the entire maxilla. Growth of the lower anterior teeth and alveolar bone compensated for the incremental vertical spaces which were induced by superior displacement of the premaxilla and inferior repositioning of the chin. In addition, the amount of anterior displacement of the upper and lower anterior teeth were significantly larger than that of the premaxilla and the chin. The dentocraniofacial growth pattern in Macaca fascicularis was quite similar to that seen in Macaca mulatta.     

Upper labial deficiency in Mobius syndrome: a previously unreported feature and its correction

Bilateral facial palsy in M?bius syndrome remains one of the greatest challenges in reconstructive plastic surgery. Facial reanimation is an invaluable aid to such patients because it allows for greater social interaction by means of the ability to smile. In performing facial reanimation surgery on patients with M?bius syndrome, it is the observation of the senior author (Harrison) that upper labial deficiency is a consistent and previously unreported feature of the syndrome. It has been the practice of the senior author to perform upper labial augmentation on M?bius syndrome patients by insertion of a lipodermal autograft, in addition to facial reanimation. Nine patients with M?bius syndrome who presented to the Department of Plastic Surgery during an 8-year period were reviewed. All nine possessed bilateral facial palsy and upper labial deficiency in addition to other abnormalities consistent with M?bius syndrome. Six patients underwent bilateral facial reanimation and upper labial augmentation alone. One patient refused facial reanimation surgery but consented to upper labial augmentation. One patient, with concomitant micrognathia, underwent bilateral facial reanimation, upper labial augmentation, and insertion of a Silastic chin implant. In one patient, a child who also exhibited micrognathia, bilateral facial reanimation alone was carried out, with further procedures for upper labial and chin cosmesis being postponed until adulthood. The indication for performing upper labial augmentation was cosmetic. The procedure improved upper labial appearance and restored balance to the mouth. Patients also expressed higher satisfaction with eating and drinking, which they related to the improved fullness of the upper lip. This was before the facial reanimation had become functional. Upper labial deficiency warrants addition to the list of facial features of M?bius syndrome and is something that must be assessed in the context of facial reanimation surgery.     

Use of Banked Tissue in Plastic Surgery

The availability of safe and reliable, banked tissues in India has enabled the use of human bone allografts as a viable alternative to autografts in reconstructive surgery. Lyophilised, irradiated bone grafts were used in 2 cases of rhinoplasty, a case of hemifacial atrophy, and as a chin implant.In the patient with revision rhinoplasty the rib graft was resorbed. The patient with hemifacial atrophy developed seroma and infection in the zygomatic and infraorbital area and the rib graft had to be removed. The graft from the same rib that was placed over the mandible was retained well and incorporated completely. The iliac crest cortico-cancellous grafts did well in the second case of augmentation rhinoplasty and in the augmentation of chin.The primary objective of reconstructive surgery in the treatment of burns, non-healing wounds and pressure sores is to remove the dead tissue and restore the continuity of the skin without delay. Lyophilised, irradiated, human amnion is a temporary biological dressing conveniently available off-the-shelf. It was used in twenty four patients with burns, eight patients with bedsores and six patients with non-healing ulcers mainly on the foot. The total surface areas of burns sustained were from 2% to 40%. The burns ranged from second degree to deep third degree burns. Amnion was not used in patients with infected third degree burns.The amnion provided good biological cover in all the patients. It was easy to handle and apply, and provided pain relief. The duration of healing varied depending on the extent and depth of the wound and the amount of exudate. The superficial bedsores healed with a single application of amnion. Reduced exudate, healthy granulation tissue and enhanced epithelisation were observed following application of amnion.     

The functional significance of primate mandibular form.

A stress analysis of the primate mandible suggests that vertically deep jaws in the molar region are usually an adaptation to counter increased sagittal bending stress about the balancing-side mandibular corpus during unilateral mastication. This increased bending stress about the balancing side is caused by an increase in the amount of balancing-side muscle force. Furthermore, this increased muscle force will also cause an increase in dorso-ventral shear stress along the mandibular symphysis. Since increased symphyseal stress can be countered by symphyseal fusion and as increased bending stress can be countered by a deeper jaw, deep jaws and symphyseal fusion are often part of the same functional pattern. In some primates (e.g., Cercocebus albigena), deep jaws are an adaptation to counter bending in the sagittal plane during powerful incisor biting, rather than during unilateral mastication. The stress analysis of the primate mandible also suggests that jaws which are transversely thick in the molar region are an adaptation to counter increased torsion about the long axis of the working-side mandibular corpus during unilateral mastication. Increased torsion of the mandibular corpus can be caused by an increase in masticatory muscle force, an increase in the transverse component of the postcanine bite force and/or an increase in premolar use during mastication. Patterns of masticatory muscle force were estimated for galagos and macaques, demonstrating that the ratio of working-side muscle force to balancing-side muscle force is approximately 1.5:1 in macaques and 3.5:1 in galagos during unilateral isometric molar biting. These data support the hypothesis that mandibular symphyseal fusion is an adaptative response to maximize unilateral molar bite force by utilizing a greater percentage of balancing-side muscle force.     

Aesthetic refinements in genioplasty: the role of the labiomental fold

The vast majority of patients requesting aesthetic enlargement of their chins have a class II skeletal deformity secondary to a small mandible. Class II skeletal patterns are frequently associated with abnormalities of lower face height, which, in turn, affect labiomental fold morphology. Of 68 patients who were to undergo sagittal advancement of their chins, 88 percent were considered to have abnormal labiomental fold morphology that was closely related to abnormalities of the facial height. Patients with decreased lower face height (40 percent) had exaggerated, deepened folds with acutely closed angles between the lower lip and chin pad, whereas those with increased lower face height (25 percent) had shallow, effaced folds. Patients with normal lower face height had variable fold morphology. Isolated sagittal advancement and/or simultaneous advancement and vertical shortening deepened the labiomental fold and closed the angle between the chin pad and lower lip. Simultaneous advancement and lengthening tended to deemphasize the fold, making it appear less deep in 20 of 34 patients, or at least mitigated further accentuation of the fold in 14 of 34 patients. Altered labiomental morphology and its relationship to the class II skeletal deformity is discussed. Treatment planning decisions are suggested, taking into account labiomental aesthetics and how they are influenced by advancement genioplasty.     

Improving aesthetic outcomes after alloplastic chin augmentation

A novel approach to increase chin projection with alloplastic material is presented. Key aspects of the technique include the consideration of anthropometric normal values in preoperative assessment and planning, a submental approach with wide subperiosteal exposure of the area to be augmented, the use of two-piece porous polyethylene implants for augmentation, and screw fixation of the implant to the mandible. Screw fixation improves the predictability and precision of reconstruction by preventing implant displacement, by obliterating gaps between the implant and the facial skeleton, and by facilitating final implant contouring. In a series of 46 patients (24 primary and 22 secondary) operated on over a 6-year period, this approach allowed anatomically correct, stable chin contours to be created. Iatrogenic problems with macrogenia, mentalis dysfunction, and soft-tissue distortion resulting from implant migration and capsular contracture have been avoided. There have been no infections. Two patients who had had multiple previous chin operations requested revisional surgery to refine contour.     

Size and placement of developing anterior teeth in immature Neanderthal mandibles from Dederiyeh Cave,Syria: Implications for emergence of the modern human chin

Evolutionary and functional significance of the human chin has long been explored from various perspectives including masticatory biomechanics, speech, and anterior tooth size. Recent ontogenetic studies have indicated that the spatial position of internally forming anterior teeth partially constrains adult mandibular symphyseal morphology. The present study therefore preliminarily examined the size and placement of developing anterior teeth in immature Neanderthal mandibles of Dederiyeh 1 and 2, compared with similarly‐aged modern humans (N = 16) and chimpanzees (N = 7) whose incisors are comparatively small and large among extant hominids, respectively. The Dederiyeh 1 mandible is described as slightly presenting a mental trigone and attendant mental fossa, whereas Dederiyeh 2 completely lacks such chin‐associated configurations. Results showed that, despite symphyseal size being within the modern human range, both Dederiyeh mandibles accommodated overall larger anterior dentition and displayed a remarkably wide bicanine space compared to those of modern humans. Dederiyeh 2 had comparatively thicker deciduous incisor roots and more enlarged permanent incisor crypts than Dederiyeh 1, but both Dederiyeh individuals exhibited a total dental size mostly intermediate between modern humans and chimpanzees. These findings potentially imply that the large deciduous/permanent incisors collectively distended the labial alveolar bone, obscuring an incipient mental trigone. It is therefore hypothesized that the appearance of chin‐associated features, particularly of the mental trigone and fossa, can be accounted for partly by developmental relationships between the sizes of the available mandibular space and anterior teeth. This hypothesis must be, however, further addressed with more referential samples in future studies. Am J Phys Anthropol 156:482–488, 2015. © 2014 Wiley Periodicals, Inc.     

Predicting masticatory jaw movements from chin movements using multivariate linear methods

Previously, we have used bivariate correlations of maximum and minimum displacement, velocity and acceleration variables to compare masticatory chin and jaw movements (J. Prosthet. Dent. 81 (1999) 179). This previous study represented a first step in exploring the hypothesis that the chin contained useful information regarding jaw kinematics. The current study extends our understanding of the relationship between masticatory chin and jaw movements by: (1) reconstructing and evaluating a more continuous trajectory of chin and jaw movements, and (2) performing multivariate correlations comparing chin and jaw movements at discrete points along the trajectory in order to gain insight into the coupling of chin and jaw movements during a chewing cycle. Results indicated that chin and jaw movement trajectories were visually similar in the lateral, vertical, and anteroposterior axes. The adjusted R(2) results in the lateral, vertical, and anteroposterior dimensions averaged 0.74, 0.78, and 0.89, respectively. Within chewing cycles, the lowest correlations between chin and jaw movements in the lateral and vertical dimensions occurred when the jaw was relatively closed, whereas the lowest correlations between chin and jaw movements in the anteroposterior dimension occurred while the jaw was opening from a closed position. The results indicated that jaw and chin movements were qualitatively similar and that at least 74% of the variation in jaw movements could be accounted for by multivariate linear models of chin movement.     

Functional and morphological correlates of mandibular symphyseal form in a living human sample

Variation in recent human mandibular form is often thought to reflect differences in masticatory behavior associated with variation in food preparation and subsistence strategies. Nevertheless, while mandibular variation in some human comparisons appear to reflect differences in functional loading, other comparisons indicate that this relationship is not universal. This suggests that morphological variation in the mandible is influenced by other factors that may obscure the effects of loading on mandibular form. It is likely that highly strained mandibular regions, including the corpus, are influenced by well‐established patterns of lower facial skeletal integration. As such, it is unclear to what degree mandibular form reflects localized stresses incurred during mastication vs. a larger set of correlated features that may influence bone distribution patterns. In this study, we examine the relationship between mandibular symphyseal bone distribution (i.e., second moments of area, cortical bone area) and masticatory force production (i.e., in vivo maximal bite force magnitude and estimated symphyseal bending forces) along with lower facial shape variation in a sample of n = 20 living human male subjects. Our results indicate that while some aspects of symphyseal form (e.g., wishboning resistance) are significantly correlated with estimates of symphyseal bending force magnitude, others (i.e., vertical bending resistance) are more closely tied to variation in lower facial shape. This suggests that while the symphysis reflects variation in some variables related to functional loading, the complex and multifactorial influences on symphyseal form underscores the importance of exercising caution when inferring function from the mandible especially in narrow taxonomic comparisons. Am J Phys Anthropol 153:387–396, 2014. © 2013 Wiley Periodicals, Inc.     

Mandibular matrix implant system: a method to restore skeletal support to the lower face

Disharmony between the skeletal support and the softtissue envelope is a common cause of aesthetic concerns regarding the lower face. A loss of volume or a genetically small mandible affects the aesthetics and function of the mouth, chin, and neck. Because of the limitations of correcting such problems with current implants made of silicone or porous polyethylene, the author developed an implant system and a method of restoring the entire volume of the mandible called the mandibular matrix implant system. This implant system is made of high-density porous polyethylene and is composed of an articulated wraparound geniomandibular implant and a wraparound gonial angle implant. A prejowl implant can be integrated in the system as an addition or as a replacement for a chin implant. This implant system has different sizes and projections, and it can be modified by carving to fit the requirements of most patients. Carving is done using an appropriate sizer. This implant system is indicated for use in patients with a congenitally small mandible, edentulous patients, and patients requesting facial enhancement. The mandibular matrix implant system is implanted either during a single procedure or simultaneously with a facial rejuvenation. The extended geniomandibular implant is introduced through an anterior oral sulcus incision or a submental incision. The mandibular angle implant is introduced through a retromolar incision. The posterior end of the chin implant overlaps the anterior end of the gonial implant, and screw fixation of each chin component helps to stabilize the entire system. Antibiotics, irrigation, and closure of the incisions are performed before any additional operative procedure. The complete system has been used in 13 patients; one additional patient had the complete system plus an overlapping additional left prejowl implant for correction of asymmetry. Complications were manageable; these included one mandibular angle implant displacement and one infection. The implant displacement required a reoperation to reset the implant. The infection was treated with irrigation and closed system suction; the implant was salvaged. The satisfaction of patients has been high, and the author can now solve aesthetic problems that in the past were considered unsolvable.     

Primary definitive nasal correction in patients presenting for late unilateral cleft lip repair

Almost 25 percent of unilateral cleft lip and palate patients present with their deformity in their teens or later years in the developing world. Because more than 80 percent of the world population lives in the developing world, the established protocol for repair of these deformities is not applicable to these patients. Despite the magnitude, there are no significant reports in the literature that deal with this problem. Several issues need to be addressed, but the author limits himself here to the correction of the nasal deformity. The patients at this age are very much concerned with the aesthetic outcome. Procedures described hitherto for primary nasal correction in infants are not successful in restoring nasal shape and symmetry at this late age of presentation. Our experience with radical correction of secondary nasal deformity in unilateral cleft lip patients presenting late prompted us to extend the concept by undertaking a definitive primary correction of the nasal deformity in cleft patients presenting late. Twenty-two patients with unilateral cleft lip deformity (nine male patients and 13 female patients) with ages ranging from 13 to 22 years, presenting between August of 1997 and December of 2000, are included in this study. Of these, 11 patients had a cleft of the lip alone, eight also had a cleft of the alveolus, and three had a cleft of the palate continuous with the cleft lip. All patients showed some maxillary hypoplasia. An external rhinoplasty with lip repair was carried out in all patients. The corrective procedures on the nose included columellar lengthening; augmentation along the pyriform margin, nasal floor, and alveolus using bone grafts; submucous resection of the nasal septum; repositioning of lower lateral cartilages; and augmentation of nasal dorsum by bone graft. Clinical follow-up ranged from 4 to 24 months, and the median follow-up period was 13 months. Results have been very good, and much better than results seen earlier with other primary rhinoplasty techniques. While repairing unilateral cleft lip in adolescents, the author thinks it would be most appropriate to address the entire gamut of the deformity in a single stage, provide complete vector reorientation, and augment the hypoplastic elements by autologous tissue. It is not just the fear of poor follow-up, but that merely correcting the lip deformity in these patients without attempting definitive rhinoplasty, in the author's opinion, would be insufficient surgical intervention.     

The ptotic (witch's) chin deformity: an excisional approach.

Ptosis of the chin pad is common and can be seen in patients of all ages. It may be associated with too little or (at times) too much anterior chin projection. Often there is an associated deep submental skin crease present. Frequently, the primary concern of the patient is the appearance or exaggeration of chin ptosis in smiling ("dynamic" ptosis). This report describes a flexible approach to the correction of developmental (and some iatrogenic) ptotic chin deformities. The key element in the approach is the direct excision of sagging or excess chin fat, muscle, and skin. No attempt is made to reposition or lift ptosis-prone soft tissues. If a deep submental skin crease is present, it too is excised. If the chin needs added anterior projection, it is accomplished with a stable alloplastic chin implant. The approach is uniquely suited to correct anterior overprojection caused by an excess of soft tissue at the front of the chin and has been successful in correcting the "dynamic" ptosis that appears with smiling.     

腊玛古猿和西瓦古猿的形态特征及其系统关系——下颌骨的形态与比较

本文通过禄丰腊玛古猿和西瓦古猿的下颌骨与现代大猿类和其它同时代的古猿及南方古猿类的下颌骨的比较得出:禄丰的两类古猿有不少特征与猩猩相似,因此它们可能与猩猩有较密切的关系,两类古猿可能是同一类型的雌雄个体。但另一方面,禄丰腊玛古猿又显示出一些与南方古猿相似的性状,因而另一种可能是腊玛古猿是与西瓦古猿不同的类型,它比西瓦古猿更接近于人猿的共同主干。     

Rare craniofacial clefts: Tessier no. 4 clefts

A major difficulty in understanding rare craniofacial clefts arises from the fact that previous reports have focused on a single case or have grouped together different types of rare clefts. Less than 50 Tessier no. 4 clefts have been reported. This paper examines our experience with eight patients treated primarily or secondarily for Tessier no. 4 clefts. A treatment plan is recommended. The primary early concern is protection of the eye. Early correction of soft-tissue deformities should include skin, muscle, and lining of the orbit, cheek, and oral cavity. Contrary to the dictum that all soft tissue must be preserved, the medial portion of the upper lip from the cleft to the philtral ridge must be resected to prevent poorly camouflaged scars, muscle deficiency, and macrostomia. Bone grafting should be undertaken at an early age using calvarial bone. Late operations will be necessary for correction of medial and lateral canthal position, epiphora, lower eyelid skin deficiency, and further bony augmentation.     

Mandibular symphysis dimensions in different sagittal and vertical skeletal relationships

BackgroundThe aim of this cross-sectional study was to compare the dimensions of mandibular symphysis (MS) between gender and the different sagittal and vertical skeletal relationships.Material and MethodsPre-treatment records of orthodontic patients were divided according to gender, sagittal (Class I, II and III) and vertical (decreased, average and increased mandibular plane [MP] angle) skeletal relationships. Measurements of MS parameters were performed on lateral cephalograms using IMAGEJ software. Comparisons between MS parameters and gender and the different skeletal relationships was performed using multifactorial and one-way ANOVA, and independent sample t-tests.ResultsA total of 104 records (25 males and 79 females) fulfilled the inclusion criteria. Males had significantly greater MS surface area, dentoalveolar length, skeletal symphysis length, total symphysis length, vertical symphysis dimension and symphysis convexity (p < 0.05). Skeletal Class II patients had significantly greater dentoalveolar and skeletal symphysis lengths while Class III had greater chin length, vertical symphysis dimension and symphysis convexity (p < 0.05). Patients with decreased vertical dimension had greater skeletal symphysis length (p = 0.026) and those with an average vertical relationship had greater chin length (p < 0.001).ConclusionsThe morphology of the mandibular symphysis is affected by gender, sagittal and vertical skeletal patterns. Males had increased mandibular symphysis surface area and linear dimensions. Class II patients had greater dentoalveolar length. Chin length was greater in patients with an average MP angle.