Mandibular Outline Research Articles

Correction of Facial Asymmetry Using Patient-Specific Implants: A Case Report

Dentofacial deformities can have a profound impact on patients’ function and facial aesthetics. Traditionally, dentofacial deformities and malocclusion have been managed with growth modification, orthodontic therapy, and orthognathic surgery, or a combination of these modalities. The aim of this article is to discuss the use of patient-specific alloplastic implants as an adjunct or alternative to orthognathic surgery in patients with dentofacial deformities. A 40-year-old man who previously underwent surgically assisted rapid palatal expansion followed by LeFort I osteotomy advancement, intraoral vertical ramus osteotomy setback (IVRO), rhinoplasty, and fat transfer to the malar region presented with a chief complaint of dissatisfaction due to significant facial asymmetry. Tear trough deformity, concave nasal dorsum with nasal tip deviation to the left, submalar fullness, chin deviation to the right, and a poorly defined mandibular border outline were all noted on physical examination. The patient was treated with lower lid blepharoplasty with fat repositioning, buccal fat pad reduction (bichectomy), and patient-specific malar and mandibular border implants. In a patient who has a moderate-to-severe malocclusion and dentofacial deformity, traditional treatment includes orthodontic correction and orthognathic surgery. Patients undergoing primary orthognathic surgery can benefit from alloplastic implants. For patients who have residual maxillary or mandibular asymmetry after orthognathic surgery, the treatment options are secondary orthognathic procedures or facial implants. These patients can benefit from treatment with alloplastic facial implants as an adjunct or alternative to orthognathic surgery to normalize skeletal contours and improve facial aesthetics. Patient-specific alloplastic implants can be used as a powerful adjunct or alternative to orthognathic surgery. Patients with mild occlusal and skeletal deformities who have traditionally been treated with orthodontic therapy alone can benefit from evaluation of alloplastic implants. Patients with residual asymmetries after orthognathic surgery can benefit from alloplastic implants as an adjunct with secondary osteotomies or as an alternative altogether.

Mandibular Contouring During Orthognathic Surgery Using the Modified Hunsuck Technique.

Square face or prominent mandibular angle is a major concern in Asian women. In class III patients, mandibular setback may lead to a wider lower face that is not preferred in Asian culture. In order to achieve better aesthetic outcomes, simultaneous mandibular contouring to reduce the width of the lower face is required for some patients. This article details the authors' procedures modified from Hunsuck techniques of sagittal split osteotomy. This modified Hunsuck technique provides an alternative option to obtain a desirable mandibular outline. The long-term stability is also comparable to traditional methods.

Three-dimensional morphometric analysis of mandibule in coronal plane after bimaxillary rotational surgery.

BackgroundThe aim of this report is to present a new reference for aesthetic mandible surgery using three-dimensional cone-beam computed tomography-based treatment planning for orthognathic surgery which can be implemented in surgical planning and perioperative procedure.MethodsTo make an objective standard for evaluating aesthetic mandibular outline, we make an aesthetic scoring criteria with consideration of asymmetry, broad mandibular border line, and prominent mandibular angle. Two maxillofacial surgeons and two orthodontists rated their aesthetical evaluation from 1 to 5. Experimental group consisting of 47 female and 38 male patients who had rotational orthognathic two-jaw surgery from 2010 to 2011 were chosen according to aesthetic scoring done by two maxillofacial surgeons and two orthodontists. A high aesthetic score (≥16) means the facial contour is symmetric, with no broad and narrow aesthetic mandible frontal profiles. Control A group consisted of ten female and ten male patients who had no orthognathic surgery experience and low aesthetic score (≤10). Control B group consisted of ten female and ten male patients who had no orthognathic surgery experience and had anaesthetic mandibular frontal profile and a high aesthetic score (≥16). The three-dimensional image of the patient was taken from dental cone-beam CT (DCT) scanning (experimental group and control A group: 6 months DCT after surgery, control B group: 1st visit DCT). Each DCT was reformatted to reorient the 3D image using 3D analyzing program (OnDemand3D, cybermed Inc, CA, USA). After selection of 12 landmarks and the construction of reoriented horizontal, vertical, and coronal reference lines, 15 measurements were taken in 3D analysis of frontal mandibular morphology. Afterwards, horizontal and vertical linear measurements and angular measurements, linear ratio were obtained.ResultsMean Go’Rt-Me’-Go’Lt angular measurement was 100.74 ± 2.14 in female patients and 105.37 ± 3.62 in male patients. These showed significant difference with control A group in both genders. Ratio of Go’Rt,Go’Lt-Me’ length to some linear measurements (ratio of Me’-Cd’RtCd’Lt to Me’-Go’RtGo’Lt, ratio of Me’-Go’ to Me’-Go’RtGo’Lt, ratio of Go’Rt-Go’Lt to Me’-Go’RtGo’Lt) showed significant difference with control A group in both genders.ConclusionThis study was intended to find some standard measurement of mandible frontal view in 3D analysis of aesthetic patient. So, these potential measurement value may be helpful for orthognathic treatment planning to have more aesthetic and perspective outcomes.

Subtle Morphological Changes in the Mandible of Tabby Mice Revealed by Micro-CT Imaging and Elliptical Fourier Quantification

X-linked hypohidrotic ectodermal dysplasia (XLHED) is a genetic disorder due to a mutation of the EDA gene and is mainly characterized by an impaired formation of hair, teeth and sweat glands, and craniofacial dysmorphologies. Although tooth abnormalities in Tabby (Ta) mutant mice – the murine model of XLHED – have been extensively studied, characterization of the craniofacial complex, and more specifically the mandibular morphology has received less attention. From 3D micro-CT reconstructions of the left mandible, the mandibular outline observed in lateral view, was quantified using 2D elliptical Fourier analysis. Comparisons between Ta specimens and their wild-type controls were carried out showing significant shape differences between mouse strains enabling a clear distinction between hemizygous Ta specimens and the other mouse groups (WT and heterozygous EdaTa/+ specimens). Morphological differences associated with HED correspond not only to global mandibular features (restrained development of that bone along dorsoventral axis), but also to subtle aspects such as the marked backward projection of the coronoid process or the narrowing of the mandibular condylar neck. These modifications provide for the first time, evidence of a predominant effect of the Ta mutation on the mandibular morphology. These findings parallel the well described abnormalities of jugal tooth row and skeletal defects in Ta mice, and underline the role played by EDA-A in the reciprocal epithelial–mesenchymal interactions that are of critical importance in normal dental and craniofacial development.

Effects of Functionally Graded Hydroxyapatite for Large Mandibular Defects in Adult Rabbits

Objectives: As an alternative to autograft harvesting, we develop a functionally graded hydroxyapatite (fg-HAp) to induce bone regeneration within extensive bone defects. The functionally graded crystallinity from the inside layer to the surface layer of the fg-HAp promotes bone remodeling and replacement. We evaluate the effects of fg-HAp alone and in combination with fibroblast growth factor (bFGF) on bone regeneration within a bone defect in a rabbit mandible. Methods: The bone defect in the rabbit mandible was 12 x 9 x 3.5 mm in size. For the control group, no material was added to the defect. The experimental groups consisted of fg-HAp alone and fg-HAp combined with 5μg of bFGF. At 2, 4 and 8 weeks after implantation, we excised the mandibles and performed histomorphometrical analysis. Results: The fg-HAp resorption and replacement with new bone occurred fastest at the lingual portion of the defect. The fg-HAp maintained the mandibular outline and was absorbed by multinucleated giant cells. Blood vessel infiltration into the framework of fg-HAp was also observed. Adding 5μg of bFGF did not accelerate bone regeneration. The fg-HAp fragment was observed at the buccal portion of the defect. Excavated bone healing was observed only in the control group. Conclusions: The fg-HAp is an effective substrate for bone regeneration in critically sized bone defects.

Quantitative use of photography in orthognathic outcome assessment

This study reports an independent audit of two aspects of orthognathic surgery, namely control of inter-alar width and mandibular outline asymmetry. Measurements were taken from standardized photographs of a consecutive series of 27 patients, using an on-screen digitizing program (IPTool). All patients had undergone bimaxillary osteotomies involving maxillary impaction and/or advancement, by one surgeon, using a cinch suture for nasal width control. Nine–twelve months after surgery, inter-alar width had increased by just 0.08 cm mean (SD 0.3). Four patients showed an increase of just over 2 mm, whilst six showed a small reduction. Based on ratios of size (area) and shape (compactness) of the right and left mandibular segments, there was a small overall improvement in mandibular symmetry (0.019 and 0.005 respectively). Whilst in most of the patients the need for surgery was primarily the correction of antero-posterior and vertical discrepancies, five patients with demonstrable asymmetry showed a clear improvement. In three patients whose asymmetry scores were very mild pre-treatment, there was a small, measured increase in asymmetry, but not to a degree that would be clinically noticeable. At a time when 3D imaging is still unavailable to many clinicians, the results of this study suggest that appropriate measurements taken from carefully standardized conventional photographs can provide a valid and objective means of assessing treatment outcome.

Variations of the mandibular shape in extant hominoids: Generic, specific, and subspecific quantification using elliptical fourier analysis in lateral view

While a number of studies have documented the mandibular variations in hominoids, few focused on evaluating the variation of the whole outline of this structure. Using an efficient morphometrical approach, i.e. elliptical Fourier analysis, mandibular outlines in lateral view from 578 adult hominoids representing the genera Hylobates, Pongo, Gorilla, Pan, and Homo were quantified and compared. This study confirms that elliptical Fourier analysis provides an accurate characterization of the shape of the mandibular profile. Differences in mandibular shape between hominoid genera, species, subspecies, and to a lesser extent between sexes were demonstrated. Mandibles in great apes and hylobatids subspecies were generally less distinct from each other than were species. However, the magnitudes of differences among subspecies of Gorilla and Pongo approached or exceeded those between Pan troglodytes and P. paniscus. The powerful discrimination between taxa from the genus down to subspecific level associated to the relatively low level of intrageneric mandibular polymorphism in great apes provides strong evidences in support of the taxonomic utility of the shape of the mandibular profile in hominoids. In addition, morphological affinities between Pongo and Pan and the clear distinction between Homo and Pan suggest that the mandibular outline is a poor estimate of phylogenetic relationships in great apes and humans. The sexual dimorphism in mandibular shape exhibits two patterns of expression: a high degree of dimorphism in Gorilla, Pongo, and H. s. syndactylus and a relatively low one in modern humans and Pan. Besides, degree of mandibular shape dimorphism can vary considerably among closely related subspecies as observed in gorillas, arguing against the use of mandibular shape dimorphism patterns as characters in phylogenetic analyses. However, the quantification of the mandibular shape and of the variations among hominoids provides an interesting comparative framework that is likely to supply further arguments for a better understanding of the patterns of differentiation between living hominoids.

A computerized photographic assessment of the relationship between skeletal discrepancy and mandibular outline asymmetry

The aim of this study was to investigate the relationship between mandibular outline asymmetry and skeletal discrepancy in a sample of orthodontic patients (33 females, 33 males) aged from 8 to 19 years. Skeletal discrepancy was assessed in both the anteroposterior and vertical planes, using standard cephalometric analyses. All were photographed under standardized conditions and the photographs were then digitized for analysis using a computerized system to assess differences in four variables (area, perimeter, compactness and moment-ratio) between the right and left sides of the mandibular outline. The results showed good repeatability of the photographic, cephalometric and digitization methods. A statistically significant relationship was found between mandibular outline asymmetry and both anteroposterior and vertical skeletal discrepancy in this sample, when compared with patients with an average skeletal pattern. There appeared to be a statistically significant relationship between a reduced ANB angle (< 3 degrees) and mandibular outline asymmetry (P = 0.051), as well as between an increase in lower face height and mandibular asymmetry (P = 0.023).

Shape of the Lateral Mandibular Outline in Lemuridae: A Quantitative Analysis of Variability Using Elliptical Fourier Analysis

While several morphometric analyses in lemurids have focused on the craniofacial complex, the characterization of their mandibular morphology has received less attention. The mandibular outline, in lateral perspective, was quantified using elliptical Fourier analysis, in an osteological sample encompassing 189 lemurid mandibles (66 Eulemur, 51 Hapalemur, 22 Lemur and 50 Varecia), and compared using multivariate statistical techniques. The taxonomic value of this outline in Lemuridae was demonstrated by the existence of significant separations between the four genera studied. In particular, the mandibular morphology of Hapalemur was markedly different from that in the group Eulemur-Lemur-Varecia. Excluding Hapalemur from analysis, the distinctions between Eulemur, Lemur and Varecia were enhanced suggesting the existence of more subtle intergeneric differences in mandibular morphology. Variation in mandibular form was greatest in Hapalemur and smallest in Eulemur and Varecia (as demonstrated by the mean values of interindividual distances); variation was higher in Lemur than in Eulemur and Varecia, but not higher than in Hapalemur. This morphological diversity may be related to functional adaptation in response to particular dietary habits. The patterns of intergeneric and intrageneric shape variations of the mandible in Lemuridae presented here provide a valuable resource for the analysis of variation among living and fossil lemurids.

Mandibular antegonial and ramus notch depths and condylar bone change

The present study sought to clarify the relationship between antegonial and ramus notch depths and condylar bone change, and analyse the effects of such change on craniofacial structure. The study sample was of 28 pre-orthodontic patients with signs and symptoms of temporomandibular joint (TMJ) disorders, who underwent helical computed tomography to diagnose their TMJ pathology. Craniofacial structures were compared between 14 subjects with bilateral condylar bone change (BBC group: two male and 12 female) and 14 subjects with no bone change (NBC group: two male and 12 female). Sella-nasion-point B (SNB) and point A-nasion-point B (ANB) angles were significantly smaller in BBC than in NBC, with ramus height and mandibular body lengths significantly shorter in BBC than in NBC. The BBC lower facial height and SN-Go-Ar angle, as well as antegonial and ramus notch depths, were significantly greater than in NBC, and the mandible was significantly more retruded in BBC than in NBC. These results showed that condylar bone change might be related not only to mandibular size (e.g. retrusion) but also to mandibular outline (including antegonial and ramus notch depth).

A quantitative approach for measuring crowding in the dental arch: fourier descriptors

Dental crowding is defined as a discrepancy between tooth size and jaw size that results in a misalignment of the tooth row. Proposed reasons for crowding include excessively large teeth, small jaws, and a combination of both. Nevertheless, the parameters that would allow the prediction of crowding have not been identified. This study compared the shape of crowded and uncrowded dental arches, matched for size and sex. The application of elliptical Fourier functions (EFFs) provided an accurate numeric description of the dental arch form. Dental casts from the Nihon University School of Dentistry at Matsudo, Chiba, Japan, were studied. Group I, the control group, consisted of 118 dental cast pairs (49 female, 69 male, aged 20.40 ± 1.68 years [mean ± SD]) with little or no crowding. Group II, which exhibited crowding, consisted of 78 dental cast pairs (64 female, 14 male, aged 19.67 ± 4.95 years). From photographs, a set of 24 homologous points describing the tooth row was identified. These points were then fitted with EFFs. Each maxillary and mandibular outline was subsequently standardized for size by scaling the bounded area to a constant 10,000 mm 2. These “shape only” data were used to assess differences between arches in the 2 groups. By multivariate analysis of variance, statistically significant shape differences between groups I and II were obtained for both arches. Patients with crowding exhibited more variability than did the controls. This variability was illustrated with canonical axes derived from discriminant function analysis.

Comparison of radiographic and photographic measurement of mandibular asymmetry

This study compared measurement of mandibular asymmetry by digitization of mandibular outlines from standardized facial photographs and posteroanterior cephalometric radiographs. Four ratios were used in calculating asymmetry: area (relative size of right and left mandibular segments), perimeter or length of outlines, compactness (shape), and moment. The records of 28 patients with varying degrees of asymmetry were used. A significant relationship was found for 3 of the ratios (area, compactness, and moment) between measurements from photographs and radiographs. A further comparison showed that measurements from the radiographs correlated more closely with those from photographs when the mastoid processes were used as a baseline, rather than latero-orbitale. Repeatability of mandibular outline digitization proved satisfactory. Although digitization from standardized photographs is the preferred approach, the results indicated that posteroanterior cephalometric radiographs can be used similarly. Unlike other cephalometric analyses for mandibular asymmetry, this method avoids problems of landmark identification, thus presenting a clinically useful method of quantifying asymmetry, eg, in auditing the surgical-orthodontic correction of asymmetry or monitoring change over time. (Am J Orthod Dentofacial Orthop 2003;123:167-74)

Mandibular outline assessment in three groups of orthodontic patients.

The feasibility of using computer-based parameters for quantifying mandibular asymmetry was investigated. Four methods of calculating asymmetry were used, based on the digitized facial photographs of three groups of patients: those with no observable asymmetry, a group with mild asymmetry, and a group presenting for orthognathic surgery. Three of the methods involved right/left difference ratios, namely, area, perimeter length, and compactness. The fourth, moment ratio (centre of area), was expressed as a percentage. Repeatability of both photography and digitization proved satisfactory, the standard deviation of the differences between repeated photographs being 0.016 and 0.014 for area and compactness ratios, respectively. Area, perimeter, and compactness successfully discriminated between the three groups. For area, median ratios (deviations from 1.00) for the 'normal', 'mild asymmetry', and 'surgical' groups were 0.015, 0.030, and 0.078, respectively. Those patients in the surgical group for whom asymmetry correction had been the main reason for surgery recorded higher asymmetry scores than the other subjects in that group. Moment ratio did not adequately distinguish between the three groups. Better repeatability for digitization was found when a baseline involving the ear insertions was used, than either the outer or inner canthi of the eyes. The potential uses of this approach are presented in relation to clinically relevant mild asymmetry, as well as auditing the outcome of surgical correction.

The human mandible in lateral view: elliptical fourier descriptors of the outline and their morphological analysis

An original procedure based on new developments in elliptical Fourier methods associated with image analysis technics was applied to 117 human mandibles in lateral view (69 males, 48 females) in order to analyze interindividual variability and sexual dimorphism. Original parameters, called elliptical Fourier descriptors, allowed for the quantification of the shape of an outline irrespective of its morphological complexity, and provided a precise individual characterization. The use of step by step reconstructions with an increasing number of harmonics allowed for demonstration of the morphological contributions of the elliptical Fourier descriptors, and relationships to precise anatomical features were established. The first harmonics (1st to 8th) described the general mandibular shape, and the later harmonics (8th to 14th) characterized accessory and finer morphological features. The proportion of individuals presenting significant sexual dimorphism was 97.1% in males and 91.7% in females, and after size normalization 84.1% in males and 81.2% in females. Even after removal of the size component, these results in regard to mandibular dimorphism remained better than those found by classical approaches; this could be due to the use of elliptical Fourier analysis which takes into account all the information of the mandibular outline. Compared to the size component, the shape component seemed to be more important in the sexual dimorphism of the human mandible than previously recognized. The present approach opens interesting anthropological and clinical perspectives for the characterization of mandibular morphology.

Sexual dimorphism of the human mandible: demonstration by elliptical Fourier analysis.

A new quantitative approach of the mandibular sexual dimorphism, based on computer-aided image analysis and elliptical Fourier analysis of the mandibular outline in lateral view is presented. This method was applied to a series of 117 dentulous mandibles from 69 male and 48 female individuals native of Rhenish countries. Statistical discriminant analysis of the elliptical Fourier harmonics allowed the demonstration of a significant sexual dimorphism in 97.1% of males and 91.7% of females, i.e. in a higher proportion than in previous studies using classical metrical approaches. This original method opens interesting perspectives for increasing the accuracy of sex identification in current anthropological practice and in forensic procedures.

加齢が骨再生機序に及ぼす影響に関する病理組織学的研究 成長期と成熟期のウサギにおける下顎骨骨空洞の治癒過程の比較

Effects of aging on the regeneration of bone were evaluated by comparing male New Zealand White Rabbits of different ages with respect to the healing process of bony cavities in the mandible. Rabbits were divided into two groups according to age: a 14-weekold group, representing young or growing rabbits, and a 30-week-old group, representing adult or aging rabbits. A bony cavity of 12×10×4mm was prepared in the mandible of both groups; the periosteum was preserved carefully. Bone formation and cellular proliferation were examined morphologically, histomorphometically, and immunohistochemically using anti-BrdU monoclonal antibody. The results were as follows:1) New bone formation and bone remodeling in the bony cavities of adult rabbit mandibles started later and the rate of bone formation was lower than that of the young rabbits.2) The number of BrdU-positive cells in the bony cavities of the adult group was significantly less than that of the young group. The results suggested that aging was associated with decreased osteoblast acitivity.3) Although adult rabbits showed significantly less new bone formation than young rabbits during the healing of bony cavities, the bony cavities in both groups were filled with new bone, and the mandibular outline was repaired by new cortical bone resulting from remodeling of newly formed bone 28 days after surgery.4) During the healing process, the periosteum seems to play an important role in the formation of the mandibular outline, irrespective of age.

Quantitative description of the shape of the mandible

The purpose of this study was to provide quantitative data on the shape of the mandible at the period around the pubertal growth spurt and to test the hypothesis that early mandibular shape may influence the amount and direction of subsequent mandibular growth. Longitudinal data from lateral cephalograms of 55 white female and 39 white male subjects were used. The mandibular outline from articulare to gnathion was analyzed into cosine curves, according to the Fourier equation. The resulting Fourier coefficients, representing mandibular outline shape, were analyzed statistically in relation to age, sex, craniofacial pattern, and mandibular growth rotation. Statistically significant growth changes of the Fourier coefficients were observed, especially during the postpubertal period, indicating a decrease in the gonial angle with age. Sex-related differences in shape were observed at all ages, male subjects showing a more rounded shape of the mandible than female subjects. Mandibular shape, as represented by the Fourier coefficients, was correlated to cephalometric variables, indicating mandibular inclination, but only poorly to cephalometric variables, indicating anteroposterior jaw relation. Total rotation of the mandible during growth could not be predicted by mandibular shape.

頭部Ｘ線規格写真による下顎骨形態の３次元分析法

Methods for three-dimensional analysis of mandibular morphology and its postoperative change in which three-dimensional coordinate values of the landmarks on the mandible were measured and standardized by a personal computer using simultaneously taken frontal and lateral cephalograms were described and the efficacy of their clinical application was evaluated.The deviations of standardized three-dimensional coordinate values of six small steel balls placed on the skull which were calculated from eight cephalograms taken in different positions as well as the differences in the distance of these balls calculated from cephalograms and direct measurements were found to be small enough for clinical use. With the exception of 0.7mm in the mean difference of mandibular outline on the ZY-plane, standard deviations of all values evaluated were within 0.5mm in the analysis of U1, L1 and outer shapes of the mandible in 25 patients whose cephalograms were taken preoperatively on two separate occasions within a period of 4 months.The prediction of postoperative position of the mandible consisted of measuring the amount and direction of the movement of defined points on a dental model and displaying the movement of other bony points in the cephalometric tracings by coordinate transformation. The accuracy of the prediction was studied by comparing the predicted and postoperative positions of the mandible in three-dimensions in 44 patients in whom mandibular prognathism was corrected by the sagittal split osteotomy. The mean differences of coordinate values at L1 were within 0.84mm and the mean differences of mandibular outlines on the XY-, ZY-and ZX-planes were 0.76, 1.09 and 1.58mm, respectively.Thus, the methods described here proved to be quite useful for the diagnosis, treatment planning and the assessment of postoperative changes in patients with skeletal deformity of the mandible.

The accuracy of measuring condylion location

In locating condylion (Co), clinicians have used cephalograms in maximum mandibular opening to provide a clearer image of the condyle. The purpose of this study was to evaluate the accuracy of identifying condylion on a sample of open and closed mouth cephalograms of 20 patients. Five orthodontists traced each mandibular outline and located condylion and the tip of the mandibular incisor (I). The incisor tip was assumed to be relatively interpretable and served as an internal control. The differences between the open and closed positions in the horizontal and vertical components of condylion relative to the mandibular plane or in the length Co-Gn were not statistically significant. The absolute deviation around condylion was significantly different ( p = 0.007), but the average absolute deviation of condylion in the open position was only 0.5 mm less than condylion in the closed position. Statistically significant differences also occurred in the means of the vertical component of the incisor tip ( p = 0.002), the length Gn-I ( p = 0.006), and the absolute deviation of incisor tip ( p = 0.004). These results indicate that the open mouth method does not significantly change the location of condylion. It does increase the accuracy of landmark identification, but this increased accuracy on the average is not clinically significant.

Investigation of Mandibular and Neurocranial Form

In a study of mandibular form, 19 traditional linear dimensions were found to be consistently greater for macrocephalics than microcephalics. As such dimensions combine both size and shape parameters together, their interpretation proved difficult. In order to examine specifically mandibular shape only, each mandibular outline form was digitized and subjected to the technique of medial axis transformation. The data indicate that the shape contrasts between the mandibles of macrocephalics and microcephalics are more complex than traditionally envisaged and emphasize the need for further study to ascertain the effect of genetic and environmental influences on mandibular form.