Geometric morphometric analysis of craniofacial variation, ontogeny and modularity in a cross-sectional sample of modern humans

Sexual differences in human cranial morphology: Is one sex more variable or one region more dimorphic?

The quantification of cranial sexual dimorphism (CSD) among modern humans is relevant in evolutionary studies of morphological variation and in a forensic context. Despite the abundance of quantitative studies of CSD, few have specifically examined intra-sex variability. Here we quantify CSD in a geographically homogeneous sample of adult crania, which includes Italian individuals from the 19th and 20th centuries. Cranial morphology is described with 92 3D landmarks analyzed using Procrustean geometric morphometrics (PGMM). Size and shape variables are used to compare morphological variance between sexes in the whole cranium and four individual regions. The same variables, plus Procrustes form, are used to quantify average sex differences and explore classification accuracy. Our results indicate that: (a) as predicted by Wainer's rule, males present overall more variance in size and shape, albeit this is statistically significant only for total cranial size; (b) differences between sexes are dominated by size and to a lesser extent by Procrustes form; (c) shape only accounts for a minor proportion of variance; (d) the cranial base shows almost no dimorphism for shape; and (e) facial Procrustes form is the most accurate predictor of skeletal sex. Overall, this study suggests developmental factors underlying differences in CSD among cranial regions; stresses the need for population-specific models that describe craniofacial variation as the basis for models that facilitate the estimation of sex in unidentified skeletal remains; and provides one of the first confirmations of "Wainer's rule" in relation to sexual dimorphism in mammals specific to the human cranium.

Pattern of Morphological Variability in Unrepaired Unilateral Clefts With and Without Cleft Palate May Suggest Intrinsic Growth Deficiency

In individuals with cleft lip and palate (CLP) an iatrogenic effect of operations on subsequent maxillary growth is well-known. Much less is known about the association between occurrence of CLP and intrinsic growth deficiency of the maxillofacial complex. The aim of this study was to compare morphological variability in subjects with unilateral cleft lip and alveolus/palate and unaffected controls using geometric morphometric methods. The research hypothesis was that if subjects with unrepaired unilateral CLP have intrinsic growth deficiency, the pattern of their craniofacial growth variation may differ from that in unaffected individuals. Lateral cephalograms were available of three groups of the same ethnic background (Proto-Malayid): (a) non-syndromic unrepaired unilateral complete cleft lip, alveolus, and palate (UCLP), N = 66, mean age 24.5 years (b) non-syndromic unrepaired unilateral complete cleft lip and alveolus (UCLA), N = 177, mean age 23.7 years, and (c) NORM (N = 50), mean age 21.2 years without a cleft. Using geometric morphometrics shape variability in groups and shape differences between groups was analyzed. Principal component analysis (PCA) was used to examine shape variability, while differences between groups and sexes were evaluated with canonical variate analysis. Sexual dimorphism was evaluated with discriminant function analysis (DA). Results showed that in comparison to NORM subjects, shape variability in UCLA and UCLP is more pronounced in the antero-posterior than in vertical direction. Pairwise comparisons of the mean shape configurations (NORM vs. UCLA, NORM vs. UCLP, and UCLA vs. UCLP) revealed significant differences between cleft and non-cleft subjects. The first canonical variate (CV1, 68.2% of variance) demonstrated that differences were associated with maxillary shape and/or position and incisor inclination, while in females, the CV1 (69.2% of variance) showed a combination of differences of “maxillary shape and/or position and incisor inclination” and inclination of the cranial base. Shape variability demonstrated considerable differences in subjects with UCLA, UCLP, and NORM. Moreover, in subjects with a cleft, within-sample variability was more pronounced in the antero-posterior direction, while in non-cleft subjects, within-sample variability was more pronounced in the vertical direction. These findings may suggest that subjects with unilateral clefts have intrinsic growth impairment affecting subsequent facial development.

Integration of Cranial Base and Face in Growing Subject

Background: many papers investigate the role of the cranial base in facial development, but the results are not in agreement. This can be due to a difference between the central and lateral parts of the cranial base. The aim of the present study is to evaluate the relationship between the central and the lateral cranial base and the facial skeleton in pre-pubertal peak subjects and at the end of growth. Material/Methods: a total sample of 52 latero-lateral cranial teleradiographs were analyzed. To test the correlation between structures, the “Partial Least Square” analysis was performed. Geometric morphometric analysis were applied and partial least square analysis was used to test correlation. Integration was studied removing the effect of allometry. Results: facial skeleton has no significant relation with central cranial base. Facial skeleton has significant relationships with the lateral portion of the cranial base. This relationship is higher in the post-peak phase of growth. Conclusion: the Integration between facial structures and cranial base is significant. The Spatial orientation and shape of the facial structures are both influenced by cranial base. This is mainly due to the lateral portion of cranial base.

Geometric morphometric analysis of malocclusion on lateral cephalograms in Malaysian population

Geometric morphometrics is a new approach for shape identification in diagnosis of malocclusion. Lateral cephalogram is an X-ray that taken for diagnosing malocclusion in dental setting. The aim of this study was to determine the differences of craniofacial shape in malocclusion by application of two-dimensional geometric morphometrics and to compile the database of malocclusion in adult Malaysian population. Lateral cephalogram radiographs of 381 adults Malaysia (age 18-45) were retrieved retrospectively and assigned to three groups according to their occlusion: class I, class II, and class III. The geometric morphometric shape study incorporated nine landmarks and was analyzed in details using tpsUtil p software. Geometric morphometric analysis such was done using MorphoJ software. The results of the principal component's analysis (PCA) yielded 14 main components responsible for 100% of the variation exhibited by the malocclusion with three highly significant PCA. The highest Mahalanobis distances were exhibited by the malocclusion class II and III population. The Procrustes ANOVA showed that the shape effect was highly significant (P<0.01). The discriminant function analysis showed the high percentage of 80% discriminate among the malocclusions after cross-validation. There are significant differences for ANB angle (A point-Nasion-B point) in all malocclusion groups. Class II has the widest ANB angle while class III has the most acute ANB angle. Skeletal shape was clearly associated with dental malocclusion and showed considerable variation. Geometric morphometrics is an alternative research tool and can be used for diagnosing individual classification of malocclusion.

Craniofacial geometric morphometrics in the identification of patients with sickle cell anemia and sickle cell trait

OBJECTIVE

The aims of this study were to identify the main characteristics regarding the shape and size of the craniofacial region in patients with sickle cell anemia (SCA) and sickle cell trait (SCT) and in unaffected patients using geometric morphometrics and to check the efficiency of this method.

MATERIAL AND METHODS

A cross-sectional analytical study of 45 patients (15 in each group) was performed. Lateral radiographs of the skull were used for the analysis. Seventeen landmarks and semilandmarks were placed for the measurements. The Pocrustes analysis of variance (ANOVA), regression analysis, multivariate analysis of variance, canonical variate analysis, Mahalanobis and Procrustes distances and unweighted pair group method with arithmetic mean (UPGMA) clustering were performed. Allometric effects and sex characteristics were not statistically significant (p > 0.05).

RESULTS

There were, however, significant differences (p < 0.05) in craniofacial shape among SCA, SCT and unaffected individuals. Those with SCA showed variations in the shape of the external auditory meatus and at the base of the occipital bone, in addition to the mandibular setback and upper incisor inclination, with a tendency towards prognathism. The individuals with SCT exhibited a similar craniofacial shape to those with SCA, but with slighter variations. Moreover, those with SCT were statistically closer in resemblance to unaffected individuals, given that SCT is not regarded as a disease.

CONCLUSION

This demonstrates the efficiency of geometric morphometrics in the categorization of the assessed groups.

Morphological variability in unrepaired bilateral clefts with and without cleft palate evaluated with geometric morphometrics

In subjects with orofacial clefts, there is an unresolved controversy on the effect of congenital maxillary growth deficiency vs. the effect of surgical intervention on the outcome of treatment. Intrinsic growth impairment in subjects with orofacial clefts can be studied by comparing facial morphology of subjects with untreated cleft and unaffected individuals of the same ethnic background. Bilateral cleft lip and palate is the most severe and least prevalent form of the orofacial cleft. The aim of this study was to compare facial morphology in subjects with unrepaired complete bilateral clefts and unaffected controls using geometric morphometrics. Lateral cephalograms of 39 Indonesian subjects with unrepaired bilateral complete cleft lip and alveolus (mean age: 24 years), or unrepaired bilateral complete cleft lip, alveolus, and palate (mean age: 20.6 years) and 50 age and ethnically matched controls without a cleft (25 males, 25 females, mean age: 21.2 years) were digitized and traced and shape variability was explored using principal component analysis, while differences between groups and genders were evaluated with canonical variate analysis. Individuals with clefts had a more pronounced premaxilla than controls. Principal component analysis showed that facial variation in subjects with clefts occurred in the anteroposterior direction, whereas in controls it was mostly in the vertical direction. Regression analysis with group, sex, and age as covariates and principal components from 1 to 6 as dependent variables demonstrated a very limited effect of the covariates on the facial shape variability (only 11.6% of the variability was explained by the model). Differences between cleft and non-cleft subjects in the direction of facial variability suggest that individuals with bilateral clefts can have an intrinsic growth impairment affecting facial morphology later in life.

Developmental shape changes in facial morphology: Geometric morphometric analyses based on a prospective, population-based, Chinese cohort in Hong Kong

BACKGROUND

Thorough understanding of developmental changes of human facial shape is lacking. The present study aimed to evaluate developmental shape changes of facial morphology based on a prospective, population-representative, Chinese cohort in Hong Kong.

METHODS

A population-representative sample of Chinese in Hong Kong was followed. Serial facial images of over 260 participants were obtained at age 12, 15, and 18 years. Facial landmarks were digitized and the corresponding coordinates were submitted for Generalized Procrustes Analysis. The resultant Procrustes shape coordinates, which captured shape information encoded by the facial landmarks, were then used for statistical shape analyses.

RESULTS

Small but significant developmental changes in mean facial shape were observed (p < 0.0001 for all pairwise comparisons). Significant age-related changes in the magnitude of variance of facial shape were also observed (p < 0.05). Phenotypic growth trajectories representing developmental shape changes were similar in size (p > 0.05) between sexes but differed in direction (p < 0.05) in shape space and trajectory shape (p < 0.05). The magnitude of shape differences between sexes remained constant from 12 to 18 years. Results of frontal facial shape analyses after removing the effect of allometry were similar to results obtained before removal of allometry. For lateral facial configurations, allometric trajectories among the age-by-sex groups were similar in slope (p > 0.05) but varied in directions in the multidimensional shape space.

CONCLUSIONS

Our findings suggested significant age-related changes in facial shape and provided a dynamic view of developmental changes in sexual dimorphism of facial shape. Allometry contributed minimally to developmental changes in frontal facial shape. In addition, the allometric trajectories for lateral facial configurations were similar in rate of shape change but differed in their directions in shape space.

Morphometric covariation between palatal shape and skeletal pattern in children and adolescents: a cross-sectional study

Objective

To assess shape covariation of the palate and craniofacial complex (CFC) in children and adolescents.

Methods

Pre-treatment lateral cephalometric radiographs and corresponding maxillary casts of 100 children (8-10 years) and 100 adolescents (15-20 years) were digitized. Exclusion criteria were previous orthodontic treatment, craniofacial syndromes, mouth breathing, finger sucking, crossbite, tooth agenesis, and tooth impaction. Palatal shape was described with 239 surface and curve semilandmarks and craniofacial shape with 10 fixed landmarks and 117 curve semilandmarks. Procrustes superimposition and principal component analysis were applied for evaluation of shape variability. Shape covariation between palate and CFC was assessed with partial least squares analysis.

Results

The first five principal components explained 77 per cent (palate) and 60 per cent (CFC) of total shape variability. The palate varied mainly in height (adolescent group) and width-length (both groups), whereas the CFC varied mainly in the vertical dimension. Significant covariation was found between the craniofacial and palatal components (RV coefficient: 0.27, children; RV: 0.23, adolescents). Variation of the CFC in the vertical and anteroposterior direction was mainly related to variation in the height-width and the width-length ratio of the palate, respectively.

Limitations

The use of lateral cephalometric radiographs eliminated the transverse dimension from the craniofacial shape analysis. The study was cross-sectional, so the observed intergroup differences should be interpreted with caution.

Conclusions

Covariation strength and pattern were similar in children and adolescents. The closer a subject was to the high-angle end of the variability spectrum, the higher and narrower was the palate, and conversely.

Geometric morphometric analysis of craniofacial growth between the ages of 12 and 14 in normal humans

Aim

There is great variation of growth among individuals. The question whether patients with different skeletal discrepancies grow differently is biologically interesting but also important in designing clinical trials. The aim of the present study was to evaluate whether growth direction depends on the initial craniofacial pattern.

Subjects and method

The sample consisted of 350 lateral cephalograms of 175 subjects (91 females and 84 males) followed during normal growth without any orthodontic treatment. The examined ages were 12 (T1) and 14 (T2) years. The cephalograms were obtained from the American Association of Orthodontists Foundation (AAOF) Craniofacial Growth Legacy Collection (Burlington, Fels, Iowa, and Oregon growth studies). We digitally traced 15 curves on each cephalogram, comprehensively covering the craniofacial skeleton, and located 127 points on the curves, 117 of which were sliding semilandmarks and 10 fixed. Procrustes alignment, principal component analysis and two-block partial least squares analysis were performed, after sliding the semilandmarks to minimize bending energy.

Results

The first 10 principal components (PCs) described approximately 71 per cent of the total shape variance. PC1 was related to shape variance in the vertical direction (low/high angle skeletal pattern) and PC2 was mainly related to shape variance in the anteroposterior direction (Class II/Class III pattern). PC3 was mainly related to the shape variance of the mandibular angle. All subjects shared a similar growth trajectory in shape space. We did not find any correlation between the initial shape and the magnitude of shape change between T1 and T2, but males showed a greater shape change than females. The direction of shape change was moderately correlated to the initial shape (RV coefficient: 0.14, P < 0.001).

Conclusions

The initial shape of the craniofacial complex covaried weakly with the direction of shape change during growth.

Craniofacial shape differs in patients with tooth agenesis: geometric morphometric analysis

Aim

To evaluate the shape of the craniofacial complex in patients with tooth agenesis and compare it to matched controls.

Subjects and methods

The sample comprised 456 patients that were allocated to three groups: the agenesis group of 100 patients with at least one missing tooth, excluding third molars, the third molar agenesis group (3dMAG; one to four missing third molars) of 52 patients and the control group (CG) of 304 patients with no missing teeth. The main craniofacial structures depicted on lateral cephalograms were digitized and traced with 15 curves and 127 landmarks. These landmarks were subjected to Procrustes superimposition and principal component analysis in order to describe shape variability of the cranial base, maxilla and mandible, as well as of the whole craniofacial complex. For statistical analysis, permutation tests were used (10 000 permutations without replacement).

Results

Approximately half of the sample's variability was described by the first three principal components. Comparisons within the whole sample revealed sexual dimorphism of the craniofacial complex and its structures (P < 0.01). Differences between the agenesis group and matched controls were found in the shape of all craniofacial structures except for the cranial base (P < 0.05). Specifically, patients with agenesis presented with Class III tendency and hypodivergent skeletal pattern. However, the comparison between the 3dMAG and matched CG revealed no differences.

Conclusion

The shape of the craniofacial complex differs in patients with tooth agenesis suggesting that common factors are implicated in tooth development and craniofacial morphology.

Morphometric covariation between palatal shape and skeletal pattern in Class II growing subjects

Objectives

To evaluate the patterns of covariation between palatal and craniofacial morphology in Class II subjects in the early mixed dentition by means of geometric morphometrics.

Methods

A cross-sectional sample of 85 Class II subjects (44 females, 41 males; mean age 8.7 years ± 0.8) was collected retrospectively according to the following inclusion criteria: European ancestry (white), Class II skeletal relationship, Class II division 1 dental relationship, early mixed dentition, and prepubertal skeletal maturation. Pre-treatment digital 3D maxillary dental casts and lateral cephalograms were available. Landmarks and semilandmarks were digitized (239 on the palate and 121 on the cephalogram) and geometric morphometric methods (GMM) were applied. Procrustes analysis and principal component analysis (PCA) were performed to reveal the main patterns of palatal shape and craniofacial skeletal shape variation. Two-block partial least squares analysis (PLS) assessed patterns of covariation between palatal morphology and craniofacial morphology.

Results

For the morphology of the palate, the first principal component (PC1) described variation in all three dimensions. For the morphology of the craniofacial complex, PC1 showed shape variation mainly in the vertical direction. Palatal shape and craniofacial shape covaried significantly (RV coefficient: 0.199). PLS1 accounted for more than 64 per cent of total covariation and related divergence of the craniofacial complex to palatal height and width. The more a Class II subject tended towards high-angle divergence, the narrower and higher was the palate.

Conclusions

Class II high-angle patients tended to have narrower and higher palates, while Class II low-angle patients were related to wider and more shallow palates.

Divergence, Convergence and Phenotypic Diversity of Neotropical Frugivorous Bats

Knowing how adaptation shapes morphological evolution is fundamental to understanding the processes that promote biological diversity. However, there is a lack of empirical evidence on the effects of adaptive radiations on phenotypic diversity, which is related to processes that promote phenotypic divergence and convergence. We applied comparative methods to identify shifts in adaptive peaks and to detect divergence and convergence in skull morphology of frugivorous bats (Phyllostomidae: Stenodermatinae and Carollinae), an ecologically diverse group with strong association between skull morphology, feeding performance and diet that suggests adaptive diversification through morphological innovation. We found divergence and convergence for skull morphology. Fifteen peak shifts were found for jaws, which result in four convergent and four divergent regimes. For skull, nine peak shifts were detected that result in three convergent and three divergent regimes. Furthermore, convergence was significant and strong for skull morphology since distantly related organisms converged to the same adaptive optima. Results suggest that convergence indicates the effect of restriction on phenotypes to keep the advantages provided by the skull phenotype that played a central role in the evolution of strict frugivory in phyllostomids. We conclude that convergence has limited phenotypic diversity of functional traits related to feeding in phyllostomid frugivores.

Three-dimensional computed tomography analysis of mandibular morphology in patients with facial asymmetry and mandibular retrognathism

INTRODUCTION

The purpose of this study was to analyze the morphologic features of skeletal units in the mandibles of patients with facial asymmetry and mandibular retrognathism using cone-beam computed tomography.

METHODS

The subjects consisted of 50 adults with facial asymmetry and mandibular retrognathism, divided into the symmetry group (n = 25) and the asymmetry group (n = 25) according to the degree of menton deviation. Three-dimensional computed tomography scans were obtained with cone beam computed tomography. Landmarks were designated on the reconstructed 3-dimensional images. Linear and volumetric measurements were made on the mandibles.

RESULTS

In the asymmetry group, the lengths of condylar, body, and coronoid units were shorter, and condylar width was narrower on the deviated side than on the nondeviated side (P <0.01). The lengths of angular and chin units were not significantly different between the deviated and nondeviated sides (P >0.05). Hemimandibular, ramal, and body volumes were less on the deviated side than on the nondeviated side (P <0.01).

CONCLUSIONS

Condylar, body, and coronoid units contribute to mandibular asymmetry in patients with facial asymmetry and mandibular retrognathism.

Use of automated learning techniques for predicting mandibular morphology in skeletal class I, II and III

BACKGROUND

The prediction of the mandibular bone morphology in facial reconstruction for forensic purposes is usually performed considering a straight profile corresponding to skeletal class I, with application of linear and parametric analysis which limit the search for relationships between mandibular and craniomaxillary variables.

OBJECTIVE

To predict the mandibular morphology through craniomaxillary variables on lateral radiographs in patients with skeletal class I, II and III, using automated learning techniques, such as Artificial Neural Networks and Support Vector Regression.

MATERIALS AND METHODS

229 standardized lateral radiographs from Colombian patients of both sexes aged 18-25 years were collected. Coordinates of craniofacial landmarks were used to create mandibular and craniomaxillary variables. Mandibular measurements were selected to be predicted from 5 sets of craniomaxillary variables or input characteristics by using automated learning techniques, and they were evaluated through a correlation coefficient by a ridge regression between the real value and the predicted value.

RESULTS

Coefficients from 0.84 until 0.99 were obtained with Artificial Neural Networks in the 17 mandibular measures, and two coefficients above 0.7 were obtained with the Support Vector Regression.

CONCLUSION

The craniomaxillary variables used, showed a high predictability ability of the selected mandibular variables, this may be the key to facial reconstruction from specific craniomaxillary measures in the three skeletal classifications.

Craniofacial characteristics of children with mild hypodontia

INTRODUCTION

The aim of our study was to evaluate the craniofacial characteristics of children with mild hypodontia using conventional and principal component (PC) analysis.

METHODS

We used radiographic images of 124 children (8-12 years old) with up to 4 missing teeth (55 boys, 69 girls) and of 676 reference children (365 boys, 311 girls) from the Rotterdam Generation R Study and the Nijmegen Growth Study in The Netherlands. Fifteen cephalometric measurements of children with hypodontia were compared with those of the reference children. Moreover, cephalometric parameters were combined into standardized PC scores using PC analysis, and the components were compared between the 2 groups.

RESULTS

PC analysis showed common dental characteristics for all types of hypodontia: a significant increase of the interincisal angle, and decreases of the maxillary and mandibular incisor angles. Other findings were consistent when both methods were applied: (1) anterior hypodontia was significantly associated with the high-angle (hyperdivergent) craniofacial pattern, (2) the tendency toward a Class III malocclusion was identified in maxillary hypodontia, and (3) we observed a significant reduction of lower posterior facial height in children with posterior and mandibular hypodontia.

CONCLUSIONS

Our findings suggest that children with mild hypodontia have distinctive skeletal and dental features.

The relationship between facial morphology, body measurements and socio-economic factors

Background and aim: The effect of socio-economic factors (living conditions) and parental smoking habits on development of facial morphology and body measurements was studied on a longitudinal Czech sample of 25 girls and 25 boys.

Subjects and methods: A set of studied digitalized photographs taken from 0.5 to 18 years in intervals of 6 months originated in the Brno Longitudinal Study. Facial shape changes of sub-adult participants were described using a configuration of 27 landmarks and further studied by using methods of geometric morphometric and multivariate statistics. In order to localize growth-related shape changes within the face, the studied region was divided into upper, middle and lower facial units and analyzed separately.

Results and conclusion: The results show that in the course of ontogenesis there is a strong correlation between facial shape change and body measurements, height included (r=0.10 and r=0.24 in boys and in girls, respectively). The pubertal spurt of the facial shape change rate was revealed at 10.5 years in girls and at 11.5 years in boys. The earlier onset of the pubertal rate increase in facial shape changes in boys was associated with records of poor living conditions. In addition, the mother’s smoking habits were linked to a noticeable facial shape change.

Patterns of morphological integration in the dental arches of individuals with malocclusion

OBJECTIVES

In humans, there is a large range of variation in the form of the maxillary and mandibular dental arches. This variation can manifest as either prognathism or retrognathism in either or both arches, which can cause malocclusion and lead to abnormal masticatory function. This study aims to identify aspects of variation and morphological integration existing in the dental arches of individuals with different types of malocclusion.

METHODS

Coordinate landmark data were collected along the gingival margins of 397 scanned dental casts and then analyzed using geometric morphometric techniques to explore arch form variation and patterns of morphological integration within each malocclusion type.

RESULTS

Significant differences were identified between Class II forms (increased projection of upper arch relative to the lower arch) and Class III forms (lower arch projection beyond the upper arch) in symmetrical shape variation, including anteroposterior arch discrepancies and abnormal anterior arch divergence or convergence. Partial least squares analysis demonstrated that Class III dental arches have higher levels of covariance between upper and lower arches (RV = 0.91) compared to the dental arches of Class II (RV = 0.78) and Class I (RV = 0.73). These high levels of covariance, however, are on the lower end of the overall range of possible masticatory blocks, indicating weaker than expected levels of integration.

CONCLUSIONS

This study provides evidence for patterns of variation in dental arch shape found in individuals with Class II and Class III malocclusions. Moreover, differences in integration found between malocclusion types have ramifications for how such conditions should be studied and treated. Am. J. Hum. Biol. 28:879-889, 2016. © 2016Wiley Periodicals, Inc.

Selecting subjects with high craniofacial shape homogeneity for clinical trials

INTRODUCTION

Morphologic homogeneity is desirable in sample selection of clinical studies that evaluate methods of treating craniofacial discrepancies in orthodontics. The purposes of this study were to assess sample selection criteria commonly used in the orthodontic literature regarding their effectiveness in achieving morphologic homogeneity, and to propose a method that can guarantee selection of a homogeneous sample, for which the degree of homogeneity and the average skeletal pattern can be specified a priori.

METHODS

Pretreatment lateral cephalograms from 170 consecutive patients (82 boys, 88 girls) aged 7 to 17 years were used. Sixteen skeletal and 4 dental landmarks were digitized and processed with Procrustes superimposition and principal component analysis. The sample was bootstrapped to a virtual population of 10,000 subjects by random sampling from the normal distribution for each principal component. A systematic literature search of randomized controlled trials showed that the most prevalent sample selection criteria, in addition to molar relationship, included overjet, ANB, and SN-GoGn. Each criterion was applied to the virtual population. The morphologic homogeneity of the samples was assessed as the percentage of shape variance of each sample relative to the shape variance of the population.

RESULTS

The first 3 principal components incorporated approximately 53% of shape variability. The evaluated criteria achieved low or moderate morphologic homogeneity scores (range, 28%-63%), and the selected patients were widely spread in the shape space. Although the criteria are commonly applied for selecting samples with skeletal discrepancies, a considerable number of subjects with an average shape were selected. The proposed procedure entails selecting a skeletal pattern appropriate for the study's purpose, setting limits in shape space within which the sample should be confined, and testing candidate patients against these limits. The patients within these boundaries have, by definition, a similar shape to the selected skeletal pattern and form a homogeneous sample.

CONCLUSIONS

The cephalometric variables that have been used in randomized controlled trials do not result in samples of high morphologic homogeneity. The proposed method guarantees high morphologic homogeneity. The extent of homogeneity, the average shape of the sample, and the sample's relationship to the general population's average can be specified a priori.

Connecting the new with the old: modifying the combined application of Procrustes superimposition and principal component analysis, to allow for comparison with traditional lateral cephalometric variables

OBJECTIVE

The combination of generalized Procrustes superimposition (GPS) and principal component analysis (PCA) has been hypothesized to solve some of the problems plaguing traditional cephalometry. This study demonstrates how to establish the currently unclear relationship between the shape space defined by the first two principal components to the ANB angle, Wits appraisal, and GoGnSN angle, and to elucidate possible clinical applications thereof.

METHODS

Digitized landmarks of 200 lateral cephalograms were subjected to GPS and PCA, after which the sample mean shape was deformed along/parallel to principal components (PC) 1 and 2, recording the ANB, Wits, and GoGnSN value at each location. Trajectories were then calculated through the PC1-PC2 space connecting locations with the same values. These were finally utilized to renormalize the PC1-PC2 space.

RESULTS

The trajectories for the Wits appraisal were almost straight and parallel to PC1.Those for the ANB angle were angled approximately 20degrees downward relative to PC1, with a more accentuated curvature. The GoGnSN curves were mildly angled relative to the PC2 axis, their curvature increasing slightly with increasing PC1 scores. By combining the aforementioned trajectories, it was possible to delineate the region of the PC1-PC2 shape space which would be regarded as normodivergent and skeletal Class I in traditional cephalometry. Geometric distortion could be avoided by assigning patients the ANB, Wits, or GoGnSN value of the sample mean shape, deformed to the patient's position within the PC1-PC2 plot.

CONCLUSION

The methodology successfully relates the shape space resulting from the GPS-PCA results with traditional cephalometric variables.

Cranial and mandibular shape variation in the genus Carollia (Mammalia: Chiroptera) from Colombia: biogeographic patterns and morphological modularity

Neotropical bats of the genus Carollia are widely studied due to their abundance, distribution and relevance for ecosystems. However, the ecomorphological boundaries of these species are poorly differentiated, and consequently correspondence between their geographic distribution, ecological plasticity and morphological variation remains unclear. In this study, patterns of cranial and mandibular morphological variation were assessed for Carollia brevicauda, C. castanea and C. perspicillata from Colombia. Using geometric morphometrics, morphological variation was examined with respect to: differences in intraspecific variation, morphological modularity and integration, and biogeographic patterns. Patterns of intraspecific variation were different for each species in both cranial and mandibular morphology, with functional differences apparent according to diet. Cranial modularity varied between species whereas mandibular modularity did not. High cranial and mandibular correlation reflects Cranium-Mandible integration as a functional unit. Similarity between the biogeographic patterns in C. brevicauda and C. perspicillata indicates that the Andes do not act as a barrier but rather as an independent region, isolating the morphology of Andean populations of larger-bodied species. The biogeographic pattern for C. castanea was not associated with the physiography of the Andes, suggesting that large body size does not benefit C. brevicauda and C. perspicillata in maintaining homogeneous morphologies among populations.

The effects of altered maxillary growth on patterns of mandibular rotation in a pig model

OBJECTIVES

A thorough understanding of influence of maxillary growth on patterns of mandibular rotation during development is important with regard to the treatment of skeletal discrepancies. In the present study, we examined whether experimentally altered maxillary position has a significant influence on patterns of mandibular rotation in a pig model.

DESIGN

Maxillary growth was altered in a sample of n=10 domestic pigs via surgical fixation of the circummaxillary sutures. We compared the experimental group to control and surgical sham samples and assessed the effects of altered maxillary growth on mandibular form using geometric morphometric techniques. We tested for significant differences in mandibular shape between our samples and examined axes of morphological variation. Additionally, we examined whether altered mandibular shape resulting from altered maxillary position was predictably associated with morphological changes to the condylar region.

RESULTS

There was a statistically significant difference in mandibular shape between the experimental and control/sham groups. As a result of vertical displacement of the snout, mandibles in the experimental sample resulted in greater anterior rotation when compared to the control/sham pigs. Variation in rotation was correlated with morphological changes in the condyle including the shape of the articular surface and condylar orientation indicative of greater anterior mandibular rotation.

CONCLUSIONS

Vertical displacement of the maxilla had a significant effect on mandibular shape by encouraging anterior mandibular rotation. This result has important implications for understanding the effects of altered mandibular posture on condylar remodeling the treatment of skeletal discrepancies such as the correction of hyperdivegent mandibular growth.

Shape covariation between the craniofacial complex and first molars in humans

The occurrence of mutual genetic loci in morphogenesis of the face and teeth implies shape covariation between these structures. However, teeth finalize their shape at an early age, whereas the face grows and is subjected to environmental influences for a prolonged period; it is therefore conceivable that covariation might modulate with age. Here we investigate the extent of this covariation in humans by measuring the 3D shape of the occlusal surface of the permanent first molars and the shape of the craniofacial complex from lateral radiographs, at two maturations stages. A sample of Greek subjects was divided into two groups (110 adult, 110 prepubertal) with equally distributed gender. The occlusal surfaces of the right first molars were 3D scanned from dental casts; 265 and 274 landmarks (including surface and curve semilandmarks) were digitized on the maxillary and mandibular molars, respectively. The corresponding lateral cephalometric radiographs were digitized with 71 landmarks. Geometric morphometric methods were used to assess shape variation and covariation. The vertical dimension of the craniofacial complex was the main parameter of shape variation, followed by anteroposterior deviations. The male craniofacial complex was larger (4.0-5.7%) and was characterized by a prominent chin and clockwise rotation of the cranial base (adult group only). Allometry was weak and statistically significant only when examined for the sample as a whole (percent variance explained: 2.1%, P = 0.0002). Covariation was statistically significant only between the lower first molar and the craniofacial complex (RV = 14.05%, P = 0.0099, and RV = 12.31%, P = 0.0162, for the prepubertal and adult groups, respectively). Subtle age-related covariation differences were noted, indicating that environmental factors may influence the pattern and strength of covariation. However, the main pattern was similar in both groups: a class III skeletal pattern (relative maxillary retrusion and mandibular protrusion), hyperdivergency, forward rotation of the posterior cranial base and upward rotation of the anterior cranial base were associated with mesiodistal elongation of the lower molars and height reduction of their distal cusps. This pattern mimics phylogeny in humans, where flexion and counterclockwise rotation of the cranial base, considered advantageous to survival, co-occur with tooth reductions that cannot be easily explained in evolutionary terms. The similarity of the phylogenetic and covariation patterns seems to support the pleiotropic gene hypothesis.

Correlation of 2D:4D digit ratio and craniofacial shape in prepubertal children

OBJECTIVES

The 2D:4D ratio is sexually dimorphic and is considered a proxy of prenatal androgen levels, or, according to recent evidence, is related to genes involved in ocular and palate development. Our aim was to investigate correlation between the 2D:4D ratio and the shape of the craniofacial skeleton in a population of prepubertal children.

METHODS

We conducted a cross-sectional study in a group of 58 male and 59 female prepubertal children aged 7-12 years. Craniofacial shape was evaluated using 15 skeletal landmarks on lateral cephalometric radiographs and fingers were measured with a computer-assisted procedure that involved tracing the finger outline. Geometric morphometric analysis was applied to the craniofacial landmarks and multivariate regression between digit ratios and craniofacial shape was computed in shape space and form space.

RESULTS

The male 2D:4D ratio was smaller than the female ratio (Cohen's d: 0.275 left hand, 0.126 right hand), but the difference was not statistically significant. Craniofacial shape did not show sexual dimorphism, but males were larger than females. No correlation was found between digit ratio and craniofacial shape in prepubertal children, either for the whole sample or for any of the two sex groups.

CONCLUSIONS

As several factors might be involved in the development and growth of both the craniofacial complex and fingers, the 2D:4D ratio, a putative proxy for fetal sex-hormone levels, is probably unable to impose a measurable effect within the variation of a normal population. Future research needs to examine an adult sample for potential covariation arising after the pubertal growth spurt.

Morphological integration of mandible and cranium: orthodontic implications

OBJECTIVES

This study aimed at clarifying the morphological interactions among the cranial base, face, and mandible, to improve the assessment and treatment of skeletal malocclusions involving the mandible.

DESIGN

Untreated adult subjects (n=187) were grouped according to standard cephalometric criteria of vertical and sagittal relationships. Geometric morphometrics were used to test the null hypothesis that integration patterns between the mandible and its associated basicranial and upper midfacial counterparts would be similar among various vertical and sagittal facial patterns.

RESULTS

The null hypothesis was rejected for vertical groups, because the dolicho- and brachyfacial subjects showed significantly different integration patterns, but was accepted for sagittal groups, which showed identical covariation patterns. The morphological integration between the cranium-face and mandible were similarly high in the three skeletal classes, which explained the similarly large covariance between the two structures (57.80% in Class II to 60% in Class III).

CONCLUSIONS

Dolicho- and brachi-facial subjects showed specific and different cranium-face and associated mandible configurations. The cranium-face configuration may have an important influence (∼60%) on the generation of sagittal (anteroposterior) skeletal malocclusions. The remaining morphological component of the skeletal malocclusion (∼40%) would be independent of this particular integration (PLS1) between the cranium-face and mandible.