Three-dimensional Bolton-Brush Growth Study landmark data: ontogeny and sexual dimorphism of the Bolton standards cohort

Using the 3D Facial Norms Database to investigate craniofacial sexual dimorphism in healthy children, adolescents, and adults

Background

Although craniofacial sex differences have been extensively studied in humans, relatively little is known about when various dimorphic features manifest during postnatal life. Using cross-sectional data derived from the 3D Facial Norms data repository, we tested for sexual dimorphism of craniofacial soft-tissue morphology at different ages.

Methods

One thousand five hundred fifty-five individuals, pre-screened for craniofacial conditions, between 3 and 25 years of age were placed in to one of six age-defined categories: early childhood, late childhood, puberty, adolescence, young adult, and adult. At each age group, sex differences were tested by ANCOVA for 29 traditional soft-tissue anthropometric measurements collected from 3D facial scans. Additionally, sex differences in shape were tested using a geometric morphometric analysis of 24 3D facial landmarks.

Results

Significant (p < 0.05) sex differences were observed in every age group for measurements covering multiple aspects of the craniofacial complex. The magnitude of the dimorphism generally increased with age, with large spikes in the nasal, cranial, and facial measurements observed after puberty. Significant facial shape differences (p < 0.05) were also seen at each age, with some dimorphic features already present in young children (eye fissure inclination) and others emerging only after puberty (mandibular position).

Conclusions

Several craniofacial soft-tissue sex differences were already present in the youngest age group studied, indicating that these differences emerged prior to 3 years of age. The results paint a complex and heterogeneous picture, with different groups of traits exhibiting distinct patterns of dimorphism during ontogeny. The definitive adult male and female facial shape was present following puberty, but arose from numerous distinct changes taking place at earlier stages.

Electronic supplementary material

The online version of this article (doi:10.1186/s13293-016-0076-8) contains supplementary material, which is available to authorized users.

Incorporating 3-dimensional models in online articles

INTRODUCTION

The aims of this article are to introduce the capability to view and interact with 3-dimensional (3D) surface models in online publications, and to describe how to prepare surface models for such online 3D visualizations.

METHODS

Three-dimensional image analysis methods include image acquisition, construction of surface models, registration in a common coordinate system, visualization of overlays, and quantification of changes. Cone-beam computed tomography scans were acquired as volumetric images that can be visualized as 3D projected images or used to construct polygonal meshes or surfaces of specific anatomic structures of interest. The anatomic structures of interest in the scans can be labeled with color (3D volumetric label maps), and then the scans are registered in a common coordinate system using a target region as the reference. The registered 3D volumetric label maps can be saved in .obj, .ply, .stl, or .vtk file formats and used for overlays, quantification of differences in each of the 3 planes of space, or color-coded graphic displays of 3D surface distances.

RESULTS

All registered 3D surface models in this study were saved in .vtk file format and loaded in the Elsevier 3D viewer. In this study, we describe possible ways to visualize the surface models constructed from cone-beam computed tomography images using 2D and 3D figures. The 3D surface models are available in the article's online version for viewing and downloading using the reader's software of choice. These 3D graphic displays are represented in the print version as 2D snapshots. Overlays and color-coded distance maps can be displayed using the reader's software of choice, allowing graphic assessment of the location and direction of changes or morphologic differences relative to the structure of reference. The interpretation of 3D overlays and quantitative color-coded maps requires basic knowledge of 3D image analysis.

CONCLUSIONS

When submitting manuscripts, authors can now upload 3D models that will allow readers to interact with or download them. Such interaction with 3D models in online articles now will give readers and authors better understanding and visualization of the results.

Three-dimensional imaging techniques: A literature review

Imaging is one of the most important tools for orthodontists to evaluate and record size and form of craniofacial structures. Orthodontists routinely use 2-dimensional (2D) static imaging techniques, but deepness of structures cannot be obtained and localized with 2D imaging. Three-dimensional (3D) imaging has been developed in the early of 1990's and has gained a precious place in dentistry, especially in orthodontics. The aims of this literature review are to summarize the current state of the 3D imaging techniques and to evaluate the applications in orthodontics.

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

This investigation aimed to quantify craniofacial variation in a sample of modern humans. In all, 187 consecutive orthodontic patients were collected, of which 79 were male (mean age 13.3, SD 3.7, range 7.5-40.8) and 99 were female (mean age 12.3, SD 1.9, range 8.7-19.1). The male and female subgroups were tested for differences in mean shapes and ontogenetic trajectories, and shape variability was characterized using principal component analysis. The hypothesis of modularity was tested for six different modularity scenarios. The results showed that there were subtle but significant differences in the male and female Procrustes mean shapes. Males were significantly larger. Mild sexual ontogenetic allometric divergence was noted. Principal component analysis indicated that, of the four retained biologically interpretable components, the two most important sources of variability were (i) vertical shape variation (i.e. dolichofacial vs. brachyfacial growth patterns) and (ii) sagittal relationships (maxillary prognatism vs. mandibular retrognathism, and vice versa). The mandible and maxilla were found to constitute one module, independent of the skull base. Additionally, we were able to confirm the presence of an anterior and posterior craniofacial columnar module, separated by the pterygomaxillary plane, as proposed by Enlow. These modules can be further subdivided into four sub-modules, involving the posterior skull base, the ethmomaxillary complex, a pharyngeal module, and the anterior part of the jaws.

Facial surface analysis by 3D laser scanning and geometric morphometrics in relation to sexual dimorphism in cerebral--craniofacial morphogenesis and cognitive function

Over early fetal life the anterior brain, neuroepithelium, neural crest and facial ectoderm constitute a unitary, three-dimensional (3D) developmental process. This intimate embryological relationship between the face and brain means that facial dysmorphogenesis can serve as an accessible and informative index of brain dysmorphogenesis in neurological and psychiatric disorders of early developmental origin. There are three principal challenges in seeking to increase understanding of disorders of early brain dysmorphogenesis through craniofacial dysmorphogenesis: (i) the first, technical, challenge has been to digitize the facial surface in its inherent three-dimensionality; (ii) the second, analytical, challenge has been to develop methodologies for extracting biologically meaningful shape covariance from digitized samples, making statistical comparisons between groups and visualizing in 3D the resultant statistical models on a 'whole face' basis; (iii) the third, biological, challenge is to demonstrate a relationship between facial morphogenesis and brain morphogenesis not only in anatomical-embryological terms but also at the level of brain function. Here we consider each of these challenges in turn and then illustrate the issues by way of our own findings. These use human sexual dimorphism as an exemplar for 3D laser surface scanning of facial shape, analysis using geometric morphometrics and exploration of cognitive correlates of variation in shape of the 'whole face', in the context of studies relating to the early developmental origins of schizophrenia.

Ontogeny of facial dimorphism and patterns of individual development within one human population

Based on a longitudinal study of radiographs of the Denver Growth Study, we investigated the morphological development of individual and gender differences in the anterior neurocranium, face, and basicranium. In total, 500 X-rays of 14 males and 14 females, each with 18 landmarks and semilandmarks, were digitized and analyzed using geometric morphometric methods. Sexual dimorphism in shape and form is already present at the earliest age stage included in the analysis. However, the nature of dimorphism changes with age. Four factors apper to contribute to cranial sexual dimorphism in human postnatal development: 1) initial, possibly prenatal, differences in shape; 2) differences in the association of size and shape; 3) male hypermorphosis; and 4) some degree of difference in the direction of male and female growth trajectories. Studying changes in individuals, we find a low correlation between newborn and adult morphology, while 3-year-olds already show a high correlation with their adult form. We conclude that the adult pattern of interindividual difference in facial form in a single human population is established within the first few years of life.

Heterochrony and geometric morphometrics: a comparison of cranial growth inPan paniscusversusPan troglodytes

Heterochrony, the classic framework in which to study ontogeny and phylogeny, in essence relies on a univariate concept of shape. Though principal component (PC) plots of multivariate shape data seem to resemble classical bivariate allometric plots, the language of heterochrony cannot be translated directly into general multivariate methodology. We simulate idealized multivariate ontogenetic trajectories and explore their appearance in PC plots of shape space and size-shape space. Only if the trajectories of two related species lie along exactly the same path in shape space can the classic terminology of heterochrony apply and pure dissociation of size change against shape change be detected. Regional heterochrony--the variation of apparent heterochrony by region--implies a dissociation of local growth fields and cannot be identified in an overall PC analysis. We exemplify a geometric morphometric approach to these issues using adult and subadult crania of 48 Pan paniscus and 47 Pan troglodytes specimens. On each specimen, we digitized 47 landmarks and 144 semilandmarks on facial curves and the external neurocranial surface. We reject the hypothesis of global heterochrony in the cranium of Pan as well as regional heterochrony for the lower face, the upper face, and the neurocranium.

Visualization of individual growth-related craniofacial changes based on cephalometric landmark data: a pilot study

OBJECTIVE

An approach based on Euclidean distances between cephalometric landmarks is presented (1) to visualize and localize the individual shape changes of the complex craniofacial skeleton during growth and (2) to depict the individual dynamic behavior of developmental size and shape changes.

PATIENTS AND METHOD

Growth-related craniofacial changes were investigated exemplarily for two male orthodontically untreated subjects from the Belfast Growth Study on the basis of lateral cephalograms at 7, 9, 11, 13, and 15 years. The interlandmark distances among seven skeletal cephalometric landmarks served as a database for the study. A modified Karhunen-Loève decomposition based on orthogonal modes and time-dependent scalar amplitudes was used to describe the growth process. The individual shape changes of the various craniofacial regions were visualized by allocation of colors to the respective distances, and overdrawn representations were reconstructed by means of multidimensional scaling.

RESULTS AND CONCLUSIONS

This visualization technique allows anatomical regions to be characterized with respect to reduced or strengthened growth, compared with pure size changes. The clinically relevant mechanisms of craniofacial changes are visualized (e.g., shifts in the anteroposterior or vertical dimensions of the jaws in relation to cranial base and structural imbalances during development). In addition, overdrawing the effects of shape change on the skeletal structures gives a more readily comprehensible impression of the growth process. Taking account of the methodical limitations of this approach (e.g., the restrictions concerning the number of landmarks), the clinician may take advantage of this technique in orthodontic or surgical diagnostics to gain additional insight into the individual complex size and shape changes during development along with their dynamic behavior.