Stefan Schlager

Anatomical shape analysis of the mandible in Caucasian and Chinese for the production of preformed mandible reconstruction plates

PURPOSE The purpose of this study was to evaluate and analyze statistical shapes of the outer mandible contour of Caucasian and Chinese people, offering data for the production of preformed mandible reconstruction plates. METHODS A CT-database of 925 Caucasians (male: n=463, female: n=462) and 960 Chinese (male: n=469, female: n=491) including scans of unaffected mandibles were used and imported into the 3D modeling software Voxim (IVS-Solutions, Chemnitz, Germany). Anatomical landmarks (n=22 points for both sides) were set using the 3D view along the outer contour of the mandible at the area where reconstruction plates are commonly located. We used morphometric methods for statistical shape analysis. RESULTS We found statistical relevant differences between populations including a distinct discrimination given by the landmarks at the mandible. After generating a metric model this shape information which separated the populations appeared to be of no clinical relevance. The metric size information given by ramus length however provided a profound base for the production of standard reconstruction plates. CONCLUSION Clustering by ramus length into three sizes and calculating means of these size-clusters seem to be a good solution for constructing preformed reconstruction plates that will fit a vast majority.

Morpho and Rvcg – Shape Analysis in R: R-Packages for Geometric Morphometrics, Shape Analysis and Surface Manipulations

Abstract The mathematical/statistical software platform R has seen an immense increase in popularity within the last decade. Its main advantages are its flexibility, a large repository of freely available extensions, its open-source nature and a thriving community. This tutorial gives an introduction into landmark/surface-mesh based statistical shape analysis in R – specifically using the packages Morpho and Rvcg. Beginning with examples based on sparse sets of anatomical landmarks, the tutorial will go on dealing with surface and curve landmarks and more challenging tasks such as mesh manipulations and surface registration. Apart from statistical analyses, emphasis will also be put on comprehensive visualization of the results. Extensive examples and code snippets are provided to allow the reader to easily replicate the analyses.

Phylogeny and adaptation shape the teeth of insular mice.

By accompanying human travels since prehistorical times, the house mouse dispersed widely throughout the world, and colonized many islands. The origin of the travellers determined the phylogenetic source of the insular mice, which encountered diverse ecological and environmental conditions on the various islands. Insular mice are thus an exceptional model to disentangle the relative role of phylogeny, ecology and climate in evolution. Molar shape is known to vary according to phylogeny and to respond to adaptation. Using for the first time a three-dimensional geometric morphometric approach, compared with a classical two-dimensional quantification, the relative effects of size variation, phylogeny, climate and ecology were investigated on molar shape diversity across a variety of islands. Phylogeny emerged as the factor of prime importance in shaping the molar. Changes in competition level, mostly driven by the presence or absence of the wood mouse on the different islands, appeared as the second most important effect. Climate and size differences accounted for slight shape variation. This evidences a balanced role of random differentiation related to history of colonization, and of adaptation possibly related to resource exploitation.

Analysis of the human osseous nasal shape--population differences and sexual dimorphism.

OBJECTIVES In this study, the shape of the outer osseous nose in a German and a Chinese sample is analyzed using a dense set of semi-landmarks. Shape differences related to population and sex as well as directional and fluctuating asymmetry were statistically evaluated and also visualized. MATERIALS AND METHODS Shape differences in the bony nose were investigated between a large sample of CT scans of German (140 ♀, 127 ♂) and Chinese (135 ♀, 132 ♂) crania. We used semi-automatic methods to represent the shape of this region as a dense point-cloud, consisting of 370 three-dimensional bilateral coordinates. Both the symmetric and asymmetric modes of shape variation were addressed. RESULTS Strong differences in nasal shape were found between the two populations, while sex was found to play a minor role in explaining the observed shape variation. The expression of sexual dimorphism was similar in both populations. Differences attributed to population affinity and to sexual dimorphism were both found to affect the shape of the ossa nasalia and the projection of the spina nasalis. The correlation with population/sex was weak for directional asymmetry, but strong for fluctuating asymmetry. The nasal region is more asymmetric in Germans than in Chinese, with males displaying more asymmetry than females in both populations. DISCUSSION While the bony nose is well suited for predicting population affinity, regarding the populations under investigation, its value for sexing unknown individuals is rather moderate. The similar expression of sexual dimorphism in those otherwise very dissimilar populations indicates common factors responsible for these differences.

Sexual dimorphism and regional variation in human frontal bone inclination measured via digital 3D models

The frontal bone is one of the most sexually dimorphic elements of the human skull, due to features such as the glabella, frontal eminences, and frontal inclination. While glabella is frequently evaluated in procedures to estimate sex in unknown human skeletal remains, frontal inclination has received less attention. In this study we present a straightforward, quick, and reproducible method for measuring frontal inclination angles from glabella and supraglabella. Using a sample of 413 human crania from four different populations (U.S. Whites, U.S. Blacks, Portuguese, and Chinese), we test the usefulness of the inclination angles for sex estimation and compare their performance to traditional methods of frontal inclination assessment. Accuracy rates in the range 75-81% were achieved for the U.S. White, U.S. Black, and Portuguese groups. For Chinese the overall accuracy was lower, i.e. 66%. Although some regional variation was observed, a cut-off value of 78.2° for glabellar inclination angles separates female and male crania from all studied populations with good accuracy. As inclination angles measured from glabella captures two sexually dimorphic features (i.e. glabellar prominence and frontal inclination) in a single measure, the observed clear male/female difference is not unexpected. Being continuous variables, inclination angles are suitable for use in statistical methods for sex estimations.

Sexual Dimorphism and Population Affinity in the Human Zygomatic Structure—Comparing Surface to Outline Data

The human zygomatic structure, consisting of the zygomatic bone and the zygomatic process of the temporal bone, is an essential part of the masticatory apparatus and has been shown to reflect population history and sexual dimorphism to varying degrees. In this study, we analyzed the predictive value of the outlines vs. the complete surface shape of the zygomatic bone in a sample of 98 Chinese (50 ♀, 48 ♂) and 96 Germans (49 ♀, 47 ♂). We first applied a surface registration process based on statistical shape modeling. A dense set of 1,480 pseudo‐landmarks was then sampled automatically from the surface of the pooled mean shape and three curves were digitized manually along the outlines of the zygomatic bone. Both sets of pseudo‐landmarks were automatically transferred to all specimens. Analysis of sex and population affinity showed both factors to be independently significant, but the interaction between them was not. Population affinity could be predicted quite accurately with correct classification of 97.9% using the surface data and 93.3% with the curve data. Sexual dimorphism was less distinct with 89.2% correct sex determination when using surface information compared with 77.8% when using the curve data. Population‐related shape differences were captured primarily in the outlines, while sexual dimorphism is distributed more uniformly throughout the entire surface of the zygomatic structure. Anat Rec, 300:226–237, 2017.

Tracing social interactions in Pleistocene North America via 3D model analysis of stone tool asymmetry

Stone tools, often the sole remnant of prehistoric hunter-gatherer behavior, are frequently used as evidence of ancient human mobility, resource use, and environmental adaptation. In North America, studies of morphological variation in projectile points have provided important insights into migration and interactions of human groups as early as 12–13 kya. Using new approaches to 3D imaging and morphometric analysis, we here quantify bifacial asymmetry among early North American projectile point styles to better understand changes in knapping technique and cultural transmission. Using a sample of 100 fluted bifaces of Clovis and post-Clovis styles in the eastern United States ca. 13,100–9,000 cal BP (i.e., Clovis, Debert-Vail, Bull Brook, Michaud-Neponset/Barnes, and Crowfield), we employed two different approaches for statistical shape analysis: our previously presented method for analysis of 2D flake scar contours, and a new approach for 3D surface analysis using spherical harmonics (SPHARM). Whereas bifacial asymmetry in point shape does not vary significantly across this stylistic sequence, our measure of asymmetric flake scar patterning shows temporal variation that may signify the beginning of regionalization among early New World colonists.

A geometric morphometric relationship predicts stone flake shape and size variability

The archaeological record represents a window onto the complex relationship between stone artefact variance and hominin behaviour. Differences in the shapes and sizes of stone flakes—the most abundant remains of past behaviours for much of human evolutionary history—may be underpinned by variation in a range of different environmental and behavioural factors. Controlled flake production experiments have drawn inferences between flake platform preparation behaviours, which have thus far been approximated by linear measurements, and different aspects of overall stone flake variability (Dibble and Rezek J Archaeol Sci 36:1945–1954, 2009; Lin et al. Am Antiq 724–745, 2013; Magnani et al. J Archaeol Sci 46:37–49, 2014; Rezek et al. J Archaeol Sci 38:1346–1359, 2011). However, when the results are applied to archaeological assemblages, there remains a substantial amount of unexplained variability. It is unclear whether this disparity between explanatory models and archaeological data is a result of measurement error on certain key variables, whether traditional analyses are somehow a general limiting factor, or whether there are additional flake shape and size drivers that remain unaccounted for. To try and circumvent these issues, here, we describe a shape analysis approach to assessing stone flake variability including a newly developed three-dimensional geometric morphometric method (‘3DGM’). We use 3DGM to demonstrate that a relationship between platform and flake body governs flake shape and size variability. Contingently, we show that by using this 3DGM approach, we can use flake platform attributes to both (1) make fairly accurate stone flake size predictions and (2) make relatively detailed predictions of stone flake shape. Whether conscious or instinctive, an understanding of this geometric relationship would have been critical to past knappers effectively controlling the production of desired stone flakes. However, despite being able to holistically and accurately incorporate three-dimensional flake variance into our analyses, the behavioural drivers of this variance remain elusive.

Prospective 3D analysis of facial soft tissue augmentation with calcium hydroxylapatite

ABSTRACT Background: Facial rejuvenation is an expanding field with an increasing number of treatment modalities. Several non-autologous filler materials are available for soft tissue augmentation. Calcium hydroxylapatite (CaOH) is aimed at increasing collagen neosynthesis and thereby producing long-term augmentation effects. Despite a multitude of observational reports, the field is suffering from lack of quantitative morphometric evaluation methods. Objective: The objective of this proof-of-principle study was to investigate whether the effects of facial tissue augmentation with CaOH (RADIESSE™) can be quantified and followed up using 3D surface scanning. Methods: 3 female subjects received augmentation of the mid and lower face with CaOH. The faces were recorded prior, directly after, and two weeks and six months after the injection using standardized photos and 3D scanning. Computational analysis allowed quantifying the change in volume and displacement of the facial surface. Additionally, a patient satisfaction questionnaire was administered. Results: In all subjects, increase in facial volume could be quantified and was present after two weeks and six months. Conclusions: 3D surface scanning is an adequate tool for objective quantification of changes after facial augmentation with filler materials. Persistent volume augmentation after CaOH injections could be quantified after two weeks and six months. Evidence level: IV.

Estimating the Temperature of Heat-exposed Bone via Machine Learning Analysis of SCI Color Values: A Pilot Study

Determining maximum heating temperatures of burnt bones is a long‐standing problem in forensic science and archaeology. In this pilot study, controlled experiments were used to heat 14 fleshed and defleshed pig vertebrae (wet bones) and archaeological human vertebrae (dry bones) to temperatures of 400, 600, 800, and 1000°C. Specular component included (SCI) color values were recorded from the bone surfaces with a Konica‐Minolta cm‐2600d spectrophotometer. These color values were regressed onto heating temperature, using both a traditional linear model and the k‐nearest neighbor (k‐NN) machine‐learning algorithm. Mean absolute errors (MAE) were computed for 1000 rounds of temperature prediction. With the k‐NN approach, the median MAE prediction errors were 41.6°C for the entire sample, and 20.9°C for the subsample of wet bones. These results indicate that spectrophotometric color measurements combined with machine learning methods can be a viable tool for estimating bone heating temperature.