Validity and sensitivity of a human cranial finite element model: Implications for comparative studies of biting performance

Finite element analysis (FEA) is a modelling technique increasingly used in anatomical studies investigating skeletal form and function. In the case of the cranium this approach has been applied to both living and fossil taxa to (for example) investigate how form relates to function or infer diet or behaviour. However, FE models of complex musculoskeletal structures always rely on simplified representations because it is impossible completely to image and represent every detail of skeletal morphology, variations in material properties and the complexities of loading at all spatial and temporal scales. The effects of necessary simplifications merit investigation. To this end, this study focuses on one aspect, model geometry, which is particularly pertinent to fossil material where taphonomic processes often destroy the finer details of anatomy or in models built from clinical CTs where the resolution is limited and anatomical details are lost. We manipulated the details of a finite element (FE) model of an adult human male cranium and examined the impact on model performance. First, using digital speckle interferometry, we directly measured strains from the infraorbital region and frontal process of the maxilla of the physical cranium under simplified loading conditions, simulating incisor biting. These measured strains were then compared with predicted values from FE models with simplified geometries that included modifications to model resolution, and how cancellous bone and the thin bones of the circum-nasal and maxillary regions were represented. Distributions of regions of relatively high and low principal strains and principal strain vector magnitudes and directions, predicted by the most detailed FE model, are generally similar to those achieved in vitro. Representing cancellous bone as solid cortical bone lowers strain magnitudes substantially but the mode of deformation of the FE model is relatively constant. In contrast, omitting thin plates of bone in the circum-nasal region affects both mode and magnitude of deformation. Our findings provide a useful frame of reference with regard to the effects of simplifications on the performance of FE models of the cranium and call for caution in the interpretation and comparison of FEA results

Characterization of three members of the Arabidopsis carotenoid cleavage dioxygenase family demonstrates the divergent roles of this multifunctional enzyme family

Arabidopsis thaliana has nine genes that constitute a family of putative carotenoid cleavage dioxygenases (CCDs). While five members of the family are believed to be involved in synthesis of the phytohormone abscisic acid, the functions of the other four enzymes are less clear. Recently two of the enzymes, CCD7/MAX3 and CCD8/MAX4, have been implicated in synthesis of a novel apocarotenoid hormone that controls lateral shoot growth. Here, we report on the molecular and genetic interactions between CCD1, CCD7/MAX3 and CCD8/ MAX4. CCD1 distinguishes itself from other reported CCDs as being the only member not targeted to the plastid. Unlike ccd7/max3 and ccd8/max4, both characterized as having highly branched phenotypes, ccd1 loss-of-function mutants are indistinguishable from wild-type plants. Thus, even though CCD1 has similar enzymatic activity to CCD7/MAX3, it does not have a role in synthesis of the lateral shoot growth inhibitor. Rather, it may have a role in synthesis of apocarotenoid flavor and aroma volatiles, especially in maturing seeds where loss of function leads to significantly higher carotenoid levels

Design and Analysis of 3D Customized Models of a Human Mandible

Polymer-based composites are ideal for applications where high strength-to-weight and stiffness-to-weight ratios are required. In the biomedical field, fiber-reinforced polymers have replaced metals, emerging as suitable alternative. Reverse engineering and additive manufacturing methods are required to achieve the design of customized devices with specific shape and size. At the same time, micromechanics and macro-mechanics play an important role in the development of highly functional composite materials. The aim of this research is to develop customized 3D models of a human mandible using reverse engineering, additive manufacturing and composite material technology. Experiments were carried out by loading the models through the condyles and the results show the potential to reproduce the mechanical behavior of a human mandible. Taking into account the curves of the load-arch width decrease, the stiffness of the 3D composite model was 14.1± 1.9 N/mm, which is close to the tested human mandible (17.5 ± 1.8 N/mm)

A sensitivity study of human mandibular biting simulations using finite element analysis

The form of human mandible reflects both genetic history and loading. In the context of archaeology, it has been used to retrodict loading history as a means of inferring subsistence strategy and paramasticatory use of the dentition. Rather than relying on form to retrodict function, an alternative is to simulate function and compare performance. Finite element analysis (FEA) offers the prospect of predicting and comparing the performance of mandibles under specific loading scenarios, for instance, simulated biting. However, its application depends on the sensitivity of the approach to variation and error in the initial and boundary conditions such as size and shape of the mandible, material properties of the bone tissue, muscle load vectors and the spatial constraints of the model. In the present paper we investigate the sensitivity of an FE model of a modern human mandible to simplifications in material properties and variations in boundary conditions. A medical CT scan of a living patient is used to create a range of FE digital models with different combinations of material properties, spatial constraints and muscle vectors. We then use ten individual CT scans of human mandibles to create simplified FE models all constrained and loaded in a standard way. We compare the development of von Mises strains over the surface of the mandibles, the output forces at the bite points and the modes and magnitudes global of deformations. Our results suggest that potential errors in segmentation, muscle force vectors, and constraints can have an appreciable effect on predictions of performance from FE analysis. Therefore, prediction of absolute strain magnitudes is uncertain. However, the errors are not large compared to the differences we find among the sample of mandibles, and FE analysis performs robustly in predicting relative, if not absolute, strains over the surface of a model. We suggest that a sensible approach in future comparative studies is to identically constrain and load ‘solid models’ comprising one homogenous material (e.g. with the properties of cortical bone). This limits studies to comparison of the effects of varying mandibular external form but such models reasonably predict relative strains, modes of global deformation and bite forces and so allow comparisons of these limited aspects of performance

Supraorbital morphology and social dynamics in human evolution

Uniquely, with respect to Middle Pleistocene hominins, anatomically modern humans do not possess marked browridges, and have a more vertical forehead with mobile eyebrows that play a key role in social signalling and communication. The presence and variability of browridges in archaic Homo and their absence in ourselves have led to debate concerning their morphogenesis and function, with two main hypotheses being put forward; that browridge morphology is the result of the spatial relationship between the orbits and the braincase, and that browridge morphology is significantly impacted by biting mechanics. Here we virtually manipulate browridge morphology of an archaic hominin (Kabwe 1), showing that it is much larger than the minimum required to fulfil spatial demands and that browridge size has little impact on mechanical performance during biting. Since browridge morphology in this fossil is not driven by spatial and mechanical requirements alone, the role of the supraorbital region in social communication is a potentially significant factor. We propose that conversion of the large browridges of our immediate ancestors to a more vertical frontal in modern humans allowed highly mobile eyebrows to display subtle affiliative emotions

Investigation of Viscoelastoplastic Response of Bone Tissue in Oral Implants Press Fit Process

According to the standard surgical protocols, the press fit is obtained inserting an implant in a drilled hole that is provided with a lower diameter. In this way, it is induced a relevant strain state in the peri-implant bone that favors the primary stability of the implant. Experimental evaluation of this phenomenon is very difficult and does not offer a complete set of information. A numerical analysis is adopted to describe the mechanical phenomena occurring in the peri-implant tissue. At this purpose, suitable constitutive models are adopted for the bone tissue for the evaluation of plastic and viscous effects caused by the real strain field induced. Specific numerical procedures are developed to model the press fit action of an implant against the surrounding bone tissue and the subsequent viscoelastoplastic effects determined. The results of the numerical analysis make it possible to estimate the deformation caused by the insertion of the implant and the evolutionary trend after insertion by considering the inelastic time-dependent behavior of bone tissue in peri-implant region. According to the viscous characteristic of the bone tissue, the numerical analyses show a stress relaxation in the order of 30% around the implant