Biomedical subjects

Mark A Spencer

Publications and source records attributed to Mark A Spencer.

4 recordsLinked to original sources

PubMed2005

Finite element analysis in functional morphology.

This article reviews the fundamental principles of the finite element method and the three basic steps (model creation, solution, and validation and interpretation) involved in using it to examine structural mechanics. Validation is a critical step in the analysis, without which researchers cannot evaluate the extent to which the model represents or is relevant to the real biological condition. We discuss the method's considerable potential as a tool to test biomechanical hypotheses, and major hurdles involved in doing so reliably, from the perspective of researchers interested in functional morphology and paleontology. We conclude with a case study to illustrate how researchers deal with many of the factors and assumptions involved in finite element analysis.

Anatomy↗

PubMed2005

Modeling masticatory muscle force in finite element analysis: sensitivity analysis using principal coordinates analysis.

Our work on a finite element model of the skull of Macaca aims to investigate the functional significance of specific features of primate skulls and to determine to which of the input variables (elastic properties, muscle forces) the model behavior is most sensitive. Estimates of muscle forces acting on the model are derived from estimates of physiological cross-sectional areas (PCSAs) of the jaw muscles scaled by relative electromyographic (EMG) amplitudes recorded in vivo. In this study, the behavior of the model was measured under different assumptions regarding the PCSAs of the jaw muscles and the latency between EMG activity in those muscles and the resulting force production. Thirty-six different loading regimes were applied to the model using four different PCSA sets and nine different PCSA scaling parameters. The four PCSA sets were derived from three different macaque species and one genus average, and the scaling parameters were either EMGs from 10, 20, 30, 40, 50 and 60 msec prior to peak bite force, or simply 100%, 50%, or 25% of peak muscle force. Principal coordinates analysis was used to compare the deformations of the model produced by the 36 loading regimes. Strain data from selected sites on the model were also compared with in vivo bone strain data. The results revealed that when varying the external muscle forces within these boundaries, the majority of the variation in model behavior is attributable to variation in the overall magnitude rather than the relative amount of muscle force generated by each muscle. Once this magnitude-related variation in model deformation was accounted for, significant variation was attributable to differences in relative muscle recruitment between working and balancing sides. Strain orientations at selected sites showed little variation across loading experiments compared with variation documented in vivo. These data suggest that in order to create an accurate and valid finite element model of the behavior of the primate skull at a particular instant during feeding, it is important to include estimates of the relative recruitment levels of the masticatory muscles. However, a lot can be learned about patterns of skull deformation, in fossil species for example, by applying external forces proportional to the estimated relative PCSAs of the jaw adductors.

Animals↗

PubMed2005

Modeling elastic properties in finite-element analysis: how much precision is needed to produce an accurate model?

The influence of elastic properties on finite-element analysis was investigated using a finite-element model of a Macaca fascicularis skull. Four finite-element analyses were performed in which the model was assigned different sets of elastic properties. In analysis 1, elastic properties were modeled isotropically using published data obtained from human limb bones. Analyses 2-4 used data obtained from skulls of a closely allied species, M. mulatta, but varied as to how those data were incorporated into the model. In analysis 2, the model was assigned a single set of isotropic elastic properties. In analysis 3, each region within the model was assigned its own set of isotropic elastic properties. Finally, in analysis 4, each region received its own set of orthotropic elastic properties. Although a qualitative assessment indicates that the locations of strain concentrations across the model are broadly similar in all analyses, a quantitative assessment of strain indicates some differences between the analyses. When strain data from the finite-element analyses were compared to strain data derived from in vivo experiments, it was found that the model deformed most realistically using the orthotropic elastic properties employed in analysis 4. Results suggest that finite-element analyses can be adversely affected when elastic properties are modeled imprecisely, and that modelers should attempt to obtain elastic properties data about the species and skeletal elements that are the subjects of their analyses.

Anatomy↗

PubMed2003

Tooth-root form and function in platyrrhine seed-eaters.

Research into the functional and adaptive basis of tooth crown form has provided a useful framework for the inference of diet in extinct primates. However, our understanding of variation in tooth-root form is limited. Studies within the clinical literature emphasize the influence of tooth-root surface area on stress resistance, but it is not known if root form has diversified during primate evolution in relation to dietary specialization. This hypothesis was tested by quantifying maxillary canine and postcanine tooth-root surface areas in four platyrrhine species that differ in the material properties of their diet: Cebus apella, Cebus albifrons, Chiropotes satanas, and Pithecia pithecia. Pairwise comparisons between closely related taxa support predictions based on dietary differences. Taxa that regularly consume resistant seeds (Cebus apella and Chiropotes satanas) exhibit significantly larger relative surface area values for those teeth used in seed processing than closely related taxa that consume resistant foods less often (Cebus albifrons and Pithecia pithecia). Additionally, relative molar-root surface area appears to be greater in Pithecia than in Chiropotes, as predicted from the more folivorous diet of Pithecia. Tooth-root surface area was also found to vary along the tooth row and should therefore have a significant influence on antero-posterior bite-force gradients. The results of this study suggest a close relationship between tooth-root form and patterns of occlusal loading. Further elucidation of this relationship could improve our inferences of diet in extinct taxa, and augment research into the mechanics and evolution of feeding.

Animals↗