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Paul C Dechow

Publications and source records attributed to Paul C Dechow.

12 recordsLinked to original sources
PubMed2006

A comparison of cortical elastic properties in the craniofacial skeletons of three primate species and its relevance to the study of human evolution.

When a force is applied to an object, the resulting pattern of strain is a function of both the object's geometry and its elastic properties. Thus, knowledge of elastic properties in craniofacial cortical bone is indispensable for exploring the biomechanics and adaptation of primate skulls. However, elastic properties, such as density and stiffness, cannot be measured in all species, particularly extinct species known only from fossils. In order for advanced engineering techniques such as finite element analysis (FEA) to be applied to questions of primate and hominid craniofacial functional morphology, it is important to understand interspecific patterns of variation in elastic properties. We hypothesized that closely related species would have similar patterns of bone elastic properties, and that similarities with extant species should allow reasonable predictions of elastic properties in the skeletons of extinct primate species. In this study, we tested this hypothesis by measuring elastic properties in five areas of the external cortex of the baboon craniofacial skeleton using an ultrasonic technique, and by comparing the results to existing data from macaque and human crania. Results showed that cortical density, thickness, elastic and shear moduli, and anisotropy varied among areas in the baboon cranium. Similar variation had previously been found in rhesus and human crania, suggesting area-specific elastic patterns in the skulls of each species. Comparison among species showed differences, suggesting species-specific patterns. These patterns were more similar between macaques and baboons for density, maximum elastic and shear stiffness, and anisotropy than between either of these and humans. This finding demonstrates that patterns of cortical elastic properties are generally similar in closely related primate species with similar craniofacial morphology. Thus, reasonable estimates of cortical bone elastic properties should be possible for extinct species through the study of phylogenetically related and functionally similar modern forms. For example, reasonable elastic property estimates of cortical bone from fossil hominid skulls should be possible once adequate information about such properties in extant great apes is added to our current data from humans, macaques, and baboons. Such data should eventually allow FEA of craniofacial function in fossil hominids.

Animals↗
PubMed2006

Elastic properties of external cortical bone in the craniofacial skeleton of the rhesus monkey.

Knowledge of elastic properties and of their variation in the cortical bone of the craniofacial skeleton is indispensable for creating accurate finite-element models to explore the biomechanics and adaptation of the skull in primates. In this study, we measured elastic properties of the external cortex of the rhesus monkey craniofacial skeleton, using an ultrasonic technique. Twenty-eight cylindrical cortical specimens were removed from each of six craniofacial skeletons of adult Macaca mulatta. Thickness, density, and a set of longitudinal and transverse ultrasonic velocities were measured on each specimen to allow calculation of the elastic properties in three dimensions, according to equations derived from Newton's second law and Hooke's law. The axes of maximum stiffness were determined by fitting longitudinal velocities measured along the perimeter of each cortical specimen to a sinusoidal function. Results showed significant differences in elastic properties between different functional areas of the rhesus cranium, and that many sites have a consistent orientation of maximum stiffness among specimens. Overall, the cortical bones of the rhesus monkey skull can be modeled as orthotropic in many regions, and as transversely isotropic in some regions, e.g., the supraorbital region. There are differences from human crania, suggesting that structural differences in skeletal form relate to differences in cortical material properties across species. These differences also suggest that we require more comparative data on elastic properties in primate craniofacial skeletons to explore effectively the functional significance of these differences, especially when these differences are elucidated through modeling approaches, such as finite-element modeling.

Animals↗
PubMed2006

Fusion patterns of craniofacial sutures in rhesus monkey skulls of known age and sex from Cayo Santiago.

Bones of the face and cranial vault meet at sutural boundaries. These sutures are of great importance for craniofacial growth. Although the effects that the sutures have on modulating craniofacial strains have been investigated, how sutural fusion influences primate craniofacial biomechanics and adaptation are less considered. Confounding this problem is the lack of any systematic data on patterns of craniofacial sutural fusion from animals of known age and sex. This study examined the status of 28 sutures in Macaca mulatta skulls from a collection of animals of known age and sex from Cayo Santiago, Puerto Rico. Survival analysis showed that most animals died before all sutures fused. There was high variation in the age at which individual sutures or sutural sections were fused in M. mulatta, and significant differences in the amount of sutural fusion among regions and between males and females. Intensive fusion of sutures took place between ages 5 and 15. Sutures in the facial area tended to be less fused than in the cranial vault. Between adolescence and adulthood, males tended to have more sutural fusion than females, especially in the facial area. These differences might be biomechanical adaptations during ontogeny to craniofacial sexual dimorphism. These findings enrich our understanding of variation in sutural morphology in rhesus monkeys. Comparative information across primate species is essential for understanding the biomechanics of craniofacial form throughout primate evolution.

Adaptation, Physiological↗
PubMed2006

Material properties of the dentate maxilla.

The aim of this study was to determine regional variability of material properties in the dentate maxilla. Cortical samples were removed from 15 sites of 15 adult dentate fresh-frozen maxillas. Cortical thickness, density, elastic properties, and the direction of greatest stiffness were obtained. Results showed that cortical bone in the alveolar region tended to be thicker, less dense, and less stiff. Cortical bone from the body of the maxilla was thinner, denser, and stiffer. Palatal cortical bone was intermediate in some features but overall was more similar to cortical bone from the alveolar region. The principal axes of stiffness varied regionally. The regions with the greatest consistency were the alveolar area and the frontomaxillary pillar, where the grain of the cortical bone was aligned vertically from the incisors to the medial external aspect of the orbit. Elastic properties in the human maxilla, especially the orientation of the principal axes of stiffness, were more variable than in the mandible. Incorporation of these properties into finite-element models should improve their accuracy and reliability.

Aged↗
PubMed2006

Inheritance of sutural pattern at the pterion in Rhesus monkey skulls.

Five of the bones that characteristically comprise the cranial vault articulate on the lateral aspect of the skull at or near the cephalometric landmark referred to as the pterion. The pattern of articulation in the sutures associated with these bones varies among and within primate species and has been used as a criterion for classification in taxonomic studies, as well as in archeological and forensic studies. Within species, the sutural patterns found within the region of the pterion have remarkable consistency, which lead to the hypothesis that these patterns have a genetic basis. Sutural pattern variations were investigated at the pterion in 422 skulls from 66 rhesus monkey families with known genealogies from the long-standing colony on Cayo Santiago. Four specific types of articulation patterns were recorded. The results demonstrated that the most common suture pattern at the pterion of Cayo Santiago rhesus monkeys (86%; similar to that seen in some other anthropoid species but not humans and some apes) was characterized by an articulation between the temporal bone and parietal bone. Articulation between the sphenoid and parietal bones (type SP) accounted for 14% of the specimens and was concentrated in a dozen families. Mothers with the SP phenotype had a high incidence of offspring with SP phenotypes. Most non-SP mothers having SP offspring had siblings or family members from previous generations with the SP type. This is the first study to examine variation in sutural patterns at the pterion in pedigrees. Variation of sutural patterns shows familial aggregation, suggesting that this variation is heritable. Future work will be focused on defining the inheritance patterns of variation at the pterion, with the ultimate objective of identifying the specific genes involved and their mechanism of action.

Animals↗
PubMed2006

Biomechanical effects of fixed partial denture therapy on strain patterns of the mandible.

STATEMENT OF PROBLEM: The mandibular posterior 3-unit fixed partial denture (FPD) is a conventional prosthodontic therapy and presumably has an effect on the direction and magnitude of occlusal forces and, thus, on the biomechanical environment of the mandible, which may in turn affect bone structure. However, the impact of FPD therapy on mandibular biomechanics is unknown. PURPOSE: The purpose of this study was to test the hypothesis that 3-unit FPD therapy alters strain patterns in the mandible during loading. MATERIAL AND METHODS: Four human cadaver mandibles missing first molars were bilaterally fixed and artificially loaded on each tooth individually. Surface cortical bone strains were measured with multiple strain gauges during loading of up to 250 N. Next, 3-unit FPDs with a chamfer finish line were fabricated using Type IV gold alloy. Strain measurements were conducted in the same manner to assess differences in strain patterns before and after therapy. Paired-sample tests for metric and angular data were used to assess difference in strain pattern before and after therapies (alpha=.05). RESULTS: When loading was applied on the teeth not involved in FPD therapy, no differences were found before and after FPD placement. When the posterior retainers were loaded, the strain distribution differed (P=.01); on the buccal cortices, strain levels increased posteriorly but decreased significantly anteriorly. However, these differences were less than 100 muepsilon, and the overall deformation pattern of the mandible after the FPD therapy was similar to that before FPD therapy. Strain distributions when the pontic was loaded were similar to those when the posterior retainer was loaded. CONCLUSION: Three-unit FPD therapy did not alter the overall deformation pattern of the mandible during loading.

Analysis of Variance↗
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

Material properties of the human cranial vault and zygoma.

The material properties of cortical bone from the diaphyses of long bones (e.g., the femur and tibia) vary by direction, such that bone is stiffer and stronger along its long axis. This configuration improves the abilities of these structures to resist axial compressive loads coupled with bending. As in long bones, cortical bone from the cranial vault is subject to mechanical loads from various orofacial functions and the contraction of attached muscles. However, experimental studies suggest that the resulting bone strains are at least an order of magnitude smaller than those found in the midshafts of the femur or tibia. The characteristics of the three-dimensional elastic properties of cortical bone are largely unexplored in regions of low bone strain, including the cranial vault, in which little is known regarding cortical structure and function. In the present study we examined variations in the cortical microstructure and material properties of the bone of the human cranial vault, including the parietal, frontal, temporal, and occipital bones. A facial bone, the zygoma, was also included to contrast the properties of the cranial vault with another craniofacial intramembranous bone that experiences larger strains. Cortical specimens from the outer cortical plate of the cranial vault were removed from 15 frozen human crania. We measured cortical thicknesses and densities, and determined the primary direction of stiffness within the bone specimens prior to ultrasonic testing to determine their elastic properties. There were statistically significant differences in elastic properties between bones and, in some cases, sites within bones, which for most variables were clustered by bone or region. In striking contrast to this pattern, elastic moduli in the direction of primary stiffness were larger in cortical regions underlying muscle attachments than in regions without muscle attachments. Few sites in the cranial vault or zygoma showed a consistent orientation of the material axes among individuals, although specimens from many regions had directional differences similar to those in cortical bone from the mandible, femur, or tibia.

Adult↗
PubMed2002

Material properties of the inner and outer cortical tables of the human parietal bone.

Even though the cranial vault functions as protection for the brain and as a support structure for facial and masticatory functions, little is known about its mechanical properties or their variations. The cranial vault bone is interesting because of its maintenance in spite of low functional strains, and because calvarial bone cells are often used in cell culture studies. We measured thickness, density, and ash weight, and ultrasonically determined elastic properties throughout the cortices of 10 human parietal bones. The results are unique for studies of the cranial vault because: 1) measurements focused specifically on the cortical components, 2) the orientations of the axes of maximum stiffness were determined before measurement of elastic properties, and 3) two related measurements (bone density and percent ash weight) were compared. Results showed that the periosteal cortical plate (outer table) and the endosteal cortical plate (inner table) had significant differences in material properties. The outer table was on average thicker, denser, and stiffer than the inner table, which had a higher ash weight percentage. Within each table there were significant differences in thicknesses, ash weight percentages, and E(2)/E(3) anisotropies among sites. Few sites on either table had significant orientations of the axes of maximum stiffness. Despite this apparent randomness in orientation, almost all sites exhibited anisotropies equivalent to other parts of the skeleton.

Aged↗