Abstract
The outer cortical table of the parietal bone has been commonly used as a calvarial bone graft site for the craniofacial reconstruction. However, little is known about how removing the outer table may affect the function and structure of the inner table, and how the knowledge of the biomechanics and material properties of cortical bones will help the calvarial graft to better integrate into the biological and mechanical functions of its surrounding native tissues. In this study, it was hypothesized that there were significant differences in both density and material properties between inner and outer cortical plates in cranial bones. Twelve cylindrical specimens, including inner-outer layers, of cortical parietal bone of a female baboon were collected. Cortical thicknesses and densities were measured, and elastic properties were assessed using an ultrasonic technique. Results demonstrated remarkable difference in both thickness (t = 8.248, p ≤0.05) and density (t = 4.926, p≤0.05) between inner and outer cortical paired samples. Orthotropic characteristics of the cortical plates were detected as well, these findings suggest that there are differences in biomechanical properties between two surfaces of cranial bones at both tissue and organ levels. How these differences are linked to the stress environments of the inner and outer cranial cortical layers awaits further studies. Further study will greatly enhance our ability to address questions derived from both morphological and craniofacial medicine fields about the development and biomechanics of craniofacial skeletons.
Highlights
The skull is a complex arrangement of bones, joined by sutures, forming the craniofacial region; this craniofacial complex is comprised of 22 facial and cranial bones of different shapes, thicknesses, and functions
The cranial shape is the result of several functional factors such as: (1) the neurocranial growth which produces osseous expansion, (2) the location, morphology, and patency of cranial sutures, (3) the presence of supraorbital ridges to enforce the connection between the orbits and the brain case, and (4) the three-layered structure of the cranial bone which is composed of an outer cortical table, a low density core known as the diploe and an inner cortical table [1]
Biomechanics of cranial bones layers are a three-layered system with two external cortical plates packing a thin layer of trabecular bone
Summary
The skull is a complex arrangement of bones, joined by sutures, forming the craniofacial region; this craniofacial complex is comprised of 22 facial and cranial bones of different shapes, thicknesses, and functions. The cranial shape is the result of several functional factors such as: (1) the neurocranial growth which produces osseous expansion, (2) the location, morphology, and patency of cranial sutures, (3) the presence of supraorbital ridges to enforce the connection between the orbits and the brain case, and (4) the three-layered structure of the cranial bone which is composed of an outer cortical table (periosteal cortical plate), a low density core known as the diploe and an inner cortical table (endosteal cortical plate) [1]. Mesenchymal cells produce the ossification centers, and osteoid is secreted within the fibrous membrane to form two layers of compact bones, ectocranial table (outer plate) and endocranial table (inner plate), and a central cavity containing red marrow (diploe) [2]
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