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

Biomechanics of the press-fit phenomenon in dental implantology: an image-based finite element analysis

<p>Abstract</p> <p>Background</p> <p>A fundamental pre-requisite for the clinical success in dental implant surgery is the fast and stable implant osseointegration. The press-fit phenomenon occurring at implant insertion induces biomechanical effects in the bone tissues, which ensure implant primary stability. In the field of dental surgery, the understanding of the key factors governing the osseointegration process still remains of utmost importance. A thorough analysis of the biomechanics of dental implantology requires a detailed knowledge of bone mechanical properties as well as an accurate definition of the jaw bone geometry.</p> <p>Methods</p> <p>In this work, a CT image-based approach, combined with the Finite Element Method (FEM), has been used to investigate the effect of the drill size on the biomechanics of the dental implant technique. A very accurate model of the human mandible bone segment has been created by processing high resolution micro-CT image data. The press-fit phenomenon has been simulated by FE analyses for different common drill diameters (D_A = 2.8 mm, D_B = 3.3 mm, and D_C = 3.8 mm) with depth L = 12 mm. A virtual implant model has been assumed with a cylindrical geometry having height L = 11 mm and diameter D = 4 mm.</p> <p>Results</p> <p>The maximum stresses calculated for drill diameters D_A, D_B and D_C have been 12.31 GPa, 7.74 GPa and 4.52 GPa, respectively. High strain values have been measured in the cortical area for the models of diameters D_A and D_B, while a uniform distribution has been observed for the model of diameter D_C . The maximum logarithmic strains, calculated in nonlinear analyses, have been ϵ = 2.46, 0.51 and 0.49 for the three models, respectively.</p> <p>Conclusions</p> <p>This study introduces a very powerful, accurate and non-destructive methodology for investigating the effect of the drill size on the biomechanics of the dental implant technique.</p> <p>Further studies could aim at understanding how different drill shapes can determine the optimal press-fit condition with an equally distributed preload on both the cortical and trabecular structure around the implant.</p

Study of Biomechanics of Porous Coated Root Form Implant Using Overdenture Attachment: A 3D FEA

The purpose of this article is to do a three-dimensional finite element stress analysis, in relation to root form implant supported by overdenture attachment, during axial and non-axial loading. Two porous coated Titanium–aluminum–vanadium (Ti–6Al–4V) implants with overdenture abutment were embedded in both simple and 3D model of interforaminal region of mandible. The material properties of tissue ingrowth bonded interface were calculated considering Iso-Strain condition. The masticatory forces: axial load of 35 N, a horizontal load of 10 N, and an oblique load of 120 N, was applied for the two qualities of cancellous bone. It implied that porous topography of the implant led to optimal stress transfer at the tissue ingrowth bonded interface and insignificant punching stress at the apex than a smooth surface implant. The inferior bone quality was deformed even under physiologic loads and showed wider stress pattern. Simulated implant abutment to implant bone interface stress may be significantly affected by the quality of the bone and the surface topography of the implant. The interface is affected to a lesser extent by the prosthetic material properties. Threedimensional anatomical model was more close to reality than the geometry of much simpler altered models