The biomechanical significance of cranial sutures in primates is an open question because their global impact is unclear, and their material properties are difficult to measure. In this study, eight suture-bone functional units representing eight facial sutures were created in a finite element model of a monkey cranium. All the sutures were assumed to have identical isotropic linear elastic material behavior that varied in different modeling experiments, representing either fused or unfused sutures. The values of elastic moduli employed in these trials ranged over several orders of magnitude. Each model was evaluated under incisor, premolar, and molar biting conditions. Results demonstrate that skulls with unfused sutures permitted more deformations and experienced higher total strain energy. However, strain patterns remained relatively unaffected away from the suture sites, and bite reaction force was likewise barely affected. These findings suggest that suture elasticity does not substantially alter load paths through the macaque skull or its underlying rigid body kinematics. An implication is that, for the purposes of finite element analysis, omitting or fusing sutures is a reasonable modeling approximation for skulls with small suture volume fraction if the research objective is to observe general patterns of craniofacial biomechanics under static loading conditions. The manner in which suture morphology and ossification affect the mechanical integrity of skulls and their ontogeny and evolution awaits further investi-

The global biomechanical impact of cranial sutures on the face and cranium during dynamic conditions is not well understood. It is hypothesized that sutures act as energy absorbers protecting skulls subjected to dynamic loads. This hypothesis predicts that sutures have a significant impact on global patterns of strain and cranial structural stiffness when analyzed using dynamic simulations; and that this global impact is influenced by suture material properties. In a finite element model developed from a juvenile Rhesus macaque cranium, five different sets of suture material properties for the zygomaticotemporal sutures were tested. The static and dynamic analyses produced similar results in terms of strain patterns and reaction forces, indicating that the zygomaticotemporal sutures have limited impact on global skull mechanics regardless of loading design. Contrary to the functional hypothesis tested here, the zygomaticotemporal sutures did not absorb significant amounts of energy during dynamic simulations regardless of loading speed. It is alternatively hypothesized that sutures are mechanically significant only insofar as they are weak points on the cranium that must be shielded from unduly high stresses so as not to disrupt vitally important growth processes. Thus, sutural and overall cranial form in some vertebrates may be optimized to minimize or otherwise modulate sutural stress and strain.

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To test the mechanical properties of regenerate cortical bone created using Mandibular Bone Transport (MBT) distraction, five adult male American foxhound dogs underwent unilateral distraction of the mandible with a novel MBT device placed to linearly repair a 30-35 mm bone defect. The animals were sacrificed 12 weeks after the beginning of the consolidation period. Fourteen cylindrical specimens were taken from the inner (lingual) and outer (buccal) plates of the reconstructed mandible and 21 control specimens were removed from the contralateral aspect of the mandible. The mechanical properties of the 35 cylindrical cortical bone specimens were assessed by using a non-destructive pulse ultrasound technique. Results showed that all of the cortical mechanical properties exhibit higher numerical values on the control side than the MBT regenerate side. In addition, both densities and the elastic moduli in the direction of maximum stiffness of the regenerate cortical bone specimens are higher on the lingual side than the buccal side. Interestingly, there is no statistical difference between elastic modulus (E 1 and E 2 ) in orthogonal directions throughout the 35 cortical specimens. The data suggest that the regenerate canine cortical bone is not only heterogeneous, but the elastic mechanical properties tend to approximate transverse isotropy at a tissue level as opposed to control cortical bone that is orthotropic. In addition, the elastic mechanical properties are not only higher on the control side but also in the lingual anatomical position, suggesting a stress shielding effect from the presence of the reconstruction plate.

Purpose Bone transport distraction osteogenesis (BTDO) provides a promising alternative to traditional grafting techniques. However, existing BTDO devices have many limitations. The purpose of this research was to test a new device, the mandibular bone transport reconstruction plate (BTRP), in an animal model with comparable mandible size to humans and to histologically and mechanically examine the regenerate bone. Materials and methods Eleven adult foxhound dogs were divided into an unreconstructed control group of 5 animals, and an experimental group of 6 animals. In each animal, a 34 mm segmental defect was created in the mandible. The defect was reconstructed with BTRP. Histological and biomechanical characteristics of the regenerate and un-repaired defect were analyzed and compared to bone on the contralateral side of the mandible after 4 weeks of consolidation. Results The reconstructed defect was bridged with new bone, with little bone in the control defect. Regenerate density and microhardness were 22.3% and 42.6% lower than the contralateral normal bone, respectively. Likewise, the anisotropy of the experimental group was statistically lower than in the contralateral bone. Half the experimental animals showed non-union at the docking site. Conclusion The device was very stable and easy to install and activate. After one month of consolidation, the defect has been bridged with new bone with evidence of active bone formation. Regenerate bone was less mature than the control bone. Studies are underway to identify when the regenerate properties compare to normal bone, and to identify methods to augment bone union at the docking site.

Purpose Reconstruction of the canine mandible using bone transport distraction osteogenesis has been shown to be a suitable method for correcting segmental bone defects produced by cancer, gunshots, and trauma. Although the mechanical quality of the new regenerate cortical bone seems to be related to the mineralization process, several questions regarding the micro-structural patterns of the new bony tissue remain unanswered. The purpose of this study was to quantify any microstructural differences that may exist between the regenerate and control cortical bone. Methods Five adult American foxhound dogs underwent unilateral bone transport distraction of the mandible to repair 30–35 mm bone defects. Animals were sacrificed 12 weeks after the beginning of the consolidation period. Fourteen cylindrical cortical samples were extracted from the superior, medial, and inferior aspects of the lingual and buccal plates of the reconstructed aspect of the mandible and 21 specimens were collected similarly from the contralateral aspect of the mandible. The specimens were evaluated using histomorphometric and micro-computed tomography techniques to compare their microstructure. Results Except for differences in Haversian canal area, histomorphometric analyses suggested no statistical differences in microstructure between regenerate and control cortical bone. Morphological evaluation suggested a consistent level of anisotropy possibly related to the distraction vector. Conclusions After 12 weeks consolidation, bone created during bone transport distraction osteogenesis is comparable to native bone in microstructure, architecture, and mechanical properties. It is proposed that after enough time, the properties of the regenerate bone will be identical to that of native bone.

The purpose of this study was to evaluate the structure and material properties of native mandibular bone and those of early regenerate bone, produced by bone transport distraction osteogenesis. Ten adult foxhounds were divided into two groups of five animals each. In all animals, a 3- to 4-cm defect was created on one side of the mandible. A bone transport reconstruction plate, consisting of a reconstruction plate with an attached intraoral transport unit, was utilized to stabilize the mandible and regenerate bone at a rate of 1 mm/day. After the distraction period was finished, the animals were killed at 6 and 12 weeks of consolidation. Micro-computed tomography was used to assess the morphometric and structural indices of regenerate bone and matching bone from the unoperated contralateral side. Significant new bone was formed within the defect in the 6- and 12-week groups. Significant differences (P ≤ 0.05) between mandibular regenerated and native bone were found in regard to bone volume fraction, mineral density, bone surface ratio, trabecular thickness, trabecular separation, and connectivity density, which increased from 12 to 18 weeks of consolidation. We showed that regenerated bone is still mineralizing and that native bone appears denser because of a thick outer layer of cortical bone that is not yet formed in the regenerate. However, the regenerate showed a significantly higher number of thicker trabeculae.