Papers by Keyword: Microbeam X-Ray Diffraction

Abstract: It was reported that one-dimensionally elongated pores in implants promote the production of new bone tissue possessing both high bone density and the preferential alignment of biological apatite (BAp) c-axis/collagen as a bone quality parameter. This finding indicates that the anisotropic orientation and/or migration of osteoblasts guided by the grooved-pore surface affected the establishment of the anisotropic microstructure of bone tissue. In this study, a grooved polytetrafluoroethylene (Teflon) implant, which may have a role in regulating osteoblast arrangement, was prepared to investigate the relationship between cell behavior and bone microstructure. A cylindrical Teflon implant with 8 grooves on its side was prepared. The width and depth of the groove cross-section were 0.5 and 0.75 mm, respectively. Each implant was inserted in a drill-hole defect created on a rabbit femur such that the groove direction was parallel or perpendicular to the long bone axis in which the BAp c-axis aligns one-dimensionally. The Young’s modulus of Teflon is approximately 0.5 GPa, much lower than that of bone; therefore, the effects of applied stress can be eliminated in this model. The oriented new bone was preferentially produced along the grooved surface. The alignment direction of the BAp c-axis was almost parallel to the grooved surface even near the surface vertically aligned to the long bone axis. The geometry of the implant surface can control the organization of BAp alignment through the arrangement of osteoblasts to orient and subsequently to migrate along the surface direction; hence, implant geometry, particularly the groove, is considered an important factor controlling the BAp orientation of regenerated bone tissues.

Abstract: The preferred crystallographic orientation of the biological apatite (BAp) c-axis has been shown to be one of the important bone quality indices that sensitively reflect in vivo stress distribution and dominate bone mechanical functions. The BAp orientation is expected to be regulated by bone modeling or remodeling by osteoblasts and osteoclasts whose primary functions are bone formation and absorption, respectively. Mouse with macrophage colony-stimulating factor (M-CSF) deficiency-induced osteopetrosis (op/op mouse) is a suitable animal model to elucidate the role of osteoclasts in the development of BAp orientation. In this study, the mandibles of 5-week-old mice were used because their mandible is subjected to complicated stresses including a biting stress locally applied just around the roots of the teeth and a bending stress applied along the mesiodistal axis of the mandibular body, and the response to the stress distribution is important to the formation of BAp orientation. The normal mouse mandible (control) has a one-dimension preferred BAp orientation in the mesiodistal direction, but just near the tooth root, the direction of BAp orientation changes locally to that of the tooth root responding to a biting stress. In the op/op mouse, the preferred BAp orientation only along the mesiodistal direction is found, but the degree is quite lower than that in normal mice. Moreover, the effect of biting was not observed in op/op mice because these mice are devoid of teeth eruption and are unable to bite. This suggests that M-CSF plays a critical role in forming the optimal BAp orientation, and therefore, the op/op mouse without osteoclasts cannot fully develop the appropriate bone microstructure in response to in vivo stress distribution, although BAp orientation is very sensitive to local in vivo stresses in normal animals with normal osteoclast function.

Abstract: The quantity and quality of regenerated bone strongly depends on the direction and amplitude of in vivo principal stress; therefore, in vivo stress distribution near bone implants should be optimized on the basis of the morphology of the interface between an implant and bone tissue. In this study, grooves were created on the implant surface in order to improve the surface morphology of the implant for optimizing in vivo stress distribution near the implant. The preferential alignment of the biological apatite (BAp) c-axis, which is a parameter of bone quality and controls the mechanical function of bones, is closely related to stress distribution; therefore, the direction of principal stress should be matched with the direction of the groove on the implant surface. Hip implants were prepared with grooves aligned at different angles from the surface; the grooves were located on the stem portion. These implants were inserted in a beagle femur to investigate the dependency of the quantity and quality of newly formed bone in the grooves on the groove angle. The degree of preferential alignment of the BAp c-axis of the regenerated bone in the grooves strongly depends on the angle of the groove to the principal stress vector that was estimated previously to an animal experiment. The regenerated bone forms anisotropic BAp orientation in response to the principal stress in the grooves; therefore, the direction of the grooves has to be designed on the basis of the stress distribution near the implant.

Abstract: The orientation of biological apatite (BAp) is one of the bone quality parameters dominating bone mechanical function. In the mandible, the preferential orientation of the BAp c-axis changes depending on alteration of the in vivo stress condition induced by a change in the biting stress. In this study, to clarify the functional adaptation of the preferential BAp orientation and bone mineral density (BMD), all beagle mandibular molars on one side were extracted to remove the biting stress, leading to changes in both BAp orientation and BMD. The BMD exhibited discontinuous distribution around the first molar, mainly responsible for mastication, on the normal side. However, the distribution was continuous along the mesiodistal axis of the edentulous side. The preferential BAp orientation was analyzed in mandibular cross-sections at the first molar root region. Molar extraction led to a change in the BAp orientation: immediately under the root region on the lingual sides, two-dimensional preferential alignment in the mesiodistal and biting directions of the normal side changed to one-dimensional alignment along the mesiodistal axis of the edentulous side. One-dimensional alignment was also observed on the buccal sides irrespective of molar extraction. These findings clarify the close relationship between in vivo biting stress and the preferential BAp orientation, and will be useful clinically for diagnosis, implant placement, and so on.

Abstract: Our group focused on the preferential degree of biological apatite (BAp) c-axis, an important bone quality parameter based on the microstructural anisotropy in intact, pathological, and regenerated bones. The preferential degree of the BAp c-axis strongly depends on the bone position, in vivo stress distribution, bone growth, degree of pathology and regeneration, activity of bone cells, gene defect, etc. We attempted to challenge clarification of the BAp preferential alignment formation mechanism and control the degree of BAp orientation by using an anisotropic biomaterial design to develop suitable distribution of the BAp c-axis orientation.