The advantage of porous materials, in general, is their ability to provide biologic fixation of the surrounding bony tissue via the ingrowth of mineralized tissue into the pore spaces. This is accomplished by increasing the available surface area for apposition (or bony contact) by having the interior of the implant accessible via pore spaces. Numerous factors may affect bone ingrowth into the pore spaces of these implants. Some of these factors include, but are not limited to, the porosity of the implant material (pore size, pore gradient. percent porosity), the time of implantation, material biocompatibility, depth of porosity into the implant, implant stiffness, and amount of micromotion between the implant and adjacent bone.
Chapter II examines porosity control of cranial bone ingrowth in the first 6 weeks post implantation. It is during this early time period that bone ingrowth into an implant is similar to fracture healing. The results indicate that porosity-independent physiology of bone growth (i.e. fracture healing, callus formation and mesenchymal ingrowth) in the first 6-weeks following implantation have greater effect than porosity. Porous nitinol is also biocompatible based upon the observations made here.
Chapter III studies the long-term implantation of a clinically accepted porous biomaterial placed in the maxilla of humans. By examining the progression of ingrowth and measuring material properties within the pores, an overall understanding Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. of the progression of craniofacial bone ingrowth and its subsequent maturation within the pore spaces is developed. In Chapter III it becomes apparent that other factors affect craniofacial bone ingrowth in longer implantation times as indicated by the relative stability of bony ingrowth after 20 months. Microhardness measurements also indicate that the ingrown lamellar bone is similar in structural integrity to the surrounding extant bone.
Chapter IV builds upon Chapter III in quantifying craniofacial bone ingrowth into porous implants both over the course of implantation time and depth into the implant. Chapter IV explores when, during the post-implantation period, and where, within the implant, porosity control comes into effect, and when the biologic factors governing bone growth are predominant. In Chapter IV it is determined that these factors include, but may not be limited to, time of implantation, depth into the implant, and porosity of the implant.
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