We can begin this presentation by asking the question “What is Osseointegration?" There've been several definitions for osseointegration, but a commonly used one is a direct, structural and functional connection between ordered, living bone and the surface of a load-carrying implant. Direct bone-to-implant contact was first described by Branemark in 1969 and histologically demonstrated by Schroeder as functional ankylosis. When an osteotomy is prepared, a wound healing cascade is initiated which can be broadly divided into three overlapping phases: inflammation, matrix formation, and remodelling. These phases are common to all healing and involve a large range of cells and molecules, as can be seen on this slide. Now the key events that lead to osseointegration occur at the implant surface, interface. There are a number of different processes that take place and these are relatively complex. The first phase of healing following implant placement into the freshly prepared osteotomy involves the formation of a blood clot. Initially, there is adsorption and desorption of proteins on the implant surface. At the same time an inflammatory cascade is initiated and the surface of the implant undergoes changes as it interacts with the blood clot. In the following days, the coagulum is replaced by tissue rich in mesenchymal cells, which will ultimately form the future osteoblasts. These cells enter through the surrounding vasculature, as well as the surrounding bone tissue. We also see signs of the formation of blood vessels. And furthermore, osteoclasts can be seen on the surgical edges of the osteotomy as the damaged bone is remodelled. In the following weeks, we start to see the signs of mineralized matrix formation as the first step towards the formation of a bone matrix. Intramembranous bone formation leads to the formation of immature woven bone. This woven bone is ultimately remodelled into lameller bone in the following months via the co-ordinated action of osteoblasts and osteoclasts. Based on histological observation at the bone-implant interface, there are two proposed mechanisms of osseointegration. The first is called distance osteogenesis. This is where a new bone is formed on the surface of existing bone on the edges of the surgically created osteotomy. In these cases, bone is laid down by opposition. The second proposed mechanism is called contact osteogenesis. This is where bone cells migrate directly onto the implant surface. They differentiate and produce a bone matrix, which then matures into a bone which is in direct contact with the implant. An important consideration is also the establishment of soft tissue integration which in many ways is very similar between implants and teeth. However, there are some important differences. Firstly, fibers around implants are parallel rather than perpendicular to the surface of the implant. The connective tissue surrounding the implant is also far less vascular than that found around teeth. Finally, we need to consider the factors that can affect the osseointegration process. This can be broadly divided into three categories. These are implant, operator, and patient related factors. In that implant category, we need to consider the material that is used, with commercially pure titanium being well-established as having the ability to support osseointegration. Then, we also have the macro level features of the implant, as well as, the micro topography of the implant surface which can both affect the osseointegration process. Then we have the operator level factors. These are usually related to the surgical technique being used with aseptic technique being essential, as well as, adequate irrigation to ensure that the osteotomy site is not overheated. Finally, there is the patient related factors. These relate to both the site meaning that the quality and quantity of bone is to be adequate for implant placement. Furthermore, the systemic health of the patient needs to be sufficient to support the osseointegration process. And factors, such as uncontrolled diabetes and severe osteoporosis may compromise the osseointegration process.
