How do oral hard tissues react to intraosseous implants?
The introduction and growing popularity of intraosseous implants has revolutionised restorative dentistry. Successful implants restore complete function to patients in areas of previously missing teeth. Although they may act like teeth, the histological hard tissue reaction to implants is a wound healing process compared to the developmental process involved in natural dentition. In addition, the healing process may vary from case to case depending on factors such as the implant material, surface texture, clinician handling and placement into the peri-implant tissue; all of which will be discussed in the following paper.
Research has identified two healing processes involved post-implant placement; osseointegration (Branemark et al 1977, 1985) or fibrosteal integration (Weiss, 1986). The later is moderated by a fibrous capsule which only provides a loose union between bone and implant. Osseointegration is triggered by direct and intimate contact between the implant and surrounding living bone. A greater success rate is seen in implant procedures which undergo osseointegration compared to fibrosteal integration.
The most common implant material in modern dentistry is Titanium or an alloy variation of the metal due to their biocompatibility properties. Titanium provides a surface for cells to differentiate and proliferate. Furthermore the material is resistant to corrosion which is key when being placed into the moist intraoral environment. Upon exposure to air, a 3-5nm oxide layer forms on the surface of the implant (TiO2) and it is the oxygen within this layer that allows the implant to be accepted as self within the body (Villar et al, 2012).
Significant bone formation is noticeable as soon as 3-4 days after the implant placement which is seen to trigger the development of a network of blood vessels. It has been hypothesized that this network is a positive regulator of bone formation. Once the implant has been surgically inserted, the space between the surrounding alveolar bed and the implant surface becomes filled with fibrin coagulum. This is swiftly infiltrated by fibroblast-like cells and vascular units resulting in the formation of granulation tissues. One week into the healing process, any bone debris from the surgical operation is resorbed by osteoclasts which are then in cooperated into the new woven bone. The coagulum and granulation tissues are then replaced with connective tissue matrix, primarily composed of fibroblast-like mesenchymal cells (Villar et al, 2012). It is from these cells that a collagen fibre matrix that has the ability to mineralise is produced. 4 weeks into the healing process, the maturing woven bone extends onto the implant surface. The following 2 months will see the new woven bone gradually being replaced by lamellar bone (Clokie and Wars
hawsky, 1995). Osteoblasts and osteocytes are microscopically seen on the implant-bone interface and within the newly...