Osseointegration

Osseointegration (from Latin osseus "bony" and integrare "to make whole") is the direct structural and functional connection between living bone and the surface of a load-bearing artificial implant ("load-bearing" as defined by Albrektsson et al. in 1981). A more recent definition (by Schroeder et al.) defines osseointegration as "functional ankylosis (bone adherence)", where new bone is laid down directly on the implant surface and the implant exhibits mechanical stability ( i.e., resistance to destabilization by mechanical agitation or shear forces). Osseointegration has enhanced the science of medical bone and joint replacement techniques as well as dental implants and improving prosthetics for amputees.             

When Titanium O2 forms over the surface of Titanium implant due to oxidation, this surface O2 formation causes osseointegration. This new field of clinical usage of biotechnology has been a boon to the dental cripples who have lost natural teeth and adnexae. Further studies on this phenomenon gave rise to different implant systems.

“A direct connection between living bone and a load-carrying endosseous implant at the light microscopic level.”

-Branemark

In order to create osseointegration

A minimal amount of remaining bone should be removed

The basic topography of the region should not be changed

The retention of the original or transitional denture should be maintained during the healing period.

After 20 years of experimental and clinical development, a screw-shaped implant made of pure titanium was selected. It had an outer diameter of 3.7 mm and a length of 10 mm. This allowed its use in almost every edentulous jaw, regardless of the volume and topography of the remaining bone tissue.

A minimum of four fixtures appears to be adequate for support of full-arch prosthesis in the edentulous jaw. However, if morphologically feasible, six fixtures are installed.

Extra oral application of titanium fixtures has been used since 1976. A specially designed fixture has been used to anchor hearing aids for bone-conducting devices. Similar fixtures have also been used as anchorage for auricular prostheses.

Osseointegration has also been applied to long bones in the reconstruction of damaged or diseased joints, lost fingers, hands, arms and lower legs.

Mechanism of Osseointegration

The healing process in the implant system is similar to primary bone healing. Initially, blood is present between the fixture and bone, then blood clot forms. The blood clot is transformed by phagocytic cells, such as polymorphonuclear leukocytes, lymphoid cells, and macrophages . The phagocytic activity level peaks during the time between the 1st and 3rd day after surgery.

About this time, the prosthesis is attached to the fixtures and with stimulation, bone remodeling occurs. Haversian bone calcifies becoming dense and homogenous. Occlusal stresses stimulate the surrounding bone. As remodeling occurs, the osseointegrated fixtures can withstand masticatory functions.

Osseointegrated fixtures under occlusal loads are surrounded by cortical and spongy bone. When osseintegration is established, and prosthesis is designed for good stress distribution, cortical bone forms along the fixture surface a few millimeters in thickness. The cortical bone-to-fixture surface interface has canaliculi participating in the electrolyte transportation near the oxide layer. A network of collagen bundles surround the osteocytes and insert into a glycoprotein layer. A 100 Angstrom glycoprotein layer is formed. The Haversian bone becomes well organized and forms osteon.

Osseointegration is a dynamic process in which characteristics of the implant (i.e. macrogeometry, surface properties, etc.) play a role in modulating molecular and cellular behavior. While osseointegration has been observed using different materials, it is most often used to describe the reaction of bone tissues to titanium, or titanium coated with calcium phosphate derivatives. It was previously thought that titanium implants were retained in bone through the action of mechanical stabilization or interfacial bonding. Alternatively, calcium phosphate coated implants were thought to be stabilized via chemical bonding. It is now known that both calcium phosphate coated implants and titanium implants are stabilized chemically with bone, either through direct contact between calcium and titanium atoms, or by the bonding to a cement line-like layer at the implant/bone interface. While there are some differences (e.g. like the lack of chondrogenic progenitors), osseointegration occurs through the same mechanisms as bone fracture healing.

zirconia implants

Dental implant

A dental implant (also known as an endosseous implant or fixture) is a surgical component that interfaces with the bone of the jaw or skull to support a dental prosthesis such as a crown, bridge, denture, facial prosthesis or to act as an orthodontic anchor. The basis for modern dental implants is a biologic process called osseointegration, in which materials such as titanium form an intimate bond to bone. The implant fixture is first placed so that it is likely to osseointegrate, then a dental prosthetic is added. A variable amount of healing time is required for osseointegration before either the dental prosthetic (a tooth, bridge or denture) is attached to the implant or an abutment is placed which will hold a dental prosthetic.

Success or failure of implants depends on the health of the person receiving the treatment, drugs which affect the chances of osseointegration, and the health of the tissues in the mouth. The amount of stress that will be put on the implant and fixture during normal function is also evaluated. Planning the position and number of implants is key to the long-term health of the prosthetic since biomechanical forces created during chewing can be significant. The position of implants is determined by the position and angle of adjacent teeth, by lab simulations or by using computed tomography with CAD/CAM simulations and surgical guides called stents. The prerequisites for long-term success of osseointegrated dental implants are healthy bone and gingiva. Since both can atrophy after tooth extraction, pre-prosthetic procedures such as sinus lifts or gingival grafts are sometimes required to recreate ideal bone and gingiva.

The final prosthetic can be either fixed, where a person cannot remove the denture or teeth from their mouth, or removable, where they can remove the prosthetic. In each case an abutment is attached to the implant fixture. Where the prosthetic is fixed, the crown, bridge or denture is fixed to the abutment either with lag screws or with dental cement. Where the prosthetic is removable, a corresponding adapter is placed in the prosthetic so that the two pieces can be secured together.

The risks and complications related to implant therapy divide into those that occur during surgery (such as excessive bleeding or nerve injury), those that occur in the first six months (such as infection and failure to osseointegrate) and those that occur long-term (such as peri-implantitis and mechanical failures). In the presence of healthy tissues, a well-integrated implant with appropriate biomechanical loads can have 5-year plus survival rates from 93 to 98 percent and 10 to 15 year lifespans for the prosthetic teeth. Long-term studies show a 16- to 20-year success (implants surviving without complications or revisions) between 52% and 76%, with complications occurring up to 48% of the time.