Osteointegration

Osteointegration

According to PI Brånemark, as early as 1965, osseointegration (from the Greek osteon (bone) and the Latin integrare (to integrate)) is defined as the direct, anatomical and functional, and intimate coaptation between living bone tissue and a biomaterial without interposition of fibrosis, it is ankylosis. This biomaterial, titanium in this case, has excellent properties both functionally and biologically. that is, the living bone can fuse with the titanium oxide layer of the implant so that the two cannot be separated without fracture of this interface.

The bone/implant interface undergoes plastic deformation which allows the perfect and permanent integration of titanium into the bone tissue. A layer of titanium oxide forms on the surface of the implant which allows the implant to fuse with the living bone tissue in order to tend towards an inseparable unit except in the case of fracture. These fractures will be mechanical in nature, of which

the origin is a bad placement or an occlusal overload in particular. This is why, after the first maxillary implantations carried out in 1965 by the team of PI Brånemark in Gothenburg, 40 years later, the implant is still present! What more durable solution can therefore compete with the titanium implant? Twenty years later, the evolution of techniques demonstrates that the conditions for obtaining osseointegration and the durability of the implant are quite coercive.

Bone response leading to osseointegration :
1. Some definitions:

The term “osseointegration” describes a functional bone response to an implant. However, it does not describe the various strong reactions that can lead to it. Therefore, these reactions need to be better defined.

Contact osteogenesis :

Contact osteogenesis occurs when new bone formation around an implant begins directly from its surface.

distant osteogenesis :

This is said when new bone formation around an implant does not start directly from its surface because it can only start from the pre-existing adjacent bone, for example a titanium implant with a smooth surface. (Davis 2003).

Common factors in bone repair:

-A stable surface

– the presence of adequate cells

– adequate nutrition of these cells

-an appropriate biomechanical environment

The cells involved in neoformation are osteoblasts and osteoclasts, which are recruited from the bone marrow or from undifferentiated mesenchymal cells in the bloodstream. In the bone site, the latter are called upon to differentiate along the osteoblastic lineage.

Bone response of cancellous bone:

Phase 1: clot formation:

Blood is the first substance to come into contact with the implant surface. After the implant is placed, a blood clot forms in the spaces left free between the drill line and the material. The cellular part contains red blood cells, platelets and white blood cells. Fibrinogen, part of the protein homeland, is deposited on the titanium, allowing preferential absorption of platelets on the surface. Immediately after their absorption, the platelets degranulate and release growth factors. These, by chemotaxis, will attract undifferentiated cells to the wound site.

Phase 2: 3D formation of a fibrin network

During clot formation, a three-dimensional fibrin network is established. This is followed by local angiogenesis. Through the newly formed capillaries, undifferentiated mesenchymal cells arrive at the repair site. If all the local biomechanical conditions are met, they differentiate along the osteoblastic line.

The fibrin network serves as a “beam” for cell migration and differentiation and therefore enables both osteoconduction and osteoinduction.

Osteogenic neodifferentiated cells migrate towards the surface because they are attracted by signals emitted during platelet degranulation in the vicinity of the surface. Their migration in the immediate vicinity of the implant surface is accompanied by tensions on the fibers which cause

a certain retraction. Depending on whether the fibers attached to the surface are able to resist the traction or not, osteogenesis continues in contact osteogenesis or distant osteogenesis.

Phase 3: first bone apposition

– Contact osteogenesis :

If the fibers are well anchored to the surface and resist cell traction, osteogenic cells can reach the implant surface directly.

They recognize the surface as a stable surface, they continue their differentiation into osteoblasts and will then express their phenotype. These osteogenic cells will first secrete a non-collagenous protein matrix, rich in ostepontins and scialoproteins, which immediately mineralizes. It is the equivalent of the cementum line, systematically encountered during any remodeling activity. The cells continue their bone apposition activity by producing woven bone. The latter is recognizable by the disorganized nature of its mineralized collagen fibers. The cells continue their bone apposition, secreting osteoblasts are included in the bone matrix and differentiate into osteocytes. Bone apposition continues centrifugally (from the surface of the implant towards the original bone) to ensure immobilization of the implant in the bone structure.

– remote osteogenesis:

When the anchoring of the fibers to the implant surface is weak, generally because the surface does not offer sufficient roughness to attach to, the fibers do not resist the traction of the osteogenic cells and detach from the surface of the implant.

Migrating cells cannot reach the implant surface directly and remain at a distance. Bone apposition will occur from the most stable adjacent surface, i.e., the edges of the drill line. As before, the non-collagenous protein matrix rich in osteopontine and scialoproteins is secreted and then mineralized. The cells continue their bone apposition activity towards the implant (centripetal activity) by producing woven bone intended to remodel into lamellar and then Haversian bone.

Bone maturation and remodeling:

After the onset of bone apposition, the woven bone goes through all the phases of maturation and remodeling, that is, the woven bone transforms into lamellar bone. With a parallel organization of collagen fibers, then into Haversian bone with a concentric circular organization of collagen fibers. As the maturation stages progress, the mechanical properties of the bone increase.

However, the initial response, contact osteogenesis or distant osteogenesis, is not without consequences on the long-term organization of the peri-implant bone structure.

The surface condition will induce a specific initial bone response, it will lead to a distinct bone structure.

A- “Trabeculization” reaction

When the initial bone reaction is a contact osteogenesis reaction, bone apposition continues according to a “trabeculization” type reaction. Around the implant, the bone forms a more or less continuous thin bone layer on which bone trabeculae are embedded, oriented more or less perpendicular to the vertical axis of the implant. These trabeculae are connected to the surrounding bone. As before, this organization is intended to persist over the long term. This reaction is typical of a rough surface.

B- “Corticalization” reaction

When the initial bone reaction is a distant osteogenesis reaction, bone apposition occurs according to a “corticalization” type reaction; around the implant, the bone forms an enveloping bone shell of a certain thickness. The organization of this structure persists in the long term. The corticalization reaction is slow and requires time to reach the Haversian phase. This reaction is typical of a machined surface.

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Summary table

Bone response and local factors:

Many factors can influence bone healing. The percentage of bone-implant contact is influenced by:

-bone quality

– the implant: the implant material, its shape, its surface condition

-the surgical technique

Bone quality:

With dense type 1 bone, primary stability is optimal compared to type 3 and 4 bone or even

5. Indeed, the bone is very dense so during implant surgery, the bone/implant contact surface will be large.

The implant:

– Related to the material:

Titanium is today the reference material with the best properties both biologically and mechanically.

-Related to the shape of the implant:

Macrogeographically, the implant has changed from a cylindrical to a conical shape, which has increased its osseointegration and primary stability capabilities. In addition, its design is of great importance. Its straight neck, the number, spacing, and orientation of the coils, its length, width, and diameter all improve its properties.

At the beginning of his work, Brånemark explained that the neck of the implants were like shoulders that fit into the bone cortex. This improves primary stability. He deduced that the design of the neck increases primary stability because it comes into contact with the bone cortex and allows the implant to “seat.” The wider the neck, the more primary stability will be improved.

The organization of the coils is also of capital importance in this type of implant. Indeed, the greater the number of coils, the greater the bone/implant contact surface will be developed. Their orientation and flared shape improve this primary stability.

-related to the surface condition:

On a microgeographical level, its surface condition is the last essential characteristic since

“The surface roughness of implants will have different consequences depending on the geometric dimension involved. A rough or porous surface can be advantageous, because from a mechanical point of view, it allows for the proper distribution of forces. Roughness can influence the biology of the interface, because from the moment the value of the roughness curve corresponds to the size of cells and large molecules, the latter can penetrate into the area concerned.”

The surgical technique:

-Related to asepsis :

First of all, it is necessary to have a very controlled asepsis protocol, even if it has evolved a little. Indeed, Brånemark, during his initial work, imposed strict asepsis during implant surgery. With the development of disinfection techniques and the improvement of knowledge on the transmission of germs, the High Authority of Health in “Conditions for carrying out oral implantology procedures: technical environment” in July 2008 published a report explaining that these surgeries can be performed in an operating room intended exclusively for this purpose, but

also, and more simply, in the practitioner’s usual treatment room. This report also demonstrates the minimal incidence of airborne contamination.

-Related to the Drilling Protocol:

Schroder promotes a “single-stage surgical” technique with a non-submerged implant. Healing times are reduced, the protocol is simplified, and the patient experiences greater comfort with an equivalent success rate. However, beware of harmful forces on the implant due to temporary prostheses.

Validation of osseointegration:

It is generally done clinically and radiologically according to criteria established by Albrektsson (1986). These factors are still relevant today:

lack of mobility,
absence of signs of infection visible clinically and radiologically,
absence of pain on percussion.
However, the criterion concerning marginal bone loss (less than 1.5 mm during the first year of operation then less than 0.2 mm per year).

3-Maintaining osseointegration over time :

It depends on many factors such as design, accuracy of fit and occlusal equilibration of the prosthetic restoration . Patient motivation and hygiene are essential to the

stability of results. Establishing maintenance sessions will help preserve tissue stability and intercept any peri-implant or prosthetic complications.