Osseointegration

   Osseointegration

1. History:

The replacement of missing teeth has been practiced since ancient times. Ivory teeth have been found embedded in jaws dating back to Ancient Egypt. Subsequently, various techniques, each more creative than the last, were tried, but they did not achieve the expected results. It was towards the end of the 1950s that Professor Bränemark made a discovery that marked a development in the treatment of edentulous patients.

In order to study the vascularization of the bone marrow, he had developed a screw-shaped optical chamber made of pure titanium. He wanted the insertion of this optical chamber to not change the physiology of the bone in any way. Having completed his observations and wanting to retrieve it, he noticed that it was impossible to unscrew it: the bone had adhered perfectly to a metal surface. He then applied this discovery to stabilize an implant-supported prosthesis (first patient in 1965), but it was not until 1982 that implantology experienced a major boom.

2. Definition

Osseointegration has been defined as:

The “direct structural and functional connection between living, remodeled bone and the surface of a load-bearing implant” (Brånemark et al. , 1969);

 The “process by which a rigid, clinically asymptomatic connection is achieved between an inert material and bone. This connection is maintained under functional loading” (Zarb and Albrektsson, 1991).

Clinically, osseointegration is defined as the stability and ankylosis of the implant in the bone. From a biomechanical point of view, an implant is said to be osseointegrated when it is stable, without any movement between the implant and the surrounding bone.

Radiologically, the implant surface is in direct contact with the bone. 

Histologically, the term osseointegration refers to the absence of fibrous tissue at the bone–implant interface.

3. The concept of osseointegration

The osseointegration of dental implants therefore takes place in two phases:

 Primary stabilization is a phase of mechanical anchoring of the implant in the prepared site. It will depend essentially on the quality of the bone and its available volume, the surgical technique and the implant morphology especially in a bone of low density (hence the importance of knowing the bone typology).

Indeed, this primary stability is a determining factor for osseointegration. It is obtained essentially by the implant portion in contact with the cortical bone tables. Cortical bone offers better primary anchorage than cancellous bone. Since the maxilla often has a thin external cortex, it is more difficult to obtain primary stability there. However, in a bone that is not very dense, it can still be obtained by under-preparing the site.

Secondary stabilization which is characterized by the formation of biological cohesion between the bone tissue and the implant. 

Although a weakly trabecularized cancellous bone provides primary stability with greater difficulty, the osseointegration reactions that lead to secondary stability are faster than for a highly corticalized compact bone.

4. Osseointegration process

Schematically, we distinguish: the immediate response, peri-implant bone formation and the bone remodeling phase after loading of the implant.

1. Immediate response : cellular and molecular events at the bone-implant interface:

Bone apposition to the implant surface results from a series of molecular and cellular events at the bone–implant interface that direct tissue responses on the implant surface. Following placement of a titanium implant, a series of 

Electrochemical modifications of the titanium surface with the formation of a layer of titanium oxides

 Protein absorption on the implant surface comes from plasma and interstitial fluid, then from the metabolic activity of cells in the peri-implant site.

 Colonization of the site by inflammatory cells (polymorphonuclear granulocytes and monocytes) then osteoprogenitor cells

The possible release of matrix proteins and the absorption of others such as bone sialoprotein (BSP) or osteopontin (OPN);

The formation of a “lamina limitans” and the adhesion of osteogenic cells.

Peri-implant new bone formation.

2. Peri-implant bone formation

Initially, the bone that forms around the implant is immature bone. For some types of implants, bone forms on the residual bone wall converging towards the implant surface (distant osteogenesis) and/or directly on the implant surface (contact osteogenesis)

Newly formed bone is immature bone with random orientation of nonlamellar collagen fibers. This healing phase lasts 4 to 16 weeks.

 From the second month of healing, the immature bone is gradually remodeled and replaced by lamellar bone with a high degree of mineralization.

Osseointegration

Osseointegration

3. Bone remodeling after loading 

After loading, the newly formed bone remodels depending on the intensity, direction and frequency of the forces applied. The process of new formation and remodeling lasts about 1 year. The long-term stability of the implant depends on this phase.

5. factors influencing the osseointegration process

Several factors determine osseointegration although their precise roles in this process are not defined. These factors are related to the patient, the implant site and the implant 

• Patient-related factors

Systemic factors can influence bone metabolism and/or bone healing and, consequently, peri-implant remodeling, to the extent that they can compromise osseointegration and even contraindicate implant placement.

• Diabetes mellitus.
• Osteoporosis.
• Smoking: It can impair healing and bone metabolism.

Bisphosphonates: they are used in the treatment of certain cancers and metastatic processes,

• Bone quality and quantity of the implant site .
• Quality and quantity of the gingiva : the height and thickness of the mucosa , the peri-implant gingival biotype are parameters to be taken into consideration
• Periodontal diseases : Bone loss around implants is high in patients with aggressive or chronic periodontitis.
• Factors related to implants

 Ideally, an implant material should be biocompatible with:

• a chemical composition that resists corrosion in a physiological environment;
• an acceptable hardness;
• high wear resistance;
• a modulus of elasticity similar to bone.

6. Criteria for successful osseointegration

Osseointegration is a prerequisite for the success of an implant. Albretksson, Zarb, Worthington and Eriksson defined the criteria for the success of an implant in 1986  

    – The implant must remain immobile when clinically tested.

    – The absence of radiolucent areas around the implant should be evident on a good quality retro-alveolar image with sufficient definition.

    – Bone loss must be less than 0.2 mm between two examinations spaced one year apart, after the loss occurring during the first year of implant operation, at most equal to 1.5 mm.

• Many persistent and/or irreversible subjective and objective clinical signs must be absent: pain, infection, tissue necrosis, paresthesia or anesthesia of the implanted area, bucco-sinus or bucco-nasal communication, effraction of the lower dental canal.
• The success rate at 5 years must be 85% and 80% at 10 years to speak of a successful technique, based on the criteria previously defined.

7. The evolution of the concept of osseointegration

Over time, improvements in the surface condition and shape of implants have led to the evolution of the concept of osseointegration. Thus, several of Bränemark’s recommendations have no longer been considered essential. Only two prerequisites for osseointegration will be retained: the use of a biocompatible material and atraumatic drilling of the bone.

The protocols have therefore evolved towards an acceleration of treatment plans with new implant concepts. We have been able to move to early and even immediate loading.

 The clinical validation of Bränemark dental implants was done on machined titanium, but teams quickly worked on the use of rough surfaces and demonstrated the improvement of mechanical anchoring.

Osseointegration

8. Failures of osseointegration

They may be due to:

   – Warming up the bone during preparation of the recipient site

   -Overpressure of the implant against the bone

   -Premature loading

   – Poor immediate immobilization of the implant

   -A per-operative infection 

Osseointegration

  Baby teeth need to be taken care of to prevent future problems.
Periodontal disease can cause teeth to loosen.
Removable dentures restore chewing function.
In-office fluoride strengthens tooth enamel.
Yellowed teeth can be treated with professional whitening.
Dental abscesses often require antibiotic treatment.
An electric toothbrush cleans more effectively than a manual toothbrush.
 

Osseointegration