OSTEOINTEGRATION
Introduction : Branmark et al were the first in 1969 to suggest the possibility of direct contact between living Haversian bone and a loaded implant which they named “osseointegration”.
1-Definition : The current definition of osseointegration is “a direct anatomical and functional junction between the remodeled living bone and the surface of the loaded implant”
The quality of osteointegration depends on the percentage of direct bone/implant contact. The definition is therefore essentially based on implant stability and radiographic analysis. Clinically, osteointegration results in ankylosis, i.e. the absence of mobility of the implant.
2-Peri-implant bone response : the bone has a strong potential for regeneration around the implants. Whatever the bone considered, the healing mechanism is identical. After the placement of an implant, approximately 1mm of adjacent bone dies (following the trauma resulting from the preparation of the implant site).
The first stage of healing is the replacement of non-living peri-implant bone tissue. New bone formation occurs rapidly. This bone is immature and trabecular, and therefore not very resistant to the forces of mastication.
The second stage involves the remodeling of this bone, over several months. The spaces between the immature bone networks will be covered with mature (lamellar) bone. Most of the bone/implant space will thus be filled with bone tissue. A non-bone interface will remain in contact with the implant, which will require approximately 18 weeks to be filled with compact bone. This bone is strong enough to withstand occlusal forces.
Maintenance of osteointegration requires continuous remodeling of bone at the interface and surrounding supporting bone.
3-Factors determining osteointegration:
A-Host related factors
1-General factors
-Age of the patient
-Sex
-Cardiovascular diseases
– Bone metabolism disorders
-Endocrine disorders
-Rheumatic diseases
-Hematological pathologies
-Medication
-Malignant diseases
-Psychiatric disorders and psychological factors
2- risk factors
-Tobacco : it is a factor in implant failure. Heavy smokers have an increased risk of impaired healing and bone metabolism.
-Alcoholism : alcoholism can lead to impaired healing. It can cause osteopenia. The degree of intoxication must be assessed before the therapeutic decision.
3-local factors:
a- state of the mucosa :
Before implant placement, treat all oral dermatoses (candidiasis, eczema, lichen planus, leukoplakia erosion)
b-bone quantity and quality :
The implant site must be well vascularized. The success rate increases with the available bone volume and its quality. Implantation in type IV, cancellous bone increases the risks of therapeutic failure.
c-primary implant stability :
This is a crucial factor for osteointegration. Stability is largely achieved at the marginal and apical parts of the implant, engaged in the bone cortices.
Cancellous bone should ideally have a high proportion of trabicles to help support the implant. Empty or fatty marrow areas should be avoided (as should sites with a low trabicles/marrow space ratio).
The maxilla often has a thin external cortex which contributes little to the stabilization of implants.
Initial stabilization should be sought at the apical portion of the implant (nasal cortex or sinus floor).
The maxillary tuberosities are not very dense while the canine, zygomatic and pterygoid regions allow better primary stabilization of the implants.
The incisive area is also a good implantation site, when the incisive canal is not widened
The anterior mandibular bone between the mental foramina usually offers good possibilities for stabilization of implants by bicortical anchoring at the level of the marginal and basal bone.
d-Degree of resorption :
Edentulous alveolar processes are subject to continuous resorption. Excessive pressure from an ill-fitting removable prosthesis can accentuate this resorption.
e-periodontal diseases :
In partially edentulous patients, periodontal pathogens present in natural teeth can colonize the peri-implant sulcus. The risk of developing peri-implant infections is higher in patients with periodontitis, particularly for aggressive forms. It is recommended to treat these pathogens before considering implant therapy.
f-Congenital defects:
Areas of dental agenesis often have insufficient bone volume.
Similarly, the maxillary bone adjacent to the palatine clefts is generally very sparse and of limited volume.
B-Factors related to implants:
1-biocompatibility of implant materials : commercially pure titanium, niobium and tantalum are materials recognized for their biocompatibility which is probably linked to the oxide layer which covers them. The latter is very adherent and very stable in the body environment. It has excellent resistance to corrosion.
Other materials such as various chromium-cobalt-molybdenum alloys and stainless steel are less biocompatible in bone tissue (local and systemic side effects after diffusion).
Silver and copper are materials with low biocompatibility.
2-Implant shape : the functionality of screw implants without clinical complications is well demonstrated. The presence of screw threads increases the contact surface between the bone and the implant, improves initial stabilization, resistance to shear forces and distribution of forces in the bone tissue. (circumferential resorption is often reported with cylindrical implants).
3- Implant surface condition : smooth surfaces do not allow acceptable bone/cell adhesion. They result in fibrous encapsulation regardless of the implant material used.
C-Surgical and prosthetic requirements:
1-operative asepsis : this is an essential condition to prevent any bacterial contamination.
2-temperature control : local temperature elevation causes destruction of the cells responsible for healing. The critical time/temperature relationship for bone tissue necrosis is 47°C, applied for one minute. The use of sharp drills, appropriate drilling speeds, and abundant irrigation prevent excessive thermal elevation.
3-Choice of implantation site : the most important principle is to obtain initial stabilization of the implants in a well-vascularized bone.
Positioning the implants according to a curve allows for better distribution of forces in the bone and on the implants.
The placement of three implants slightly offset from each other, in a tripod, ensures better distribution of occlusal forces.Photo
4-Adaptation of the implant to the bone site : The adequacy of the bone site and the implant must be perfect.
5-Length of implants : Short implants, 7 mm and 8.5 mm in length, have lower success rates than implants of a length greater than or equal to 10 mm.
6-Number of implants : The available bone volume is assessed preoperatively by CT scan. The choice of the number of implants will depend on the available bone volume, bone quality and prosthetic and occlusal requirements. The distribution of occlusal forces is carried out according to the number and prosthetic seat of the implants. Ideally, each tooth should be replaced by an implant in the partially edentulous and five implants constitute a minimum for a complete bridge, provided that the implants are adequately distributed on the arch.
7-Inclination of implants : the inclination of the implant sites depends on:
– local bone anatomy : the implant must be completely circumscribed by the bone. A vestibular, palatal or lingual orientation is sometimes necessary to avoid bone concavities.
– the inter-arch relationship : if post-extraction bone resorption is accompanied by significant prognathism in totally edentulous people, lingual positioning of the mandibular implants and vestibular inclination of the maxillary implants aim to compensate for the shift in the bone bases.
8-Implant insertion forces : excessive insertion forces can induce peri-implant bone resorption.
A delicate placement of the implant, allowing good stability, is therefore recommended.
9-Distribution of occlusal forces : surgical and prosthetic imperatives have the ultimate goal of obtaining and maintaining osteointegration. The bone/implant contact surface (quality and quantity of osteointegration) largely determines the capacity to support occlusal forces. For example, four 15 mm long implants have an anchoring surface equivalent to six 10 mm implants.
10-Tissue manipulation : Manipulation of the covering gingival tissues and preparation of the implant site must be delicate and atraumatic.
11-Treatment of dental and maxillary pathologies : Any intervention on the bone leads to a healing and remodeling process. Secondary healing after treatment of maxillary cysts or after dental extraction can result in new bone formation or the formation of fibrous scar tissue.
It is not uncommon to find alveoli filled with fibrous tissue following tooth extraction without complete enucleation of the granulation tissue. These sites are often unsuitable for implantation.
12-Bone healing time and loading conditions: Histological observations on osteointegration have shown that the implant is surrounded by non-mineralized tissue during the initial healing period. The implant is sensitive to pressure and movement during the first weeks of healing. Bone cell differentiation is disrupted by any micromovement of the implant which promotes the creation of a fibrous interface leading to implant failure. The osteointegration time during which any implant loading is prohibited depends on the volume and quality of the bone as well as the condition of the implant surface.
A period of 3 to 4 months for the mandible and 6 months for the maxilla is recommended before loading the implants.
13-Maintenance of osseointegration : The sustainability of osseointegration depends on the health of the peri-implant tissues and the control of occlusal forces. Any inflammation of the peri-implant tissues due to a bacterial infection can cause marginal bone resorption. In the presence of a healthy peri-implant mucosa, a bone loss of approximately 1.5 mm after one year of function and then 0.2 mm per year is normal.
Strict oral hygiene and professional maintenance aim to eliminate pathogenic bacteria that can cause inflammation of the peri-implant mucosa and even partial loss of osteointegration.
4-Success factors in implantology : to be considered a success an implant must meet several criteria:
– Functional (chewing, speaking)
– Psychological (absence of pain and discomfort, aesthetic results)
-Physiological (achievement and maintenance of osteointegration, absence of tissue inflammation).
Failure to meet any of these criteria is considered a failure, even if the other conditions are met.
The most commonly used success criteria are those of Albrektsson et al:
- absence of clinical mobility of an implant
- absence of peri-implant radiolar image.
- vertical bone loss less than 0.2 mm per year after 1 year of implant function. (marginal bone loss must be less than 1.5 mm during the first year of function)
- absence of irreversible signs or symptoms: pain, infection, neuropathy, paresthesia or mandibular canal intrusion.
- The authors recommended that an implant system, to be reliable, should meet the above conditions in 85% of cases at 5 years and 80% of cases after 10 years.
Conclusion: Patients who maintain implant treatment must be healthy to withstand surgical procedures. The scar potential of patients must allow the soft and hard tissues to progress normally to achieve osseointegration. In addition, systemic factors must be able to ensure the health of the implant over time.
OSTEOINTEGRATION
Bibliography:
-Ashok Sethi, Thomas Kaus Clinical Implantology Diagnostics, Surgery and Restorative Techniques for Aesthetic and Functional Harmony Quintessence International
M.DAVARPANAH, H.MARTINEZ, M.KEBIR, JF. TECCUCIANU Manual of clinical implantology Cdp edition
OSTEOINTEGRATION
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