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ContentsIntroductionHistorical reviewDefinitionBone density classificationBiological considerations forosseointegrationϒ Bone implant interfaceϒ Bone remodelingϒ Foreign body reaction
…ϒ Bone to implant interfaceϒ Mechanism of osseointegrationϒ Ultrastructure in osseointegrationϒ Destruction of osseointegrationϒ Soft tissue implant interfaceϒ Peri-implant membraneϒ Disease activity in peri-implant tissueϒ Neuromuscular system as it relates to the implant
…. Factors influencing osseointegration Osseointegration vs biointegration Success criteria for osseointegrated implants Clinical applications of osseointegration Future of osseointegration Summary & Conclusion References
IntroductionThe ideal goal of modern dentistry is to restore thepatient to normal contour, function………..Implant dentistry is unique because of its ability toachieve this goal regardless of the stomatognathicsystem.
….. The primary function of an implant is to act as an abutment for prosthetic device. The present surge in the use of implants was initiated by Branemark (1952)……….. Described the relationship between titanium and bone for which they coined the term osseointegration.
DefinitionThe word osseointegration consists of “OS”the Latin word for bone and “integration”derived from Latin word meaning the state ofbeing combined into a complete whole.Osseointegration is defined as a direct boneanchorage to an implant body which canprovide a foundation to support a prosthesis.ϒ “Direct structural and functional connection between ordered, living bone and surface of a load carrying implant ”.
….. American Academy of Implant Dentistry defined it as “contact established without interposition of non bone tissue between normal remodeled bone and on implant entailing a sustained transfer and distribution of load from the implant to and within bone tissue”.
Historical Reviewϒ The concept of osseointegration was developed and the term was coined by Dr. Per-Ingvar Branemark,ϒ Professor at the institute for Applied Biotechnology, University of Goteborg, Sweden.
Initial concept of osseointegration stemmedfrom vital microscopic studies ofmicrocirculation in bone repair mechanisms.Titanium chamber was surgically insertedinto the tibia of of a rabbit.It was considered the best material forartificial tooth root replacement.
….. Many studies followed involving titanium implants being placed into jaws of dogs. Direct bone anchorage has been shown to be very strong. A force of over 100kg was applied to dislodge an implant. Based on such a consequence the foundation for Osseo integration and the Branemark implant system was established in 1952.
Studies on humans wereconducted by means of animplant optical titanium chamberin a twin pedicle skin tube on theinside of the left upper arm ofvolunteers.Tissue reactions were studied inlong term experiments.All this lead to the treatment offirst edentulous patient in 1965.
History of Branemark system categorized inthree stagesϒ Early stage (1965-1968)ϒ Developmental stage (1968-1971)ϒ Production stage (1971 – present)
Bone density classification (Misch)
Biological Considerations for OsseointegrationBone implant interfaceϒ When compared to compact bone spongy bone has less density and hardness is not a stable base for primary fixture fixation.ϒ In the mandible the spongy bone is more dense than maxilla.ϒ With primary fixation in compact bone, osseointegration in the maxilla require a longer healing period.
Bone remodeling Osseointegration requires new bone formation around the fixture. A process resulting from remodeling within bone tissue. Osteoblastic and osteoclastic activity helps maintain blood calcium without change in quantity of bone.
….. To maintain a constant level of bone remodeling there should be proper local stimulation, crucial levels of thyroid hormone, calcitonin and vitamin D. Occlusion or occlusal force stimulus are both important to optimal bone remodeling.
Foreign body reaction Organization or an antigen antibody reaction occurs when a foreign body is present in the body. This reaction occurs in the presence of a protein but with implant materials devoid of proteins no antigen antibody reaction.
….. When titanium is used no foreign body reaction are seen. The implant material is an important factor for Osseo integration to occur.
Bone to implant interface Two basic theories ϒ Fibro-osseous integration by Linkow, James & Weis ϒ Osseointegration by Branemark ϒ Meffert divided osseointegration Adaptive osseointegration Biointegration
American Academy of implant dentistry definedfibrous integration as tissue to implant contact withhealthy dense collagenous tissue between theimplant and bone.
….. The fibers are arranged irregularly, parallel to the implant body, when forces are applied they are not transmitted through the fibers. So no bone remodeling expected in fibro- integration.
Ichida & Caputo (1986) used photo-elastic analysis tostudy the stress concentration along the implantthreads and sharp edges when a connective tissue likestructure was included in the analysis.Even stress distribution was seen when there wasdirect contact with a bone like structure.They concluded that implants with fibro-osseousintegration had a tendency of increased mobility.
A direct bone implant interface occurs when animplant is allowed to heal in bone undisturbed.Main factors affecting osseointegration includeϒ Implant oxide layer contamination.ϒ Poor temperature control during drilling.
……A minimum of 3 month healing in mandible and 6months in maxilla is necessary before load isapplied.If osseointegration does not occur or a fibrousconnective tissue forms around the implantorganization process continues.
Biological process of implant osseointegrationThe healing process of implantsystem is similar to primarybone healing.Titanium dental implants showthree stages of healing.
….. OSTEOPHYLLIC STAGE ϒ When a implant is placed into the cancellous marrow space blood is initially present between implant and bone. ϒ Only a small amount of bone is in contact with the implant surface; the rest is exposed to extracellular fluids. ϒ Generalized inflammatory response to the surgical insult.
…..ϒ By the end of first week, inflammatory cells are responding to foreign antigens.ϒ Vascular ingrowth from the surrounding vital tissues begins by third day.ϒ A mature vascular network forms by 3 weeks.ϒ Ossification also begins during the first week and the initial response observed in the migration of osteoblasts from the trabacular bone which can be due to the release of BMP’s.ϒ The osteophyllic phase lasts about 1 month.
OSTEOCONDUCTIVE PHASEϒOnce they reach the implant, the bone cells spreadalong the metal surface laying down osteoid.ϒInitially this is an immature connective tissuematrix and bone deposited is a thin layer of wovenbone called foot plate.
….. ϒ Fibro-cartilaginous callus is eventually remodeled into bone callus. ϒ This process occurs during the next 3 months ϒ Four months after implant placement the maximum surface area is covered by bone.
OSTEOADAPTIVE PHASEϒ The final phase begins approximately 4 months after implant placement.ϒ Once loaded implants do not gain or loose bone contact but the foot plates thicken in response and some reorientation of the vascular pattern may be seen.
….. ϒ Grafted bone integrates to a higher degree than the natural host bone to the implant. ϒ To achieve optimal results an osseointegration period of 4 months is recommended for implants in graft bone and 4 to 8 months for implant placed in normal bone.
Ultrastructure in osseointegrationϒ Osseointegrated fixtures under occlusal loads are surrounded by cortical and spongy bone.ϒ The cortical bone to fixture surface interface has canaliculi participating in electrolyte transportation near oxide layer.
….Osseointegration in spongy bone occurs asbone trabaculae approaches the fixture andcome into intimate contact with oxide layer.Ground substance forms and fills spacesbetween bone trabeculae this fuses withoxide layer.
Destruction of OsseointegrationThe main contributing factor to bone resorption arelocal inflammation from plaque and trauma fromocclusionϒ Direct action of plaque products induces formation of osteoclasts.ϒ Plaque products at directly on bone destroying it through a non cellular mechanism.ϒ Stimulate gingival cells, which release mediators for osteoclast formation.
ϒ Plaque causes gingival cells to release agents which act as cofactors in bone resorption and which destroy bone by direct chemical action without osteoclasts.Bone resorption can be caused by prematureloading.12 months following fixture insertion verticalbone loss is observed due to traumaticsurgical procedure.ϒ Vertical bone loss approximately 1 to 1.5 mm in first yearϒ Marginal bone loss is 0.05 to 0.1 mm in first yearϒ These measurements can be used a reference and in a bone loss condition should be evaluated to minimize failure.
Peri-implant membraneϒ With the osseointegrated implant the abutment to fixture junction corresponds to cementoenamel junction present in natural dentition.ϒ Peri-implant membrane is similar to that present in natural dentition, consisting of peri- implant free gingiva.
….The sulcular epithelium forms the peri-implant gingival crevice and junctionalepithelium attaches to the abutment forminga cuff.With a tight cuff and filamentous attachmenta membrane is sealed tightly andfunctionally to the abutment surface.
Disease activity in peri-implant tissueThe fibrous connective tissue capsuleformed around an implant generally has lowdifferentiating capabilities such that it alsohas less resistance against bacterial bi-products and does not respond well toocclusal stimulation.An osseointegrated implant has periosteumdirectly covering the neck of the fixture.Which may act as a barrier againstinflammation.
….Although the abutment to junctional epitheliumattachment is not strong, a connective tissue bandis tightly attached to the abutment surface and actsas resistant barrier.
The neuromuscular system as it relates to the osseointegrated implantA fixture site does not have periodontal ligament buthas nerve endings located near the fixture, sensingpain and temperature.Patients with osseointegrated implants have a highthreshold and low sensitivity for discriminatingthickness.
….. As the periodontal ligament is lost the fixture remains with reduce amount of receptors. Impulses from the fixture sites are transmitted through motor nucleus of trigeminal nerve.
Osseointegration Vs BiointegrationdePutter et al in 1985 observed that there are two waysof implant anchorageMechanical and Bioactive
Mechanical retentionmetallic substrate system such as titaniumor titanium alloy.The retention is based on undercut formssuch as vents, slots, dimples, screws etc.,Direct contact between the dioxide layer onthe titanium and bone with no chemicalbonding.
Bioactive retentionBioactivityϒ characteristic of an implant material that allows attachment to living tissues, whereas a non bioactive material would form a loosely adherent layer of fibrous tissue at the implant interfaceBioactive retention is achieved withbioactive materials such as hydroxyapatite(HA), which bond directly to bone
Plasma spraying & ion sputter coatingTwo techniques used to coat metallic implantswith HA.
Plasma sprayingInvolves heating the HA by a plasma flameat a temperature of approximately 15,000° Cto 20,000°C.The HA is then propelled onto the implantbody in an inert environment like argon, to athickness of 50 to 100 μm.
Ion-sputter coatingProcess by which a thin, dense layer of HA can becoated onto an implant substrate.Directing an ion beam at a solid-phase HA block,Vaporising it to create a plasma and thenrecondensing this plasma on the implant.Bone formation and maturation occurs at a fasterrate in the initial phases on HA coated implantsthan on non-coated implants
Advantages of increased surface roughness of Cp Ti implant Increased surface area of the implant adjacent to bone. Improved cell attachment to the implant surface. Increased bone present at the implant surface. Increased biomechanical interactions of the implant with bone. Promoted inflammation of the periimplant area.
Clinical advantages of TPS or HA coatings Increased surface area Increased roughness for initial stability Stronger bone-to- implant interfaceAdditional advantages of HA over TPS include the following ϒ Faster healing bone interface ϒ Increased gap healing between bone and HA ϒ Stronger interface than TPS
Disadvantages of CoatingsFlaking, cracking, or scaling upon insertionIncreased plaque retention when placed above thebone.Increased bacteria adhesion and acts as a nidus forinfectionComplications of treating the failing implantsIncreased cost
Factors influencing Osseointegrationϒ Biomaterial for dental implantϒ Surface composition and structureϒ Implant designϒ Heatϒ Contaminationϒ Primary stability or initial stabilityϒ Bone qualityϒ Epithelial down growthϒ Loading
1.Biomaterial for dental implantImplants must not induce a host immuneresponse Titanium and certain calcium-phosphate ceramics are biocompatibleand do not stimulate a foreign bodyrejection reaction.
2. Surface composition and structureϒ It is thought that cp Ti owes its ability to form an osseointegrated interface to the tough and relatively inert oxide layer, which forms very rapidly on its surface.ϒ This surface has been described as osseoconductive, that is, conducive to bone formationϒ Other substrates also have this property and may also stimulate bone formation, a property known as osseoinduction
3. Implant DesignThe vast majority of commercially availableimplants claiming osseointegration statusare cylindrical in shape.Their design may be threaded or else lacksimilar microscopic retentive/stabilizationaspects
4. HeatHeating of bone to a temperature inexcess of 47°C during implant surgery canresult in cell death and denaturation ofcollagen.As a result, osseointegration may notoccur, instead the implant becomessurrounded by a fibrous capsule and theshear strength of the implant-hostinterface is significantly reduced.
5. Contaminationϒ Contamination of the implant site by organic and inorganic debris can prejudice the achievement of osseointegration.ϒ Material such as necrotic tissue, bacteria, chemical reagents and debris from drills can all be harmful in this respect.
6. Primary stability or Initial stabilityϒ It is known that where an implant fits tightly into its osteotomy site then osseointegration is more likely to occur.ϒ This is often referred to as primary stability, and where an implant body has this attribute when first placed failure is less probable.ϒ This property is related to the quality of fit of the implant, its shape, and bone morphology and density.
7. Bone qualityIt is a function of bone density, anatomy and volume, and has been described using a number of indices. ϒ The classifications of Lekholm & Zarb and of Cawood & Howell are widely used to describe bone quality and quantity. ϒ The former relates to the thickness and density of cortical and Cancellous bone, ϒ and the latter to the amount of bone resorption. ϒ Bone volume does not by itself influence osseointegration, but is an important determinant of implant placement
8. Epithelial down growthϒ Early implant designs were often associated with down growth of oral epithelium, which eventually exteriorized the device.ϒ When the newer generation of cp Ti devices was introduced great care was taken to prevent this by initially covering the implant body with oral mucosa while osseointegration occurred.ϒ The implant body was then exposed and a superstructure added, since it was known that the osseointegrated interface was resistant to epithelial down growth.
9. Loading schemesϒ Delayed loading: The prosthesis is attached at the second procedure after a conventional healing period of 3 to 6 months 8, 23.ϒ Early loading: The prosthesis is attached during a second procedure, earlier than the conventional healing period of 3 to 6 months. Time of loading should be stated in days to weeks 8, 23.ϒ Immediate / Direct loading: The prosthesis is attached to the implants the same day the implants are placed.
Success criteria for Osseo integrated Implantsϒ Durabilityϒ Bone lossϒ Gingival healthϒ Pocket depthϒ Effect of adjacent teethϒ Functionsϒ Estheticsϒ Presence of infectionϒ Intrusion on the mandibular canalϒ Patient emotional and psychological attitude
Revised criteria for implant successϒ Individual unattached implant is immobile when tested clinically.ϒ No evidence of peri implant radiolucency is present as assessed on an undistorted radiograph.ϒ Mean vertical bone loss is less than 0.2 mm after 1st year of service.ϒ No persistent pain, discomfort or infection.ϒ A success rate of 85% at the end of a 5-year observation period and 80% at the end of a 10-year period are minimum levels of success.
Clinical applications of osseointegration
Futuristic concepts of Osseointegration OSSEOPERCEPTION ϒ The interaction between the osseointegrated fixture bone tissue, receptor systems and nervous system has to be studied. “Owing to the nature of osseointegration it is not easy to dissect the system of anchorage from the clinical level downto the molecular level or even the real interface which is still largely a mystery”
Mechanism of Osseointegration Blood clot (between fixture & bone) Clot transformed by phagocytic cell (1st to 3rd day) Procallus formation (containing fibroblasts & phagocytes) Procallus becomes dense connective tissue (Differentiation of osteoblasts & fibroblasts) Callus (Osteoblasts on the fixture) Fibro cartilagenous callus (between fixture & bone) Bone callus (Penetrates & matures)Prosthesis attached to the fixtures stimulating bone remodeling
It is because of the attention to training, research & clinicalstudies that osseointegration has now become an accepted part ofthe treatment regime in many countries world wide and no longerregarded as the last resort when all else has failed but often as a treatment of choice
Referencesϒ Hobo, Ichida, Garcia “Osseointegration and occlusal rehabilitation” Quintessence Publishing.ϒ Jan Lindhe “Clinical periodontology and implant dentistry” 4th edition, Blackwell Publishing.ϒ Elaine McClarence “Branemark and the development of osseointegration” Quintessence publicationϒ Carl E. Misch “Implant dentistry” 2nd edition, Mosby.ϒ Hubertus Spiekermann “Color atlas of dental medicine implantology” Theime Publishers.
….. ϒ Charles M.Weis “Principles and practice of implant dentistry” Mosby. ϒ Charles Babbush “Dental implants the art and science” W.B. Saunders. ϒ Per Ingvar Branemark “Osseointegration and its experimental background” JPD 1983 Vol. 50, 399-410. ϒ Hanson, Alberktson “Structural aspects of the interface between tissue and titanium implants” JPD 1983 vol. 50, 108-113.
….ϒ T. Alberktson “Osseointegrated dental implants” DCNA Vol. 30, Jan 1986, 151-189.ϒ Richard Palmer “Introduction to dental implants” BDJ, Vol. 187, 1999, 127-132.ϒ Geroge A. Zarb “Osseointegrated dental implants: Preliminary report on a replication study”. JPD 1983, Vol 50, 271-276.ϒ Bergman “Evaluation of the results of treatment with osseointegrated implants by the Swedish National Board of Health and Welfare”. JPD 1983, vol. 50, 114-116.