osseointegration and mineralised tissue Flashcards
(28 cards)
what uses are there for implants?
BONE DEFECTS
- Dental Surgery
- prosthetic implants.
- Orthopaedic Surgery
- replacement of worn / diseased joints.
- Craniofacial reconstruction
- e.g. tumour surgery.
what is osseointegration?
Success & reliability of biomaterials, based on adaptation & interaction of healthy bone to the implant surface
what types of biomaterials are used as dental implants?
- Metals Titanium
- Pure and alloy
- Zirconium
- Stainless steel
- Cobalt-chromium alloy
- Hydroxyapatite ceramic materials
- Hydroxyapatite-coated materials
- Glass ionomer
what are the mechanisms of osseointegration?
- Forcible insertion of implant
- Trauma
- Re-establishment of normal tissue structure and function
- As other tissues, occurs via multiple overlapping phases
- Soft tissue repair
- Additional mineralisation processes also occur
- Vasoconstriction, haemostasis & inflammation occur as in soft tissues
what occurs after implant insertion?
- Blood vessel injury increases blood release.
- vasoconstriction
- protein adsorption
after implant insertion what are the consequences of blood vessel injury?
- increases blood release
- coagulation - formation of a fibrin clot
- rich in
- fibronectin, hyaluronan, vitronectin, thrombospondin.
- Functions
- Reservoir of pro-inflammatory cytokines / growth factors.
- e.g. PDGF, EGF, TNF-a, TGF-b.
- Provisional matrix for inflammatory cell migration / activation
- rich in
what occurs during the inflammatory phase after implant insertion?
- Initial cell recruitment to the implant site
- predominantly neutrophils, monocytes / macrophages.
- Neutrophil degranulation / phagocytosis.
- M1 subtype macrophages
release:
- Proinflammatory cytokines - IL-1, TNF-a.
- Enzymes (MMPs, myeloperoxidase, lysozyme).
- Attack bacteria
- Reactive oxygen species (ROS) :
- Superoxide radicals -
- O2
- Hydrogen peroxide -
- H2O2.
- Hydroxyl radicals -
- .OH.
- Superoxide radicals -
if the inflammatory phase is an acute response, what occurs after?
migration / proliferation of undifferentiated mesenchymal stem cells induced towards implant surface (osteoinduction phase).
- Aims to increase numbers of undifferentiated mesenchymal stem cells at the implant site
what occurs during the granulation phase after implant insertion?
- inflammatory infiltration ceases
- replaced with M2 macrophages
- role in removal of tissue debris
- fibrin clot changes in composition
- degraded into granulation tissue
- rich in hyaluronan
- Granulation tissue acts as provisional matrix to allow mesenchymal stem cells to differentiate into mature osteoblasts
- Osteoconduction
- stem cells and M2 macrophages produce growth factors to regulate the healing process
- VEGF, bFGF, TGF-ßs, BMPs, PDGF, IGF.
- angiogenesis takes place
- Endothelial cell migration, proliferation & differentiation.
- Formation of vascular loops & capillary network.
what occurs during osteoinduction?
Migration / proliferation of bone marrow derived MSCs
- Enhanced by TGF-ßs, BMPs, PDGF, VEGF
- Also stimulate stem cells to proliferate at the implant site
what occurs during osteoconduction?
Induced by BMPs, TGF-ß, VEGF
- Also induce differentiation of MSCs into osteoprogenitor cells
- = Osteoconduction
Inhibited by PDGF & bFGF
- RUNX2
- Expression required to form mature osteoblast
what are phenotypic markers of osteoblasts?
Alkaline phosphatase
Type I collagen
Osteocalcin
Osteonectin
Osteopontin
what occurs during the tissue remodelling phase after implant insertion?
- mature osteoblasts synthesise ECM - osteoid
- rich in proteoglycans and hyaluronan
- lacks type 1 collagen
- added later
- matrix mediated mineralisation occurs - HAP formation
- formation of disorganised trabecular woven bone
- weak, high porosity
- matures into lamellar bone
- more mineralised
- osteoadaptation occurs
- bone resorption and remodelling by osteoblastsandclasts
- due to mechanical loading
how does osteoclast resorption occur?
- Migration to resorption site & attachment to bone.
- Formation of sealing zone & ruffled border.
- HAP dissolution.
- ECM degradation & removal from resorption pit.
- Apoptosis or return to non-resorbing state.
- HAP dissolution by HCl secretion through ruffled border to the resorption pit.
- Carbonic anhydrase II (CAII) activity.
- Low pH(pH=4)duetoH+ &Cl- pumps.
- ECM degradation by cysteine proteinases (especially cathepsin K) & MMPs (MMP-9, -14).
- Also TRAP & ROS.
what is osseointegration?
what occurs
what types are there?
- Mature osteoblasts formed during osteoconduction
- Begin to form osteoid
- ECM
- Can occur adjacent to implant surface/directly attached/towards implant
- Osteoid fills space between implant and adjacent bone tissue
- Becomes mineralised by matrix mediated mineralisation later
- Begin to form osteoid
- contant osseointegration
- distance osseointegration
what is distance osseointegration?
what occurs?
Distance osseointegration
- Bone formation from the adjacent tissue
- Osteoblasts are not attached
- Form bone towards the implant surface
- Osteoblasts can then :
- Undergo apoptosis
- Become embedded in bone as osteocytes
- Osteoclasts migrate into site by osteoadaptation
- Work with osteoblasts to have best fit to bone around implant surface
what is contact osseointegration?
what occurs?
- Osteoblasts are attached to the implant
- osteoid (ECM) is formed adjacent to the implant surface
- mineralised later by MMM
how is soft tissue remodelled after implant insertion?
- restoration of the dental gingival junction
- fibroblast migration and proliferation
- growth factors : PDGF, TGF-b, EGF, FGF
- ECM synthesis
- collagen type I
- proteoglycans, hyaluronan, elastin, fibronectin
- re-epithelialisation
- de-differentiation
- migration
- proliferation
- differentiation/stratification
- ecm synthesis
what lies between bone and the implant surface
Bone NEVER in direct contact with implant surface !!!
Cement line (CL).
which material has best osseointegration and mechanical properties?
and why?
- titanium
- has a narrower cement line
- allows mineralised layers to be closer to the implant surface
-> increased osseointegration and mechanical properties
what are the properties of the cement line?
ECM layer identified at bone-implant interface.
- Rich in CS-decorin, CS-biglycan, hyaluronan.
- Collagen-free
- INHIBIT MINERALISATION. - no gap zones
what changes are there to the structure of the layers at the bone-implant interface as you move away from the implant surface?
As you move from implant surface
- Increase in type I collagen - more structured
- therefore more mineralisation
why is titanium used as an implant material?
- is good
- Biocompatible,
- low corrosion / toxicity,
- good mechanical properties.
- cement line is narrower
why is the cement line narrower with titanium as the implant material?
- ROS produced by neutrophils and macrophages during the inflammatory phase
- react with titanium oxide surface
- Result in formation of titanium peroxy gel (TiOOH)
- ROS in TiOOH elps degrade ECM components of cement layer
- proteoglycan and hyaluronan
- Therefore mineralised tissues are closer to the implant surface
