osseointegration and mineralised tissue Flashcards
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
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
