Lecture 5 Flashcards
(25 cards)
Which ions have been reported to induce angiogenic activity in biological conditions?
Silicon
What are the conditions for bioactivity?
bonding between tissue and material (chemical or biological)
What are some features of non-oxide ceramics? How do they compare to alumina and zirconia?
Are there any limitations?
silicon nitride = biocompatible
supports bone growth on elongated grains
crack deflection
better mech properties than alumina
better stability than zirconia
very expensive and hard to machine
What are the benefits and limitations of porosity? What is the minimum size?
allows for better tissue integration but decreases strength
min size is 100um
How does bone bonding onto HA work?
saturates with Ca and potassium to form bone-like layer between HA and host bone
Compare HA and beta TCP - what is the combination ratio?
HA = insoluble
beta-TCP = resorbable, good in vivo but mechanically unstable
GOOD to combine - 60 HA 40 TCP
What are some features of calcium phosphate ceramics?
Group of ceramics
HA and beta TCP
not good for load bearing
highly dissolvable = less strong
What are some features of bioactive glass?
forms oxides
quenching = amorphous forming = brittle
direct bonding to bone
can be used to composite with polymers
Do ceramics have a high or low young’s modulus? How does this compare with cortical bone?
High - ~20x cortical bone
What is zirconia-toughened alumina (ZTA)?
10-20% volume
What does stress do to material? How does water affect it?
crack propagation
inducces phase transformation
makes it toucher
water can trigger degradation too
What are the 2 main phases of zirconia? How can they be both stable at room temp?
monoclinic = stable @ room temp
tetragonal = stable @ high temps (stabilised with yttria)
What are some features of zirconia? Bioinert or bioactive?
BIOINERT
stronger and tougher than alumina
What are some features of alumina? Bioinert or bioactive?
BIOINERT
doesn’t leach anything
thinnest tissue
good wear resistance
can be strengthened with zirconia
What materials are not as strong but bioactive?
Calcium phosphates, bioactive glasses and calcium silicates
What materials are strong but bioinert?
Zirconia and alumina
What types of dental implants use ceramics?
Dental crowns = alumina and zirconia
Bone defect fillers = granules of bioactive glass
What ceramic is used for ball-socket hip joints?
Alumina
When would ceramics be used?
High strength high wear resistance joints
bioactive coatings
dental implants
minimal loading profile
What are some properties of ceramics?
brittle
strain to failure < 0.5%
corrosion and wear resistance
bioinert and bioactive
What are the different types of crystallinity?
purely, semi and amorphous?
What are ceramics?
inorganic compounds with ionic and covalently bonded attoms
What ion would you add to existing calcium phosphate ceramic material to achieve better vascularization?
copper
What are the 6 stages of carbonated HA formation on the surface of bioactive glasses?
Rapid ion exchange
increase in pH which attacks the silicon network
Condensation and polymerisation of the surface
Interaction between calcium and potassium ions
Glass dissolving and ions crystalising
Bone forming