Implant Materials Flashcards
Why does stainless steel in dental implant have high corrosion resistance
Low carbon content (<0.03%)
Chromium forms surface oxide
What happens if implant is more rigid than bone
Corticol bone elasticity modulus 30-40
If implant more rigid than bone, implant does not deform under stress, bone receives more energy —> damage
Properties of titanium based alloy for implant
Lighter, low density
Good mechanical properties
Good corrosion resistance due to formation of TiO2 solid oxide layer
Less rigid than stainless steel
Why were vanadium free alloys developed
Toxicity ocncerns, may be linked to dementia
a, b, a+B type alloys: which is heat treatable
B
A+b to varying extents
Rank strength of a, b, a+B alloys
Lowest to highest: a, a+b, b
a, b, a+B: which has best ductility
A
A+b is weldable with risk of some loss of ductility
Alloy more highly alpha, how does that affect oxidation resistance
Good oxidation resistance
Cold formability of b type alloy
Excellent cold formability in solution treated condition
What is cold working
Plastic deformation (permanent) without being damaged. At room temperature, below recrystallisation temperature —> increase hardness and strength
a, b, a+B: which has good hot forming qualities
A+b
What factors promote corrosion ie degradation of metals to oxide, hydroxide, other compounds
Water, dissolved o2, proteins, chloride, hydroxide, pH
How to make passive metal
Immerse in 40% nitric acid
Anodisation
Form titanium oxide which is very stable and inert and very thin
What is the purpose of passivation
Enhance oxide layer to minimise release of metallic ions
Oxide film prevents further attack on metal
Allows osteointegration because stable and inert
Why are ceramic implants coated with zirconium oxide/tricalcium phosphate/etc
These are bioceramic. Coat the inert y-tzp to make it more bioactive
Pros of ceramic implants vs titanium
Can be coloured, more aesthetic esp if there is bone loss
Improved mechanical properties (mechanical strength and fracture toughness)
High corrosion resistance
Does not cause allergy
Cons of ceramic implants vs titanium
One piece design, must be fully replaced if component fails
Most zirconia implants cannot heal under gums
Brittle, angulation adjustments can cause crack
Can generally only be cemented
How does y-tzp prevent crack propagation
Crack propagation triggers tetragonal to monoclinic transformation in surface region, which is accompanied by substantial increase in volume of about 4.5%.
This induces surface compressive stresses and closes the crack tip, enhancing resistance to further propagation
What is low temperature degradation of y-tzp
Water enters —> stress corrosion, isolated grain transforms from tetragonl to monoclinic and increases in volume. This stresses neighbouring grains, resulting in microcracking, causing further water penetration and crack propagation, destabilising the phase
