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Flashcards in Implant Materials Deck (19)
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1
Q

Why does stainless steel in dental implant have high corrosion resistance

A

Low carbon content (<0.03%)

Chromium forms surface oxide

2
Q

What happens if implant is more rigid than bone

A

Corticol bone elasticity modulus 30-40

If implant more rigid than bone, implant does not deform under stress, bone receives more energy —> damage

3
Q

Properties of titanium based alloy for implant

A

Lighter, low density

Good mechanical properties

Good corrosion resistance due to formation of TiO2 solid oxide layer

Less rigid than stainless steel

4
Q

Why were vanadium free alloys developed

A

Toxicity ocncerns, may be linked to dementia

5
Q

a, b, a+B type alloys: which is heat treatable

A

B

A+b to varying extents

6
Q

Rank strength of a, b, a+B alloys

A

Lowest to highest: a, a+b, b

7
Q

a, b, a+B: which has best ductility

A

A

A+b is weldable with risk of some loss of ductility

8
Q

Alloy more highly alpha, how does that affect oxidation resistance

A

Good oxidation resistance

9
Q

Cold formability of b type alloy

A

Excellent cold formability in solution treated condition

10
Q

What is cold working

A

Plastic deformation (permanent) without being damaged. At room temperature, below recrystallisation temperature —> increase hardness and strength

11
Q

a, b, a+B: which has good hot forming qualities

A

A+b

12
Q

What factors promote corrosion ie degradation of metals to oxide, hydroxide, other compounds

A

Water, dissolved o2, proteins, chloride, hydroxide, pH

13
Q

How to make passive metal

A

Immerse in 40% nitric acid

Anodisation

Form titanium oxide which is very stable and inert and very thin

14
Q

What is the purpose of passivation

A

Enhance oxide layer to minimise release of metallic ions

Oxide film prevents further attack on metal

Allows osteointegration because stable and inert

15
Q

Why are ceramic implants coated with zirconium oxide/tricalcium phosphate/etc

A

These are bioceramic. Coat the inert y-tzp to make it more bioactive

16
Q

Pros of ceramic implants vs titanium

A

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

17
Q

Cons of ceramic implants vs titanium

A

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

18
Q

How does y-tzp prevent crack propagation

A

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

19
Q

What is low temperature degradation of y-tzp

A

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