Implant Materials

Question 1

Why does stainless steel in dental implant have high corrosion resistance

Answer 1

Low carbon content (<0.03%)

Chromium forms surface oxide

Question 2

What happens if implant is more rigid than bone

Answer 2

Corticol bone elasticity modulus 30-40

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

Question 3

Properties of titanium based alloy for implant

Answer 3

Lighter, low density

Good mechanical properties

Good corrosion resistance due to formation of TiO2 solid oxide layer

Less rigid than stainless steel

Question 4

Why were vanadium free alloys developed

Answer 4

Toxicity ocncerns, may be linked to dementia

Question 5

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

Answer 5

B

A+b to varying extents

Question 6

Rank strength of a, b, a+B alloys

Answer 6

Lowest to highest: a, a+b, b

Question 7

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

Answer 7

A

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

Question 8

Alloy more highly alpha, how does that affect oxidation resistance

Answer 8

Good oxidation resistance

Question 9

Cold formability of b type alloy

Answer 9

Excellent cold formability in solution treated condition

Question 10

What is cold working

Answer 10

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

Question 11

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

Answer 11

A+b

Question 12

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

Answer 12

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

Question 13

How to make passive metal

Answer 13

Immerse in 40% nitric acid

Anodisation

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

Question 14

What is the purpose of passivation

Answer 14

Enhance oxide layer to minimise release of metallic ions

Oxide film prevents further attack on metal

Allows osteointegration because stable and inert

Question 15

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

Answer 15

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

Question 16

Pros of ceramic implants vs titanium

Answer 16

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

Question 17

Cons of ceramic implants vs titanium

Answer 17

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

Question 18

How does y-tzp prevent crack propagation

Answer 18

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

Question 19

What is low temperature degradation of y-tzp

Answer 19

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