Biomaterials Exam - Biomechanics and Biomaterials

Question 1

What does a contact angle measure?

Answer 1

how a liquid interacts with a solid

Question 2

Explain what a low contact angle (approaching 0) would mean.

Answer 2

good wetting because the liquid would rather interact with the surface than itself

Question 3

Explain what a high contact angle (approaching 180) would mean.

Answer 3

poor wetting because the liquid would rather associate with itself than the surface

Question 4

What is the difference between hydrophobic and hydrophilic?

Answer 4

• hydrophobic is “water-fearing” which means that the surface will not interact well with water
• hydrophilic is “water-loving” which means that the surface will interact readily with water

Question 5

True or false: Molecules can have both hydrophilic and hydrophobic components.

Answer 5

true

Question 6

What is a hydrophilic primer/adhesive used for?

Answer 6

Tooth structure is hydrophilic, but composite is hydrophobic so they wouldn’t be able to attach to one another. A hydrophilic primer/adhesive is used which has a hydrophilic portion that adheres to the tooth structure and a hydrophobic portion that adheres to the composite.
This is called surface wetting.

Question 7

When is surface wetting important?

Answer 7

• anytime two different materials come into contact
• impression materials
• adhesives
• bacterial adhesion

Question 8

What affects primary bonding?

Answer 8

chemical and electro-chemical reactions

Question 9

What affects secondary bonding?

Answer 9

processes such as adsorption (onto) and absorption (into)

Question 10

Define corrosion.

Answer 10

the spontaneous destructive oxidation of metals

Question 11

Which are the only metals not to corrode spontaneously in Earth’s normal atmosphere?

Answer 11

gold, platinum, and palladium (noble metals)

Question 12

Differentiate between active and passive corrosion.

Answer 12

• active corrosion - leads to destruction ((gamma)2)

- passive corrosion - produce corrosion film that prevents further corrosion (titanium implants)

Question 13

What are the 4 types of corrosion? Explain each.

Answer 13

• galvanic corrosion - one metal acts as cathode and one metal acts as anode
• structure selective corrosion - each phase in a two-phase mix acts as either a cathode or an anode
• crevice corrosion - surface of the restoration acts as a cathode and crack tip of prep acts as anode
• stress corrosion - stressed restoration acts as anode and unstressed region acts as cathode

Question 14

What does an anode do during corrosion? What does a cathode do during corrosion?

Answer 14

• anode - corroding metal

- cathode - different metal (passive-supplied electrons to solution)

Question 15

How are ceramics affected through chemical dissolution? Give examples.

Answer 15

normally occurs through dissolution of oxides created by the hydrogen bonding effects of water in local areas of high acidity

• examples:
  
  • acids dissolve hydroxyapatite (caries, acid etch for enamel bonding)
  • acidulated fluoride treatments dissolve ceramic crowns and may roughen surface or remove surface stain

Question 16

How are the primary and secondary bonds of polymers affected over time?

Answer 16

• absorption of water into polymers (secondary bonds) causes dimensional changes
• hydrolytic degradation and release of components (primary bonds); water, enzymes (esterases), and bacterial byproducts contribute to wear problem with composites

Question 17

What two molecules are of concern due to their toxicity if amalgam or composite restorations should break down?

Answer 17

• mercury

- bisphenol A (BPA) - concern of cancer (especially in children)

Question 18

What metal ions and compound are of concern when they interact with amalgams/composites due to sensitivity? What breakdown product is of concern?

Answer 18

• mercury, nickel, and monomers (latex) are of concern when they interact with amalgams/composites
• small organic molecules like formaldehyde is a breakdown product of concern

Question 19

On the stress-strain curve, what is represented at the highest point of the linear portion of each curve?

Answer 19

proportional limit (elastic limit) - the highest amount of stress/strain in which the material is still able to return to its original form

Question 20

What is represented by the peak of each curve? Where is this located on the curves for metals? For ceramics? For polymers?

Answer 20

ultimate strength - the largest amount of stress that can be applied before the material fails

• for metals and ceramics, this is the last point on the curve
• for polymers, the curve continues downward from this point

Question 21

Rank the materials (metal, ceramic, and polymer) in order of steepest slope to flattest slope on the stress-strain curve.

Answer 21

steepest: ceramic
metal
flattest: polymer

Question 22

What is represented by the slope of the linear portion of each curve in the stress-strain graph?

Answer 22

elastic modulus - measurement of stiffness of material (higher modulus = more stiff = steeper slope)

Question 23

How is the plastic deformation for a material found on a stress-strain graph?

Answer 23

draw a line from the point of ultimate strength (endpoint for ceramic and metal curves) to the x-axis with the same slope as the slope of the curve; the length of the x-axis between the intersection of the curve and the new line is plastic deformation (which is irreversible)

Question 24

A curve with a very steep linear slope and a short rounded curve represents a material that is: stiff/ductile, stiff/brittle, or flexible/ductile?

Answer 24

stiff/brittle

Question 25

A curve with a very flat slope and a very long curved portion represents a material that is: stiff/ductile, stiff/brittle, or flexible/ductile?

Answer 25

flexible/ductile

Question 26

A curve that has a slightly steep slope and a longer curve represents a material that is: stiff/ductile, stiff/brittle, or flexible/ductile?

Answer 26

stiff/ductile

Question 27

What does modulus measure?

Answer 27

stiffness

Question 28

What is the difference between resilience and toughness?

Answer 28

• resilience - the amount of absorbed energy before deformation occurs
• toughness - the amount of absorbed energy before failure or fracture occurs

Question 29

If a metal is heated, how does its stress-strain curve change?

Answer 29

becomes more similar to the stress-strain curve of a polymer with a flatter slope and longer curve

Question 30

What is the definition of creep?

Answer 30

the deformation over time in response to low constant stress

Question 31

What is the definition of fatigue?

Answer 31

under many cycles, small amounts of deformation accumulate until failure occurs at low stresses

Question 32

What does fracture toughness measure?

Answer 32

measures a material’s resistance to crack propagation; deliberately put a crack in a sample and pull it apart to measure how much stress is needed to propagate crack

Question 33

True or false: Teeth are completely rigid.

Answer 33

FALSE. Teeth are not completely rigid. When teeth are subject to chewing forces (stresses), they undergo subclinical movements (strains).

Question 34

What can the lack of rigidity in teeth lead to?

Answer 34

abfraction

Question 35

What does an abfraction look like clinically?

Answer 35

heavy wear facets near the CEJ

Question 36

What is buccal-lingual stability?

Answer 36

the stability that is created when the buccal and lingual cusps meet each other in the central groove; they stabilize each other

Question 37

What may happen to the buccal-lingual stability during a cavity prep? What could this result in?

Answer 37

• buccal-lingual stability will be weakened if the prep removes the central groove and part of the buccal and lingual cusps because the cusps would no longer be able to support each other
• this could result in cusp fracture