Biomaterials Lecture 2

Question 1

• What is the definition of physical properties?

Answer 1

• Characteristics determined by atomic structure and bonding only.

Question 2

• What are the seven physical properties?

Answer 2

• CTE, elastic modulus (Stiffness), melting temp, optical properties, electrical properties, density, viscosity

Question 3

• What is CTE and what is the formula?

Answer 3

• Change in volume per change in temp α = (ΔL/Lo)/(ΔT)

Question 4

• What are the thermal expansion ranges for ceramics, metals, and polymers?

Answer 4

• Ceramics (1-15 ppm/C)
• Metals (10-30 ppm/C)
• Polymers (30-600)

Question 5

• What are the CTE for tooth structure, porcelain and alloy, PFM, Amalgam anterior and posterior composite

Answer 5

• Tooth structure: 9-11ppm/c
• Porcelain for PFM: 14’’
• Alloys for PFM: 14’’
• Amalgam: 25’’
• Anterior composite: 35-45’’
• Posterior composite: 25-35’’

Question 6

• What is dental amalgam percolation?

Answer 6

• Micro gaps between filling and tooth surface that can allow leakage

Question 7

• *What are some situations related to thermal stress related to elastic modulus and CTE?

Answer 7

• PFM tension and thermal fatique(hot to cold)

Question 8

• What is viscosity? What is it analogous to?

Answer 8

• Resistance to flow, modulus of solid

Question 9

• What is a Newtonian Fluid?

Answer 9

• Shear stress is constant at all shear rates

Question 10

• What is a pseudoplastic fluid?

Answer 10

• A liquid in which shear stress decreases with rate, ketchup in bottle

Question 11

• What is a dilatant fluid?

Answer 11

• Shear stress increases with rate

Question 12

• What is bingham body?

Answer 12

• The critical resistance that must be exceeded to flow

* Will not flow until a certain amount of stress is applied

Question 13

• What is thixotropic?

Answer 13

• Critical resistance must be exceeded to flow

* I.e. bingham body and pseduplastic

Question 14

• What is the ultimate Strength/Fracture Strength/Yield Strength?

Answer 14

• The ultimate strength of a material before it encounters plastic deformations (breaking bonds)

Question 15

• Elastic vs. Plastic deformations?

Answer 15

• Elastic deformations are the stretching of bonds while plastic deformations are the breaking of bonds

Question 16

• Brittle vs. Ductile materials

Answer 16

• Brittle materials such as porcelain or ceramics can only undergo elastic deformations before failure while ductile materials can undergo plastic deformation before failure occurs

Question 17

• What is the equation for stress?

Answer 17

• σ = P/A (load divided by cross-sectional area)

Question 18

• What is the equation for strain?

Answer 18

• ε = ΔL/Lo (total strain is sum of elastic and plastic strain)

Question 19

• Elastic limit = ?

Answer 19

=proportional limit = yield strength

Question 20

• Hookes law equation?

Answer 20

• σ = Eε, (or can be written as E = σ/ε)

Question 21

• What is toughness?

Answer 21

• Area under σ−ε curve, inherent resistance to flaw propagation, ie, fracture)

Question 22

• What is the definition of Hardness?

Answer 22

• Relative resistance to onset of plastic deformation