Test One: Polymers And Polymerization

Question 0

What elements are typically present in polymers?

Answer 0

C, H, O, N, P

Question 1

What are the three main types of bonding present in

polymer systems?

Answer 1

Intra and interchain bonding(covalent and hydrogen bonds) and mechanical bonding

Question 2

Diff between homopolymer and copolymer

Answer 2

Homopolymer uses only one monomer while copolymer uses multiple monomers

Question 3

What are the three different types of polymer chain architecture?

Answer 3

• Linear has poor physical properties
• Branched are stronger and longer branches can resist temperature effects
• Cross-linked has the best resistance to deformation, solvents, and heat

Question 4

What are the two main types of polymerization used in dentistry?

Answer 4

1-condensation where two components react to yield a product that is often volatile. Ie: pvs releases H2 as a byproduct
2-addition where the two components react without any byproduct. Ie: composite setting, glass ionomers, and some pvs

Question 5

Free radical

Answer 5

Compound with unpaired electron

Question 6

Four steps of free-radical polymerization

Answer 6

1-activation of the radical
2-initiation of polymerization
3-propagation of polymer chain
4-termination of chain growth

Question 7

What is the glass transition/gel point of a polymer?

Answer 7

At a certain stage during polymerization, the developing matrix reaches a sufficient stiffness (modulus) that it starts to take on the properties of a solid. This stage in development is termed the “gel point”.

Question 8

What are the differences between the degree of polymerization and the extent of monomer conversion of a polymer?

Answer 8

Degree of Polymerization: Refers to the average NUMBER of monomer units which have been incorporated into a polymer chain.
Extent of Monomer Conversion: Refers to the amount of MONOMER originally available for reaction which actually took part in the polymerization reaction: monomer CONVERTING into polymer.

Question 9

three clinical situations where a polymer exotherm can be of clinical relevance

Answer 9

heating of the tooth while curing directly in place, denture reliners, and temporary crown and bridge resins

Question 10

intrapulpal temperature increase which is correlated with irreversible pulpitis.

Answer 10

Increase of pulp temp more than 5.5 degrees Celsius

Question 11

What are the factors influencing polymerization shrinkage?

Answer 11

Inter carbon bond length actually increases, but that is overcome by the decrease in intermolecular distance

Question 12

What are the effects of increased chain length and pendent group length on the properties of a polymer?

Answer 12

Increased chain length increases physical state to solid, melting temp, strength, and stiffness.
Longer pendent groups (branches) decreases chance for crystal formation, lowers softening temp, and increases flexibility

Question 13

two methods of polymer crosslinking

Answer 13

During the polymerization (composites and denture base materials) or after initial process has occurred (rubber base, the vinyl impression materials, and the polyethers)

Question 14

What is the type of molecule necessary to produce crosslinking between polymer chains?

Answer 14

Multifunctional molecule needed at a functional end-where there is a group that will react during polymerization

Question 15

What are the property changes in polymers seen with increased crosslinking?

Answer 15

Decrease flexibility. Increase strength, hardness, impact resistance, solvent resistance, and softening temp

Question 16

How do fluids affect polymers?

Answer 16

Fluids can be absorbed by polymers and cause swelling but can also cause degradation like with composites before being cured

Question 17

How do polar groups affect monomers?

Answer 17

More polar groups increases potential for water absorption causing stickiness like with uncured resins

Question 18

Diff between thermoplastic and thermoset polymers

Answer 18

Thermoplastic materials soften when heated and can be molded. When it cools it retains this deformity.
Thermoset materials have higher cross linking and does not deform with increased temp

Question 19

Why do polymers have a large coefficient of thermal expansion?

Answer 19

Because of the random nature of the polymer chain orientation, we tend to see uniform expansion and contraction of dental polymers when they are heated or cooled because they are isotropic materials.

Question 20

Anisotropic

Answer 20

Expansion or contraction in one direction

Question 21

Plasticizers

Answer 21

function by interfering with inter-chain HYDROGEN bonding and inter-chain mechanical entanglement, thus INCREASING the ability of one chain to move with respect to another, ie: Phthalates and absorbed fluids from saliva

Question 22

What are the problems associated with Phthalates in tissue conditioners?

Answer 22

Loss of the plasticizer to leaching results in the tissue condition becoming hard and not providing the cushioning effect it is intended to have. They have also been known to have significant biological action on tissues: elicit estrogen-like reactions.