Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

DENT 221 > Chapter 6 > Flashcards

Chapter 6 Flashcards

1
Q

Define backbone

A

The main chain of a polymer.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

define block copolymer

A

Polymer made of two or more monomer species and identical monomer units (“mers”) occurring in relatively long sequences along the main polymer chain. See also random copolymer and graft or branched copolymer.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

define chain transfer

A

Stage of polymerization in which the free radical on the growing end of one polymer chain is transferred to either a monomer or a second polymer chain. This terminates chain growth in the first chain and initiates chain growth in the monomer or second polymer chain

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

define curing

A

Chemical reaction in which low-molecular-weight monomers (or small polymers) are con- verted into higher-molecular-weight materials to attain desired properties

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

define crosslink

A

A difunctional or multifunctional monomer that forms a link between two polymer chains. Crosslinked polymers have many such crosslinks between neighboring chains such that a three- dimensional interconnected polymer network results.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

define denture base

A

The part of the denture that rests on the soft tissues overlying the maxillary and mandibular jawbone and that anchors the artificial teeth.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

define elastic recovery

A

Reduction or elimination of elastic strain (deformation per unit length) when an applied force is removed; elastic solids recover elastic strain immediately on removal of the applied force, whereas viscoelastic materials recover elastic strain over time. The greater the viscous nature of an elastomer, the more incomplete the recovery.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

define final set

A

Stage at which the curing process is complete.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

define free radical

A

An atom or group of atoms (R) with an unpaired electron (•). R•-producing reactions
that initiate and propagate polymerization and eventually lead to a final set.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

define glass transition temp

A

(Tg)—The temperature at which macromolecule molecular motion begins to force the polymer chains apart. Thus, polymeric materials soften when heated above this temperature.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

define graft or branched copolymer

A

Polymer in which a sequence of one type of mer unit is attached as a graft (branched) onto the backbone of a second type of mer unit.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

define initial set of a polymer

A

The stage of polymerization during which the polymer retains its shape.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

describe induction

A

Activation of free radicals, which in turn initiates growing polymer chains.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

define macromolecule

A

A large high-molecular-weight compound usually consisting of repeating units in a chainlike configuration

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

define “mer”

A

The term used to designate the repeating unit or units in a polymer chain; thus, mers are the “links” in the chain.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

define methacrylate polymers

A

Type of macromolecule derived from monomers with the chemical structure CH2=C(CH3)–COOR.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

define monomer

A

Chemical compound that is capable of reacting to form a polymer.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

define plastic flow of a polymer

A

Irreversible deformation that occurs when polymer chains slide over
one another and become relocated within the material.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

define polymer

A

Chemical compound consisting of a large organic molecule (“macromolecule”) formed by the union of many smaller repeating units (mers).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

define polymerization

A

Chemical reaction in which monomers of a low molecular weight are converted into chains of polymers with a high molecular weight.

Monomer+Monomer+Monomer⎯⎯→−Mer−Mer−Mer−

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

what is PMMA and MMA?

A

Poly(methylmethacrylate), a commonly used acrylic thermoplastic (or thermoset?) dental material derived by polymerization of the monomer, methylmethacrylate (MMA).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

what is propagation?

A

Stage of polymerization during which polymer chains continue to grow to high molecu- lar weights.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

define random copolymer

A

Polymer made of two or more monomer species but with no sequential order between the mer units along the polymer chain. See also block copolymer and graft or branched copolymer.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

define resin or synthetic resin

A

Blend of monomers and/or macromolecules with other components, which form a material with a set of useful properties.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

define resin-based composite

A

A highly crosslinked resin reinforced by a dispersion of amorphous silica, glass, crystalline, or organic resin filler particles and/or fibers bonded to the polymer matrix by a coupling agent.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

define setting of a polymer

A

Extent to which polymerization has progressed.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

define thermoplastic polymer

A

Macromolecule material made of linear and/or branched chains that softens when heated above the glass-transition temperature (Tg), at which molecular motion begins to force the chains apart and soften the polymer. Thermoplastics can be heated above the Tg, molded to a new shape, and then cooled below the Tg to retain the new configuration–undergo reversible change

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

define thermosetting polymer

A

Polymeric material that becomes permanently hard when heated above the temperature at which polymerization occurs and that does not soften again on reheating to the same temperature.==undergo irreversible change

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

define termination

A

Stage of polymerization during which polymer chains no longer grow.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

define viscoelastic

A

Term describing a polymer that combines the spring-like behavior of an elastic solid (such as a rubber band) with that of the puttylike behavior of a viscous, flowable fluid (such as honey).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

what is an elastomer?

A

something that can undergo extensive reversible deformation

32
Q

what can polymers be used in prosthodontics?

A

denture bases and teeth, so liners, custom trays, impression materials, core buildup materials, temporary restoratives, cementing/luting materials, and maxillofacial prostheses

33
Q

what can polymers be used in operative dentistry?

A

dentin bonding agents, cavity ll- ings, resin and glass-ionomer cements, pit and ssure sealants, splinting materials, and veneers

34
Q

what can polymers be used in orthodontics?

A

brackets, bracket bonding resins and cements, and spacers

35
Q

what can polymers be used in endodontics?

A

gutta-percha points, root canal sealants, and rubber dams

36
Q

what can polymers be used in equipment?

A

mixing bowls and spatulas, mouth guards (sports equipment), and protective eyewear

37
Q

Polymeric resins are increasing in use for restoring and replacing tooth structure and missing teeth. ese resins can be bonded with other resins, directly to tooth structure, or to other restorative materials such as amalgam.

A

ye

38
Q

CQ: xHow do the mechanical properties of a polymer change as the molecular weight increases?

A

coming soon

39
Q

what are two most signi cant features of polymers?

A

they consist of very large macromolecules and that their chainlike molecular structure is capable of virtually limitless con gura- tions and conformations.

40
Q

what determins the properties of polymers?

A

Chain length, the extent of chain branching and crosslinking, and the organization of the chains among themselves

41
Q

how do chain length and molecular weight affect

A

increasing chain length–>greaternumber of entanglements (temporary connections); therefore, the longer the chain, the more difficult it is to distort the polymeric material; thus, such properties as rigid- ity, strength, and melting temperature increase with increas- ing chain length

like spaghetti–>cutting spaghetti makes it easier to separate the noodles

Polymers with equal value of Mw but different values of polydispersity will exhibit somewhat different properties. For example, poly- mers of higher polydispersity will begin to melt at a lower temperature and have a larger temperature range of melting.

42
Q

what are the different ways to calculate average molecular weight?

A

Two types of averages are commonly used: the number average, Mn, based on the average number of mer repeating units in a chain, and the weight average, Mw, based on the molecular weight of the average chain;

Mw is always > than Mn except when all polymers are of the same length– then Mw = Mn

43
Q

what is residual monomer?

A

unreacted monomer; can leach out and cause allergic reaction/toxcity; also reduces Mn of a polymer

44
Q

what is polydispersity?

A

the ratio of Mw/Mn–>indicates the range and distribution of polymer chain lengths

45
Q

how do chain branching and crosslinking affect polymer properties

A

polymer chains are o en connected together to form a nonlinear, branched, or crosslinked polymer. Branching is anal- ogous to extra arms growing out of a polymer chain; thus, the probability of entangled, physical connections among chains increases;

as well, branching = tangles = relative low E to untanglwd but crosslinking = actual bonds =high E to break

Crosslinking forms bridges between chains and dramati- cally increases molecular weight–>therefore physical & mechanical props vary with composition and extent of x-linking; the 3D network of x-linked polymers makes them more rigid, & increases resistance to solvents (will decrease water sorption and solubility)

low molec weight x-linked polymers have lower softning temp (glass transition temp); x-linking only has a modest influence on strength

46
Q

what are copolymers and what are the types?

A

polymer made up of two or more types of mer units;

random: no pattern with the mer units

block copolymer: AAAABBBBABAABB–> basicall y same # adjacent chunks/blocks of each different polymer

grafted/branched copolymer; backbone of polymer A, with branches of B

47
Q

polymers can be amurhphous (chains entangled in random pattern) or crystalline (highly ordered sections); the entire compound can consist of areas of crystalline and amorphous

A

ye

48
Q

how does crystallinity change polymer properties?

A

Polymer crystallinity usually increases strength, rigidity, hardness, and melting temperature, but at the price of reduced ductility—that is, increased brittleness.

Crystalline regions act as physical cross- links, reducing swelling and solubility.

49
Q

what factors reduce or prevent crystallinity formation?

A
  • Copolymer formation, which inhibits polymer chain alignment
  • Polymer-chain branching, which also interferes with chain alignment
  • Random arrangement of substituent groups, particu- larly large side groups that keep polymer chains separated
  • Plasticizers, which tend to separate the chains
50
Q

describe plastic strain in polymers

A

Plastic strain is irreversible deformation that cannot be recovered and results in a new, permanent shape as the result of slippage ( ow) among polymer chains.

51
Q

describe elastic strain in polymers

A

reversible deformation and will be quickly and completely recovered when the stress is eliminated, as the result of polymer chains uncoiling and then recoiling.

52
Q

describe viscoelastic strain

A

strain is a combination of both elastic and plastic deformation, but only the elastic portion is recovered when the stress is reduced; Also, recovery is not instantaneous and occurs over time because the elastic recovery process is impeded by the viscous ow resistance among chains. e amount of deformation that is not recovered at the moment the stress is eliminated is known as plastic deformation.

53
Q

Chain slippage decreases as chain length increases because the bonds between chains, together with chain entanglements, resist dislodgment of the individual chains.

A

ye

54
Q

Chain slippage decreases as chain length increases because the bonds between chains, together with chain entanglements, resist dislodgment of the individual chains.

A

ye

55
Q

CQ: What is the difference between elastomers and plastics? What causes some polymers to respond elastically to stresses and others to act viscoelastically?

A

elastomers–have some plastic deformation during loading, but mostly elastic

plastics = mostly plastic deformation, some elastic

56
Q

rheometry = flow

A

ye

57
Q

describe plastic flow

A

Irreversible strain behavior that occurs when polymer chains slide over one another and become relocated within the material, resulting in per- manent deformation. Branching and crosslinking impede plastic ow.

58
Q

describe elastic recovery

A

Reversible strain behavior that occurs in the amorphous regions of polymers when the ran- domly coiled chains straighten and then recoil, like springs that return to their original locations without sliding past one another when the applied force is removed

59
Q

CQ: Which effects are likely if a plasticizer is leached out of a polymer?

A

coming soon

60
Q

describe what influences polymer solvation

A
  • The longer the chains (the higher the molecular weight), the more slowly a polymer dissolves.
  • Polymers tend to absorb a solvent, swell, and soften rather than dissolve. Any dissolution occurs from the swollen state.
  • Crosslinking prevents complete chain separation and retards dissolution; thus, highly crosslinked polymers cannot be dissolved.
  • Elastomers swell more easily and to a greater extent than do plastics.
  • Absorbed molecules (e.g., water) spread polymer chains apart and facilitate slippage between chains. is lubri- cating e ect is called plasticization.
  • Swelling of dental polymeric devices can adversely affect it—as, for example, with full and partial dentures.
61
Q

purpose of plasticizers?

A

Plasticizing compounds, known as plasticizers, are o en added to resins to reduce their so ening or melting/fusion temperatures. can make a polymer that is normally hard and stiff at room temperature, flexible and soft by adding a plasticizer.

62
Q

how do plasticizers work?

A

A plasticizer acts to partially neutralize secondary bonds or intermolecular attractions that normally prevent the resin chains from slipping past one another (plastic flow)–>

external plasticizer–> diffuses inbetween the macromolecules and increases intermolecular spacing (not part of the polymer structure); extremely important that it has a high affinity to the desired polymer so it does not leach out/volatilize into the body/environment

can have a plasticizer built into the polymer structure–>e.g. utyl methacrylate is added to methylmethacrylate before polymerization, the polymerized resin is plasticized internally by the bulky butyl methacrylate segments–>pendant butyl methacrylate increases intermolec. spacing–>enhances plastic flow

63
Q

plasticizer mech. prop?

A

Plasticizers usually reduce the strength, hardness, and so ening tempera- ture of the resin.

64
Q

cq: What is the difference between thermoplastic and thermosetting polymers? Which involves a reversible physical change and which involves an irreversible change?

A

Thermosetting polymers generally have supe- rior abrasion resistance and dimensional stability compared with thermoplastic polymers, which have better exural and impact properties.

65
Q

temp effects on polymers?

A

higher temp = softer polymer

66
Q

describe thermoplastic resins

A
  • So en on heating, and harden on cooling
  • Can be reprocessed by heating and cooling
  • Undergo a reversible reorganization among the molec- ular chains upon heating, as in denture-base resins

made up on linear and/or branched chains; soften upon heating above glass trans. temp and then harden once cooled–>cycle can be repeated indefinitely bc of low energy to break apart molec. chains

can melt and are dissolvable in organic solvents

67
Q

describe thermosetting resins

A

Thermoset- ting resins (1) undergo a chemical change during the setting reaction; (2) are not so ened by heat; (3) char; (4) decompose rather than melt; and (5) are crosslinked and as insoluble as resin-based composites.

Thermosetting polymers undergo a chemical change and become permanently hard when heated above the tempera- ture at which they begin to polymerize; they do not so en again on reheating to the same temperature–>cross-linked so they do not melt

68
Q

If two otherwise similar linear polymers are compared, the one with the higher molecular weight will also have a higher Tg.

A

ye

69
Q

cq: What are the benefits and drawbacks of a heavily crosslinked polymer?

A

too much corsslinking–rigid and brittle, not good for impressions;

70
Q

describes the types of polymerization

A

addition–sequential adding of monomer to a growing chain; simple but process is difficult to control; can either happen when C=C double bond (vinyl groups) is broken->creates single bonded-mer, or opening up of a 3-bond ring to single bonds–>empirical formula same as actual formula bc just monomers joining together–>no change in composition

condensation–stepwise linking of bifunctional monomers which often results in low molec. weight byproducts such as water or alcohol

71
Q

cq: What are the stages of activation and free radical initiation and curing? Which three activation processes are used for dental polymers?

A

induction– two processes: activation (heat, chemical, or light generating free radicals from the initiator) and initiation; a source of free radicals (initiator chemical–NOT a catalyst; most commonly benzoyl peroxide) in needed to begin activation (e.g. from curing light) and a double bond (something is unsaturated)– free rad pairs with one e- from the db, leaving the other e- from the db free; initiation greatly influenced by purity of monomer sol’n–>impurities can react with the initiator molecules and use them up;
–can also have separate initiator and monomer sol’n which activate upon mixing at ambient oral temp (special type of heat activation; amines in initiator reduce needed temp to gen. free rads–binds & creates complex w/ BPO

propagation–the free-rad-monomer complex now acts as a new FR centre which it approaches another monomer; also, can have chain transfer (two polymers coming together)–>considerable heat given off

chain transfer–>one chain is growing (FR on end) and attaches to another inert chain; the inert chain may become reactivated (how???); however, may end up in termination

termination–can happen from chain transfer; also addition polymerization reactions are most often terminated either by direct coupling of two free radical chain ends or by the exchange of a hydrogen atom from one growing chain to another, thus forming a double bond

72
Q

cq: What mechanisms are responsible for the inhibition of polymeriza- tion? What are the benefits of inhibitors in dental resins? What role does O2 play as an inhibitor?

A

ye

73
Q

how to inhibit polymerization?

A

add something that will react with the free rads will inhibit or retard polymerization; a common inhib. is hydroquinone; -inhibits spontaneous polymerization if no initiator is present and retards the polymerization in the presence of an initiator.

inhibitors a ect both the storage stability and the working time of a dental resin–so inhibitors present in a very small amount; still prevents self-polym in storage

also O2 reacts with free rads–>this is why there is an air-inhibited layer of resin that does not harden

74
Q

describe the ring-opening addition polym

A

monomers with one or more 3-atom ended rings–>opens and joins to other broken rings to form a single-bonded string of mers;

use either imines (two carbons and a nitrogen) or epoxies (two C and an O)

75
Q

describe step-growth/condensation polym

A

reactive groups leave the monomer and join to another monomer; As the reaction proceeds, progressively longer chains form until ultimately the reaction contains a mixture of polymer chains of large molar masses

slower bc stepwise fashion–monomer to dimer to trimer etc

stop before the chains have reached a truly large size because they become less mobile and less numerous as their chains grow.

76
Q

CQ: What are the practical benefits of using copolymer resins for dental applications?

A

ye

DENT 221 (28 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions