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Direct/Cariology > Polymerization (Week 14) > Flashcards

Polymerization (Week 14) Flashcards

1
Q

Most modern resins are made with what monomer molecule?

A

Bis-GMA

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2
Q

What happens to the resin when exposed to light

A

polymerization ( monomers form polymeric chains)

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3
Q

During polymerization the resin composite (contracts/expands)

A

contracts

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4
Q

By what percentage does the volume of the resin contract to

A

2.6-7.1%

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5
Q

The process of reorganization of the molecules (or polymerization is also called (3 names)

A

gelation, contraction and hardening

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6
Q

What is the pre-gel phase

A

viscous-plastic phase, material is able to flow

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7
Q

What is the gel- point phase

A

viscous, flow cannot keep up with contraction

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8
Q

What is the post-gel phase

A

rigid elastic phase when contraction is obstructed stress occurs all around where the composite is bonded

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9
Q

What happens when the bond strength to the wall is lower than the stress generated

A

gap formation

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10
Q

What happens with the bond strength is higher than the stress

A

deformation

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11
Q

During deformation (bond strength>stress) the resin shrinks (contracts) to…

A

the center of the restoration

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12
Q

Contraction leads to __

A

stress

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13
Q

Stress (units of Megapascal) is about

A

4-7 MPa

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14
Q

The resin undergoes __ stress during the polymerization process

A

compressive

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15
Q

The adhesive undergoes __ stress during the polymerization process

A

tensile

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16
Q

Does the tooth undergo stress during the polymerization process

A

yes

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17
Q

Polymerization contraction in posterior teeth is associated with what clinical problems?

A
  • Separation of the resin at the weakest margins
  • Formation of tensional forces at the margins
  • Fractures in the enamel
  • Deformation of the cusps
  • Secondary caries
  • Postoperative sensitity
  • Penetration of bacteria
  • Passage of dentinal fluid from tubules to the gap at the dentin-resin interface
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18
Q

What technique do you use to prevent the fracturing of enamel in posterior teeth

A

do not restore two cusps together (use the oblique method)

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19
Q

What factors are important in prevention of formation of stress?

A

resins
preparations
curing lights
polymerization techniques

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20
Q

What is the optimal energy needed to polymerize resin?

A

16 joules

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21
Q

the unit joule represents what relationship…

A

the amount of power per time

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22
Q

1 joule= 1…

A

milliwatt/cm^2/sec

23
Q

How long do you have to polymerize resin if you have a 400 milliwatt light?

A

400 x 40 sec = 16 J

24
Q

(T/F): When you double the amount of energy, the curing time can be reduced by 50%

A

F

25
Q

Why is it that the intensity of the light and the time polymerizing are not proportional to one another

A

because the photo-initiators require time to absorb energy

26
Q

How can you reduce polymerization time of resin

A

add more photo initiators to absorb the energy faster

27
Q

What are the advantages of rapid polymerizing resins?

A
  • Placed faster

- Deeper depth of cure

28
Q

What are the disadvantages of fast polymerizing resins

A
  • Short working time
  • **Greater marginal stress
  • Incomplete reaction leaving a more fragile material? –may end up with more unreacted monomer
  • Greater micro leakage?
29
Q

A (Fast/slow) polymerizing resin should be used for the first increment and why?

A

-Slow best we want this layer to mimize marginal stress

30
Q

There are 2 theories as to where the resins contract upon polymerization, what are the two theories

A
  • Shrinks towards the center (debonds from the walls to the center of its mass)
  • Away from margins were it is bonded the weakest
31
Q

(T/F) Each resin requires the same amount of energy to polymerize

A

F- different

32
Q

(T/F) There are both slow and fast polymerizing resins

A

t

33
Q

When does stress form

A

when the resin cannot adequately contract due to the bond between the resin and the walls

34
Q

During the initial stages of polymerization, what are the only surfaces that can act as stress relievers during plastic deformation of the resin

A

Free surfaces- not coded to anything

35
Q

The (more/less) free surfaces a restoration has the greater the stress

A

less

36
Q

C-factors stands for__ and is the relationship between__

A

Configuration factor…. Ration of bonded to unbounded surface

37
Q

Class I preps and deep boxy Class V preps have a C factor value of __

A

5

38
Q

What is the C fact value for a class II restoration (MO or DO)

A

2

39
Q

What is the C factor value of a shallow class III

A

2

40
Q

What is the Cfactor of a deep Class III (facial and lingual exposed

A

1

41
Q

What is the Cfactor value of a veneer or shallow class V

A

0.2 or (1/5)

42
Q

What is the Cofactor value of a class IV

A

0.5 or (1/2)

43
Q

What are the 4 types of curing lights

A
  • Halogen
  • Plasma arc
  • Argon laser
  • LED
44
Q

What is the value range of intensity (mW/cm^2) of a halogen light

A

600-800

45
Q

What are LED lights popular now

A

last a long time because they do not degrade the filter like halogen lights do

46
Q

Low intensity is within the range of…

A

50-400 mW/cm^2

47
Q

Medium intensity is within the range of…

A

400-800 mW/cm^2

48
Q

High intensity is within the range of…

A

1000 + mW/cm^2

49
Q

What are the two theories that aim to reduce stress

A
  • Regulate the amount of energy given to the resin

- Control the amount of resin polymerized at a given time

50
Q

Describe how we can regulate the amount of energy given to the resin

A

-Soft (low intensity to start with)

51
Q

Describe how we can control the amount of resin being polymerized

A

When you add composite in bulk it will add more stress than in thin layers (indirect)

52
Q

What are the two rules to minimize stress

A
  • Keep the 1st layer thin

- Never connect opposing cusps (enamel) with single layer –> use oblique increments

53
Q

(T/F): After application of the adhesive, you can add a thick layer of flowable composite to reduce stress

A

F- THIN layer of flow

Direct/Cariology (20 decks)

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