Polymerization (Week 14)

Question 1

Most modern resins are made with what monomer molecule?

Answer 1

Bis-GMA

Question 2

What happens to the resin when exposed to light

Answer 2

polymerization ( monomers form polymeric chains)

Question 3

During polymerization the resin composite (contracts/expands)

Answer 3

contracts

Question 4

By what percentage does the volume of the resin contract to

Answer 4

2.6-7.1%

Question 5

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

Answer 5

gelation, contraction and hardening

Question 6

What is the pre-gel phase

Answer 6

viscous-plastic phase, material is able to flow

Question 7

What is the gel- point phase

Answer 7

viscous, flow cannot keep up with contraction

Question 8

What is the post-gel phase

Answer 8

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

Question 9

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

Answer 9

gap formation

Question 10

What happens with the bond strength is higher than the stress

Answer 10

deformation

Question 11

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

Answer 11

the center of the restoration

Question 12

Contraction leads to __

Answer 12

stress

Question 13

Stress (units of Megapascal) is about

Answer 13

4-7 MPa

Question 14

The resin undergoes __ stress during the polymerization process

Answer 14

compressive

Question 15

The adhesive undergoes __ stress during the polymerization process

Answer 15

tensile

Question 16

Does the tooth undergo stress during the polymerization process

Answer 16

yes

Question 17

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

Answer 17

• 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

Question 18

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

Answer 18

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

Question 19

What factors are important in prevention of formation of stress?

Answer 19

resins
preparations
curing lights
polymerization techniques

Question 20

What is the optimal energy needed to polymerize resin?

Answer 20

16 joules

Question 21

the unit joule represents what relationship…

Answer 21

the amount of power per time

Question 22

1 joule= 1…

Answer 22

milliwatt/cm^2/sec

Question 23

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

Answer 23

400 x 40 sec = 16 J

Question 24

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

Answer 24

F

Question 25

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

Answer 25

because the photo-initiators require time to absorb energy

Question 26

How can you reduce polymerization time of resin

Answer 26

add more photo initiators to absorb the energy faster

Question 27

What are the advantages of rapid polymerizing resins?

Answer 27

- Placed faster | - Deeper depth of cure

Question 28

What are the disadvantages of fast polymerizing resins

Answer 28

- Short working time - **Greater marginal stress - Incomplete reaction leaving a more fragile material? --may end up with more unreacted monomer - Greater micro leakage?

Question 29

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

Answer 29

-Slow best we want this layer to mimize marginal stress

Question 30

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

Answer 30

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

Question 31

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

Answer 31

F- different

Question 32

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

Answer 32

t

Question 33

When does stress form

Answer 33

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

Question 34

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

Answer 34

Free surfaces- not coded to anything

Question 35

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

Answer 35

less

Question 36

C-factors stands for__ and is the relationship between__

Answer 36

Configuration factor.... Ration of bonded to unbounded surface

Question 37

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

Answer 37

5

Question 38

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

Answer 38

2

Question 39

What is the C factor value of a shallow class III

Answer 39

2

Question 40

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

Answer 40

1

Question 41

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

Answer 41

0.2 or (1/5)

Question 42

What is the Cofactor value of a class IV

Answer 42

0.5 or (1/2)

Question 43

What are the 4 types of curing lights

Answer 43

- Halogen - Plasma arc - Argon laser - LED

Question 44

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

Answer 44

600-800

Question 45

What are LED lights popular now

Answer 45

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

Question 46

Low intensity is within the range of...

Answer 46

50-400 mW/cm^2

Question 47

Medium intensity is within the range of...

Answer 47

400-800 mW/cm^2

Question 48

High intensity is within the range of...

Answer 48

1000 + mW/cm^2

Question 49

What are the two theories that aim to reduce stress

Answer 49

- Regulate the amount of energy given to the resin | - Control the amount of resin polymerized at a given time

Question 50

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

Answer 50

-Soft (low intensity to start with)

Question 51

Describe how we can control the amount of resin being polymerized

Answer 51

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

Question 52

What are the two rules to minimize stress

Answer 52

- Keep the 1st layer thin | - Never connect opposing cusps (enamel) with single layer --> use oblique increments

Question 53

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

Answer 53

F- THIN layer of flow