Week 14 Polymerization Flashcards
Modern composite systems are made with:
bis-GMA
What happens when resin is exposed to light?
reorganization of the molecules
volumetric contraction of composite:
2.6% to 7.1%
Reorganization of molecules in polymerization:
gelation, contraction, or hardening
3 gel phases:
- pre-gel phase 2 gel-point 3. post-gel phase
This gel phase is viscous, flow cannot keep up with contraction:
gel-point
This gel phase is the rigid-elastic phase when contraction is obstructed stress occurs:
post-gel phase
This gel phase is the viscous-plastic phase, material is able to flow:
pre-gel phase
What results if the bond strength is lower than stress?
gap formation
What results if the bond strength is higher than stress?
deformation, shrinks toward the center of the mass
Invisible polymerization contraction:
stress
Stress due to shrinkage is approximately:
4-7 MPa
What type of stress is applied to resin?
compressive stress
What is polymerization contraction in posterior teeth associated with?
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 sensitivity, penetration of bacteria, passage of dentinal fluid from tubules to the gap at the dentin-resin interface
Factors we need to understand to prevent the formation of stress:
Resins, preps, curing lights, polymerization techniques, restorative techniques
Each resin needs a minimum amount of ___ to obtain clinically acceptable results.
energy, from paste to hard
unit of energy is measured in __ in dentistry.
joules: power per time
1 joule =
1 milliwatt/cm^2/sec
Optimal energy to polymerize modern composite resin:
16 joules, most monomers converted to polymeric chains
40 seconds at 400 mW/cm^w =
16 (450-475 non-motile of light)
Joules =
watts X time
400 miliwatts X 40 seconds =
16 joules
800 milliwats X 20 seconds =
16 joules
1600 milliwats X 10 seconds =
16 joules
True or False? When you double the amount of energy, the curing tim could be reduced by 50%
F
What requires time to absorb energy in curing a resin?
photo-initiator, this is why the relationship between intensity and time is not proportional.
True or False? The relationship between intensity and time is proportional.
F
How do manufacturers reduce polymerization time of composite?
add proprietary initiators to the resin so they can absorb the energy faster, material absorbs energy faster
Advantages of fast polymerization resins:
rapid polymerization, place faster, deeper depth of the cure
Disadvantages of fast polymerization resins:
short working time, greater margins stress, incomplete reaction leaving a more fragile material (conversion is never 100%, more unreacted monomer?, more fragile?), greater microleakage.
Theories regarding shrinkage upon polymerization resins:
away from margins to which is bonded the weakest
True or False? Each resin needs a different amount of energy to polymerize.
T
Stress is formed when the resin:
cannot adequately contract due to the bond between the resin and the walls
What surfaces act as stress relievers during the plastic deformation of the resin (the initial stages of polymerization)?
only the free surfaces (of the tooth structure or the placed resin?)
True or False? The fewer the free surfaces, the higher the stress
F. greater
What does C-Factor stand for?
configuration factor
C =
bonded surface/ unbonded surface
The higher the C-factor,
the greater the stress generated
What classes of lesions produce the greater stress when restored?
class I and class V
What Class of lesions produce the least stress when restored?
Class III and Class IV
Types of curing lights:
halogen, plasma arc, argon laser, LED
How many mW/cm^2 are halogen lights?
600-800
True or False? Halogen lights have different polymerization modalities.
T
Benefit to LED curing lights:
last years
Low intensity:
50-400 mW/cm^2
Medium intensity:
400 - 800 mW/cm^2
High intensity:
1000+ mW/cm^2
Types of light output:
continuous vs. discontinuous
3 divisions of continuous light output:
High, medium, and low/light intensity
2 divisions of discontinuous light output:
high and low intensity
What is high intensity continuous light output?
high energy
What is medium intensity continuous light output?
continuous uniform
What is low/high intensity continuous light output?
pulsed, ramp, or step
What is high intensity discontinuous light output?
stroboscopic
What is low intensity discontinuous light output?
delayed pulse
Theory regarding polymerization method to reduce stress by regulating the amount of energy given to the resin:
soft polymerization , ramp (lower intensity to higher, to prolong the preferred-gel stage, less generation of stresses) polymerization, and discontinuous polymerization?
Theory regarding polymerization method to reduce stress by controlling the amount of resin polymerize (restorative technique):
in bulk (more stress than layers), in layers (thin layers, less stress), in direct
True or False? Direct, conventional light causes stresses in the resin whereas direct, high intensity light does not.
F. both do
When to use the layers technique:
if you polymerize from the occlusal, polymerization incrementally
composite restorations, rule #1:
keep first layer thin
Filling a preparation:
dentin adhesive, flowable composite (check?), microhybrid composite (with oblique addition for occlusal restorations)
Composite restorations, Rule #2:
never connect opposing cusps (enamel) with a single layer
What is a Class II slot preparation also called?
modified Class II, Class II box-only
When is a Class II Slot preparation indicated?
when only the proximal surface is carious with no lesions on the occlusal surfaces
Where do you gain access when preparing a Class II Slot Preparation?
the marginal ridge area/ Bur is held parallel t the long azis of the tooth
What are he facial, lingual, and gingival extensions dictated by?
the caries
When is a Class II MOD preparation indicated?
when both proximal surfaces and the occlusal surface are carious
True or False? MOD can be either conventional Class II or Slot Class II.
F. conventional only
True or False? Both MO and DO can be either conventional Class II or Slot Class II.
T
True or False? bis GMA both expands and contracts
T.
Where are there tensional forces?
adhesion layer
How do you avoid connecting cusp tips with addition of resin?
addition in oblique layers
True or False? There is never complete polymerization into chains.
T
Advantage of slow polymerization in the first layer of the restorations
helps dissipate stresses that are being formed
What can polymerization shrinkage result in?
formations of gaps around the margins, white lines on cavosurface margins of the restorations
What kind of fractures can you see on enamel?
cohesive
What does the addition of proprietary materials to resin control?
polymerization time
Which have higher C-factors, posterior or anterior teeth?
posterior (more prone to stresses)
This class is the conventional box type preparation:
Class I
How many bonded and unbounded surfaces in a Class 1 restoration?
5 bonded surfaces and one unbounded (occlusal - the only stress reliever) C factor = 5
How many bonded and unbounded surfaces in a Class 2 restoration?
4 bonded, 2 unbonded: C factor = 2 (occlusal and distal are stress relievers)
How many bonded and unbounded surfaces in a Class III restoration?
4 bonded, 2 unbonded (MF: 2 unbonded = M and F) C factor = 2 OR (MFL: 3 bonded, 3 inbonded: C-factor = 1)
How many bonded and unbounded surfaces in a Class IV restoration?
2 bonded, 4 unbonded (axial and pulpal) C factor = 0.5
How many bonded and unbounded surfaces in a Class V restoration?
1 bonded (axial), 5 unbonded = C-factor of 0.2
The lower the C-factor, the better in terms of:
stresses
Type of lights in lab:
Quartz, tungsten, LED or halogen
Which curing lights are not commonly used?
plasma arc and argon laser
2 most commonly used curing lights:
LED and halogen
Are halogen lights of higher or lower intensity
lower intensity
What color light is used for LED curing lights?
blue, no degradation of filters
Direct light curing is specifically recommended for:
occlusal restorations
Point of adding flowable composite as the first layer to a restoration:
to keep first layer very thin (0.5 movements or so)
What teeth are we restoring today?
Tooth #12 MOD Class II with 2 boxes andTooth #21 MO/DO Class II modified slot preparation
What does adhesive allow?
pathology specific preparations, no need for aggressive preparations
What are 2 boxes connected by?
isthmus
Which preparation do we use if only proximal tooth structure is carious?
Slot preparation (modified class II, class II, box only)
Where on the proximal surface of tooth structure do caries typically form?
under the contact area with the adjacent tooth
Access for our preparation in the slot preparation:
margins ridge area
True or False? You always need to use a hatchet to remove unsupported enamel.
T
