DM L1 Composites pt 2

Question 1

what is a composite

Answer 1

2 or more material put together with each contributing to the overall properties

Question 2

what are the 3 types of ways you can cure a composite + what system do they use

Answer 2

polymerisation/initiator system

1. heat cured
2. room temp cured
3. light cured

Question 3

how are light cured composites available to use + what does it contain

Answer 3

only 1 paste
DHPT (tertiary amine) + camphorquinone (light initiator)
both only react on presence of blue light

Question 4

how do light curing composites set

Answer 4

polymerising (setting) = when light directed onto the paste

tertiary amine + light initiator react -> forms free radicals -> starts addition polymerisation reaction

Question 5

what are the 6 advantages of light cured composites

Answer 5

• single component system
• less discolouration
• minimal porosity
• virtually command set (only set when light directed)
• rapid polymerisation
• thin inhibited layer

Question 6

what are the disadvantages of light cured composites

Answer 6

• light sensitive during application (sunlight can set it)
• retina damage
• limited depth of cure

Question 7

what does light cured composites have a limited depth of cure mean

Answer 7

cant pack whole restoration in at once, must do in small layers
OR ELSE
uncured resin at base of cavity -> soggy bottom

Question 8

for curing composites , why do we need a high degree of conversion

Answer 8

high degree of conversion of C=C for optimum mechanical properties otherwise, restoration has poor foundation + will facture

Question 9

what do the mechanical properties of composites depend on + percentages of how much is converted in monomers of light, self and heat cured

Answer 9

mech props depend on how much monomer is converted to polymer (via free radical polymerisation)

light cured: 65-80%
self cured: 60-75%
heat cured >90%

Question 10

what must you ensure about the quality of the light source for curing composites + why

Answer 10

• VLA (visible light activated) between 450-500nm

- bc max light output of 460-480nm for camphorquinone absorption

Question 11

how do you light cure a composite

Answer 11

1. tip of light source close as possible to restoration surface - curing efficiency ↓ when light tip moved away
2. light tip mustn’t be contaminated - curing efficiency ↓
3. cure for recommended time + no less
4. large restorations - no fanning, curing spots must overlap

Question 12

what else affects depth of cure for composites

Answer 12

type + colour affects it

darker shades take longer to set than lighter

Question 13

what current light sources are being used now for light curing units

Answer 13

VLA (visible light activated)
All light cured composites contain α-di-ketone (initiator)/Amine (activator)
E.g. Camphorquinone (activates 460-480nm) + DHPT

Question 14

what are come examples of physical light curing units

Answer 14

1. quartz-tungsten- halogen unit
2. LED unit
3. Plasma Arc (PAC) unit
4. Argon laser unit

Question 15

what are main advantages of using LED curing unit

Answer 15

• cordless (rechargeable battery)
• slimline
• ↓ lateral heat production (cf halogen)
• Long lasting light source
• Narrow emission spectrum (460-480 nm)
  Peak 470 nm
• Ultra energy efficient
• Near absorption of camphorquinone
  1st gen cost >2nd gen
  1 st gen low intensity radiation < 2 nd gen higher intensity radiation

Question 16

what does PAC curing unit use + what are advants + disadvants

Answer 16

• Use xenon gas-ionised  plasma
• High intensity white light filtered (↓heat) and allow emitting of blue light
• Claim to cure in 1-3secs -> used privately - expensive

Question 17

what does Argon laser curing unit use + what are advants + disadvants

Answer 17

• Not used - high energy, intensity.
• expensive - lots of caution required
• Emits light at a SINGLE wavelength (490nm)

Question 18

what are the 3 advantages of using composites

Answer 18

excellent easthetic results
less tooth tissue removed
command set if light cured

Question 19

what are the disadvantages of using composites

Answer 19

1. Lining materials limited - Ca(OH)2 , GIs
2. Setting inhibited with eugenol based materials
3. Doesn’t adhere intrinsically to enamel + dentine
4. Adhesion to tooth cavity possible with acid-etch and adhesives
5. Incremental placement + light-cure (3x’s longer to place compared to amalgam)
6. Caries tends to progress more rapidly (-> polymerisation shrinkage on setting)
7. Stick to instruments – problems with marginal adaptation

Question 20

why does polymerisation shrinkage occur in setting composites + why problems occur bc of it

Answer 20

shrinkage -> double bonds converting to single bonds

1. marginal adaptation
2. breakdown of bonds to tooth tissues
3. results recurrent caries

Question 21

why do problems caused by composition up-taking water by adsorption

Answer 21

• glass filler adsorbs water onto its surface
• amount of water depends on resin content + quality of bond between filler + resin
• hydrolytic breakdown of bond between filler + resin

Question 22

why do problems caused by composition up-taking water by absorption

Answer 22

as water absorbed:
- unreacted monomer ( incomplete polymerisation) + high soluble fractions in composite are released –> leaves a space which fills up with water
- water fills pores/air voids in cured resin -> due to mixing/placement
absorbed water affects wear resistance + colour stability

Question 23

how can composite staining occur

Answer 23

• marginal - gap between restoration + tooth tissue - debris penetrates -> staining
• surface roughness of composite - debris gets trapped in spaces
• bulk discolouration - 2 paste amine cured systems

Question 24

how can composite wear occur (disadvant)

Answer 24

abrasive, fatigue + corrosive wear

with time, resin matrix wears + filler particles protrude through surface giving material a dull appearance

Question 25

describe the biocompatibility disadvantage of composites

Answer 25

• composite components + breakdown products released
• uncured resin leads to:
• cytotoxic + delayed hypersensitivity from eluted materials
• oestrogenic effects

Question 26

what is the advantage of light curing composites (thin inhibited layer) mean

Answer 26

-Air + resin interface -> sticky resin surface (good to have as layers stick together)
- Oxygen inhibits the cure of the resin surface
= incremental placement -> well-bonded material

Question 27

what is the problems of light curing composites - (thin inhibited layer)

Answer 27

= final increment surface sticky which is solved using:

clear matrix strip; overfill cavity + polish; sometimes can apply bonding agent!

Question 28

what are flowable composites that were used before (?)

Answer 28

Less filler and more diluent -> flow into cavity

BUT less filler = less mechanical properties and low viscosity!

Question 29

what is packable composities that were used before (?)

Answer 29

Reduced filler loading/increased filler size; so much filler added = ↑properties
BUT margins weren’t right; aesthetics compromised; ↑ viscosity
∴ thin layer of flowable put first before packing!

Question 30

silorane (?)

Answer 30

(self-etch primer and bond) 2007:
o POLYMERISATION SHRINKAGE PROBLEM SOLVED but vanished off the market 
 Properties:
 Polymerisation shrinkage reduced
 Low water absorption
 Mechnical properties “within the
range of other composites)
 Requires alternative silanes for filler
treatment and bonding agent used

Question 31

bulk fill restorative composite (?)

Answer 31

o One-step placement, no additional capping layer
o Excellent adaptation without additional expensive dispensing devices
o Stress relief to enable up to 5mm depth of cure
o Excellent handling and sculptability
o Available in capsule or syringe delivery in 5 shades