composites

Question 1

What are the 6 definite advantages of resin composites?

Answer 1

1. esthetic colors and shades
2. direct intraoral application possible
3. insulation of the pulp against sensitivity to heat and cold
4. do not corrode or dissolve
5. adhesive to acid-etched enamel
6. adhesive to dentin when combined with a dentin bonding material

Question 2

what are the 6 variable advantages of resin composites?

Answer 2

1. polishable to an excellent smoothness
2. comparatively strong and wear resistant
3. acceptable color stability
4. resistant to water softening and dissolution
5. can be made radiopaque for better diagnostic utility by addition of heavy-metal-containing fillers
6. can be used for class 1,2,3 and 5 restorations where there is a stress involved

Question 3

what are the 6 disadvantages of resin composites?

Answer 3

1. still too much polymerization shrinkage/shrinkage stress although much reduced over unfilled acrylic restoratives
2. incomplete curing
3. mismatch between the thermal expansion/contraction of the resin and tooth
4. marginal leakage of soluble components left from incomplete curing can leach and cause inflammation and/or sensization
5. degrade by hydrolysis and esterases
6. wears more than amalgam

Question 4

megafill

Answer 4

0.2-0.5 mm

Question 5

macrofill

Answer 5

10-100 nm

Question 6

midfill

Answer 6

1-10 nm

Question 7

minifill

Answer 7

0.1-1 nm

Question 8

microfill

Answer 8

0.01-0.1 nm

Question 9

nanofill

Answer 9

0.005-0.01nm

Question 10

hybrid

Answer 10

microfill + larger fillers

Question 11

optimal size

Answer 11

higly fillable and polishable point 4- kerr, esthet-x-caulk

Question 12

function of filler

Answer 12

• strrnghten and partially replace the matrix material
• reinforce- increase hardness, strength and wear resistance.
• offset polymerization shrinkage
• control workability- liquid monomer+filler=paste < the more filler the the thicker the paste
• reduce thermal expansion and contraction
• decrease water sorption> less softening and less staining
• Impart radiopacity- adequate for diagnostic purposes

Question 13

function of matrix

Answer 13

add rigidity and strength- cross-linked polymer structure

reduce polymerization shrinkage

Question 14

function of coupling agent

Answer 14

adheres matrix to the filler particles

Question 15

Bis-Gma

Answer 15

main component of matrix in the vast majority of dental restoratives in europe UDMA

Question 16

TEGMA

Answer 16

dilute the matrix to gain a more workable consistency

Question 17

3-methacryloxy-propyltrimethoxysilane

Answer 17

form a chemical interfacial bond between filler and polymer matrix- it is a coupling agent

Question 18

dimethyl amine ethylmethylamine

Answer 18

form a free radical initiating the reaction

Question 19

EDMAB

Answer 19

form a free radical initiating the reaction

Question 20

what are the methods used to develop bulk fill composites

Answer 20

1. match the indices of refraction of the filler and the resin< when the index of refraction matches less light is scattered, transparency is increased, and more light can penetrate
2. low-color initiators are being sed to reduce the color of the composite and allow more light to be transmitted
3. dual-cure initiators can be used to give unlimited depth of cure

Question 21

what are the the methods used to develop low shrinkage in composites

Answer 21

1. particle size distribution of the filler is tightly controlled to produce a very highly filled composite
2. Oxirane monomers open their aromatic rings and expand to form chemical bonds- you can reduce shrinkage even more by mixing in other expanding monomers
3. flexible methacrylate end groups that provide a rod-like shape that facilitates assembly into compact structures- combined with dilution of polymerizable end groups reduce shrinkage
4. reactive ends are long and provide a double bond dilution- also, hydrophobic center restricts water absorption and solubility - leads to formation of 2 separate phases during polymerization and a small expansion

Question 22

unique properties of copomers

Answer 22

compared to resin- include reaction, ion-leachable glass particles and polymerizable acidic monomers
compared to hybrid they have larger filler particles and do not polish as well

Question 23

how are microfillers produced?

Answer 23

cured and then pulverized to make a filled resin powder

Question 24

what are the advantages of a hybrid composite?

Answer 24

restoring stress prone sites where esthetic considerations dominate

Question 25

advantages of light cured

Answer 25

no mixing needed, lower porosity, less staining, stronger - no aromatic amine accelerator; greatly improved color stability - working time is controlled by the clinician - small increments of composite can be polymerized at at time allowing the use of multiple shades within a single restoration and accommodating for shrinkage within each increment as opposed to bulk shrinkage

Question 26

properties of microfilled

Answer 26

- highly polishable- collects less stain - scatter more light so it needs more curing time- - -lower inorganic loading that other types of composites

Question 27

properties of hybrid compposites

Answer 27

intermediate between the two extremes, yielding good balance between strength and polishability

Question 28

disadvantages of light cure

Answer 28

- limited cure depth - mildly sensitive to room light - special lamp is needed - darkness and shade of material lengthens required exposure time - cure is affected by additives such as uv absorbers, florescent dyes, or excess inhibitors they all absorb light and inhibit the rxn - -problems with the lamps- glare is harmful-generates heat and pain- bulb dims with age- intensity decreases with distance- can have incomplete curing due to lamp issues

Question 29

what contributes to matrix constraint

Answer 29

thermal stress- the filler with the lower coefficient of thermal expansion prevents the matrix from expanding or contracting

Question 30

what contributes to increased toughness?

Answer 30

--dependent on the ability of the coupling agent to transfer stresses from the weak matrix to the strong filler particles --when the crack propagates it is not strong enough to break the bond between the matrix and the filler so it has to go around the particle< this increases the path and surface area the crack has to create< this increases the energy it needs to crack -crosslinked polymers because it prevents chains from drawing and separating -crack blunting- the void it perpendicular to propagating crack and more force would be required to propagate the crack -

Question 31

why do you need a bond strength of greater than 24Mpa?

Answer 31

you need it to prevent a gap from forming in a composite system- has not eliminated marginal gap formation

Question 32

how does incremental build up and C-factor affect cure stress

Answer 32

c factor is thee area of the unbonded tooth by the area of the bonded tooth- as bonded surface area increases the more stress applied to the tooth bonded interface

Question 33

what are the 3 different curing regiments that combat cure stress

Answer 33

self-cure light-cure duel cure

Question 34

what are the differences between 2 and 3 body wear

Answer 34

2bw tooth-tooth or restoration | 3bw- food or foreign object in between

Question 35

advantages of duel-cured

Answer 35

Sets up very slowly when mixed via the self-cure mechanism • Cure is accelerated on "command" via light-curing • Major advantage is assurance of completion of cure throughout, even if photocure is inadequate. However, many studies have reported that many dual-cure resins do not fully cure when only selfcured without light. • Major disadvantage is porosity caused by the required mixing. This has been much alleviated with the use of mixing syringes. • There is less color stability than with the light-cured resins due to the aromatic amine accelerators, but this is still better than self-cure systems since the concentration of the accelerators are reduced as compared to self-cure resins.