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Dental Materials > 7 composites > Flashcards

7 composites Flashcards

1
Q
A
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2
Q

In terms of make up, which two types of phases does composite consist of?

A

a dispersed phase (filler particles) distributed within a continuous phase (matrix phase)…the matrix phase is often fluid at some point

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3
Q

A dental composite has traditionally indicated a mixture of _______ glass particles within an _______ monomer that is polymerized during the application

A

silcate glass particles acrylic monomer

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4
Q

what is the function of the silicate glass particles in composite? function of acrylic monomers in composite?

A

silicate glass- provides mechanical strength and scatters light to produce enamel like translucency acrylic- make the initial composite mixture moldable and fluid so it can flow into preperations

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5
Q

what are bonding systems for composites generally made of?

A

acrylic monomers

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6
Q

name three ways a bonding system interacts with a prep.

A

1- micromechanically interlock with the etched surfaces, 2- seal the walls of the preparations, and 3- copolymerize with the composite restorative material that fills the tooth preparation

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7
Q

name some other terms we use for dental composite

A

composite restorative materials, filled resins, composite resins, resin composites, resin-based composites, or filled composites

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8
Q

the earliest composites used were which? what were they mixed with? name some disadvantages of this material

A

silicates

phosphoric acid and glass polymers

were too soluble in the oral environment and were too hard on the pulp

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9
Q

what is PMMA? Disadvantage of MMA? Disadv of PMMA?

A

poly methyl meth acrylate the methacrylate monomer (MMA) contracted too much during polymerization, permitting marginal leakage PMMA was not strong enough to support occlusal loads

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10
Q

MMA matrices were replaced by which material?

A

BIS-GMA (a difunctional monomer)

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11
Q

what is BIS GMA and UDMA (similar to BIS GMA) diluted with so they aren’t so viscous?

A

TEGDMA

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12
Q

To increase the bond between the silica particles and the continuous resin phase, the silica particles are precoated with films of_______

A

silane coupling agents

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13
Q

what are silane coupling agents?

A

difunctional molecules; one end bonds to the hydroxyl groups on the silica surface, the other is capable of copolymerizing with double bonds of monomers in the matrix phase

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14
Q

why are lithium and Aluminum used as filler particles? what filler particles are used to increase radioopacity?

A

makes the glass easier to crush to generate small particles Barium (Ba), Zinc (Zn), Boron (B), Zirconium (Zr), and Yttrium (Y) ions have been used to produce radiopacity

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15
Q

Pure silica occurs in several crystalline forms in addition to glass….name 3 of them

A

crystobalite tridymite quartz

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16
Q

Crystalline forms of silica are stronger and harder, but results in composites that are difficult to _______ what gives you a smoother polish?

A

polish using smaller filler particles (ie microfill instead of midifill)

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17
Q

Which 3 silicate glasses are currently the most popular fillers?

A

arium, zinc, and yttrium

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18
Q

The fluidity of a mixture of filler and matrix monomer is affected by the fluidity of the ______ and the amount of ______ The principle factor controlling fluidity in composite is what?

A

monomer and the amount of filler incorporated

friction between the filler particle surfaces and the monomer

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19
Q

As the filler surface area increases, the fluidity _______ Large filler particles have a relatively ________ amount of surface area per unit of filler particle volume

A

decreases small

20
Q

what happens to surface area when smaller filler particles replace large ones? This situation is further exacerbated for microfiller particles made of _____, which tend to agglomerate into chains

A

surface area increases SiO2

21
Q

Define Surface Roughness (RA)?

Surfaces with roughness values of what are considered to be very smooth?

what is the most common range when using submicron polishing pastes?

A
  • average up and down symmetry

1um

0.2 - 0.6um

22
Q

the most common classification of composite material is based on what?

A

The most common classification method is based on: filler content (weight or volume percent), filler particle size, method of filler addition

23
Q

Almost all important properties of composites are improved by using higher _______ levels

A

filler

24
Q

Disadvantage of large filler particle size? Disadv of small filler particle use?

A

tough to polish

weaker

25
Q

The degree of filler addition is represented in terms of what? Because silica is about 3 times as dense as the matrix polymer, 75 weight % filler is equivalent to about _____volume % filler

A

weight % or volume % of filler

50

26
Q

in dentistry, what is more common: using weight% or volume% to measure filler addition?

A

much easier to measure and formulate composites using weight percentages rather than volume percentages

27
Q

particle size for macrofill? midifill? minifill? microfill? nanofill?

A

Macrofill: 10-100 μm

Midifill: 1-10 μm

Minifill: 0.1-1 μm

Microfill: 0.01-0.1 μm

Nanofill: 0.005-0.01

28
Q

What is a hybrid composite? what is used to define the hybrid type

A

Composites with mixed ranges of particle sizes

the largest particle size range is used to define the hybrid type

29
Q

what is a homogeneous composite? what is a heterogeneous composite? If it includes novel filler modifications in addition to conventional fillers, then it is called_____ composite

A

consists simply of filler and uncured matrix

If it includes precured composites or other unusual filler, it is called heterogeneous modified

30
Q

what is a traditional or “conventional composite”? filler particle size?

A

they replaced the silicate composites

filler particles are 8-10um in size

31
Q

another name for a microfill (0.02-0.04um) composite? What does having a small filler particle size do?

A

fine finishing composites The small filler particle produce high viscosities, requiring addition of more monomer diluents, along with a reduced overall filler content to make it workable

32
Q

To lessen the viscosity problem of small filler particles in microfill composites, 2 strategies were developed. Describe them. What were these types of composites called?

A
  1. the microfill composite was precured 2. then ground into 1-20 μm particle powder, which bonded with the new material, providing islands with better properties, but could still be finished nicely These are known as heterogeneous microfills (or organic filler composites)
33
Q

After it was learned that highly filled microfills were difficult to use, composites were formulated with particles in the microfill range and also 2-5 μm range. These allowed for higher filler levels and also good finishing, and were called ______ composites

A

hybrid

34
Q

do nanofiller particles interact with visible light?

A

no, the filler particle size is below the wavelength range for visible light = NO SCATTERING OR ABSORPTION OF LIGHT

35
Q

adv for using non silicate based composite fillers?

A

Non-silicate-based compositions can be used for nanofillers because they are effectively invisible, and do not tend to agglomerate in chains like silica particles

36
Q

what is an adv of using non silicate based composites as nanofillers?

A

they are effectively invisible, and do not tend to agglomerate in chains like silica particles Nanofillers are so small that they fit between polymer chains, permitting very high filler loading levels while still maintaining workable consistencies

37
Q

what is the advantage to using fibers in composite? disadv? Fibers must be longer than 1um…WHY? what are the dimensions of most current fibers?

A

The main advantage is their strength along the fiber axis

hard to pack them efficiently or to orient their direction

addition of fibers less than 1um long are carcinogenic (ie asbestos)

Most current fibers are from 20-40 μm long and 5-10 μm in diameter

38
Q

what are flowable composites? what procedures are flowable composites best used for?

A

**Low-viscosity** materials that possess particles size distributions similar to those of hybrid composites, but with reduced filler content

pit-and-fissure sealants or small anterior restorations

39
Q

True/ False ? In general, the mechanical properties of flowable composites are superior to those of standard hybrid composites

A

FALSE Flowable composites are weaker

40
Q

how is packable composite different from flowable composite?

A

less stickiness, have a higher viscosity (stiffness)

41
Q

_____ monomers for composites used in the United States traditionally have been based in BIS-GMA as the primary monomer

A

Matrix

42
Q

T/F UDMA, which is more popular than BIS GMA in Europe, is predicted to have better adhesion and/or resistance to color changes than BIS GMA

A

FALSE clinical studies have not been able to show this

43
Q

how were the original composites cured? most popular way of curing composite today?

A

self cured (chemical cured) amine accelerators (but discoloured in 3-5 years)

most popular= visible light cured

44
Q

in what situations can light curing be inadequate? what part of the tooth can it be be tough to light cure?

A

If the composite thickness exceeds 1.5 to 2.0 mm, the light intensity can be inadequate to produce complete curing,

especially with darker composites

Interproximal locations

45
Q

what has been done to overcome the disadvantages of light curing?

A

compositions are dual-cured, combining self-curing and light-curing.

Self-curing rate is slow and designed to cure only those portions not adequately light-cured

46
Q

List some light sources that can be used to cure composites

A

quartz-tungsten-halogen (QTH)

plasma-arc (PAC)

laser light-emitting diode (LED)

47
Q

Moving the tip of the curing light closer to the surface ______ the depth of the cure

A

INCREASES

Dental Materials (15 decks)

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