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Dental Materials korn > Composite > Flashcards

Composite Flashcards

1
Q

Accelerator

A

Substance that facilitates decomposition of an initiator.

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2
Q

Initiator

A

Substance capable of decomposing into free radicals that initiate polymerization.

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3
Q

Rheology

A

Science of the deformation and flow of matter.

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4
Q

Addition Polymerization

A

polymerization process involving free radicals in which no by-product is formed as the chain grows.

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5
Q

Condensation Polymerization:

A

polymerization process in which a by-product, such as water or alcohol, is formed as the chain grows.

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6
Q

Copolymer

A

polymer consisting of two or more different types of monomers (mers) or units joined together.

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7
Q

Crazing

A

Minute surface cracks on polymers; precursors to crack growth and subsequent failure of the material.

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8
Q

Cross-linking agent

A

monomer having two or more groups per molecule capable of polymerization (for example, a dimethacrylate). When polymerized, each active group is capable of incorporation in a growing polymer chain, causing either a loop in the chain or a cross-link between two chains.

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9
Q

Degree of Conversion or Polymerization

A

percentage change in the number of methacrylate (C=C) groups which have polymerized and converted into units (-C-C-) of the polymer system. The total number of mers in one polymer molecule.

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10
Q

Glass-Transition Temperature (Tg)

A

(softening temperature) The temperature at which the polymer ceases to be a glass (ie, fractures in a brittle manner) and becomes a rubber or leather (ie, tends to permanently deform under a load too small to cause fracture).

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11
Q

Glassy polymer:

A

amorphous polymer (those with irregular molecular arrangements, i.e. non-crystalline molecular arrangements) that behaves as a brittle solid.

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12
Q

Molecular weight:

A

sum of the molecular weights of the mers (monomers) of which the polymer is made.

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13
Q

Oligomer

A

polymer made up of two, three, or four monomer units.

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14
Q

Polymer

A

molecule made up of thousands or millions of repeating units. Polymers may be linear, branched, or cross-linked.

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15
Q

Polymerization

A

process by which monomers unite to form a polymer.

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16
Q

Thermoplastic

A

polymer that softens upon heating and rehardens upon cooling

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17
Q

Thermoset

A

polymer that is not able to undergo softening upon heating.

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18
Q

Free Radical

A

Free radicals are compounds with a free electron.

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19
Q

Monomer

A

molecule that can be bonded to other identical molecules to form a polymer.

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20
Q

Characteristics of THERMOPLASTIC Polymers:

A 
o 1) Linear or branched polymers
o 2) Weak bonds break with heat
o 3) Bonds reform on cooling
o 4) Can be molded with heat
 6,6 Nylon
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21
Q

Characteristics of THERMOSET Polymers:

A 
o 1) Crosslinking between chains
o 2) Strong covalent bonds
o 3) One big macromolecule
o 4) Cannot be softened by heat
 PMMA, BisGMA/TEGDMA
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22
Q

The chemical stages of polymerization are:

A

o 1) Initiation by activation of monomer
o 2) Propagation by chain growth
o 3)Termination by reaction completion

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23
Q

The polymerization of polymethylmethacrylate (PMMA) is

A 
ADDITION polymerization (Free radical initiation); No by-product formed. 
o Free radical à acting on C double bonds
o We see shrinkage
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24
Q

Free radical polymerization can be initiated by:

A

o 1) Heat (thermal decomposition of an initiator like BPO)
o 2) Light energy (Visible light energy absorbed by CQ and accelerated by an amine)
o 3) Chemical [chemical reaction between an initiator (BPO) and chemical accelerator (an amine)

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25
Q

BPO (for the purposes of polymerization of dental polymers) is initiated (decomposed) by two methods:

A

o 1) Heat (i.e., polymerization of PMMA dentures)

o 2) Chemical (co-initiated/ accelerated by a tertiary amine)

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26
Q

The Polymethylmethacrylate (PMMA) polymer system has several intended uses in dentistry:

A

o 1) Denture base polymer
o 2) A resin material for temporary crowns and bridges
o 3) Orthodontic resin or resin for night guards
o 4) A repair material for items 1-3

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27
Q

The Polymethylmethacrylate (PMMA) polymer system involves two components:

A

o 1) PMMA Powder (in the form of microscopic polymer beads) + Initiator- small amount of benzoyl peroxide - responsible for starting the polymerization process initiator
o 2) Methyl methacrylate monomer liquid + Inhibitor- small amounts of hydroquinone (inhibitor) - prevents undesirable polymerization during storage.

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28
Q

In pmma what can be added to the monomer liquid

A

▪ A cross-linking monomer (glycol dimethacrylate) at low levels (1-2%) can also be added to the monomer liquid

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29
Q

What is the purpose of the inhibitor (hydroquinone) in mma monomer liquid

A

prevents undesirable polymerization during storage.

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30
Q

Components of a PMMA Polymer Product:

A

POLYMER: powder/ MONOMER:liquid
EXAMPLE: Heat activated denture base resins

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31
Q

Composition of pmma

A

Powder

- Prepolymerized spheres of PMMA
- Initiator- small amount of benzoyl peroxide
    - responsible for starting the polymerization process initiator

Liquid

- Methyl Methacrylate
- Inhibitor- small amounts of hydroquinone(-inhibitor)

    inhibitor - prevents undesirable polymerization during storage

- Cross linking agent - glycol dimethacrylate.... 1-2%
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32
Q

Surface chemistry of PMMA/MMA polymerization:

A

o Monomer is rapidly ab- and adsorbed by the PMMA polymer beads, causing swelling of the PMMA polymer bead with monomer
o Monomer polymerizes linking PMMA beads together in rigid polymer

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33
Q

Increased crosslink of polymer systems can cause an increase in the following parameters:

A

o STRENGTH, HARDNESS, BRITTLENESS, STIFFNESS, CREEP RESISTANCE

34
Q

Polymer resin systems for composite resins include

A

Bis-GMA: bisphenol A-glycidyl methacrylate; UDMA: urethane dimethacrylate; TEGMA: triethylene glycol methacrylate (diluent to decrease viscosity).

35
Q

What can be used for reduced polymerization shrinkage compared to PMMA polymer.

A

Higher molecular weight oligiomers

36
Q

How do Oligomers like Bis-GMA compare to mma

A

still flexible but stiffer than MMA.

Viscosity higher to permits better handling than PMMA/MMA.

37
Q

Chemical Initiated Polymerization (i.e., BPO/Amine) also is referred to by other names:

A

o Autopolymerizing
o Cold-curing
o Self-curing

38
Q

How do physical properties change with molecular weight

A

the physical properties increase as the molecular weight increases up to a level when there are approximately 150 to 200 recurring monomer units in the polymer chain; more strength between polymer units

39
Q

What molecular weight distribution yields best polymers

A

In general, a narrow molecular weight distribution yields the most useful polymers

40
Q

Physical Stages of PMMA Polymer Change (After Mixing Powder & MMA Liquid):

A

o 1: SANDY
o 2: RUNNY OR LIQUID
o 3: PUTTY OR DOUGH
o 4: RUBBERY; HARD

41
Q

Usual stage at which the mixed PMMA material is placed in a matrix of some type to then conform to the shape of a temporary prosthesis or a denture

A

3: PUTTY OR DOUGH

42
Q

PROBLEMS WITH ACRYLIC-BASED MATERIALS:

A

Polymerization shrinkage: (from 10 to 21%, pure monomer highest)
​Water sorption (highest with chemical-cold cure)
​Porosity (inclusion of air bubbles)
​Conversion (lowest with chemical-cold cure)

43
Q

Single Component, Light-Cured Alternatives To PMMA/MMA Polymers:

A

o 1) TRIAD Light-Activated Resin (Custom trays, temporary dentures and retainers, temporaries for crowns and bridges, surgical stents, etc)
o 2) Radica Light Activated Resin System (Denture Bases - Temporaries)

44
Q

Composition of lights cured composite resin

A

o Base Oligomer - Urethane dimethacrylate
o Other Resin Oligomers - HMW acrylic monomers
o Fillers -Microfine silica, Acrylic resin beads
o Camphorquinone initiator:Amine Accelerator - LIGHT ACTIVATION

45
Q

Why lights cured composite resin over pmma

A
  • No residual monomers

* Command Curing (Light Activation by Handheld and High intensity Light Box)

46
Q

Disadvantages of light cures composite resin

A

o 1) Need light-access to all areas of the material-prosthesis
o 2) For dentures or large prosthesis - lower properties than heat-processed PMMA/MMA material

47
Q

COMPOSITE MATERIALS HAVE, AT LEAST, TWO DISTINCT PHASES:

A

two or more distinct substances (metals, ceramics or polymers)
o 1- ORGANIC POLYMER MATRIX (continuous phase)
o 2- INORGANIC PARTICULATE FILLER (dispersed phase)

48
Q

Composites are

A

solid formed from two or more distinct phases that have been combined to produce properties superior to or intermediate to those of the individual constituents

49
Q

DENTAL RESIN COMPOSITE

• 3 components:

A

1- Resin matrix continuous phase
2- Inorganic filler dispersed phase
3- Coupling agent (silane)

50
Q

Resin Matrix:

A

Oligomers/monomers, initiator/accelerator, inhibitors, pigments

51
Q

Inorganic Filler:

A

glass, quartz, colloidal silica (hard, inorganic-filler

particles - ceramic based)

52
Q

Coupling Agent

A

Silane à link the particulate phase to the resin phase

o Without this linking phase à no stress distribution

53
Q

FILLERS in composite (Rationale & Effect):

A

o The inorganic and/or organic resin particles that are designed to strengthen a composite, decrease thermal expansion, minimize polymerization shrinkage and reduce the amount of swelling caused by water sorption.

54
Q

COMPOSITION OF FILLERS:

A 
o Quartz
o Amorphous Silica
o Glass fillers with metals (Barium-Boro-Alumino-Silicate Glass)
o Colloidal Silica
o Ceramics
o Organically modified Ceramics/ORMOCERS
55
Q

TYPES OF FILLERS:

A

o 1) Conventional
o 2) Microfine
o 3) Hybrid

56
Q

CONVENTIONAL FILLER:

A 
o Irregular glass or ceramic
o 4µm - 40µm
o Used in 1960’s- 1970’s
o First generation Composites:
▪ 1-50µm
▪ 60-80 wt%
o Later - Small Particle Composite:
▪ 1-5µm
▪ Ba, Sr, Zn, Yb glasses- fine fillers -Radiopacity
57
Q

MICROFINE FILLER:

A

o Pyrogenic silica: 0.01µm- 0.1µm
o Colloidal silica: 30-60 wt%
o To increase filler loading - organic filler - colloidal silica filler added to resin-heat cured-ground to large particles (organic filler)-remixed with more resin and colloidal/pyrogenic filler to make microfill composite resin
o Rare earth metal compounds (YbF3) are added for radiopacity (microfil not radiopaque)
o Homogeneous Microfill (no organic filler - only fumed silica) & Heterogeneous Microfill (organic filler - plus fumed silica)

58
Q

HYBRID FILLER:

A

o Conventional glass/ ceramic filler particles - Produced by grinding/air-impact classification/sol-gel synthesis- Zirconia/ Silica: 0.5µm - 10µm plus Pyrogenic silica: 0.01µm - 0.1µm
o Bariumaluminoborate & Sr glasses- Radiopacity — 78-85 wt%

59
Q

Ways that the Amount of Filler Is Measured:

A

o 1) By weight percent of filler content (Filler Wgt/Total Composite Wgt x 100)
o 2) By volume percent of filler content (Filler Volume/Total Composite Volume x 100)

60
Q

STURDEVANT’S CLASSIFICATION

A
  • HOMOGENEOUS: One primary particle size
  • HETEROGENEOUS: Mixture of cured + uncured, but one primary particle size
  • HYBRID: Mixtures of various particle sizes
61
Q

Classification based on largest, primary particle size:

A
  • Megafill: 0.5 - 2 millimeters
  • Macrofill: 10 - 100 microns
  • Midifill: 1 - 10 microns
  • Minifill: 0.1 - 1 microns
  • Microfill: 0.01 - 0.1 microns
  • Nanofill: 0.005-0.01 microns
62
Q

Hybrid means

A

Combining two different types (by composition & size) of fillers.

63
Q

the combination of microfiller (fumed & agglomerated silica 0.04 - 0.1 micron) plus minifiller (heavy metal ceramic glass-silica filler - 0.1 to less than 1 micron) is called

A

microhybrid

64
Q

nanofiller (nanoparticles 0.01 - 0.001 micron) plus minifiller (heavy metal ceramic glass-silica filler - 0.1 to less than 1 micron) is called

A

nanohybrid

65
Q

WAYS OF CLASSIFYING COMPOSITE RESINS:

A

• By filler composition (inorganic/organic)
• By filler mean particle size. (macro/small particle/mini/micro/nano)
• By composite resin viscosity (flowable/universal/packable)
• By whether filler composition is homogeneous or
heterogeneous (multiple sized filler-various compositions)
• By polymerization reactions (Light Cure/Chemical Cure/Dual Cure)

66
Q

Eugenol inhibits the setting of all dental polymeric materials that cure by

A

free-radical (addition) polymerization

67
Q

composite resins have a significantly higher coefficient of thermal expansion (CTE) compared to

A

tooth structure or ceramic materials, but lower than metals.

68
Q

Polymer matrix absorbs water which causes

A

expansion,

▪ This expansion is LESS than the polymerization shrinkage.

69
Q

Composite resins are also soluble in water (1-2% weight), but can be more soluble in

A

organic solvents (alcohol, acetone).

70
Q

Curing light intensity is measures by the units

A

milliwatts/square centimeter (MW/cm2).

71
Q

Curing light intensities range from

A

300 - 800 MW/ cm2 for QTH and 800 - 1400 MW/ cm2 for LED lights.

72
Q

Two types of curing lights are

A
  1. Quartz-Tungsten-Halogen (QTH) and 2. Light-Emitting-Dioide (LED) Lights.
73
Q

COMPOSITE TYPES/EXAMPLEs

A

Lowest viscosity o 1. Sealants (filled)
o 2. Flowable Composite
o 3. Anterior/Posterior (midrange viscosity /non-sticky)
Highest viscosity o 4. Packable (condensable)

74
Q

increasing filler loading of composite resin materials improves

A

physical properties, including improving wear resistance, and reducing polymerization shrinkage

75
Q

DEGREE OF CONVERSION:

A

The percentage of initial monomer that is converted to polymer after the completion of the polymerization reaction:
Mi – Mf / Mi

76
Q

Inadequate polymerization results in

A

inferior physio-mechanical properties, such as poor resistance to wear, poor color stability, secondary caries and adverse soft tissue/pulp reactions, increased water sorption, solubility, and early restoration failure.

77
Q

The “depth of cure” (DOC) – usually referring to the thickness of a RBC that is “adequately” cured – is limited by

A

light absorption and scatter within the material, irradiation source, material shade, and irradiation duration

78
Q

Color Stability:

A

Yellowing due to tertiary amine accelerator breakdown in chemically-cured systems.

79
Q

Light-cured systems do not contain tertiary amine and so have improved

A

color stability

80
Q

CLINICAL PERFORAMANCE & LONGEVITY OF COMPOSITE RESINS:

A
  • Annual clinical failure rates are lower for anterior composite resin restorations as compared to posterior composite resin (PCR) restorations.
  • Overall annual failure rates for posterior PCRs are 50 - 100% or more higher than amalgam.
  • Annual failure rates for multi-surface (MO, DO, MOD) posterior PCRs are even higher compared to similar amalgam restorations. Class 1 (occlusal only) failure rates for PCRs are similar to amalgam failure rates.
  • MAIN REASONS FOR FAILURES: Secondary Caries & Restoration Fracture

Dental Materials korn (5 decks)

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