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Dental Material Science > Glass Ionomers > Flashcards

Glass Ionomers Flashcards

1
Q

Name the different types of GIC’s (2)

A
  1. Conventional GI
  2. Resin Modified GI
    - Self cure
    - Light cured
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2
Q

State the uses of GIC’s (4)

A
  1. Restorative
    - filling material e.g. RIVA, vitremer
  2. Core build up
    - Prior to restoration with crown e.g. vitremer crown core
  3. Lining
    - Underneath permanent fillings
    e. g. Vitrebond
  4. Luting
    - Cementing indirect restorations
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3
Q

What are the components of a GIC? (2)

A
  1. Acid
    - Liquid
  2. Base
    - Glass powder
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4
Q

What makes up the acid component of a GIC? (2)

A
  1. Polyacrylic acid
    (Ionic monomers)
  2. Tartaric acid
    (added to control setting characteristics of the material)
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5
Q

What makes up the base component of a GIC?

A
  1. Silica
  2. Alumina
  3. CaF
  4. AlF
  5. Aluminium Phosphate
  6. NaF
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6
Q

Advantage of adding more silicone to a GICl?

A

More translucent

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7
Q

Define the term radiopaque

A

White area seen in an X-ray

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8
Q

Advantage of adding Strontium and Lithium salts to a GIC?

A

Can increase radiopacity (but play no part in chemistry reaction)

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9
Q

What affects the translucency of a GIC?

A

Ratio of alumina/silica

More silica = more translucent

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10
Q

Compare:

Anhydrous materials

Encapsulated materials

A

Anhydrous materials:

  • The acid is freeze dried and added to the powder
  • Liquid is distilled water (easier handling of material, particularly mixing)

Encapsulated materials:

  • Consistent powder/liquid ratio
  • Easier to use
  • More consistent properties of mixed material
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11
Q

What are some of the variations that can exist in GIC composition? (2)

A
  1. Powder particle size can vary
    <20um required for luting cement to give a low film thickness
  2. Molecular weight of acid changes
    - The higher the weight the better the mechanical properties of the set material
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12
Q

Advantage of small particle size?

A

> Smaller the particle size, the quicker the setting reaction and the more opaque the set cement

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13
Q

What are the 3 phases of the setting reaction?

A
  1. Dissolution
  2. Gelation
  3. Hardening
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14
Q

What happens during dissolution? (4)

A
  • Acid into solution
  • H+ ions attack the glass surface
  • Ca, Al, Na and F ions are released
  • Leaves silica gel around unreacted glass
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15
Q

What happens during gelation? (3)

A
  • Initial set of material caused by formation of calcium polyacrylate, can take several mins
  • Material will appear hard in mouth
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16
Q

What is the initial set of material due to?

A
  • Ca ion cross linking with the polyacid by chelation with the carboxyl groups
  • Ca ions = bivalent so can react with 2 molecules joining them
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17
Q

Why is crosslinking of Ca ions not ideal

A

The Ca can chelate with 2 carboxyl groups on the same molecule

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18
Q

What happens during the setting reaction? (4)

A
  • Trivalent Al ions ensure good cross linking with an increase in strength
  • Al polyacrylate formation takes a long time, doesn’t start for at least 30mins and can take a week/longer to be complete
  • Al reaction ensures a higher degree of cross linking
  • This improves mechanical properties of material
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19
Q

How does contamination affect the setting reaction?

A
  • Al ions diffuse out material
  • Excessive drying means water will be lost
  • Saliva contamination causes absorption of water
  • Leading to a weak material which will be rough, break up and have poorer aesthetics
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20
Q

How is conventional GIC protected during placement?

A
  1. Varnishes
  2. Resins
    - Dentine/enamel bonding agents
    - Unfilled Bis-GMS resins
  3. Greases/gels
    - Vaseline in paeds
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21
Q

Compare the GIC protection efficacy of varnishes to resins

A

Varnishes + resins provide better protection

Petroleum gel is quickly removed by lips/tongue so offers little protection

22
Q

State properties of GIC (2)

A
  1. Handling
  2. Adhesion
    - Good sealing ability with little leakage around margins

Can bond to enamel and dentine without need of intermediate material (i.e. acid etch)

23
Q

How does tartaric acid favour the GIC?

A

Setting time shorted, working time unchanged

24
Q

Bond strength of GIC

A

5MPa

25
Q

Describe the bonding mechanism

A
  1. Chelation between carboxyl groups in the cement and Ca on tooth surface
  2. Re-precipitation of complex mixture of Calcium phosphate and calcium salts form the polyacid onto and into the tooth surface
  3. Hydrogen bonding or metallic ion bridging to collagen
26
Q

Requirements of a good bond?

A
  1. Clean surface
  2. Conditioned surface (NOT etched)
  3. Little or no tissue removed
27
Q

Whats the best conditioner to use?

A

Polyacrylic acid

28
Q

Function of conditioner

A

To produce a clean smooth surface

29
Q

Disadvantages of GIC’s in terms of aesthetics (2)

A

> Colour is ok but lacks translucency (improves a bit over time)

> Opaque in colour, if they dry out can become chalky

30
Q

Disadvantages of GIC’s, in terms of mechanical properties

A
  1. Poor tensile strength
  2. Lower compressive strength than composite (less than half)
  3. Poorer wear resistance than composite
    - Subject to abrasion
  4. Lower hardness than composite
  5. Higher solubility than composite
    - Dissolution of unprotected material during gelation phase
    - Long term erosion by acids
31
Q

Mechanical properties of GIC

A
  1. Good thermal properties expansion similar to dentine
  2. No contraction on setting
  3. Once set less susceptible to staining and colour change than composites
  4. Fluoride release
32
Q

Function of fluoride release in GIC’s (3)

A

> GIC’s can release fluoride without damage to their structure
In vitro this has been shown to be beneficial against secondary caries

FLUORIDE RELEASE INHIBITS BACTERIAL GROWTH

GIC can take up fluoride from the environment

33
Q

When do GIC’s recharge their fluoride (2)

A

> They can recharge their fluoride when the FI concentration around them is higher than that in the cement

> They then release FI again when the ambient concentration falls

34
Q

Uses of GIC’s (7)

A
  1. Dressing
  2. Fissure sealant
  3. Endodontic access cavity temporary filing
  4. Luting
  5. Ortho cement
  6. Restoration of deciduous teeth
  7. Restoration of permanent teeth
  8. Base or lining
35
Q

GIC advantages (5)

A
  1. Stable chemical bond to enamel and dentine
  2. Low microleakage
  3. Fluoride release
  4. Good thermal properties
  5. No contraction on setting
36
Q

GIC disadvantages (7)

A
  1. Brittle
  2. Poor wear resistance
  3. Moisture susceptible when first placed
  4. Poor aesthetics
  5. Poor handling characteristics
  6. Susceptible to acid attack and drying out over time
  7. Possible problems bonding to composite
    - Etching damages the surface
37
Q

Why were cermets developed?

A

To overcome the GIC brittleness

But theres no advantages and theres worse aesthetics (they look like dull amalgam fillings)

38
Q

Why were RMGIC’s developed?

A

To add advantages of composite technology:

> Light curing (command set)
Improved physical properties
Better aesthetics

39
Q

What makes up a RMGIC? (2)

A
  1. Powder

2. Liquid

40
Q

Name constituents of RMGIC powder (4)

A
  1. Barium glass
    - Provides radiopacity
  2. Potassium Persulphate
    - Redox catalyst to provide resin cure in the dark
  3. Ascorbic acid
  4. Pigments
    - Varies shade
41
Q

Name constituents of RMGIC liquid (5)

A
  1. HEMA
    - Water miscible resin
  2. Polyacrylic acid with methacrylate groups
    - This can undergo both acid base and polymerisation reactions
  3. Tartaric acid
    - Speeds up the setting reaction
  4. Water
    - Allows reaction between polyacid + glass
  5. Photo-initiators
    - Enable light curing
42
Q

What happens during the setting reaction of RMGIC’s

A

DUAL CURING
> Begins same as conventional GIC
> On light activation leads to free radical methacrylate reaction which makes a resin matrix
> Light activation complete in 20 seconds
> Acid base reaction continues within the resin matrix for several hours

43
Q

Why should RMGIC be placed in layers?

How is this problem counteracted?

A

Material quite opaque, so light does not penetrate deeply into the material

REDOX reaction to counteract this

44
Q

How does light affect the properties of RMGIC’s?

A

Physical properties of the set material are reduced by 25%

45
Q

State the 2 types of curing for RMGIC’s

A
  1. Dual curing

2. Tri curing

46
Q

Does Vitrebond require pre-conditioning of the tooth surface?

A

NO

47
Q

Does vitremer require pre-conditioning of the tooth surface?

A

YES

48
Q

State RMGIC’s properties (6)

A
  1. Good bond to enamel and dentine
  2. Better physical properties
  3. Lower solubility
  4. Fluoride release
  5. Better translucency and aesthetics
  6. Better handling
49
Q

State RMGIC’s disadvantages (4)

A
  1. Polymerisation contraction
  2. Exothermic setting reaction
  3. Swelling due to uptake of water
    - HEMA is extremely hydrophilic
  4. Monomer leaching
    - Hema is toxic to the pulp, it must be polymerised completely
  5. Benzoyl iodides and bromides can be released, which are cytotoxic
50
Q

Compare RMGIC to conventional GIC (3)

A
  1. Better aesthetics
  2. Easier to use
  3. Stronger
51
Q

Compare RMGIC to composite resin (2)

A
  1. Easier to use

2. Fluoride release

52
Q

RMGIC uses (7)

A
  1. Dressing
  2. Fissure sealant
  3. Endodontic access cavity temporary filling
  4. Luting
  5. Orthodontic cement
  6. Restoration of deciduous/permanent teeth
  7. Base or lining

Dental Material Science (7 decks)

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