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BDS2: Dental Material Science > Glass Ionomer Cement > Flashcards

Glass Ionomer Cement Flashcards

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0
Q

What are the uses of GIC/RMGIC?

A 
Restorative - filling material, endodontic access cavity temporary filling
Core build up - prior to crown placement
Lining - underneath restorations
Luting - cementing indirect restorations
Fissure sealant
Orthodontic cement
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1
Q

What are the two components of conventional GIC?

A

Acid - liquid

Base - glass powder

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2
Q

What are the three stages in the setting reaction of conventional GIC?

A

Dissolution - bath bomb
Gelation - calcium ion cross linking
Hardening - aluminium polyacrylate formation

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3
Q

What is dissolution?

A

Acid into solution
H+ ions attack the glass surface
Ca, Al, Na & F ions are released
Leaves silica gel around unreacted glass

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4
Q

What is gelation?

A

Calcium ion crosslinking with the polyacid by chelation with the carboxyl groups. Caused by formation of calcium polyacrylate.
Equates to the initial set of the material.
Takes several minutes depending on the particular material.
Following this, the material appears hard in the mouth.

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5
Q

What is hardening?

A

Does not start for at least 30 mins and can take a week+ to complete.
Trivalent aluminium ions ensure a higher degree of crosslinking and increase strength. Triggered by aluminium polyacrylate formation?
Improves mechanical properties of material.

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6
Q

What problems are caused if contamination occurs during placement of conventional GIC?

A 
Aluminium ions diffuse out
Excessive drying - water will be lost
Saliva contamination - absorption of water
Weak material
Poor aesthetics
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7
Q

How can conventional GIC be protected?

A

Varnishes (copal ether, acetate)
Resins (DE bonding agents)
Greases or gels (vaseline)

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8
Q

Why was tartaric acid added to the composition of GIC?

A

To improve ease of use as older formulations had v long working and setting times.

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9
Q

What is the bond strength of GIC?

A

5MPa

Bonds without need for an intermediate material

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10
Q

How does GIC bond to the tooth’s surface?

A

Chelation between carboxyl groups in the cement and Ca on the tooth surface.
Hydrogen bonding or metallic ion bridging to collagen.

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11
Q

What is key for good bond formation?

A 
Clean surface
Conditioned surface (e.g. polyacrylic acid)
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12
Q

What are the aesthetics of GIC like?

A

Colour okay but lacking in translucency
New materials with higher silica content are better
Translucency improves over 24hrs due to extra cross linking

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13
Q

What are the thermal properties of GIC?

A

Expansion similar to dentine

No contraction on setting

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14
Q

What are the mechanical properties of GIC?

A 
Poor tensile strength
Lower compressive strength than composite
Poor wear resistance
Lower hardness than composite
Higher solubility than composite
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15
Q

What are the benefits of fluoride release from GIC?

A

Doesn’t damage the GIC structure
Beneficial against secondary caries
Inhibits bacterial growth
Ability to recharge it’s fluoride supply

16
Q

What are advantages of GIC?

A

Stable chemical bond to enamel and dentine
Low microleakage
Fluoride release
Good thermal properties - no contraction on setting

17
Q

What are the disadvantages of GIC?

A 
Brittle
Poor wear resistance
Moisture susceptible when first placed
Poor aesthetics
Poor handling characteristics
Susceptible to acid attack & drying out over time
Possible problems bonding to composite
18
Q

What are cermets?

A

Material composed of ceramic and metallic materials.

Silver was added to the glass to increase toughness and wear resistance of GIC. Only ended up making silver GIC.

19
Q

What is RMGIC?

A

GIC with added 75% HEMA bis-GMA
Combine the acid-base reaction of traditional GIC with a self-cure amine-peroxide polymerization reaction.
Developed to overcome the disadvantages of traditional GIC - command set, improved physical properties, better aesthetics.

20
Q

What are the components of RMGIC?

A 
Powder:
Fluoro-alumino-silicate glass
Barium glass
Vacuum dried poyacrylic acid
Potassium persulphate
Ascorbic acid
Pigments
Liquid:
HEMA
Polyacrylic acid with pendant methacrylate groups
Tartaric acid
Water
Photo-initiators
21
Q

What is the purpose of barium glass in RMGIC?

A

Provides radiopacity

22
Q

What is the purpose of potassium persulphate in RMGIC?

A

Redox catalyst to provide resin cure in the dark

23
Q

What is the purpose of pigments in RMGIC?

A

Varies shade

24
Q

What is the purpose of tartaric acid in RMGIC?

A

speeds up the setting reaction

25
Q

What is the purpose of water in RMGIC?

A

allows the reaction between polyacid and glass

26
Q

What is the setting reaction for RMGIC (dicuring)?

A

Much more complex than conventional.
Initially on mixing the acid-base reaction begins in the same way as conventional GIC.
On light activation a free radical methacrylate reaction occurs resulting in a resin matrix being formed.
Light activation is complete v quickly (20s).
Acid-base reaction continues within the resin matrix for several hours.

27
Q

What is the setting reaction of GIC?

A

Alumino-silicate glass powder + polyalkenoic acid -> calcium + aluminium polyalkenoates
base + polyacid -> polysalt + water

28
Q

What is the setting reaction for RMGIC (tricuring)?

A

Initially the same as conventional GIC
REDOX reaction begins
On light activation, free radical methacrylate reaction occurs resulting in a resin matrix being formed
Light activation complete 20s
REDOX reaction continues for around 5mins after initial mixing
Acid-base reaction continues within the resin matrix for several hours
Final hardening of the acid/base phase with aluminium polyacrylate can take days

29
Q

What are the negative properties of RMGIC?

A

Polymerisation contraction
Exothermic setting reaction
Swelling due to uptake of water
Monomer leaching (if HEMA is not fully polymerised)
Light curing slows down the acid-base setting reaction
Benzoyl iodides and bromides can be released which are cytotoxic

30
Q

What are the beneficial properties of RMGIC?

A 
Good bond to enamel and dentine
Better physical properties
Lower solubility
Fluoride release
Better translucency and aesthetics
Better handling
31
Q

What are the two components of GIC?

A

acid - liquid

base - glass powder

32
Q

What caries risk should patient be to justify use of GIC?

A

High caries risk
Frequent attenders
Medium risk - compomer
Low risk - composite resin

BDS2: Dental Material Science (9 decks)

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