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Y3 Dental Materials > L13 Glass Ionomers > Flashcards

L13 Glass Ionomers Flashcards

1
Q

Why do we use glass ionomer cements?

A

Natural adhesion
Can manipulate glass chemistry, dope it with fluoride or other elements to have potential therapeutic effect if release into local environment

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2
Q

Give some properties of GIC

A

Versatile type of material - many different types
Lack mechanical strength

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3
Q

Why do we not place GIC in stress bearing situations in adult teeth?

A

Because they lack mechanical strength
Contraindicated for large restorations or stress bearing sites

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4
Q

What are the different types of GIC?

A

Restorative materials - type II
Cavity bases and liners - type III/IV
Luting agents - type I

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5
Q

Clinical applications of restorative GIC materials

A

Non carious lesions (abfractions class V)
Class III (involving exposed root dentine
Class II (not in paeds though)
Temporary restorations
Crown margin repair

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6
Q

Clinical application of GIC in cavity bases and liners

A

Procedures using a base in large cavities
Bases under resin composites

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7
Q

Why might we use GIC as a base in large deep cavities?

A

Line the base before veneering the top? Reduces the amount of shrinkage compared with all resin based composite, providing adhesion at the base. Potential resin-modified glass ionomers.

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8
Q

What should we use instead of GIC in deciduous teeth?

A

‘Hall technique’ NiCr crown has improved outcomes compared with standard fillings used in deciduous teeth

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9
Q

Clinical applications of GIC as a luting agent?

A

Cementation of crowns and bridges

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10
Q

What is the basic mixing procedure of GIC?

A

Mixing procedure - required water in order to ionise the acidic components of the system, which go on to react with the base (filler particles silicate glass), which create a cross-linking reaction and setting of the material

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11
Q

What is the first option for the composition of GIC?

A

Powder: fluoro-aluminosilicate glass, pigments
Liquid: poly(acrylic)(maleic)(itaconic) acid, distilled water, TARTARIC ACID!

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12
Q

What is the second option for composition of GIC?

A

Powder: fluoro-aluminosilicate glass, vacuum dried poly-acrylic acid, pigments
Liquid: distilled water

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13
Q

What is the purpose and importance of tartaric acid?

A

Important, essential to control handling properties and setting time of the material

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14
Q

Why would we use option 2 over 1?

A

Vacuum dried poly-acrylic acid improves the shelf-life

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15
Q

How many shades of GIC is there?

A

Not a lot, 3-4

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16
Q

What is the acid base reaction for GIC setting?

A

Glass + acid —> salt + silica gel + water
MO•SiO2 + H2A —> MA + SiO2 + H2O

Creating a cross-linked matrix from reaction of acid and filler, with by-product of water. (Water also needed as a reactant)

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17
Q

What are the 3 stages of setting a GIC?

A

Dissolution, gelation, maturation

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18
Q

Describe dissolution

A
  • either mix the distilled water with the dehydrated acid and silicate glass; or break the seal of encapsulated form and mix vigorously
  • this produces dissolution of ions due to the acid (H+ ions) attacking the outside of the glass particle
  • differential ion release
  • left with hydrated aqueous layer around the periphery of the particle
  • poly salt matrix (Ca and Al poly salts) formed after cross-linking has occurred
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19
Q

What is the order of differential ion release?

A

Ca2+ > Al3+ > F- > Na+

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20
Q

Describe gelation

A

Ions are reacting with something or each other to create bonds/cross-links which rapidly increase the viscosity of the material. Initial calcium ions come out and cross-link

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21
Q

How would we control the setting reaction?

A

By controlling the release of calcium ions.

22
Q

What is regular set working time for GIC?

A

4-5 minutes

23
Q

Describe maturation phase

A

Takes more time to reach full potential. Aluminium ions will increase their cross-link density of the poly salt matrix. Nature of ions released controls the setting speed.

24
Q

Depending on the manufacturer, how long can it take for GIC to fully mature?

A

3-4 weeks

25
Q

Describe the release of ions with time

A

Calcium comes out of solution fastest, cross-linking with polymer chains of polyacrylic acid
Aluminium slightly lower rate of release
Fluoride comes out, sodium fluoride used as a carrier. Not involved in the cross-linking of polymer chains and thus doesn’t affect setting reaction

26
Q

What is the GIC structure?

A

TEM image pg104

27
Q

Describe briefly the properties of GIC

A

Naturally adhesive
Low bond strength
Lack of aesthetics
Fluoride release
Adjustable setting reaction

28
Q

How is GIC naturally adhesive?

A

H-bonding to collagen - calcium ions within the inorganic enamel form a hybrid layer of inorganic tooth matter (apatite) with the chemical ion bond between carbonyl groups of poly acid chains, and H-bonding

29
Q

What is the bond strength of GIC and compare to RBC?

A

5-7MPa (4-5x less than a RBC)

30
Q

What is the benefit of low bond strength of GIC?

A

Low bond strength means little stress generated when this is setting, because there is little volumetric change, no shrinkage, and occurs over a long period of time, so less worry of micro leakage.

31
Q

Will RBCs or GICs degrade?

A

Resin composites will breakdown because it relies on mechanical and not chemical bonds. GIC is advantageous because it can break and reform, and not degrade like an RBC, so bonds will last longer.

32
Q

Does GIC stick to dental instruments?

A

Yes, so wipe fast

33
Q

How does viscosity change with time of GIC?

A

Increase in viscosity with time. Limited working time therefore.

34
Q

How does morphology of fillers or glass particles affect setting time?

A

Making fillers or glass particles smaller increases the SA, so more surface to react, rate of reaction will increase so reduces the setting time. (Graphs pg105)

35
Q

How does tartaric acid affect the setting reaction?

A

Tartaric acid reacts with released Ca2+ and extends the working time. It increases rate of formation of Al polyacid cross links and shortens the set time. Without this it would set too quickly as it slows the reaction. (Graphs pg 105)
(Shortens set time but increases working time)

36
Q

What 3 factors affect setting time of GIC?

A

Surface area/size of filler particles and glass
Tartaric acid
Powder to liquid ratio

37
Q

How does changing the powder to liquid ratio affect set time?

A

Increasing amount of powder (thus sites of reaction), will reduce the set time and improve strength characteristics (as remaining filler will act as a reinforcer)

38
Q

What are the limits to changing the set of GIC using powder/liquid ratio?

A

If you increase powder ratio too high it becomes unworkable, increasing porosity and reducing mechanical strength

39
Q

Why can’t you mix and match different GIC types?

A

Because they will have adjusted filler size to suit the purpose. Can’t manipulate viscosity so it fits the situation, need to use right type for right situation.

40
Q

Why might there be a loss of GIC?

A

Dissolution - protective layer required
Erosion - chemical attack
Abrasion - low wear resistance

41
Q

Why is GIC susceptible to dissolution and how is this avoided?

A

The material is hydraulic, requiring water to work, but can become oversaturated, meaning it is susceptible to dissolution. Protective layer required, eg varnish.

42
Q

What patients should you not put GIC in and why?

A

Perhaps avoid putting these materials in patients with salivary dysfunction. If not enough moisture to create setting reaction, it might be detrimental.

43
Q

What do fluoride ions do?

A

Not involved in salt formation - mobile F- ions diffuse to the surface
Might replace hydroxyl groups in apatite

44
Q

What is the affect of fluoride integrating into apatite?

A

Increase resistance to erosion
Reduced likelihood of caries formation

45
Q

How is fluoride also absorbed from the surroundings?

A

Acts as a reservoir, can recharge and discharge. Eg topical fluoride treatments can be placed on GIC.

46
Q

Why are there a lack of shades causing poor aesthetics with GIC?

A

Lack of translucency
Phase separation of the glass
Refractive index mismatch due to the size of particles and difference in density of glass particle and poly salt matrix that is formed

47
Q

Typical example of GIC brand?

A

Fuji IX

48
Q

Why is encapsulation better than separated GIC?

A

Activation through breaking the seal, with a special mixing device
Allows homogenous thorough mixing, avoiding issues with powder/liquid ratios.

49
Q

Summarise the advantages of GIC properties?

A

Bulk placement
Sustained release of fluoride
Direct adhesion to enamel and dentine

50
Q

Summarise the disadvantages of GIC properties?

A

Short working time
Long setting time
Susceptible to early moisture contamination
Susceptible to desiccation (dehydration)
Technique sensitive (P/L ratio)
Low strength/fracture toughness
Poor wear resistance
Poor aesthetics (cf RBCs)

Y3 Dental Materials (16 decks)

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