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Dental Materials Y2 > GIC > Flashcards

GIC Flashcards

1
Q

What is the main reaction involved in GIC

A

Acid base reaction between polyalkenoic acid and calcium fluoro silicate glass

Glass base (powder) + poly acid (liquid) —> poly salt gel + silica gel (particle coating)

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2
Q

What compounds does the glass base powder in gic contain (3)

A

Silica oxide

Aluminium oxide

Calcium fluoride
(Some strontium fluoride instead because imparts radioopacity)
** fluoride releasing!

SAC

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3
Q

Why is calcium fluoro aluminosilicate glass able to react with polyalkenoic acid (a weak acid)

A

Calcium fluoro aluminosilicate glass has increased ratio of alumina to silica which increases reactivity of the glass

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4
Q

Function of itaconic acid in gic

A

Itaconic acid is liquid component

Reduce viscosity of liquid

Inhibit gelation caused by intermolecular hydrogen bonding

Ie make more liquidy

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5
Q

Function of tartaric acid in gic

A

Improve handling characteristics

Increase working time, decrease setting time

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6
Q

Name the 2 phases in setting reaction in gic

A

Dissolution and gelation

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7
Q

What happens in dissolution phase in gic setting

A

Surface of glass is attacked by poly acid, corroding surface and increasing environmental availability of ions

Limited dissolution of glass with release of calcium, aluminium, fluoride

Calcium is released more readily than aluminium, which has a slower rate of diffusion

Calcium and aluminium form complexes with fluoride. AlF more stable and is formed preferentially

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8
Q

What happens in gelation phase of setting reaction in gic

A

Crosslinking of coo- with more mobile, more readily available calcium to form clcium polysalt. Ph increases as polyacid is converted to polysalt

At maturation phase, over the next 24 hours, aluminium salts are formed leading to more rigid cross linking. Initial sharp increase in physical properties

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9
Q

How does glass composition affect setting time of gic

A

Higher alumina:silicate ratio increases setting rate as more al3+ released over time. Setting time decreases

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10
Q

How does powder liquid ratio affect setting rate of gic

A

Increased powder:liquid ratio increases the setting rate

Also:
Increased number of unreacted particles which agglomerate and form impurities, decreasing mechanical properties

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11
Q

How does particle size affect gic setting rate

A

Smaller particle size, more surface area for acid to attack, increase setting rate

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12
Q

How long is the total setting time and working time for gic setting

A

Total setting time 7 min

Working time 2 min

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13
Q

What does the matrix in gic contain

A

Hydrated fluoridated calcium and aluminium polysalt

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14
Q

What are some effects of increased liquid to powder ratio in gic

A

Increase pulp irritation
- more liquid, more unreacted acid, lower pH

Lower setting rate, longer working time, longer setting time

Lower mechanical properties because powder more dilute given fixed cavity volume

Lower resistance

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15
Q

Why is GIC hydrolytically unstable during initial stages of setting reaction

A

Gic is a water based hydrophilic cement

Hence sensitive to water uptake and loss (for at least 1 hour after uptake). This dilutes ions and there is movement of ions along with water in and out, Al3+ move out ie essential ions eluted

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16
Q

Importance of water in gic setting

A

Water is reaction medium that cement forming cations are leached

Water hydrates cross linked matrix, increasing material strength

Desiccation can retard reaction
Dessication can cause shrinkage and crazing (minute cracks)

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17
Q

Effect of water loss/uptake in early stages of setting reaction of gic

A

Decrease physical properties

Compromise colour and translucency

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18
Q

What is gic compressive strength

A

High compressive strength, 200MPa

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19
Q

What are the two key properties of gic

A

Self adhesion, fluoride releasing

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20
Q

What is the flexural strength of gic

A

Low flexural strength 5-40MPa (composite has 3x greater flexural strength 120MPa)

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21
Q

How does strength of gic change over time

A

Cement gets stronger over time

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22
Q

How does moisture in mouth affect gic strength

A

Desiccation eg in dry mouth will weaken gic

Water serves to hydrate cross linked matrix!

23
Q

What to use to form barrier over gic to protect from water loss/uptake

A

Layer of low viscosity resin ie adhesive or varnish

Temporary layer that can peel off after one day

24
Q

Increased powder to liquid ratio affects gic how

A

Increased mechanical properties

25
Q

Why is gic biocompatible

A

Polyacrylic acid (liquid component) is a weak acid. Also it has large molecular weight, limited diffusibility of acid

26
Q

How does linear co efficient of thermal expansion of gic compare to tooth

A

Similar to tooth

Unlike amalgam which expands more than tooth due to heat leading to microcracks leading to stress fracture

27
Q

Can gic keep on releasing fluoride for many years

A

Yes, the set cement can reabsorb fluoride from the oral environment if appropriate concentration gradient present

28
Q

Where is fluoride in gic located

A

In the matrix, not all will get released

29
Q

Is gic aesthetic

A

Not very aesthetic, poor optical properties. More opaque than composite though translucency improves with maturity

30
Q

How may water affect aesthetic of gic

A

Early contamination of gic with water can cause it to become more opaque

Cement can be damaged by dehydration at subsequent visits. Dehydration lead to microcrack formation —> poor visual property and more opaque

31
Q

Contraindications for gic

A

Stress bearing areas

Aesthetic areas

32
Q

Which requires stricter moisture control: GIC or CR

A

GIC

33
Q

How quickly does GIC bond strength form

A

80% of bond strength developed in 15min

34
Q

What is the mechanism of adhesion for gic

A

Self-adhesion, acid base reaction. A true ionic exchange that requires presence of water

Adheres to dentine collagen through hydrogen bonding or metallic ion bridging between carboxyl groups

35
Q

What should you do before placing gic gto improve adhesion

A

Remove surface contaminants including the smear layer using pumice-water slurry or surface conditions. These help to increase surface energy, allowing cement to come into close contact with demineralisaing tooth surface

36
Q

What are some disadvantages of gic compared to composite

A

Weaker mechanical properties

More opaque, less aesthetic

37
Q

Advantages of using resin modified gic over gic

A

Increase mechanical properties

Faster setting reaction

Overcome problems of moisture sensitivity and low early mechanical strength (presence of resin matrix converse immediate resistance to water gain or loss)

More translucent

Improved adhesion to tooth structure due to superior wetting ability of HEMA

38
Q

Disadvantages of using resin modified gic versus conventional gic

A

Lower fluoride release and lower self adhesion

Higher setting shrinkage

39
Q

How to achieve resin modified gic

A

Replace water components with water/hydroxyl methacrylate mixture

Replace polyacrylic acid with modified paa

40
Q

What is type 1 gic

A

Luting cements, fast set with early resistance to water uptake used for cementation of crowns, bridges, etc

Radio opaque

41
Q

What is type 2.1 gic

A

Restorative aesthetic cements

Restore primary and permanent teeth (class 1, 2, 3, 5, nccl), repair defective restoration margins

Temporary restorations

42
Q

What is type 2.2 gic

A

Restorative reinforced cements

Restoration of posterior primary teeth and permanent teeth (class 2 tunnel restoration)

Restore root surfaces in overdenture

Seal bifurcation area in periodontically involved teeth

AESTHETIC CONSIDERATIONS NOT IMPORTANT, RAPID SET AND GOOD PHYSICAL PROPERTIES

43
Q

How does compomer bind to tooth

A

Mechanical bonding, bonding agents required

44
Q

Of gic, resin modified gic, composite, compomer, which has the best handling properties

A

Compomer

45
Q

Of gic, resin modified gic, composite, compomer, which has the highest CLT

A

Composite

46
Q

Does resin modified gic or conventional gic have higher polymerisation shrinkage

A

Resin modified GIC

47
Q

Of gic, resin modified gic, composite, compomer, which has the CLT closest to that of tooth structure

A

GIC

48
Q

What is type 3 gic

A

Lining/base cements or pit and fissure sealants

Liners are less than 0.5mm in length to place over exposed dentine

Base is a relatively thick layer to replace some dentin, protect pulp via thermal insulation and absorb occlusal forces

49
Q

What is a possible cause of loss of translucency in gic

A

Moisture contamination/dehydration during setting

50
Q

What are some possible reasons for loss of retention in gic filling

A

Failure to clean and condition tooth

Manipulation of cement after initial set

Carving and polishing too soon

Early removal of celluloid strip (transparent matrix)

51
Q

What are some possible reasons for cracks and crazing in gic filling

A

Dehydration

Finishing/polishing too soon

52
Q

What are some possible reasons for chipped margins in gic filling

A

Lack of bulk in restoration

FInishing/polishing too soon

53
Q

What are some possible causes of gingival irritation in gic placement

A

Failure to finish/polish restoration

Failure to remove excess

Poor finishing/polishing techniques

54
Q

Setting of gic vs resin modified gic

A

Gic: acid base reaction between polyalkenoic acid and calcium fluoro alumino silicate glass

Resin modified gic: fundamental acid base reaction supplemented by 2nd polymerisation reaction

Dental Materials Y2 (11 decks)

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