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Dental Materials Y2 > GIC > Flashcards

GIC Flashcards

(54 cards)

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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

Study These Flashcards
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

Study These Flashcards
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

Study These Flashcards
A

Increased mechanical properties

25
Why is gic biocompatible
Polyacrylic acid (liquid component) is a weak acid. Also it has large molecular weight, limited diffusibility of acid
26
How does linear co efficient of thermal expansion of gic compare to tooth
Similar to tooth Unlike amalgam which expands more than tooth due to heat leading to microcracks leading to stress fracture
27
Can gic keep on releasing fluoride for many years
Yes, the set cement can reabsorb fluoride from the oral environment if appropriate concentration gradient present
28
Where is fluoride in gic located
In the matrix, not all will get released
29
Is gic aesthetic
Not very aesthetic, poor optical properties. More opaque than composite though translucency improves with maturity
30
How may water affect aesthetic of gic
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
Contraindications for gic
Stress bearing areas Aesthetic areas
32
Which requires stricter moisture control: GIC or CR
GIC
33
How quickly does GIC bond strength form
80% of bond strength developed in 15min
34
What is the mechanism of adhesion for gic
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
What should you do before placing gic gto improve adhesion
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
What are some disadvantages of gic compared to composite
Weaker mechanical properties More opaque, less aesthetic
37
Advantages of using resin modified gic over gic
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
Disadvantages of using resin modified gic versus conventional gic
Lower fluoride release and lower self adhesion Higher setting shrinkage
39
How to achieve resin modified gic
Replace water components with water/hydroxyl methacrylate mixture Replace polyacrylic acid with modified paa
40
What is type 1 gic
Luting cements, fast set with early resistance to water uptake used for cementation of crowns, bridges, etc Radio opaque
41
What is type 2.1 gic
Restorative aesthetic cements Restore primary and permanent teeth (class 1, 2, 3, 5, nccl), repair defective restoration margins Temporary restorations
42
What is type 2.2 gic
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
How does compomer bind to tooth
Mechanical bonding, bonding agents required
44
Of gic, resin modified gic, composite, compomer, which has the best handling properties
Compomer
45
Of gic, resin modified gic, composite, compomer, which has the highest CLT
Composite
46
Does resin modified gic or conventional gic have higher polymerisation shrinkage
Resin modified GIC
47
Of gic, resin modified gic, composite, compomer, which has the CLT closest to that of tooth structure
GIC
48
What is type 3 gic
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
What is a possible cause of loss of translucency in gic
Moisture contamination/dehydration during setting
50
What are some possible reasons for loss of retention in gic filling
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
What are some possible reasons for cracks and crazing in gic filling
Dehydration Finishing/polishing too soon
52
What are some possible reasons for chipped margins in gic filling
Lack of bulk in restoration FInishing/polishing too soon
53
What are some possible causes of gingival irritation in gic placement
Failure to finish/polish restoration Failure to remove excess Poor finishing/polishing techniques
54
Setting of gic vs resin modified gic
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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