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Dental Materials > Glass Polyalkenoates > Flashcards

Glass Polyalkenoates Flashcards

1
Q

what are GI’s derived from?

A

silicate cements

polycarboxylate cements

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2
Q

what are polycarboxylate cements?

A

zinc oxide with polycarboxylic acid

set cement = adhesive to tooth, poor appearance, poor mech properties

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3
Q

replace zinc oxide of polycarboxylate cements with what? Advantage?

A

replace zno with ion leachable glass
better appearance
less soluble
better mech. properites

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4
Q

Glass ionomer came about when?

A

1970’s

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5
Q

GI comes as?

A

powder to liquid
powder mixed with water
encapsulated

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6
Q

powder of GI?

A

sodium aluminasilicate glass plus 20% caF

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7
Q

liquid of GI?

A

aqueous solution of acrylic/iatonic acid copolymer

plus tartaric acid to control setting

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8
Q

GI setting reaction essentially?

A

an acid base reaction

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9
Q

unreacted what left?

A

glass cores

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10
Q

powder/water gi, powder?

A

sodium aluminasilicate glass + 20% caf

plus vacuum dried polyacid

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11
Q

powder reconstituted by mixing with?

A

either water or dilute aqueous solution of tartaric acid

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12
Q

proportioning of powder and liquid

A

scoop/dropper bottle

encapsulated

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13
Q

how to mix GI

A

spatula

mechanical by oscialltory/rotary

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14
Q

what does hand spatulation cause?

A

more air incorporation

increased porosity

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15
Q

porosity of viscous cements?

A

low porosity

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16
Q

porosity causes stress of material which causes?

A

cracks

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17
Q

properites of powder to water gi altered by?

A

p:l ratio

if encapsulated = consistent

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18
Q

cored structure description?

A

outer is rich in calcium

inner rich in aluminium

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19
Q

calcium 2+ allows?

al 3+

A

2 arms for cross linking the acid chain

3 arms

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20
Q

in the initial set reaction what is there more of?

A

calcium ion predominates over al

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21
Q

why is there more calcium in the initial set reaction?

A

calcium is at the outer surface so is the 1st thing the acid meets
calcium is more mobile in solution that Al
more likely that 2 chains will come along rather than 3

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22
Q

why is mixing difficult if GI stored in the fridge?

A

initiates acid crystallisation

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23
Q

how does GI bonded to the tooth?

A

by calcium ions

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24
Q

how does GI bond to collagen?

A

by H bonding - metallic ion bridging

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25
Q

how might bonding be boosted?

A

with a tooth cleanser

26
Q

what does citric acid do?

A

removes the smear layer

gives no increased bond strength

27
Q

what does polyacrylic acid do?

A

increases the bond strength

28
Q

can only enhance the bond strength to what point?

A

to the limit of the tensile strength of the glass polyalkenoate cement
greater than tensile strength = failure of cement

29
Q

thermal diffusivity of GI close to?
chemical set of GI is?
what can GI release and uptake?

A

dentine
exothermic
fluoride

30
Q

GI has poor?
is it brittle?
what is GI susceptible to?

A

poor abrasion resistance
brittle
acid erosion = synergy of acid and mechanical wear

31
Q

GI has a lack of?

what is its appearance like?

A

lack of radiopacity

good appearance

32
Q

what are cermets?

A

Ag pellized mixture of glass and metal particles

33
Q

are cermets able to release fluoride?

appearance is?

A

yes some

poor appearance

34
Q

cermets have an increased?

A

compressive strength and fatigue limit

35
Q

what is modified composite?

A

The filler is replaced with aluminosilicate glass - aims to encourage F release

36
Q

how is modified composite set?

A

by light cured free radical polymerisation

37
Q

reaction of modified composite?

A

no acid base reaction until later in process

resin contains acidic groups, once resin is set, water enhances and ionises then acid base takes place

38
Q

what is a Giomer?

A

aluminasilicate glass is pre reacted with polyacid to give a prereacted glass polyalkenoate complex

39
Q

2 types of reaction of a giomer?

A

1) surface reaction - reaction happens at surface. Gives better physical properties
2) Full : reaction of all particles at expense of properties. Sold because of F release. Hema added

40
Q

how are giomers set?

A

both reactions are single paste VLC free radical polymerisation set

41
Q

what form does RMGIC come in?

A

Powder to Liquid or encapsulated

42
Q

what is the powder RMIGC?

A

ion leachable glass

43
Q

what is the liquid for RMGIC? and what does it enable?

A

methacrylate resin = enables setting by polymerisation

44
Q

what is the role of the polyacid in RMGIC?

A

reacts with glass by acid/base reaction

45
Q

what is the role of HEMA in RMGIC?

A

enables resin/acid components to co exist in aqueous solution

46
Q

what is the role of water in RMGIC?

A

essential for ionisation for acid/base reaction

47
Q

what can also be present in some RMGIC?

A

chemical activators

48
Q

on mixing RMGIC what happens?

if chem activators present what happens?

A

acid base starts
light activation = resin polymerisation
chem activators = further cure

49
Q

what do the 3 setting reactions of GI allow?

A

work more quickly

incremental cure

50
Q

the presence of the resin in RMGIC allows?

A

varnish not needed

51
Q

when can you finish a RMGIC?

A

immediately

52
Q

what is there significant amounts of with RMGIC?

A

shrinkage

53
Q

RMGIC’s expand in what?

what can this benefit?

A

expand in water

can help seal

54
Q

RMGIC’s are adhesive but are limited because?

what does this mean needs to be used?

A
  • lack of free acid to form effective bond
  • lack of sufficient ionic character to form bon
  • lack of mobility of active spaces to form bond
    = some need extra agents to bond
55
Q

do RMGIC’s release fluoride?

A

yes varies material to material

major release conventional with high initial burst and capacity to reuptake

56
Q

modified composite’s fluoride release is?

A

a lower sustained release

57
Q

giomers and compomers have the same fluoride release because?

A

low pH allows greater release, at expense of material disintegration

58
Q

advantages of composite?

A

strong
tough
radiopaque
quick set

59
Q

disadvantages of composite?

A

no inhert adhesion
shrinkage
no f release

60
Q

advantages of GI?

A

inhert adhesion
little shrinkage
F release
biocompatible

61
Q

disadvantages of GI?

A 
brittle
not radiopaque
wear prone
slow set
water sensitive

Dental Materials (13 decks)

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