Glass Ionomer Cements Flashcards Preview

BDS2 Dental Material Science > Glass Ionomer Cements > Flashcards

Flashcards in Glass Ionomer Cements Deck (37)
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1
Q

what are the different types of GIC?

A
  • conventional GI

- resin modified GI

2
Q

what are some uses of GIC?

A
  • restorative
  • core build up (prior to crown restoration)
  • lining
  • luring
3
Q

what are the two main components of conventional GI?

A
  • acid (liquid)

- base (glass powder)

4
Q

what acids are found within conventional GI?

A
  • polyacrylic acid

- tartaric acid

5
Q

why is tartaric acid added to glass ionomer?

A

added to control the setting characteristics of the material

6
Q

what is the powder aspect of convential GI composed of?

A
  • silica
  • alumina
  • calcium fluoride
  • aluminium fluoride
  • aluminium phosphate
  • sodium fluoride
7
Q

what additional molecules may be added to the powder of GI and why?

A
  • strontium and lithium salts

- increase radiopacity

8
Q

what determines the translucency of GIC?

A

ratio of alumina to silica

9
Q

a GIC containing high levels of silica will be…

A

more translucent

10
Q

what are the variations of chemical compositions of conventional glass ionomer?

A
  • anhydrous materials

- encapsulated materials

11
Q

what is meant by an anhydrous GI material?

A
  • acid is freeze dried and added to the powder
  • liquid is distilled water
  • makes for easy handling of material (mixing)
12
Q

why are encapsulated GI materials superior to anhydrous materials?

A
  • consistent powder/liquid ratio
  • easier to use
  • more consistent properties of the mixed material
13
Q

how does powder particle size in GIC determine the setting reaction of the material?

A

smaller particle size = quicker setting reaction (more opaque cement)

14
Q

how does the molecular weight of the acid found in GIC relate to the mechanical properties of the material?

A

higher molecular weight (of acid) = better the mechanical properties

15
Q

what are some contraindications of high molecular weight acids used in GIC?

A
  • very viscous

- hard to mix

16
Q

what are the three phases of the (conventional) glass ionomer setting reaction?

A
  • dissolution
  • gelation
  • hardening
17
Q

what is the acid base reaction for GIC?

A

glass + acid —> salt + silica gel

18
Q

what occurs during the dissolution phase of the glass ionomer setting reaction?

A
  • acid into solution
  • H+ ions attack the glass surface
  • Ca, Al, Na and F ions are released
  • leaves silica gel around unreacted glass
19
Q

what is meant by gelation (in reference to the GIC setting reaction)?

A

the phase that initially makes the material hard

20
Q

what occurs during the gelation phase of the glass ionomer setting reaction?

A
  • initial set due to calcium ion crosslinking with the poly acid by chelation with the carboxyl groups
  • calcium ions are bivalent so they can react with 2 molecules joining them
  • formation of calcium polyacrylate
21
Q

why is crosslinking during gelation of GIC not ideal?

A

Ca can chelate with two carboxyl groups on the same molecule

22
Q

how long does the gelation phase of GIC setting reaction take?

A

several minutes

23
Q

what occurs during the hardening phase of the glass ionomer setting reaction?

A
  • trivalent aluminium ions ensure good cross linking with an increase in strength
  • aluminium polyacrylate is formed
24
Q

how long does the hardening phase of the glass ionomer setting reaction take?

A
  • does not start for at least 30 mins

- can take a week/longer to be complete

25
Q

what must GIC be protected from during its setting phase?

A

moisture and desiccation (following gelation)

26
Q

what occurs if GIC is contaminated during the setting reaction?

A
  • aluminium ions diffuse out of the material
  • excessive drying means water will be lost
  • saliva contamination causes absorption of water
  • all lead to a weak material
27
Q

what are the different methods of protection used following glass ionomer placement?

A
  • varnishes
  • resins
  • greases/gels
28
Q

what protect the GIC better, varnishes, resins or gels?

A
  • varnish & resins provide better protection

- petroleum gel is quickly removed from mouth

29
Q

what is different between GIC and composite in terms of bonding to teeth surfaces?

A
  • GIC can bond to enamel and dentine without the need for use of an intermediate material
  • GIC bond is weaker than composite bond
30
Q

what is the bond strength of GIC compared to composite?

A
GIC = 5MPa
Composite = 20MPa
31
Q

what is the bonding mechanism of GIC?

A
  • chelation between carboxyl groups in the cement and Ca on the tooth surface
  • hydrogen bonding or metallic ion bridging to collagen
32
Q

before placing GIC, what must be done to the tooth surface?

A

surface must be CONDITIONED to produce clean, smooth surface

33
Q

what is used to condition a tooth before placement of GIC?

A

polyacrylic acid

34
Q

what are disadvantages of GIC when compared to composite?

A
  • lower bond strength

- poorer aesthetics

35
Q

what are some poor mechanical properties of GIC?

A
  • poor tensile strength
  • subject to abrasion (poorer wear resistance than comp)
  • lower hardness than comp
  • high solubility
36
Q

what are some good mechanical properties of conventional GIC?

A
  • good thermal expansion (similar to dentine)
  • no contraction on setting
  • fluoride release
  • lower modulus can be a good thing
37
Q

what are some advantages of conventional GIC to composite?

A
  • stable chemical bond to enamel and dentine
  • low micro leakage
  • fluoride release
  • good thermal properties
  • no contraction on setting