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BDS2 Dental materials science > Glass ionomer cements > Flashcards

Glass ionomer cements Flashcards

1
Q

What are the two types of Glass ionomer cements

A
  • Conventional GI

- Resin modified GI (self and light cure)

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2
Q

What are the uses of Glass ionomer cement

A
  • restorative filling material
  • core build up prior to restoration with crown
  • lining underneath permanent fillings
  • luting (cementing indirect restorations)
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3
Q

How did GIC originate

A

The original cement came from two different materials:

  • zinc polycarboxylate cement
  • silicate cement
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4
Q

What are the components of GIC

A
  • acid (liquid polyacrylic acid and tartaric acid)

- base (powder alumina/silica base)

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5
Q

What is the function of tartaric acid

A

added to control the setting characteristics of the material

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6
Q

How does the ratio of alumina/silica affect the translucency?

A

more silica more translucent

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7
Q

What is the function of strontium and lithium salts in the powder base of GIC

A

increase the radiopacity

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8
Q

What are the different variations in composition of GIC

A

anhydrous materials

encapsulated materials

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9
Q

What is the benefit and disadvantage of encapsulated GICs

A

you get the same product every time (good and a bad thing)

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10
Q

What is the name of the machiene that mixes encapsulated GIC

A

amalgamator

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11
Q

What impact does the size of the particles have on GIC

A

Bigger particles = better aesthetic

smaller particles = good for cementing (quicker setting but more opaque)

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12
Q

What impact does the length/molecular weight of the chain have on GIC

A

Longer chain = better mechanical properties but harder to mix so need a compromise

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13
Q

Describe the acid base reaction which occurs

A

MO.SiO2 + H2A –> MA + SiO2 + H2O

Glass + acid –> salt + silica gel

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14
Q

What are the 3 phases involved in the setting reaction

A
  1. dissolution
  2. gelation
  3. hardening
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15
Q

Describe the dissolution phase

A

acid dissolves the glass particles, ions go into solution, end up with silica gel outside of unreacted glass core

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16
Q

Describe the gelation phase

A

ca ions cross link with polyacrylic acid molecules (bivalent)

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17
Q

Describe the hardening phase

A

Trivalent aluminium ions ensure good crosslinking with an increase in strength.
Aluminium Polyacrylate formation takes a long time but greatly improves mechanical properties

While it’s setting its moisture sensitive, relatively soluble even though it feels hard (for about a week). If it’s too wet to begin with it will be weaker so you need to protect it

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18
Q

What can be used to protect GIC from contamination while setting is completed?

A

Varnishes

Resins - e.g. bonding agent

Greases or gels - vaseline will not last long

(varnishes and resins are best)

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19
Q

How has tartaric acid improved handling properties

A

working time largely unchanged but setting time is shortened

20
Q

Describe the adhesion properties of GIC

A
  • can bond to enamel and dentine
  • not as strong as composite
  • good sealing ability with little leakage around margins
21
Q

What is the bonding mechanism of GIC

A
  • chelation between carboxyl groups in the cement and Ca on the tooth surface
  • Re- precipitation of complex mixture of calcium phosphate and calcium salts from the poly acid onto and into the tooth surface
  • hydrogen bonding or metallic ion bridging to collagen
22
Q

What does good bonding require

A
  • clean surface

- conditioned surface (not etched, polyacrylic is best conditioner)

23
Q

What are the aesthetics of GIC like

A

Colour okay but lacks translucency

suitable for a posterior tooth but not where aesthetics are of prime importance

24
Q

What are the disadvantageous mechanical properties of GIC

A
  • poor tensile strength
  • lower compressive strength than composite
  • poorer wear resistance than composite
  • lower hardness than composite
  • higher solubility than composite
25
Q

What are the advantageous mechanical properties of GIC

A
  • good thermal properties expansion similar to dentine
  • no contraction on setting
  • once set less susceptible to staining and colour change than composites
  • fluoride release
  • lower modulus
26
Q

Describe GIC flouride release capability

A

Releases loads initially but after about a week much less.
But, they can recharge their fluoride when the Fl concentration around them is higher than that in the cement
They then release Fl again when the ambient concentration falls
They can act as a fluoride reservoir or fluoride sink

27
Q

What are the uses of GIC

A
  • dressing
  • fissure sealant
  • endodontic access cavity temp filling
  • luting
  • orthodontic cement
  • restoration of deciduous teeth
  • restoration of permanent teeth
  • base or lining
28
Q

Advantages of GIC

A
  • Stable chemical bond to enamel and dentine
  • Low microleakage
  • Fluoride release
  • Good thermal properties
  • No contraction on setting
29
Q

What are the disadvantages of GIC

A
  • Brittle
  • Poor wear resistance
  • Moisture susceptible when first placed
  • Poor aesthetics
  • Poor handling characteristics
  • Susceptible to acid attack and drying out over time
  • Possible problems bonding to composite
  • Etching damages surface
30
Q

What are cermets

A

silver coloured GICs

no advantages and worse aesthetics (aim was for silver to overcome brittleness)

31
Q

Why were RMGICs developed

A

take advantages of GIC - bonding to tooth, fluoride release

and add advantages of composite:

  • light curing (command set)
  • improved physical properties
  • better aesthetics
32
Q

What is in the powder of a RMGIC

A
  • fluro-alumino-silicate glass
  • barium glass (radiopacity)
  • vacuum dried polyacrylic acid
  • potassium persulphate (allows resin cure in the dark)
  • ascorbic acid
  • pigments (shades vary)
33
Q

What is in the liquid of a RMGIC

A
  • HEMA (water miscible resin)
  • polyacrylic acid with pendant methacrylate groups
  • tartaric acid
  • water
  • photo-initiators
34
Q

Describe the dual curing setting reaction that RMGICs undergo

A
  • acid-base reaction
  • light activation a free radical methacrylate reaction occurs resulting in a resin matrix being formed (20s)
  • acid base reaction continues
  • redox reaction also occurs
  • material will set even if insufficient light although will have reduced physical properties
35
Q

Describe the tri curing setting reaction that RMGICs undergo

A
  • acid-base reaction
  • redox reaction begins
  • light activation = free radical reaction –> resin matrix formed (20s)
  • redox (5mins) and acid-base (hours) reactions continue
  • final hardening of the acid/base phase with aluminium polyacrylate formation can take days
36
Q

In what ways are RMGICs better than conventional GICs

A 
Better physical properties
Lower solubility
Fluoride release 
Better translucency and aesthetics
Better handling
37
Q

In what ways are RMGICs worse than conventional GICs

A
  • Polymerisation Contraction
  • Exothermic setting reaction
    (both polymerisation and dark cure)
  • Swelling due to uptake of water (HEMA is extremely hydrophilic)
  • Monomer leaching (HEMA is toxic to the pulp it must be polymerised completely)
  • Reduced strength if not light cured
  • Light curing slows down the acid base setting reaction
  • Benzoyl iodides and bromides can be released which are cytotoxic
  • Fluoride release no better than conventional GIC
38
Q

What are the main benefits of RMGIC compared to conventional GIC

A
  • better aesthetics
  • easier to use
  • stronger
39
Q

What are the main benefits fo RMGIC compared with composite resin

A
  • easier to use

- fluoride release

40
Q

Uses of RMGIC?

A

(same as conventional GIC)

  • Dressing
  • Fissure sealant
  • Endodontic access cavity temporary filling
  • Luting
  • Orthodontic cement
  • Restoration of deciduous teeth
  • Restoration of permanent teeth
  • Base or Lining
41
Q

Why might you pick conventional GIC or RMGIC

A

to do with light curing

42
Q 
Which of these ions is not released in the glass ionomer setting reaction:
A.	Sodium
B.	Fluoride
C.	Calcium
D.	Magnesium
E.	Aluminium
A

Magnesium

43
Q 
Which of these is not a constituent of conventional glass ionomers:
A.	Polyacrylic acids
B.	Camphorquinone
C.	Silica
D.	Alumina
E.	Calcium Fluoride
A

camphorquinone

44
Q

Identify the incorrect statement:
A. The glass ionomer setting reaction involves 3 phases
B. Glass ionomers are brittle with poor tensile strength and wear resistance
C. RMGI’s have poorer mechanical properties than conventional GI’s
D. Glass ionomers are susceptible to acid attack
E. Glass ionomers bond to enamel and dentine, reducing susceptibility to microleakage

A

C. RMGI’s have poorer mechanical properties than conventional GI’s

45
Q

What speeds up the setting of GIC

A

tartaric acid

46
Q 
Which direct restorative material relies on chelation between carboxyl groups and the calcium in the tooth as a major component of the bonding mechanism?
Select one:
A. Amalgam
B. Glass ionomer cements
C. Composite resin
D. Zinc phosphate
E. Zinc oxide eugenol
A

Glass ionomer cements

BDS2 Dental materials science (10 decks)

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