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Dental Materials Y2 > Acid-Base Cements > Flashcards

Acid-Base Cements Flashcards

1
Q

What are the general uses of acid-base dental cements

A
  • Cavity liner or base
  • Permanent or temporary filling
  • Root canal sealer
  • Permanent or temporary luting of crown/bridge
  • Attachment orthodontic processes
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2
Q

What are the ideal features of an acid-base dental cement

A
  • non-irritant and non-toxic to the oral tissues
  • Insoluble in oral fluids or anything taken into the mouth
  • Adhesive to tooth structure
  • Thermally, chemically and electrically insulating
  • Aesthetic
  • radio-opaque
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3
Q

What is the definition of an acid base cement

A

Formed on mixing the powder and liquid, which, through an acid-base reaction, produces a solid matrix that binds the mass together

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4
Q

what do you get when you react an acid and base together

A

Salt and water

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5
Q

Is neutralisation exothermic or endothermic

A

Exothermic

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6
Q

When is the acid base reaction that forms the cement finished

A

It is never complete as there is always unreacted powder particles that act as filler and increase the strength of the cement

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7
Q

What factors can affect the setting of the acid base cement

A
  • Particle size
  • Powder/Liquid ratio
  • Temperature
  • Moisture
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8
Q

How can particle size affect acid base cement setting

A

The smaller the particle size the greater the specific surface area and the faster the setting reaction

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9
Q

How can powder/liquid ratio affect acid base cement setting

A

Higher powder content will give a faster set

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10
Q

How can temperature affect acid base cement setting

A

Increasing the temperature will increase the setting rate. Setting reaction is exothermic so may further accelerate the setting.

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11
Q

How can moisture affect acid base cement setting

A

Presence of moisture accelerates setting of some of the cements but slows it down for other cements

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12
Q

What are the different features that can be used to classify acid-base dental cements.

A
  • Type
  • Bonding
  • Liquid component
  • Powder
  • Application
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13
Q

Name as many types of acid base dental cement as you can

A
  • Zinc Phosphate cements
  • Zinc Polycarboxylate cements
  • Glass ionomer cements (GICs)
  • Zinc oxide/eugenol (ZOE) cements
  • Calcium hydroxide cements
  • Ethoxybenzoic acid (EBAs) cements
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14
Q

What are the different classifications of application for acid base dental cements

A
  • Type 1 - luting, particle size ~25um
  • Type 2 - restorative or a lining, particle size ~40um
  • Type 3 - lining or base
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15
Q

What are the different classifications of chemical bonding for acid base dental cements

A
  • Phosphate bonded = Zinc phosphate cements
  • Polycarboxylate bonded = Zinc polycarboxylate cements, Glass ionomer cements
  • Phenolate bonded = calcium hydroxide cements, zinc oxide/eugenol cements (ZOE), EBA-based cements
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16
Q

What are the different classifications by liquid for acid base dental cements

A
  • Water based = zinc phosphate, zinc polycarboxylate, Glass ionomer (polyalkenoate)
  • Oil based = calcium hydroxide, zinc oxide/eugenol (ZOE), EBA
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17
Q

What are the different classifications by powder for acid base dental cements

A
  • Zinc Oxide = Zinc phosphate, zinc polycarboxylate, zinc oxide eugenol (ZOE), Calcium hydroxide, EBA
  • Ion leachable glass = glass ionomer (polyalkenoate)
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18
Q

What is the main component of zinc phosphate cement powder

A

Zinc Oxide

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19
Q

Why is zinc oxide used in acid base dental cements

A
  • Low cost
  • Good radiopacity and whiteness
  • Low toxicity - is a component of many enzymes and body can tolerate in excess
  • Reactivity can be controlled
20
Q

How can the reactivity of zinc oxide be controlled

A

If heated, oxygen ions are lost and the structure becomes zinc rich, less reactive and the powder changes to yellowish

21
Q

Besides zinc oxide what can you find in zinc phosphate cements and what purpose do they have

A

MgO = increases strength, maintains whiteness

Al2O3, SiO2 = mechanical reinforcement

22
Q

What purpose would SnF2 serve in a dental cement

A

Serves as a fluoride source, providing short term fluoride release, also improves mixing and increases strength

23
Q

What is the main component of the liquid component of zinc phosphate cements

A

Phosphoric acid

24
Q

Why can you find Al3+ and Zn2+ cations in the liquid component of zinc phosphate cements

A

They partially neutralise the phosphoric acid and slow the setting of the cement

25
Q

What can you add to phosphoric acid to accelerate the setting of zinc phosphate cement

A

water

26
Q

Phosphoric acid is hygroscopic, what does this mean

A

easily absorbs moisture

27
Q

Why should a bottle of phosphoric acid be kept close

A

The acid is cooking hygroscopic

28
Q

What are the 2 main steps of the zinc phosphate cement setting reaction

A
  1. Zinc Phosphate + Phosphoric Acid = Zn(H2PO4)2 + Water
  2. Formation of Hopeite -
    ZnO + Zn(H2PO4) + 2H2O =
    Zn3(PO4)2.4H2O
29
Q

What is the zinc phosphate cement sensitive to when setting

A

Water contamination

30
Q

What are the advantages of using a zinc phosphate cement

A
  • Adequate strength
  • Sharp set
  • Rapid hardening, attaining most of the strength in the first three hours
  • Fairly good retentive properties achieved by mechanical interlocking
  • Good thermal insulator
  • Cheap
  • SnF2 or tannin fluoride containing short term F release
31
Q

What are the disadvantages of using a zinc phosphate cement

A
  • Low initial pH = causing enamel solubility and pulpal irritation
  • Slow to neutralise
  • SnF2 contains weaker
  • Brittle - tensile strength 5-7MPa
  • High Acidic Solubility
  • A linear setting shrinkage
  • No chemical adhesion, only mechanical
32
Q

What are all properties of zinc phosphate cement dependent on

A

Powder/liquid ratio

especially true of strength, compressive strength 40-140MPa

33
Q

What is the primary use of zinc phosphate cements

A

As a luting cement for restorations and orthodontic appliances because of their adequate strength

34
Q

What is the secondary use of zinc phosphate cements

A
  • As a thermal insulating base

- Temporary restorative

35
Q

What is the main reactant in zinc polycarboxylate cements

A

Zinc Oxide

36
Q

What other oxides can you find in zinc polycarboxylate cements

A

MgO or SnO

Al2O3, SiO2 (mechanical reinforcement)

37
Q

What does heat treatment of ZnO + MgO/SnO do

A

Decreases the reactivity

38
Q

What is the primary component of the liquid component of zinc polycarboxylate cements

A

Polyacrylic acid (PAA)

39
Q

What else might you find in the liquid component of zinc polycarboxylate

A

copolymers with other unsaturated carboxylic acids

40
Q

How can you convert the liquid component of zinc polycarboxylate to just water

A

Freeze dry the PAA so it becomes a powder

41
Q

Describe the setting reaction of zinc polycarboxylate cement

A

Zinc Oxide reacts with the carboxyl group of the PAA

42
Q

What are the advantages of zinc polycarboxylate cement

A
  • Chemical adhesion
  • Loww irritancy despite the low initial pH and rapid neutralisation
  • tensile strength and water solubility similar to zinc phosphate but less acid soluble
  • Strength not so dependent on using an optimum powder/liquid ratio
  • Attain strength quickly
  • SnF2/tannin fluoride
43
Q

What are the disadvantages of zinc polycarboxylate cement

A
  • lower compressive strength that zinc phosphate cements (55-85MPa)
  • Short working time
  • Not necessarily adhesive to all metal or porcelain restorations
44
Q

What is the primary uses of zinc polycarboxylate cements

A
  • As a luting agent because of their adhesive potential

- Thermal insulating base because of low irritancy

45
Q

What is the secondary uses of zinc polycarboxylate cements

A
  • Luting of orthodontic bands

- Intermediate and temporary restorations

Dental Materials Y2 (13 decks)

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