Acid-Base Cements

Question 1

What are the general uses of acid-base dental cements

Answer 1

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

Question 2

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

Answer 2

• 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

Question 3

What is the definition of an acid base cement

Answer 3

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

Question 4

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

Answer 4

Salt and water

Question 5

Is neutralisation exothermic or endothermic

Answer 5

Exothermic

Question 6

When is the acid base reaction that forms the cement finished

Answer 6

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

Question 7

What factors can affect the setting of the acid base cement

Answer 7

• Particle size
• Powder/Liquid ratio
• Temperature
• Moisture

Question 8

How can particle size affect acid base cement setting

Answer 8

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

Question 9

How can powder/liquid ratio affect acid base cement setting

Answer 9

Higher powder content will give a faster set

Question 10

How can temperature affect acid base cement setting

Answer 10

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

Question 11

How can moisture affect acid base cement setting

Answer 11

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

Question 12

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

Answer 12

• Type
• Bonding
• Liquid component
• Powder
• Application

Question 13

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

Answer 13

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

Question 14

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

Answer 14

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

Question 15

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

Answer 15

• 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

Question 16

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

Answer 16

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

Question 17

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

Answer 17

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

Question 18

What is the main component of zinc phosphate cement powder

Answer 18

Zinc Oxide

Question 19

Why is zinc oxide used in acid base dental cements

Answer 19

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

Question 20

How can the reactivity of zinc oxide be controlled

Answer 20

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

Question 21

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

Answer 21

MgO = increases strength, maintains whiteness

Al2O3, SiO2 = mechanical reinforcement

Question 22

What purpose would SnF2 serve in a dental cement

Answer 22

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

Question 23

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

Answer 23

Phosphoric acid

Question 24

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

Answer 24

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

Question 25

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

Answer 25

water

Question 26

Phosphoric acid is hygroscopic, what does this mean

Answer 26

easily absorbs moisture

Question 27

Why should a bottle of phosphoric acid be kept close

Answer 27

The acid is cooking hygroscopic

Question 28

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

Answer 28

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

Question 29

What is the zinc phosphate cement sensitive to when setting

Answer 29

Water contamination

Question 30

What are the advantages of using a zinc phosphate cement

Answer 30

- 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

Question 31

What are the disadvantages of using a zinc phosphate cement

Answer 31

- 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

Question 32

What are all properties of zinc phosphate cement dependent on

Answer 32

Powder/liquid ratio | especially true of strength, compressive strength 40-140MPa

Question 33

What is the primary use of zinc phosphate cements

Answer 33

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

Question 34

What is the secondary use of zinc phosphate cements

Answer 34

- As a thermal insulating base | - Temporary restorative

Question 35

What is the main reactant in zinc polycarboxylate cements

Answer 35

Zinc Oxide

Question 36

What other oxides can you find in zinc polycarboxylate cements

Answer 36

MgO or SnO | Al2O3, SiO2 (mechanical reinforcement)

Question 37

What does heat treatment of ZnO + MgO/SnO do

Answer 37

Decreases the reactivity

Question 38

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

Answer 38

Polyacrylic acid (PAA)

Question 39

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

Answer 39

copolymers with other unsaturated carboxylic acids

Question 40

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

Answer 40

Freeze dry the PAA so it becomes a powder

Question 41

Describe the setting reaction of zinc polycarboxylate cement

Answer 41

Zinc Oxide reacts with the carboxyl group of the PAA

Question 42

What are the advantages of zinc polycarboxylate cement

Answer 42

- 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

Question 43

What are the disadvantages of zinc polycarboxylate cement

Answer 43

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

Question 44

What is the primary uses of zinc polycarboxylate cements

Answer 44

- As a luting agent because of their adhesive potential | - Thermal insulating base because of low irritancy

Question 45

What is the secondary uses of zinc polycarboxylate cements

Answer 45

- Luting of orthodontic bands | - Intermediate and temporary restorations