Acid-Base Cements Flashcards
What are the general uses of acid-base dental cements
- Cavity liner or base
- Permanent or temporary filling
- Root canal sealer
- Permanent or temporary luting of crown/bridge
- Attachment orthodontic processes
What are the ideal features of an acid-base dental cement
- 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
What is the definition of an acid base cement
Formed on mixing the powder and liquid, which, through an acid-base reaction, produces a solid matrix that binds the mass together
what do you get when you react an acid and base together
Salt and water
Is neutralisation exothermic or endothermic
Exothermic
When is the acid base reaction that forms the cement finished
It is never complete as there is always unreacted powder particles that act as filler and increase the strength of the cement
What factors can affect the setting of the acid base cement
- Particle size
- Powder/Liquid ratio
- Temperature
- Moisture
How can particle size affect acid base cement setting
The smaller the particle size the greater the specific surface area and the faster the setting reaction
How can powder/liquid ratio affect acid base cement setting
Higher powder content will give a faster set
How can temperature affect acid base cement setting
Increasing the temperature will increase the setting rate. Setting reaction is exothermic so may further accelerate the setting.
How can moisture affect acid base cement setting
Presence of moisture accelerates setting of some of the cements but slows it down for other cements
What are the different features that can be used to classify acid-base dental cements.
- Type
- Bonding
- Liquid component
- Powder
- Application
Name as many types of acid base dental cement as you can
- Zinc Phosphate cements
- Zinc Polycarboxylate cements
- Glass ionomer cements (GICs)
- Zinc oxide/eugenol (ZOE) cements
- Calcium hydroxide cements
- Ethoxybenzoic acid (EBAs) cements
What are the different classifications of application for acid base dental cements
- Type 1 - luting, particle size ~25um
- Type 2 - restorative or a lining, particle size ~40um
- Type 3 - lining or base
What are the different classifications of chemical bonding for acid base dental cements
- 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
What are the different classifications by liquid for acid base dental cements
- Water based = zinc phosphate, zinc polycarboxylate, Glass ionomer (polyalkenoate)
- Oil based = calcium hydroxide, zinc oxide/eugenol (ZOE), EBA
What are the different classifications by powder for acid base dental cements
- Zinc Oxide = Zinc phosphate, zinc polycarboxylate, zinc oxide eugenol (ZOE), Calcium hydroxide, EBA
- Ion leachable glass = glass ionomer (polyalkenoate)
What is the main component of zinc phosphate cement powder
Zinc Oxide
Why is zinc oxide used in acid base dental cements
- Low cost
- Good radiopacity and whiteness
- Low toxicity - is a component of many enzymes and body can tolerate in excess
- Reactivity can be controlled
How can the reactivity of zinc oxide be controlled
If heated, oxygen ions are lost and the structure becomes zinc rich, less reactive and the powder changes to yellowish
Besides zinc oxide what can you find in zinc phosphate cements and what purpose do they have
MgO = increases strength, maintains whiteness
Al2O3, SiO2 = mechanical reinforcement
What purpose would SnF2 serve in a dental cement
Serves as a fluoride source, providing short term fluoride release, also improves mixing and increases strength
What is the main component of the liquid component of zinc phosphate cements
Phosphoric acid
Why can you find Al3+ and Zn2+ cations in the liquid component of zinc phosphate cements
They partially neutralise the phosphoric acid and slow the setting of the cement
What can you add to phosphoric acid to accelerate the setting of zinc phosphate cement
water
Phosphoric acid is hygroscopic, what does this mean
easily absorbs moisture
Why should a bottle of phosphoric acid be kept close
The acid is cooking hygroscopic
What are the 2 main steps of the zinc phosphate cement setting reaction
- Zinc Phosphate + Phosphoric Acid = Zn(H2PO4)2 + Water
- Formation of Hopeite -
ZnO + Zn(H2PO4) + 2H2O =
Zn3(PO4)2.4H2O
What is the zinc phosphate cement sensitive to when setting
Water contamination
What are the advantages of using a zinc phosphate cement
- 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
What are the disadvantages of using a zinc phosphate cement
- 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
What are all properties of zinc phosphate cement dependent on
Powder/liquid ratio
especially true of strength, compressive strength 40-140MPa
What is the primary use of zinc phosphate cements
As a luting cement for restorations and orthodontic appliances because of their adequate strength
What is the secondary use of zinc phosphate cements
- As a thermal insulating base
- Temporary restorative
What is the main reactant in zinc polycarboxylate cements
Zinc Oxide
What other oxides can you find in zinc polycarboxylate cements
MgO or SnO
Al2O3, SiO2 (mechanical reinforcement)
What does heat treatment of ZnO + MgO/SnO do
Decreases the reactivity
What is the primary component of the liquid component of zinc polycarboxylate cements
Polyacrylic acid (PAA)
What else might you find in the liquid component of zinc polycarboxylate
copolymers with other unsaturated carboxylic acids
How can you convert the liquid component of zinc polycarboxylate to just water
Freeze dry the PAA so it becomes a powder
Describe the setting reaction of zinc polycarboxylate cement
Zinc Oxide reacts with the carboxyl group of the PAA
What are the advantages of zinc polycarboxylate cement
- 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
What are the disadvantages of zinc polycarboxylate cement
- lower compressive strength that zinc phosphate cements (55-85MPa)
- Short working time
- Not necessarily adhesive to all metal or porcelain restorations
What is the primary uses of zinc polycarboxylate cements
- As a luting agent because of their adhesive potential
- Thermal insulating base because of low irritancy
What is the secondary uses of zinc polycarboxylate cements
- Luting of orthodontic bands
- Intermediate and temporary restorations
