Cavity Lining (Acid-Base Cements) Flashcards
What are some general uses of acid-base dental cements? (5)
- Cavity liner
- Permanent/Temporary filling
- Root canal sealer
- Permanent/Temporary luting of crown/bridge
- Attachment of orthodontic appliances
Name some of the ideal properties of an acid-base cement (11)
- Non-irritant and non-toxic to the oral tissues
- Insoluble in oral fluids or anything taken into the mouth
- Adhesive to the tooth structure
- Adequate mechanical properties
- Thermally, chemically and electrically insulating
- Provide a therapeutic effect, e.g. bacteriostatic and obtundent
- An appropriate thermal expansion coefficient
- Good optical properties (aesthetics)
- Radio-opaque
- Appropriate rheological properties
- Easily manipulated
Definition of acid-base cement
Mixing of powder and liquid, which, through an acid-base reaction, produces a solid matrix that binds the mass together.
What does the unreacted powder in the set cement act as? What does this do?
The unreacted powder particles act as a filler. Increasing strength of the set cement
How does particle size affect setting of a cement?
The smaller the particle size the greater the specific surface area and the faster the setting reaction
How does powder:liquid affect setting of a cement?
A higher powder content will give a faster set
How does temperature affect setting of a cement?
Why does it have this affect?
- Increasing the temperature will increase the setting rate
- Setting reaction is exothermic so may further accelerate set
How does moisture affect setting of a cement?
Presence of moisture accelerates setting of some of the cements but slows it down for other cements
What are the 6 types of acid-base cements?
- Zinc phosphate cements
- Zinc polycarboxylate cements
- Glass ionomer cements (GICs)
- Zinc oxide eugenol (ZOE) cements
- Calcium hydroxide cements
- Ethoxybenzoic acid (EBAs) cements
Type I acid-base cements;
Use?
Particle size?
- Luting
- ~25µm
Type II acid-base cements;
Use?
Particle size?
- Restorative or a lining
- ~40µm
Type III acid-base cements;
Use?
Lining or base
Which acid-base cements are phosphate bonded?
Zinc phosphate cements
Which types of acid-base cements are polycarboxylate bonded? (2)
(Chemical bond!!)
- Zinc polycarboxylate cements,
- Glass ionomer cements
Which types of acid-base cements are phenolate bonded? (3)
- Calcium hydroxide cements
- Zinc oxide/eugenol cements (ZOE)
- EBA-based cements
Which types of acid-base cements are water based? (3)
- Zinc phosphate
- Zinc polycarboxylate,
- Glass ionomer
Which types of acid-base cements are oil based? (3)
- Calcium hydroxide
- Zinc oxide/eugenol (ZOE)
- EBA
What powder do all cements except GIC use?
Zinc oxide
What is the main reactant in a zinc phosphate cements?
What are the minor reactants?
- Roughly 90% ZnO
- 10% MgO, aluminum oxide and silicon dioxide
Advantages of having ZnO in based cements?
- Low cost
- Good radiopacity and whiteness
- Low toxicity
- Reactivity can be controlled
What is the primary liquid component used in zinc phosphate cements?
Phosphoric acid (H3PO4)
What is the correct way to mix zinc phosphate cements?
Mix using a cool mixing slab and incorporate the powder in small amounts
What are some disadvantages of zinc phosphate cements? (6)
- Low initial pH
- Slow to neutralise
- Brittle
- High acidic solubility
- No chemical adhesion
- Setting shrinkage
What can be used to modify the set of Zinc polycarboxylate cements?
Bismuth salts
What is the advantage of having SnF2 (Stannous Fluoride) in cements? (3)
- Fluoride source
- Improves mixing
- Increases strength
What is the primary liquid component used in zinc polycarboxylate cements?
Polyacrylic acid (PAA)
Disadvantages of Zinc polycarboxylate cements (3)
- Lower compressive strength than zinc phosphate cements
- Short working time
- Not necessarily adhesive to all surfaces
What is cavity varnish designed to do? (3)
- Seal dentine
- Reduce diffusion through dentine
- Decrease microleakage
What is cavity liner designed to do? (2)
- Seal exposed dentine
- Promotes health of pulp
What is cavity base designed to do? (4)
- Act as dentine replacement
- Strengthens restoration
- Blocks out undercut
- Insulates tooth
What will happen to Zinc eugenolate in the presence of excess water?
The complex is not stable and the setting reaction will reverse in the presence of excess water
What is the..
Mixing time?
Working time?
Setting time?
Of ZOE cement
- 60-90 seconds
- 2-3 minutes
- Less than 5 minutes
What are the disadvantages of ZOE cements? (4)
- Low compressive and tensile strengths
- High water solubility
- Eugenol is potential allergen
- Eugenol inits C=C polymerisation so cannot be used with composites
How are ZOE cements reinforced? (2)
Add what to the powder?
Add what to the liquid?
- 10-40% of a synthetic resin is added to the powder
- Styrene or MMA is added to liquid
Advantages of reinforced ZOE? (3)
- Increased compressive strength
- Increased tensile strength
- Reduced water solubility
Compare EBA cements with ZOE cements (2)
- EBA cements have better strength
- EBA cements have lower water solubility
What is a disadvantage of EBA cements?
Poor handling characteristics
If a patient is allergic to eugenol what other oils can form a cement with ZnO instead?
Nonaoic acid
What is the..
Mixing time?
Working time?
Setting time?
Of a Calcium hydroxide cement
- 5-30 seconds
- 30-60 seconds
- 1-2 minutes
Disadvantages of calcium hydroxide cements (4)
- Low strength
- Weakened by moisture
- Dissolved by acidic conditions
- Can undergo plastic deformation at mouth temperature
Compare ZOE cements to Calcium hydroxide cements (4)
- ZOE stronger and less soluble than CH
- ZOE has a calming effect
- CH is alkaline, antibacterial
- CH stimulates secondary dentine formation
