Zinc Oxide Eugenol Cements Flashcards
Composition of ZOE, what is the liquid and what is the powder?
Powder: ZnO
Liquid: Eugenol
Characteristics of ZOE:
- Sedative effect on pulp ( due to eugenol )
- Neutral pH
Advantages of using ZOE:
- Thermal properties: about same as dentine (so less sensitivity in cold n hot temp)
- Biological properties: pH 6.6-8.0, least irritating to pulp
Disadvantages of using ZOE:
- Low compressive strength (smaller particle size => increased strength)
- High solubility: eugenol released disintegrates cement (means that when used as crown cement, disintegration can lead to marginal leakage => caries, thus, it is only used for temporary cementation)
- To decrease solubility, 1. Increase P/L ratio or 2. Decrease Eugenol - No chemical adhesion: does not adhere well to enamel/dentine
- Optical properties: opaque, not aesthetic
- Film thickness: 25μm, higher than other cements
How do you mix ZOE cements?
- Liquid/Powder
- mix on oil-resistant paper pad, 30-60s (cannot use glass slab cuz oil will itll seep into glass)
- setting time about 3-5 mins in mouth - Paste
- 2 paste system, as temporary cement
- dispense equal length & mix on paper pad - Impression paste
^ same as paste
What are the 3 forms of ZOE cements avail?
- Powder/Liquid
- Paste
- Impression paste
What are the uses of ZOE impression paste?
- Impression of full arch edentulous patient w no/minor undercuts
- Wash impression (very thin layer of low viscosity impression material which is used to record fine details)
- Bite registration
- Temporary cementation
- Temporary filling
List the advantages of using ZOE impression paste
- Very low viscosity
- Irreversible chemical change
- Low dimensional change (stable, as opposed to things like alginate)
- Good surface detail reproduction
- Inexpensive
List the disadvantages of using ZOE impression paste
- messy
- non-elastic (only can be used when there is no/minimal undercuts)
- unstable setting
- can irritate tissues (free, unreacted eugenol)
- must use rigid tray
What are the factors that affect the setting time of ZOE cements?
- Particle size: smaller size = larger surface area => faster ST
- P/L ratio: more powder=> faster ST
- Heat: cool glass slab => slower
- Accelerators: alcohol & water => faster
- Retarders: glycol & glycerine => slower
What is the working & setting time like for ZOE cements?
WT: long, moisture required for setting
ST: 4-10mins
- complete reaction takes 12hrs => tooo sloooww
Uses of ZOE cements in general:
Mainly:
1. Temporary cementation of cast restorations (e.g. easily remove provi)
2. Temporary filling material
3. Cavity liner
Sometimes
4. Periodontal & surgical dressing => cover stitches & ‘numb’ pulp
5. Displace gingiva to take crown impression (not done anymore)
6. Root canal sealant (but have better materials now)
What is the ‘types’/classification of ZOE cements?
Type I: temporary cementation
Type II: permanent cementation
Type III: temporary filling & thermal insulation
Type IV: cavity liner
