Zinc cements Flashcards
What is the composition of zinc phosphate?
Powder:
- Zinc oxide
- Magnesium oxide
- Pigments
Liquid:
- Phosphoric acid
- Water
- Aluminium phosphate
- Zinc phosphate
What is the composition of zinc polycarboxylate?
Powder:
- Zinc oxide
- Magnesium oxide
- Pigments
Liquid:
- Polyacrylic acid
- NaOH
What is the composition of ZOE?
Powder:
- Zinc oxide
- White rosin (decrease brittleness, decrease solubility)
- Magnesium oxide
- Zinc stearate (accelerator, plasticiser)
- Zinc acetate (accelerator, increase strength)
Liquid:
- Eugenol
- Olive oil (plasticiser)
Zinc cements set by an acid-base reaction. True or false?
True. Reaction of zinc phosphate is exothermic
How to increase working time of zinc cements?
- Decrease P:L ratio
- Add small increments of powder into liquid
- Cool slab - Lower temperature of chemical reaction
- Retarders: Glycol, glycerine
Type of bonding to tooth for zinc phosphate, zinc polycarboxylate and ZOE?
Zinc phosphate: Mechanical bonding
Zinc polycarboxylate: Chemical bonding
ZOE: No adhesion to tooth structure
Which cement has the lowest film thickness?
Zinc phosphate; ZOE has the highest (~25um)
What are the properties of zinc polycarboxylate? (Mechanical, physical and biological)
- Not as brittle as zinc phosphate; Ability to deform plastically
- Pseudoplastic
- Neutral pH: Acidic liquid is neutralised by basic powder (pH increases rapidly)
What are the properties of ZOE? (Mechanical, physical and biological)
- Low film thickness
- COTE comparable to dentin
- High solubility (can be reduced by increasing P:L)
- Set cement is opaque
- Least irritating to pulp: Has an obtundent effect
- Bacteriostatic effect
What are the advantages and disadvantages of zinc phosphate?
Advantages:
- History of use as a luting agent
- Low film thickness
- High strength
- Longevity in oral cavity
- Good handling properties
Disadvantages:
- Weak adhesion to tooth structure - only mechanical bonding
- Risk of pulpal irritation due to phosphoric acid component (line cavity with CaOH or ZOE as precaution)
- Brittle
- Solubility in organic acids and oral fluids
- Lack anticariogenic property
- Not used when aesthetic need is high
What are the advantages and disadvantages of zinc polycarboxylate?
Advantages:
- Good adhesion to tooth structure via chemical bonding
- Little pulpal irritation: Larger molecule size of polyacrylic acid prevents it from penetrating dentinal tubules
Disadvantages:
- Short working time (~2.5min)
- Clean dry surface required
- Accurate proportioning is needed
What are the advantages and disadvantages of ZOE?
Advantages:
- Bacteriostatic
- Obtundent effect on pulp
Disadvantages:
- No adhesion to tooth structure
- Solubility of set cement is high
What is the effect of increasing P:L on the mechanical and physical properties of zinc cements?
- Faster set
- Increased viscosity of mix
- Increased strength
- Lower solubility
- Less acidic (acid is in liquid)
