Definition: A cement formed by chelation between zinc oxide and eugenol (from clove oil), producing zinc eugenolate in the presence of moisture, often reinforced with resins or other fillers for improved strength.
Clinical Case
A 38-year-old patient presents with a very deep occlusal carious lesion on a lower first molar. After careful excavation, the remaining dentine is thin and leathery, and the tooth is symptomatic but vital. You plan to place an amalgam restoration, but you want a pulp-soothing lining that provides good thermal insulation and can be placed quickly. You choose a reinforced zinc oxide–eugenol (ZOE) cement as a base, possibly combined with a zinc phosphate base above if needed.
Uses
Cavity linings/bases in deep cavities under metallic restorations, particularly amalgam.
Temporary luting cement for provisional crowns and bridges.
Temporary filling material (intermediate restorations).
Components of some endodontic root-canal pastes (covered in the endodontics chapter).
How to use them in clinical practice?
Select formulation
Powder/liquid system or paste/paste system.
Reinforced ZOE if additional strength is desired.
Prepare the tooth
Remove caries as indicated.
Rinse and gently dry; a small amount of residual moisture will aid setting but avoid puddles.
Dispense
Powder/liquid: scoop powder and add recommended drops of liquid.
Paste/paste: extrude equal lengths of base and catalyst pastes onto a mixing pad.
Mix
Blend quickly to a homogenous, creamy or putty-like consistency, depending on intended use.
For bases: aim for a thicker, more body-rich mix.
For temporary luting: aim for a smoother, more flowable mix.
Place
For linings/bases: place a uniform layer over the pulpal floor or deepest area; avoid covering all walls if an adhesive restorative will be used later.
For temporary luting: apply to the fitting surface of the provisional restoration and seat.
Set and follow-up
Allow the material to set under the influence of oral moisture and temperature.
For bases, proceed with overlying base (if planned) and definitive restoration once sufficiently set.
Constituents
Powder
Zinc oxide (primary reactive component)
Zinc acetate (1–5%) as an accelerator
Optional resin (e.g. hydrogenated rosin, polystyrene) in reinforced ZOE to improve strength
Liquid
Eugenol (active chelating agent)
Vegetable oil (e.g. olive oil, 5–15%) to control viscosity
Chemistry
The key reaction is chelation:
Zinc oxide + water → zinc hydroxide + eugenol → zinc eugenolate
Zinc eugenolate can readily undergo hydrolysis forming zinc hydroxide and eugenol again.
The reaction is very slow in the absence of water, but in the moist environment of a cavity:
Residual dentinal moisture and saliva accelerate setting dramatically.
Oral temperature further speeds the process