1-12. PROPERTIES OF ZINC PHOSPHATE CEMENT
a. Advantages. Some advantages of zinc phosphate cement as a cementing
Speed and ease of usage.
(3) Sufficient flow to form a thin layer for the cementing of closely adapted
crowns, fixed partial dentures, and inlays.
b. Disadvantages. Some disadvantages of zinc phosphate cement as a
cementing medium are:
Low crushing strength that varies between 12,000 and 19,000 psi.
Slight solubility in mouth fluids.
Opaque material not suitable for visible surfaces.
c. Strength. The ratio of powder to liquid increases the strength of phosphate
cements to a certain point. For this reason, the dental specialist must use as thick a mix
as practical for the work being performed.
1-13. SETTING REACTIONS OF ZINC PHOSPHATE CEMENT
a. Chemical Reaction. The chemical reaction that takes place between the
powder and liquid of setting phosphate cement produces heat. The amount of heat
produced depends upon the rate of reaction, the size of the mix, and the amount of heat
extracted by the mixing slab.
b. Powder to Liquid Ratio. The less powder used in ratio to the liquid, the
longer the cement will take to harden. Good technique minimizes the rise in
temperature and acidity of the setting cement that can injure the pulp. Generally, for
increased strength, decreased shrinkage, and resistance to solubility, it is advisable to
blend as much powder as possible to reach the desired consistencies.
c. Setting Time. The setting time of zinc phosphate cement is normally
between 5 and 9 minutes. Four actions that may be taken to maintain and prolong the
normal setting time are given below.