Fundamentals of Dental Materials

dental02.jpg (11342 bytes) Fundamentals of
Dental Materials

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Restorative Materials

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.

(1) Lower the temperature of the glass mixing slab to between 65° and 75° F (18° to 24° C), if the glass mixing slab is not already cooled below the temperature at which moisture will condense on it.

(2) Blend the powder slowly.

(3) Mix the powder over a large area of the cool slab.

(4) Use a longer mixing time, within optimum limits.

Primary Content Providers: The U. S. Army, The U.S. Navy
Ancillary Content and Online Version: David L. Heiserman
Publisher: SweetHaven Publishing Services