Zinc Phosphate Cement
One of the oldest, and today, most reliable choice for dental cements is zinc phosphate. This cement is used to adhere permanently crowns, bridges, onlays, inlays, and orthodontic bands and brackets. Of all the cements zinc phosphate is the most perilous, leaving no room for improper techniques. Zinc phosphate is acidic and is very irritating to the pulp of the tooth, a base or liner is required for this type of cement.
Zinc phosphate cement is a two-part mix. The combination of the liquid and the powder cause an exothermic reaction to occur, which causes the zinc phosphate to set quickly. There are several ways to avoid the too-fast setting up of this cement. Typically this cement has a one to two minute mix time, and a working time of approximately 4 minutes. When getting ready to mix, have a chilled glass slab to mix on, introduce the powder to the liquid in increments, smash the mixture together firmly and efficiently. You will know when the cement has reached proper luting consistency when the mixture follows the spatula about one inch off the slab before it breaks and sinks back into the main body of the cement.
Zinc phosphate is a high strength cement, reaching over half of its strength in less than an hour. If you follow the mixing precautions you will have no trouble mixing this cement. Being the oldest, most reliable, and most commonly used cement it is imperative for a dental assistant to know and understand all of zinc phosphate cement qualities.
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