Zinc Phosphate Cement

Zinc phosphate cement the one of the oldest and widely used cements, and is commonly used for luting permanent metal restorations and as a base. It is a high-strength cement base, mixed from zinc oxide powder and phosphoric acid liquid. Due to its low initial pH, it may cause pulpal irritation, especially where only a thin layer of dentin exists between the cement and the pulp; thus is especially important to follow the correct procedures and precautions when using zinc phosphate cement.

Armamentarium:

• Zinc Oxide Powder
• Phosphoric Acid Liquid
• Thick glass slab
• Spatula (long, flexible side)
• Condenser
• Spoon excavator or Beaver tail to remove excess cement
• Explorer
• Timer/Stopwatch
• Cotton rope

Click on image to view Video Demonstration

Right-click here to download this video.
( Choose the "Save As ..." option from the menu.)

Procedure:

Carefully shake the powder to evenly distribute the contents. First, fill approximately three-quarters of the tip of the capas indicated by the red markand place the powder onto the lower right corner of the glass slab (for left-handed operators, place in lower left corner of the glass).
Then refill the entire tip portion of the cap with powder and place this measure in the upper right corner of the glass slab (for left-handed operators, place in upper left corner of the glass).

Before dispensing the liquid, divide the first, smaller measure of powder into six even portions. Carefully shake the liquid and, holding the bottle 90 degrees to the glass slab, dispense six drops in the center of the slab.

Mix each of the six portions of the powder in one at a time; after these have been added, the mixture should produce about a 1 inch ”string when stretching the mixture up with a spatula. (This consistency is used for cementation of inlays, onlays and crowns.)

Add the additional powder from the upper corner of the glass into the mixture as necessary, mixing for about two minutes. The final mixture should be putty-like; it should be tacky but malleable, and stiff enough to be properly condensed when placed.

Roll the mixed cement into a long roll and cut it into small pieces using the spatula.

Using the large condenser, pick up a piece and place it into the prepared cavity and lightly condense; the cement should be placed up to 0.5 mm short of the DEJ. Be sure not to contaminate the walls of the cavity. Carefully remove any excess cement.