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Improving your crown cementation when using zinc phosphate
by Drs. Lloyd Baum, DDS, and Bruce Walter SD'73

Figure 1

The last step, and possibly the most important step in the process of crowning a tooth is the cementation. Maintaining a dry surface at the crown/dentin interface is essential especially along the margin (Fig. 1). This is best accomplished by having an assistant help with the procedure.

Any saliva on the tooth surface hopefully will be displaced by the cement. Unfortunately, this doesn’t always happen. Although the liquid is displaced it leaves a non-attached interface between the tooth and the cement. To “wet” the dentin with the cementing medium (e.g., zinc-phosphate cement) requires a dry surface. Any previous moisture serves as a separating medium which in time will become an open passageway for the carious process.

As a precaution to prevent this from happening, the following sequence is suggested.

1. Cement is mixed in a routine manner using at least six or seven drops of liquid. A small, high-quality sable brush is bent to a comfortable angle for access to the sulcus (see diagram).

2. Pretending that the crown is a small dappen dish, it is filled with cement and held above the lower lip…very close to the tooth.

Figure 2

3. The brush is dipped into the cement, carried to the tooth, and brushed into the sulcus, smearing it over the gingival third of the preparation (Fig. 2).

4. A second and third brush load may be needed to cover the dentin where seepage of fluid is likely to occur.

5. The crown is then seated in a traditional manner.

Factors to keep in mind are:

1. Zinc-phosphate is, and will probably remain, popular as the cementing medium of choice.

2. Zinc-phosphate cement, upon mixing, is water soluble and can absorb small amounts of saliva and crevicular fluid.

3. Small amounts of moisture can be brushed away simultaneously with the impregnation of fresh cement over the surface of the dentin.

4. In only a matter of seconds, a brush can accomplish this process and give the operator a sense of security that crown failure from a leaky margin will be less likely to occur in years to come.