3M ESPE manual Boxing the Impression

Boxing the Impression

Empty the entire package of the pre-measured Celara™ alginate into a clean mixing bowl and use the lower half of the container full of water for the measure of water. It is important that you use the amount of alginate in the package with a full lower container of water. This consistency produces a loose mix of alginate. Too thick a mix will result in the alginate rolling at the denture borders exposing too much of the denture flange. This can result in the denture locking on the cast. Too much water or too little alginate will result in too thin a mix, and can result in the denture sinking into the alginate. The proper mix of alginate results in a thin mix which may be lumpy and may contain bubbles having the consistency of oatmeal. It is okay to have a few lumps and a few bubbles. We are using the alginate mainly to box the impression — alginate is just as accurate an impression material if mixed thin or thick.

Pour the thin mix of alginate in the lower half of the container to within approximately 1/4" from the top, or 7/8 full (Figure 9). This leaves enough room for the displacement of the denture when submerged in the alginate. Cover the palate, occlusal, and incisal edges of the teeth with the alginate and immerse the denture in the lower container filled with alginate teeth side down so that 1–2mm of the borders are above the alginate to prevent the denture from locking on the cast. It is important that only 1–2mm of the borders are above the alginate to prevent the denture from locking on the cast (Figure 10A).

The alginate may run onto the posterior surface of the impression and cause the anterior flanges of the denture to rise above 1–2mm. If this occurs, you can tease the anterior border down in the alginate by holding it with your fingers or even placing a pencil across the impression (Figure 10B).

After the alginate sets — approximately 2 minutes — ALL THE ALGINATE MUST BE REMOVED FROM THE IMPRESSED SURFACES OF THE IMPRESSION. It is extremely critical that all the impressed surfaces of the impression be exposed by removing all alginate which is over the impression. The alginate can be easily removed by trimming it away with a dull knife (Figure 11A, 11B). It is recommended that the alginate at the heals of the impression be removed by cutting it away on a bevel. This places excess stone behind the heal of the cast — strengthening the heals of the cast which is where most casts fracture.

When boxing the mandibular impression, the posterior heals of the impression will be immersed in the alginate and all the alginate covering these areas of the impression must be removed prior to pouring a cast. This is easily accomplished cutting the alginate away with a dull knife. When

the alginate covers the posterior heals of the mandibular impression, the alginate can only be removed to the edge of the impression and therefore 1–2mm of these borders will not be above the alginate. (Figure 12).

If any of the alginate ran out over the rim of the container, it is easily removed with a dull knife. This assures the upper and lower containers have a positive seat.

Figure 9

Figure 10A

Figure 10B

Figure 11A

Figure 11B

Figure 12

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